Stream flows are of great importance in maintaining a stable hydrosphere and assessing available water resources of a nation. However, previous satellite-methods are difficult to retrieve stream flows for middle- or small-scale rivers due to the satellite course spatial resolution whereas near-ground measuring methods have too complex procedure, requirement of expensive apparatus, or low-efficiency. These shortcomings hindered them to be used widely in non-gauged areas and situations needing non-contact measurement, e.g., accidental pollution events. This paper presented a novel, non-contact, fast method to calculate streamflow using UAV images which can be easily applied to rivers with different scales of width. Using this method, stream flows can be calculated with or without ground-measured cross-section data. With UAV images it produced point-cloud and DSM (digital surface model) which were then used to calculate values of river-width, roughness, longitudinal water-surface slope and cross-section above water surface. With all these values, the hydraulic method was finally adopted to calculate stream flows. Results show that the method has a satisfactory performance with modelled streamflow values slightly higher than observed ones at high-flow periods (R ²= 0.997, RMSE = 4.55 m ³/s) with ground-observed cross-section data. When the cross-section data were absent, the cross-section under water can be generalized with the UAV measured above-water cross-section data. Errors in estimating stream flows induced by cross-section generalization decreased with increment of water-level and water-width. The maximum accumulated errors accounted for 8.28% of the bankfull streamflow. The errors were resulted from the generalization of river bottom with un-regular cross-sections. All the results and methodologies could be of great help in streamflow measurement in accidental pollution events and in ungauged areas across the globe.

The Integrated Multi-satellitE Retrievals for GPM (IMERG) and Global Satellite Mapping of Precipitation (GSMaP) are two high precisely multi-satellite precipitation estimates in the GPM era. In order to evaluate the applicability of both IMERG and GSMaP series products (IMERG_Uncal and IMERG_Cal, GSMaP_MVK and GSMaP_Gauge) over the Sichuan region in China, six statistical indices are used to systematically analyze the error characteristics of these products, benchmarked by a set of ground-based dataset from China Meterological Administration (CMA). Results show that: (1) All products show the dramatic regional difference over Sichuan at both daily and hourly scales. The GSMaP series products overestimate precipitation and the most overestimations occur over the high altitude areas located in the Western Sichuan. GSMaP_Gauge shows relatively higher correlation coefficient and lower relative bias and root mean square error due to the employment of gauge-based adjustments. On the contrary, IMERG_Uncal shows underestimation over the mountainous areas, while the relatively slight overestimation appears in the basin area with lower elevation at both daily and hourly time scales, suggesting that gauge-calibrated dataset IMERG_Cal has effectively improved the relative bias in the mountainous areas but not in the flat basin area. (2) By synthesizing the three classified statistical indices, IMERG series products exhibit better potentials in detecting precipitation events. Although GSMaP_Gauge shows a higher hit rate of precipitation, it has more false alarm ratios of precipitation. All products show better hit rate and lower false alarm rate over basin area and southern Sichuan. Furthermore, it is found that the ground-based dataset has some errors in those areas without meteorological stations, which leads to the apparent uncertainty in assessing the accuracy of satellite precipitation products over the Northwest Sichuan Plateau. (3) IMERG_Cal performs better in capturing the rainfall amounts and events compared with other products, especially for the lowest and highest rainfall intensity ranges, demonstrating its application potential for monitoring the extreme weather events. Overall, both IMERG and GSMaP estimates have relatively high uncertainties over the mountainous areas than ones over the flat basin areas. Additionally, the gauge-calibrated products obviously outperform the uncalibrated datasets. On the basis of the findings, future efforts focus on reducing and correcting the errors and biases of satellite precipitation estimates by considering both spatio-temporal characteristics and the topographical information.

Medieval Climate Anomaly (MCA, 950-1250 A.D.) was the most recent and lasting hundreds of years warm period, which has aroused more attention from climate scholars, because MCA provided similar patterns to research on the impact and adaption of global and regional warming. In this study, we investigate the characteristics of temperature variation on inter-decadal to centennial scale during MCA in four regions (including Northeast, Northwest, Central-east and Tibetan Plateau) in China based on high-resolution temperature reconstructions longer than 1000 years and related warm-cold records from historical documents. Ensemble empirical mode decomposition method is used to analyze the cycles and fluctuations of four regional temperature series. The results show that the longest warm period during the last 2000 years occurred in the 10th-13th centuries over the whole country, although there existed several cold decadal intervals in the mid to late 12th century, different starting-ending warming periods and warming magnitudes in four regions. On quasi-30-year scale, regional temperature variations were similar during 950-1130 A.D. while their amplitudes became smaller and the phases did not match well each other in 1130-1250 A.D. On centennial scale, all the four regions began a warm period in the early 10th century and experienced two cold intervals during MCA. However, temperature variations of Northwest and Central-east kept in phase each other, but out phase in Northeast and Tibetan Plateau, where the ending of the warm period was earlier about 40-50 years than that of Northwest and Central-east. On multi-centennial scale, the mean temperature difference between MCA and Little Ice Age in Northeast and Central-east is significant, but did not appear in Northwest and Tibetan Plateau. Compared with the mean temperature of the 20th century, Central-east had a comparable warming level, Northeast was a little cooler, and both Northwest and Tibetan Plateau had significantly lower temperatures in MCA.

In 1991, the collapse of the Soviet Union and the independence of the five Central Asian countries led to profound changes in land cover and evapotranspiration pattern. This study used the five Central Asian countries as target areas. European Space Agency Climate Change Initiative and Global Land Data Assimilation System data were utilised to analyse the spatio-temporal variation of land cover and evapotranspiration from 1992 to 2015 and to further study the cropland evapotranspiration water consumption. This study investigated the continuous change of land cover, specified the characteristics of and differences in land cover and evapotranspiration, strengthened the understanding of land cover and evapotranspiration in the current situation, and provided data references for water and soil resource management and environmental protection. Results show that the changes in land cover in the five countries were characterised by stages, and cropland expansion modified the land cover pattern. From 1992 to 2003, cropland increased rapidly (1.1×10 ⁴ km ²), whereas forest land and grassland decreased. From 2003 to 2015, cropland increased slowly (0.3×10 ⁴ km ²), whereas forest land and grassland increased slightly. Bare land and water bodies continued to decrease, whereas settlements continued to increase; the annual evapotranspiration was 276.8 mm. Evapotranspiration increased rapidly from 1992 to 2003 (11.3 mm/a) and then slowly from 2003 to 2015 (2.4 mm/a). The evapotranspiration of cropland (352.2 mm) and grassland (322.1 mm) was significantly higher than that of forest land (254.7 mm) and bare land (173.2 mm). The evapotranspiration changes in the five Central Asian countries were consistent with the land cover patterns; the evapotranspiration water consumption of the five countries was affected by the cropland area. From 1992 to 2015, the water consumption of cropland evapotranspiration increased by 3.2%, and the contributions of grassland, forest land and bare land continued to decrease. The cropland of Turkmenistan accounted for only 11% of the total evapotranspiration water consumption, whereas that of the other countries accounted for more than 25%.

Atmospheric CO₂ uptake by carbonate rock weathering is continuously transported from the land to the ocean by rivers in the form of HCO₃ ^-, and it has become an important carbon sink of terrestrial ecosystems. In the existing research, the estimation and distribution of carbonate weathering-related carbon sink in global major river basins are still unclear. In this study, we collect hydrochemical and discharge data of multiyear average (runoff modulus, main ion concentration, and dissolved inorganic carbon) in large river basins over 100, 000 km ². By using hydrochem-discharge method, we estimate that the CO₂ uptake rates (F_v) of carbonate weathering in global major river basins is 0.43 ± 0.15 Pg CO₂ yr ^-1 and the average CO₂ uptake flux(F) is 7.93 ± 2.8 t km ^-2 yr ^-1. The CO₂ uptake F and uptake F_v are substantially different under various climatic zones. The annual uptake F_v of tropical and warm regions accounts for 62.95% of the total annual F_v. The cold temperate zone is widely distributed, and its CO₂ uptake F_v accounts for 33.05%, which is second only to the tropics. We also propose the nine critical zones of global CO₂ uptake F (four in the middle and low latitudes, two in the western hemisphere and three in the eastern hemisphere). The CO₂ uptake F in the intersection of the critical zones is high. The average CO₂ uptake F in the karst-outcropped basins is 8.50 t km ^-2 yr ^-1, which is approximately three times that in the non-karst basins. Carbonate weathering carbon sinks in global karst-outcropped basins play an important role in the study of global carbon cycle, water cycle, and carbon budget balance estimation. On the basis of river basin scales, various factors (e.g., carbonate composition, exogenous acid, and climatic environment) for carbonate weathering carbon sinks should be considered. The hydrochem-discharge method should be further improved in future research. Moreover, the effects of the photosynthesis of river aquatic organisms on rock weathering carbon sinks should be considered, and carbonate rock weathering carbon sinks should be refined and extrapolated to the world.

Based on the revised First and Second Chinese Glacier Inventory and Landsat OLI remote sensing images during 2015-2016, we analyzed the spatial-temporal variation characteristics of glaciers in the Gangdisê Mountains during 1970-2016. The results of this study provide a scientific basis for the rational use of water resources in this region. The results showed that there were 3953 glaciers with a total area of 1306.45 km ² and ice volume of ~58.16 km ³ in the Gangdisê Mountains during 2015-2016. The glaciers in sizes of 0.1-5 km ² and < 0.5 km ² had the largest area and the greatest number of glaciers in the Gangdisê Mountains, respectively. In the past five decades, the area of glaciers decreased by 854.05 km ² (-1.09%/a), accounting for 39.53% of the total area of glaciers in the region in 1970. The increase of temperature in the ablation period was the most important cause of glacier retreat. Compared to other mountains in western China, the Gangdisê Mountains was the region with the strongest glacier retreat and had an accelerating tendency in recent years. The decrease of glacier area was mainly concentrated at elevations of 5600-6100 m a.s.l. and there was no change in elevation above 6500 m a.s.l. in the Gangdisê Mountains. Except for the south and southeast orientations, the number and area of glaciers were decreasing in all the orientations. Specifically, the north orientation suffered the largest area loss of glaciers and the northwest orientation witnessed the fastest retreat of glacier area. A significant feature of spatial variation showed that the rate of glacier retreat was faster from west to east in the Gangdisê Mountains. The relative change of glacier rate in the eastern section was high at -1.72%/a, followed by the middle section (-1.67%/a), and that in the western section was only -0.83%/a.

The Tibetan Plateau is sensitive to climate changes induced by interactions of large scale atmospheric circulations, including the East Asian monsoon, Indian monsoon and mid-latitude westerlies. In this paper, we present a high-resolution chemical element dataset covering the past 2000 years from Lake Yamzhog Yumco (28°27′N-29°12′N, 90°08′E-91°45′E, altitude in 4440 m a.s.l.), which is a representative inland lake located in the southern Tibetan Plateau. These data were acquired using an X-ray fluorescence (XRF) core scanner, which is used for in situ, high-resolution, continuous, multi-element analyses. The chronology presented herein is based on ²¹⁰Pb and AMS ¹⁴C dates from the macro-remains of plants. The interpretation of elemental geochemistry, together with magnetic susceptibility and grain-size, enabled the reconstruction of the environmental changes in the southern Tibetan Plateau over the past 2000 years. Reconstructions of the temperatures, precipitation and lake levels indicated that the Medieval Warm Period (MWP) and Current Warm Period (CWP) were associated with low precipitation and high temperatures. In contrast, the Dark Cold Age Period (DCAP) and Little Ice Age (LIA) were associated with high precipitation and low temperatures. Moreover, the level of warmth during the peak of the MWP may equal or slightly exceed the 20th century warming. In addition, the prolonged LIA may have experienced a warm event on a centennial timescale, and the 17th and 18th centuries may be the coldest centuries in the last two millennia. Our reconstructions also indicated that the lake level evolution has been affected by interactions of temperature and precipitation. More specifically, during the cold periods, an increase of precipitation amplified the rise of lake levels, and vice versa. The climate records from Lake Yamzhog Yumco have confirmed a cold-moist/warm-dry climate pattern on the southern Tibetan Plateau over the past 2000 years. Additionally, the temperature variations inferred from the records were strongly correlated with the solar irradiance and northern hemispheric temperature changes, which suggests a possible link between the solar forcing and climate variability in the past 2000 years on the southern Tibetan Plateau. In addition, the enhancement and southward shift of the westerlies was determined to have significantly contributed to the high precipitation conditions during the LIA on the southern Tibetan Plateau.

The intense erosion of a near-shore riverbed is one of the main factors for the slope failure of a bank. During a detailed investigation carried out in August 2017 and May 2018 of underwater topography of the Yangtze Estuary, a large scour pit was recognized near the shore of the Hengsha passage. The morphological and geometrical parameters of the scour pit were measured using the SeaBat7125 multi-beam system. Dual-frequency ADCP was used to collect hydrodynamic data near the scour pit. Further, a historic nautical chart was digitalized to analyze the evolution and formation mechanism of the scour pit. The results indicated that the scour pit is in the shape of an oval, with a length and width of around 430 m and 150 m, respectively; the deepest point is approximately 38 m below the surrounding riverbed. Since the formation of the -20 m isobaths line in 1992, the scour pit area has been expanding continuously, and the average depth has been increasing yearly; in particular, after 2005, the depth increased sharply. From 1984 to 2017, the riverbed around the scour pit underwent the process of erosion-silting-erosion. In the 33 years, the scouring amount is 3.45×10 ⁷ m ³, and the average scouring depth is 4.68 m. The ebb tide from the North Channel flows into the Hengsha passage, forming a circulation flow, thereby eroding the channel near the west bank of the Hengsha island and forming a scour pit. After 2005, the scour pit grew rapidly and expanded southward. This is mainly because the reclamation engineering performed in North Changxing reduced the curvature radius of the bend that resulted in intensified erosion. The reservoir construction engineering performed in Qingcaosha moved the thalweg in the upper and middle sections of the North Channel, and the northward entrance of the Hengsha passage expanded owing to the ebb current, which is also one of the main reasons for rapid erosion. In addition, the construction of reclamation and deep-water channel projects in the vicinity has contributed to the erosion of the channel bed, thereby accelerating the expansion of the scour pit. It can be seen that human engineering activities are the main driving factors for the rapid development of large scour pits in the Changjiang Estuary.

Studies on spatial-temporal characteristics and influencing factors of flash floods are key contents to the assessment and management of flash flood. Based on the historic flash flood data in southwest China from 1960 to 2015, the spatial and temporal distribution of flash flood and its influencing factors were analyzed by using the linear regression model, standard deviation ellipse, spatial autocorrelation, and logistic regression model. The results show that: (1) The annual frequency of flash floods in southwest China shows an exponential growth trend, and the annual variation reveals a stable, slow and rapid increase fluctuation during 1960-1980, 1981-1998 and 1999-2015, respectively; the monthly characteristics are obvious and precipitation is mainly concentrated in June, July and August. (2) The obvious spatial difference of flash flood is observed in the study area, and the high-density areas are mainly concentrated in central Yunnan plateau, Sichuan Basin and their surrounding mountainous areas. The flash flood distribution has a significant spatial positive correlation and spatial agglomeration (Moran's I index is 0.127, Z = 5.784, P = 0.007). (3) The gravity center of historical disasters has a distinct trend of moving to the west during the year. The standard deviation ellipse angle gradually weakens, the long axis gradually lengthens, and the short axis gradually shortens. (4) Rainfall factors have the maximum impact on flash floods, followed by human activity factors, and the minimal is surface environmental factors. Among the rainfall factors, the one-hour rainfall has the strongest impact on flash floods, and its dominant ratio reached 3.654. The results can provide techinical support for research on forming mechanism, monitoring and early warning, and implementation of disaster prevention and mitigation measures of flash floods.

Changes in the regional differentiation patterns of moisture conditions under the impact of climate change are an important scientific question. Based on the five global climate models (GCMs) participating in the Coupled Model Intercomparison Project Phase 5 (CMIP5), this paper projected the trend in the area of arid/humid climate regions in China for the next hundred years, and analysed the sensitive regions of arid/humid patterns change and its sensitivity of responses to climate change. Results show that the future arid/humid patterns change would be characterized by a significant decrease in the humid region and a significant expansion in the arid/humid transition zones. In particular, the area of sub-humid region would increase by 28.69% in the long term (2070-2099) relative to the baseline period (1981-2010). Under 2 ℃ and 4 ℃ warming, the area of shifts between arid/humid climate regions was projected to increase from 10.17% to 13.72%. Particularly in the south of the Huaihe River basin, which was mainly affected by the future increase in reference evapotranspiration, the humid region would retreat southward and shift to the sub-humid region. In general, the sensitivity of responses of arid/humid patterns to climate change in China would intensify with the acceleration of global warming.

In this study, we developed a high-resolution grid dataset of air temperature and precipitation for the Qinling-Daba Mountains in central China, which includes monthly precipitation and temperature, seasonal precipitation and temperature, annual precipitation and temperature. Spatial interpolation was performed using thin-plate smoothing spline in the software ANUSPLIN, with latitude, longitude and elevation as independent variables. Our dataset is consistent with the widely-used WorldClim 2.0 dataset, but has more accuracy, because it is based on a larger number of meteorological stations and higher-resolution elevation data. Our results show that the southern foot of Qinling Mountains is the 0 ℃ isothermal line in the coldest month (January). The Qinling-Daba Mountains has obvious vertical temperature zones. The maximum temperature lapse rate occurs in June, which is 0.61 ℃ per 100 m, while the minimum temperature lapse rate is 0.38 ℃ per 100 m, occurring in December. The annual mean temperature lapse rate is 0.51 ℃ per 100 m. Both summer and autumn precipitations decrease from southwest to northeast, with heavy rainfall center located on the southwestern slope of the Daba Mountains, while winter precipitation decreases from southeast to northwest. The Daba Mountains is the 1000 mm isohyetal line of annual precipitation and 500 mm isohyetal line of summer precipitation, while the Qinling Mountains is the 800 mm isohyetal line of annual precipitation and 400 mm isohyetal line of summer precipitation. Comparison with large-scale atmospheric circulation indicates that the spatial distributions of air temperature and precipitation in the Qinling-Daba Mountains are mainly controlled by the East Asian monsoon and topography. In summer, the Daba Mountains prevents the northward penetration of East Asian summer monsoon and therefore influences the spatial distribution of precipitation. In winter, the Qinling Mountains prevents the southward penetration of East Asian winter monsoon and therefore influences the spatial distribution of air temperature. In summary, our high-resolution grid dataset contributes to a better understanding of regional climate and will have many applications in future researches.

The Qinling-Daba Mountains, as the north-south transition zone of China and the watershed between the Yellow River and the Yangtze River, are characterized by multi-dimensional and high-degree heterogeneity and variations in climate and landscape. Especially, the spectra of altitudinal belts show outstanding areal differentiation in the study region and could be considered to serve as a criterion for determining the boundary between warm temperate and subtropical zones in the Qinling-Daba Mountains. This paper designs a digital integrated system for 33 spectra of altitudinal belts in the study region and analyzes their structures and the spatial patterns of the main altitudinal belts from north-south, from west-east and with exposures. The results show that: (1) From south to north, the basal belt gradually transfers from subtropical evergreen broadleaved forest to warm temperate deciduous broadleaved forest; the spectra of altitudinal belts change from complex to simple; the dominant belt changes from mixed broadleaf-conifer forest and evergreen-deciduous broadleaved mixed forest, and then to deciduous broadleaved forest belt; and the upper limit of the evergreen-deciduous broadleaved mixed forest decreases from 1600-2000 m in the Daba Mountains to 700-800 m in the Xunhe Basin of the Qinling Mountains. (2) From west to east, the structures of altitudinal belt spectra show a complex pattern in the eastern and western sections but a simple one in the middle section; the upper limits of both evergreen-deciduous broadleaved mixed forest belt and mountain deciduous broadleaved forest belt present a quadratic curve distribution pattern in longitude direction; however, the upper limit of mountain broadleaf-conifer mixed forest belt exhibits a nearly linear decrease in west-east direction from 2700 m to 2000 m in the Qinling Mountains and from 3300 m to 1600 m in the Daba Mountains. (3) In the Qinling Mts., the basal belt is just warm temperate deciduous broadleaved forest both in the northern and southern flanks, with only some evergreen trees mixed in the basal belt in the southern flank; while in the Daba Mts., the basal belt is evergreen-deciduous broadleaved mixed forest in the northern flank and evergreen broadleaved forest belt in the southern flank. The north flanks of the Qinling and Daba Mountains have similar dominant belts, namely, mountain broadleaf-conifer mixed forest belt or mountain deciduous broadleaved forest belt. However, the southern flank of the Daba Mountains has its own unique dominant belt, i.e., evergreen-deciduous broadleaved mixed forest belt. This implies that the Daba Mountains are more appropriate than the Qinling Mountains to act as the boundary between subtropical and warm-temperate zones in central China.

The urban heat island effect has received an increasing attention recently with the acceleration of urbanization. However, so far few studies have focuses on the effects of urban morphology and wind conditions on land surface temperature (LST). This study utilizes a range of multi-source data including architecture and remote sensing and applies a GIS spatial method combined with urban building frontal area index (FAI) and LST. This research aims to evaluate spatiotemporal differences in the FAI of urban built-up areas as well as to explore the influence of urban form on surface temperature. Results initially reveal that building FAI conforms to a spatial trend comprising outward diffusion from the city center and shows that high density, higher elevation buildings hinder the wind strongly. Data show that FAI values for the north of Chaoyang District are the largest, reaching a maximum of 15.1, while those for edge areas for each district are the smallest, falling to a minimum of 0.01. Secondly, the results of this analysis reveal large differences in surface temperature between day and night within the study area, ranging between 18.15 ℃ and 31.73 ℃ and between 4.27 ℃ and 18.43 ℃, respectively. Spatial distribution values exhibit the same characteristics as those for the FAI; the urban central city is characterized by high temperature, which gradually spreads out in a concentric manner. The range of high temperature areas during the day is also larger than that at night as these values are influenced by other variables including urban architectural form and artificial heat sources. Thirdly, the data assembled here show that FAI is related to surface temperature to a certain extent; recorded correlations between day and night are 0.371 and 0.355, respectively, both significant at the 0.01 level. It is also the case that building spatial shape is distinct in both vertical and horizontal directions and that the influence of surface temperature varies. Wind environmental data is an important component of quantitative research on building form and is necessary if urban climate scientists and planners are to explore and enhance potential ventilated corridors within cities.

Tens of millions of people each year now engage in birdwatching activities and birdwatching tourism has become an important part of the world wildlife watching industry. Climate change has changed the phenology and distribution of birds, which will affect not only birdwatchers' tourism activities but also the livelihoods of the stakeholders in birdwatching tourism. Monitoring and identifying these effects as early as possible and encouraging stakeholders to implement effective adaptive strategies is of great significance. Climate change has adverse effects on many sectors; however, the extent of its effects on birdwatching tourism is relatively unknown. Therefore, in the present study, the relationship of phenophases-climate change indicators - with variations in the activity timing and habitat pattern of birds was assessed. These are two important aspects that can be exploited for the development of birdwatching tourism. In this milieu, a meta-analysis was conducted using ornithological research data for 98 phenological series (1980-2010) from 26 regions in China. Changes in the departure and arrival times, stay duration, and habitat pattern of birds in China were recorded. The departure and arrival of birds were determined to have advanced in spring and summer but to be delayed during autumn. In general, the stay duration of birds has increased. Furthermore, increase in temperature has resulted in longer stays, thus favouring the development of birdwatching tourism; stay duration is particularly long in the low-latitude areas and western region of China. Their habitats have shifted northward and westward. When birds migrate to places not previously used as habitats, these places become more attractive for tourism because of the presence of these new birds. Conversely, if the birds no longer migrate to places where they were previously observed, these places might lose their attractiveness in this regard. The effect of changes in the activity timing and habitat pattern of birds on the birdwatching tourism has already been perceived by tourists and working staff in scenic areas.

Global historical land use datasets play a quite significant role in gaining a profound understanding of the global or regional environmental change. As an important component of these global datasets, the reliability of historical forest data at the regional scale is rarely assessed. Based on the Chinese historical forest dataset (CHFD) that is reestablished by Chinese scholars using historical documents, we conducted an evaluation of the reliability of China's forest data within these global datasets (SAGE, PJ and KK10) adopting comparative analysis from three aspects, including the change tendency of forest area, the area of forestland, and the differences at grid scale. The results indicated that: (1) Although Chinese forest area from multiple datasets was decreasing, there was a large difference in the quantity of forest area. Specifically, the forest area of China from 1700-1990 in SAGE dataset was 20%-40% greater than that in CHFD, while the forest area of China in KK10 dataset from 1700-1850 was approximately 32%-46% greater than that in CHFD. Due to the adoption of regional research results, the total forest area of China within PJ dataset was closen to CHFD, and the quantitative biases of most years were less than 20%. (2) At provincial scale, in terms of the PJ dataset which was relatively close to the CHFD, the proportion of the provinces with large difference in the changing trend was 84%, and the proportion of the provinces with large difference in the quantity could be up to 92%. (3) At grid cell scale, the percentage of grid cells having biases greater than 70% accounted for up to 60%-80%. Therefore, there was an apparent discrepancy of spatiotemporal dynamic patterns between PJ and CHFD datasets. (4) These global datasets failed to reveal the process and pattern characteristics of Chinese forest dynamics in an objective way. The major reasons were that different data sources were used in reconstructing historical forest data within global and regional datasets, and different reconstruction methods at different spatial scales were adopted.

In the Yangtze River Estuary, saltwater intrusion threatens eco-environment and freshwater intake. The estimation of the critical discharge for saltwater intrusion control helps improve the regulatory schemes of reservoirs in the Yangtze River Basin. In this study, the upper south branch of the Yangtze River Estuary was selected as a typical area to determine the critical discharge for saltwater intrusion control using different empirical models. Measured salinity data of more than 60 tidal cycles were used to analyze the characteristics of saltwater intrusion processes, and the validity of four empirical models was tested. Results indicated that (1) the intensity of saltwater intrusion changes with different combinations of discharges and tidal ranges, and saltwater intrusion occurs when the discharge at the Datong station is less than 30000 m ³/s. Approximately 69% of saltwater intrusion days occur when the discharge is less than 15000 m ³/s. The probability of saltwater intrusion is 65% when the discharge is less than 12000 m ³/s. (2) The tidal range in the Yangtze River Estuary shows a distinct feature of a semi-monthly (15 days) periodical change, that is, the condition of "saltwater intrusion that ensues for more than 10 days" occurs with two-thirds frequency when the discharge is maintained at a certain critical value. On the basis of statistical analysis, the tidal range that corresponds to two-thirds frequency is determined to be 2.7 m at the Qinglonggang station. With the exponential relationship between salinity and tidal range, the critical discharge at Datong has been estimated to be slightly higher than 11000 m ³/s. (3) The periodical changes in tidal range can be roughly described using sinusoidal functions. By introducing the tidal range functions into empirical models for saltwater intrusion, the change process of salinity under a certain discharge can be calculated. By using three empirical models, the calculation results show that the critical discharge at Datong is between 11000 and 12000 m ³/s. Thus, 11500 m ³/s can be regarded as the critical discharge to control the duration of saltwater intrusion to less than 10 days. (4) After the operations of the Three Gorges Project and its upstream cascade reservoirs, the minimum discharge into the sea in 2008-2015 increased but remained lower than the critical discharge. Therefore, the regulatory schemes of reservoirs in the Upstream Yangtze River must be optimized to release additional water during dry season. In particular, the minimum discharge into the sea should be maintained to be higher than 11500 m ³/s.

The focus of urbanization effects on floods has gradually extended from the design of hydraulic channels to the control of imperviousness ratio and urban land use pattern in urban areas or the urbanized watershed. The stormwater management needs to integrate multiple floods perspectives in a spatial hierarchical unit, such as building, lot, city, watershed and region. However, the spread of the use of the urban landscape for managing and controlling stormwater in urbanized basins has been rather slow. The Low Impact Development (LID) model, which is used as the word of sponge city development in China, is used widely in Chinese cities. But most of Chinese cities, especially in East China have a high urban land intensity and no enough sponge city spaces to absorb surface runoff. The strong floods relationship exists among these spatial scales such as lot, city, watershed and region. Thus, the impact of land use change on environmental conditions improves the scientific knowledge on the floods correlation between new urban districts and downtowns, and expands the range of application of the LID/sponge city development. Then, the decline in the infiltration capacity resulted primarily from the transformation between construction land, cultivated land and other land use changes. However, there is low correlation between the infiltration capacity (CNc) and the construction land growth intensity in the overall sequence of development intensity (CLI15), but a high correlation in local parts of the CLI15 value. The high correlation occurs in the two parts of the CLI15 such as 8%-15% and 24%-39%, which are located in the "hot areas" of urban land growth around big cities and some rapidly developing towns. There is plenty of construction land and ecological infiltration space, and more opportunities to spatially contact together. Especially, three important target factors of the infiltration capacity in land use, such as the protection of infiltration spaces, land use control and LID-IMPs, are insufficient in the integrated planning and management. Last, the paper proposed a "3+4+5" stormwater management model in improving land use infiltration capacity, namely, three target factors, five key management elements and four management strategies models. Most parts of Area A in Taihu Lake watershed have a high intensity of land development, and implement the offensive strategy of improving the capacity of the hydraulic channels in the flood-prone areas, and create new ecological spatial elements in the right places. Area B around big cities is the main implementation area of the sponge city development/LID-IMPs, and controls the size of incremental construction land, and optimizes the pattern of construction land and natural spaces based spatial forms. Areas C and D are the main protection areas, and integrate stromwater management with land use zones, and expand and improve the ecological quality of natural service function.

Loess slopes covered with aeolian sand are unique geomorphic features in the wind-water erosion crisscross region on the Chinese Loess Plateau. On these loess slopes, runoff and sediment production patterns are unique and complex and the thickness of covering sand and its interaction with other factors may largely interfere soil erosional responses. Therefore, quantifying the variations of runoff and sediment yields and assessing the possible factors are of great importance to understand the erosion mechanism in such unique landscapes. To quantify the effects of sand layer thickness and sand size composition on runoff generation and sediment yield, sand-covered loess slopes with 15° were subject to simulated rainfall events (intensity 1.5 mm/min) in this study. Sand layers of three different thicknesses, 2 cm, 5 cm and 10 cm, were respectively placed on loess surface. For each sand thickness, there were five kinds of compositions, i.e. 100% sand diameter ≤ 0.25 mm, 75% sand diameter ≤ 0.25 mm + 25% sand diameter > 0.25 mm, 50% sand diameter ≤ 0.25 mm + 50% sand diameter > 0.25 mm, untreated sand, and 100% sand diameter > 0.25 mm. Our results show that as sand thickness increased, it prolonged initiation time of runoff, reduced runoff yield, increased sediment yield and enhanced the variability in runoff and soil loss rates during rainfall. Our findings also indicate that with coarser sand, the total runoff loss tended to increase even though the initiation time of runoff and sediment yield was not obviously changed. The sand layer thickness, sand size composition, and their interactions respectively contributed 68.03%, 15.77%, and 3.85% to the variation of initiation time of runoff (p < 0.05), respectively. For the runoff production, the sand layer thickness can explain 23.89% to 52.22% of the variation of runoff rates during a 15-min rainfall sub-rainfall, and 41.10% to 48.94% of total runoff loss for different rainfall durations. For the sediment production, the sand layer thickness can explain 29.19% to 62.01% of the variation of soil loss rates during a 15-min rainfall sub-rainfall, and 13.53% to 30.31% the total sediment yield for different rainfall durations. Moreover, the sand size composition had less impact on runoff and sediment yields than the thickness of the sand layers. Their combined effects were significant during the early and intermediate stages (p < 0.05), and contributed to 13.12%-26.62% of runoff loss and 3.22%-43.12% of sediment yield. Overall our observations suggest that runoff and sediment generation on sand-covered loess slopes were mainly affected by the sand layer thickness rather than sand size composition, and their combined effects also varied as erosion proceeded.

The special geographic and human environment of the Qinghai-Tibet Plateau has created the unique hydrochemical characteristics of the region's natural water, which has been preserved in a completely natural state. However, as the intensity of human activities in the region continued to increase, the water environment and hydrochemical characteristics on the plateau have changed. In this study, we collected, analyzed, and measured water samples in the western, southern, and northeastern border areas of the Qinghai-Tibet Plateau, where human activities are ongoing, and the regional differences and factors controlling them were investigated. The key results were obtained as follows. (1) There were differences in the physical properties and hydrochemical characteristics, and their controlling factors in the different boundary areas of this plateau. These differences were mainly caused by the effects of the geographical environment and geological conditions. (2) The average pH of the water samples was 7.75, the average total dissolved solid (TDS) content was 171 mg/L, and the average hardness (TH) content was 168 mg/L. Overall, the water quality was good and suitable for drinking, with most samples meeting national and WHO drinking water standards. (3) The main cations were Ca ²⁺ and Mg ²⁺ in water samples, while HCO₃ ^- and SO₄ ^2- were the main anions. The chemical properties of water were mainly controlled by the weathering of carbonates and the dissolution of evaporative rocks, with the weathering of carbonate rocks being most influential. (4) The biological quality indicators of natural water in the border areas was far superior to national and WHO standards, which indicated that these areas were rarely affected by human activities.

Quantitative research on the effects of ecological conservation projects and climate variations on vegetation changes is vital to the ecological benefit evaluation of ecological conservation projects, and has important implications for sustainable ecological rehabilitation management strategies in the source region of the Yangtze River. Based on the normalized difference vegetation index (NDVI) data and meteorological data during 1982-2015, this paper examines the temporal and spatial variations of NDVI; constructs back propagation artificial neural network (BPANN) model to simulate the responses of NDVI to climate factors; and quantifies the effects of ecological conservation projects and climate variations on vegetation changes at the annual and seasonal scales in the source region of the Yangtze River. The results indicate that: (1) Because of the effects of ecological conservation projects and climate variations, vegetation degradation curbed in the source region of the Yangtze River. (2) NDVI increased greatly near the Tongtian River located at relatively low altitudes. Minor increases in NDVI were observed near the Tuotuo and Dangqu rivers located at relatively high altitudes. (3) A time lag (about 1-2 months) existed between NDVI and major climate factors in the source region of the Yangtze River. The goodness of fit of the BPANN model shows that the simulation accuracy is relatively high. The model can be used to simulate the responses of NDVI to climate variations. (4) Ecological conservation projects exerted a slightly greater impact on NDVI changes than they did on climate variations at the yearly time scale (58.5% and 41.5%, respectively). During growing season, ecological conservation projects also exerted a slightly greater impact on NDVI changes than they did on climate variations (63.3% and 36.7%, respectively). During non-growth season, climate variations are the key factor affecting vegetation growth in the source region of the Yangtze River (52.8%). The research results provide a basis for scientific decision-making about the vegetation ecosystem rehabilitation, management and utilization strategies in the source region of the Yangtze River.

Based on the MOD09A1 and MOD16A2 datasets with a temporal resolution of 8 days during a period from 2001 to 2016, Drought Severity Index (DSI) was quantified to characterize spatiotemporal distribution of droughts of different drought intensities. The correlation coefficients were quantified between drought-affected cropland area and the climatic winter wheat yield. In addition, relevant impacts of droughts with different drought intensities were investigated on the winter wheat yield during different growing periods. The results show that: (1) drought regimes during 2001-2016 showed a declining trend in terms of drought intensity at annual and inter-annual scales. The most severe drought occurred during 2001-2002 while regional and intermittent droughts could be observed during 2003-2010, and were alleviated during 2011-2016 with persistent wetting tendency thereafter. In terms of annual drought distribution, droughts occurred mainly in spring and autumn, some occurred in summer and few droughts in winter; (2) Generally, in terms of the spatial distribution of droughts, central and northern Hebei, southern Henan, Anhui and Jiangsu, and eastern Shandong provinces were dominated by frequent droughts though droughts were in decreasing trends; (3) analysis results concerning effects of droughts on winter wheat yield show that the incipient drought during the winter period can promote the winter wheat yield, while in the milking stage of the winter wheat, occurrence of droughts may decrease crop yield. The mild drought potential has significant effects on winter wheat yield during the ripening interval, while the moderate drought occurs during flowering, milking and ripening periods can have a significant impact on the winter wheat yield. Meanwhile, droughts with higher degree of intensity will have more significant impacts on winter wheat at its earlier growing season. In addition, water shortage due to drought effects during planting periods will reduce the yield of winter wheat, and severe and extreme droughts in particular. Therefore, it is of great merits in quantification of impacts of droughts with different intensities on winter wheat yield in different growing seasons, and it has important theoretical and practical significance for the planning of irrigation and the increase of soil moisture in the study region.

The water diversion scheme is important for the sustainable development of the economic, social and ecological environment in different parts of the basin, especially for the rivers in arid areas. In order to curb the trend of ecological degradation in the lower reaches of the Heihe River, the Heihe River water diversion scheme, approved in 1997 by the Chinese government, was carried out in 2000. With the implementation of the water separation scheme, the allocation of domestic water, production and ecological water tends to be reasonable, and the trend of ecological environment deterioration has been relieved. However, there are still queries on the rationality of water diversion schemes because it is difficult to complete water diversion indicators in wet years. Therefore, it is necessary to comprehensively analyze the implementation of the water diversion scheme and evaluate its adaptability in the Heihe River under the changing background. In this paper, based on the analysis of the impact of water diversion scheme, the technical characteristics and adaptability of water diversion under the changing background were analyzed. By establishing water resource allocation model of the Heihe River, the implementation of water resource allocation under different water demands and the operation of Huangzangsi (Huangzang Temple) Reservoir for long-time series (from 1958 to 2012) were simulated, and then the adaptability of water diversion schemes was analyzed. The result shows that the Heihe River water diversion scheme cannot meet the requirements of water diversion under the current condition due to the changes of economic society and river connectivity in the Heihe River basin. Water diversion indicators can be accomplished when the area of farmland in the middle reaches decreases to the level of 2000 and the construction of Huangzangsi Reservoir is finished, but there is still over exploitation of groundwater in the middle reaches. In conclusion, "97" water diversion plan is inadaptable to the current situation to some extent on the basis of the economic, social and hydrologic conditions of the Heihe River in the mid-1980s.

Based on the data of relative soil moisture obtained from 653 agricultural meteorological stations in China during the period of 1993-2013, the spatial and temporal differentiations of relative soil moisture in China's farmland were analyzed and discussed by using geostatistical methods. The results show that the relative soil moisture of China's farmland has fluctuated and increased since 1993, exceeding 60% in general. The distribution area has been expanding to the north and west with the summer monsoon since mid-April, and in late October, the region began to shrink to the east and south. The value of relative soil moisture increases with the increase of soil depth, and the distribution of farmland in high-value area increases with the increase of soil depth. The relative soil moisture of farmland increases fastest in summer and autumn, and the range of change decreases with the increase of soil depth. There is a strong positive correlation between relative soil moisture and precipitation. Relative soil moisture has a strong negative correlation with potential evaporation and temperature. The annual mean value of relative soil moisture in paddy field is higher than that in dry land, and the difference between the annual mean values of relative soil moisture of two types of farmland increases with the increase of soil depth.

There are 66 tributaries in the Three Gorges Reservoir (TGR) area, where most of them witnessed pronounced deposition in mouth reach since the impoundment of the TGR. The lasting sedimentation may lead to the formation of outlet bar at mouth section, which generated adverse effects on storage capacity of the TGR and navigation of tributaries. This paper, taking the Modao Creek and Xiangxi River as examples, examines the characteristics and causes of sediment deposition in their mouth sections based on detailed observation data such as flow, sediment, cross section and channel topography. The results show that: (i) after the impoundment of the TGR, a large amount of deposition occurred in its tributary mouth. The maximum deposition thickness of Modao Creek and Xiangxi River mouth sections exceeded 10 m from 2004 to 2017. Deposition was basically within the range of 15 km of the mouth section, and the strong depositing zone was focused in the reach of about 5 km away from the river mouth. The sediment deposition in the river mouth mainly occurred in the initial operation period of the TGR, and slowed down particularly since 2010 when the cascade hydropower stations in the middle and lower Jinsha River began to operate; (ii) the weakened hydrodynamic condition in dry season at the tributaries mouth, and the significantly reduced sediment-carrying capacity, are the fundamental causes in responsibility to the intense deposition. Sediment deposited at Modao Creek and Xiangxi River mouth sections mainly came from the mainstream in the form of inverted flow, and partially came from their own basin. The deposition range of sediment and its influence on channel morphology were related to local river regime; (iii) Optimized operation of the TGR since 2010 has not affected the sediment deposition in the tributaries mouth. Decreased sediment concentration in mainstream and tributaries and the maintenance the low water level in flood season do not support the formation of outlet bar of tributaries in the TGR.

The Yellow River Delta is one of the most famous river deltas in the world. Since Xue and Cheng (1989) first systematically proposed the spatio-temporal distribution of ten Holocene superlobes in the delta, this hypothesis remains unchanged in the last three decades. To redefine the characteristics of sedimentary evolution and spatial-temporal distribution of Lijin superlobe in the Yellow River Delta, 4 boreholes with a length of 20-30 m were obtained in the coastal plain of South Bohai Bay. Combined with the achievements of previous boreholes in the study area, the stratigraphical data and AMS¹⁴C dating results in these boreholes revealed that the river channel and flooding plain dominated the study area in the early Holocene. It turned to be saltmarsh, tidal flat and shallow sea environments in the chronological order when the Holocene transgression reached the study area. Delta progradation began as the sea level decelerated, and was finally capped by the terrestrial sediments in this area. The ancient river channel of the Yellow River might enter the sea by the southern area of Huanghua during 9000-8000 cal a BP. After ~8000 cal a BP, the main river channel shifted southward between Binzhou and Huiming, which led to the development of Lijin superlobe from 7000 cal a BP to 5500 cal a BP. The northern boundary of Lijin superlobe may link Mashanzi with Yangxin while the southern one was located between Guojingzi and Mihe River. The ancient Yellow River mouth might return to Huanghua after ~5500 cal a BP and formed the Huanghua superlobe ranging from 5500 cal a BP to 3500 cal a BP. The Yellow River changed its main course to Tianjin earlier than 3500 cal a BP and might turn back to Qikou in Hebei province after ~700 BC.

Central Asia, consisting of extended arid and semiarid areas, is one of the major sources of global dust and aerosol in the Northern Hemisphere. Dust emission, transportation and deposition over the region have received an increasing interest. Loess deposits, as a geologic record of dust, enable the possibility of archiving dust variabilities over the past, and give insights into the underlying mechanisms of dust activities. Here, we examined the grain size data of two late Pleistocene loess-paleosol sequences, named Nilka (NLK) and Qingshuihe (QSH), in the Ili Basin, eastern Central Asia, with focus on intervals with the highest sedimentation rates in both loess sections. Both sites are located on the south slope of the northern Tianshan Mountains, but represent different topographies and climate conditions. Parametric curve-fitting and hierarchical cluster analysis techniques were applied to partition the whole spectrum of the measured grain size distributions and provided a more reliable and more representative statistical descriptors. The end members unmixed under distant eolian dynamics were used to reveal the dust accumulation processes in the Ili Basin in detail. The results suggest that the Ili loess mainly consists of distal and proximal sediments, with the high-level westerlies and the meso-scale regional winds as the transport agents respectively. Distal clayed mineral particles transported by the high-level westerlies can contribute to the loess sediments from the eastern basin due to the wet deposition, where precipitation is high. Nevertheless, this is not true for the western part of the basin where the clay fractions are difficult to deposit. Proximal sediments dominate the Ili loess, and the grain-size composition and formation process of the Ili loess can be dependent on the availability of the local particulate materials with different sizes. Additionally, the floating dust derived from "non-dust storm processes" (after sand and dust storms) has significant impacts on the loess formation during periods of decreasing dust storm frequency. Whereas sparse vegetation is likely to create favorable conditions to the resuspension of the floating dust components when dust storms occur frequently. A conceptual model about dust accumulation in the Ili Basin is proposed based on the above results.

The sedimentary environments of the Yangtze Estuary riverbed have changed a lot with the construction of water conservancy projects in the drainage basin and the estuary, which have significantly influenced the river regime evolution and accretion/erosion of the estuary riverbed. However, less has been reported on detailed sedimentary characteristics of the current estuary riverbed, which restrains further evaluation on the impact on both hydrology and sedimentology of the Yangtze Estuary. Therefore, based on the large-scale surface sediment samples and associated flow-sediment data collected during September 2015, we analyzed the sedimentary characteristics in the seven riverbeds within the estuary and discussed the influencing factors and mechanisms. The particle sizes of the sediment samples were analyzed by Model LS-13320 Coulter laser particle size analyzer and the types of the surface sediments were classified by Folk’s classification. The results are shown as follows. The riverbed sediments of the whole estuary is dominated by sandy silt and silty sand. The coarsest surface sediments are observed in the outer estuary of north branch/north channel above 10 m and upper north/south branch, while the finest surface sediments are found in the north passage, lower south passage and the outer estuary of north/south passage deeper than 5 m. Generally, the particle sizes of the river sediments are coarser in the main channels and finer on the shoals, and decrease from west to east and from north to south. The lateral sedimentation distribution characteristics are affected by the sediment transportation and deposition in ebb and flow process. The longitudinal sedimentation distribution reflects the differences of the sedimentary environment strengthened by the wind wave. The sediments in the north branch are coarsened remarkably due to the intense north wind wave action. The difference of sediment origins is the factor leading to deviation of the sedimentary environment. The sediment in the south branch and upper south channel show a characteristic of riverine sediments, while the sediments in the north channel, north passage and south passage show a mixture of riverine and marine sediments. Sediments in the outer estuary mainly provide fine-grained particles to the inner estuary.

In this study, data measured from 1955-2016 was analyzed to study the relationship between the water level and river channel geometry adjustment in the downstream of the Three Gorges Dam (TGD) after the impoundment of the dam. The results highlighted the following facts: (1) for the same flow, the drought water level decreased, however, flood water level changed little. The lowest water level increased, while the highest water level decreased at the hydrologic stations in the downstream of the dam; (2) the distribution of erosion and deposition along the river channel changed from "erosion at channels and deposition at bankfulls" to "erosion at both channels and bankfulls"; the ratio of low water channel erosion to bankfull channel erosion was 95.5% from October 2002 to October 2015, with variations in different impoundment stages; (3) the drought water level decrease slowed down during the channel erosion in the Upper Jingjiang River and the reaches ahead but sped up in the Lower Jingjiang River and the reaches behind; concrete measures should be taken to prevent the decrease in the channel water level; (4) erosion was the basis for channel dimension upscaling in the middle reaches of the Yangtze River; the drought water level decrease was smaller than the thalweg decline; both channel water depth and width increased under the combined effects of the channel and waterway regulations; and (5) the geometry of the channels above the bankfulls did not change much; however, the comprehensive channel resistance increased under the combined effects of the river bed coarsening, bench vegetation, and human activities; as a result, the flood water level increased markedly and moderate flood to high water level phenomena occurred, which should be considered. The Three Gorges Reservoir effectively enhances the flood defense capacity of the middle and lower reaches of the Yangtze River; however, the superposition effect of tributary floods cannot be ruled out.

Fieldwork investigations were carried out in the Hukou-Longmen reach in the Jin-Shaan (Shanxi-Shaanxi) Gorges of the Yellow River. Paleo-aeolian sand layers were found interbedded in the Late Pleistocene and Holocene loess-soil profile—Beisangyu profile (BSY). Analytical results, including field investigation, magnetic susceptibility, grain-size distribution, surface textures of quartz sand, and geochemical elements, indicate that the paleo-aeolian sands are medium-sized sandy fine sands, which were formed in a dry and windy climate. And the extreme drought events recorded by paleo-aeolian sand layers were dated to 12.5-11.6 ka, with optically stimulated luminescence (OSL) dating method. The extreme drought event coincided with the Younger Dryas that was recorded by the lacustrine sediment profiles and the aeolian loess-soil profiles in the desert/loess transitional zone in the adjacent region. The paleo-aeolian sands were sourced mainly from ancient riverbed sands in the Jin-Shaan Gorges of the Yellow River. The Jin-Shaan Gorges is situated in a semi-arid zone with a temperate continental monsoonal climate. The region responds sensitively to global change. During the Younger Dryas period, the region is in an extremely dry and cold environment, with strong winter monsoon and weak summer monsoon. The water level of the Yellow River will decline obviously. Consequently, floodplains and channel bars in the river are exposed in a broad area, and a large quantity of sand material drifts to the banks of the river under the force of the wind, which becomes the main source of the paleo-aeolian sand layer in the platforms on the gentle slopes on both sides of the river valley. These results would be of great significance in further understanding the temporal regularities of the extreme drought event and the relations between extreme drought event and monsoonal climate change.

The scenario deduction and dynamic pre-assessment of urban natural disasters emergency plan play vital roles in emergency decision optimization. However, traditional plan assessments usually consist of scenario deduction of time slices and post-disaster assessment based on limited information. Based on the full-chained multi-dimensional scenario deduction plan coupled with water-logging model and multi-agent urban road condition model, this article conducts pre-assessment of emergency plan with multi time scales and rescuing targets. By examining the scale of damaged cars and the number of people threatened by the disaster, the assessment is performed regarding the quantity of people, time, and spatial arrangement of the plan. Based on this, the article provides a new solution in conducting disaster scenario deduction plan and optimizing emergency decisions. The emergency plan based on the number of people indicates that the rescuing force is firstly arranged at areas with higher risk, including North Fengwo Road, South Fengwo Road, Guanglian Road and Lianhua Bridge. In reality, only limited force participates in rescuing in time, and the spatial direction based on the number of force plays a vital role in optimizing rescue decision. Meanwhile, we also prove that the amount of rescue force stands for the fundamental position in emergency dispose. From the emergency plan based on the initiating time of rescue, it can be seen that the best initiating time is between 45 and 75 minutes, and the appropriate time of initiating can efficiently avoid the improper configuration of rescue space due to the premature rescue and the loss of efficacy when it starts too late. Different spatial arrangements of rescue could lead to different rescue force arrangement features and optimized conditions.