This study, through establishing the regression model, inverts the annual runoff of 1766-1911 AD, builds up and improves the annual runoff series of 1766-2000 AD in flood season in Lanzhou, Qingtongxia and Sanmenxia by using the records of water level stake of three gauge stations in the Upper-Middle Yellow River (UMYR) in the Qing Dynasty. Combining the annual runoff of 1766-1911 AD at Tangnaihai Station in riverhead reach, the study builds the runoff series of four stations at the riverhead and UMYR, which is presently the clearest runoff curve of the Yellow River by historical records. According to the research, the heavy "river disaster" that appeared in the lower Yellow River in the mid-19th century was caused by sudden changes of the runoff at the Qingtongxia-Sanmenxia section. Drought period of the river in the 1920s existed from the riverhead to the middle reach, but it was not caused by sudden changes. Meanwhile, the study also reveals that PDO and the runoff of the UMYR had a periodic inverse phase relationship on the interdecadal scale. In the early and mid-20th century, the runoff of the four stations had an inverse phase relationship on the scale of 8-16 years. In the 1830-1850s, the inverse phase relationship between PDO and flow on the scale of 4-6 years was more obvious at Lanzhou-Sanmenxia section. According to the interactive wavelet analysis, there is a significant inverse correlation between PDO and the amount of water in the UMYR on a scale of 8-16 years, but only at the Sanmenxia-Lanzhou section, suggesting that the relationship between summer rainfall in the UMYR and PDO had obvious temporal and spatial differences. (1) During the study period, the change of runoff flow in the UMYR had obvious differences; On the natural state, there was no obvious consistency in the flow change of the UMYR. The occurrence of sudden change time point was not synchronous in history. In the long term, the runoff change of the UMYR had a unique phenomenon. The simultaneous reduction of flows of each reach since the 1970s is a special phenomenon, at least it is the only phenomenon discussed in this study within this time range. (2) It is concluded that the correlation between the PDO and runoff in the UMYR is periodic and there is no special obvious linear relationship, but regional differences are more obvious. The inverse correlation between PDO and runoff in the study reaches is mainly on a decadal scale. The Lanzhou-Sanmenxia section is relatively sensitive in the face of the change of the PDO on the decadal scale. When formulating the water resources strategy of the Yellow River, we should notice the differences in the response of different sections to the same environmental background. (3) In the mid-19th century, many large-scale floods in the lower reach resulted from the sudden increase of runoff in the middle reach. In the reign of Emperor Daoguang of the mid-19th century, the Qing Dynasty declined rapidly. During this period, large-scale flood disasters occurred in many parts of eastern China, especially in the populous North China Plain and Taihu Basin. The flood brought huge financial and social losses. Among them, eastern Henan of North China Plain suffered from the flood disaster in successive years by burst of the Yellow River in the 1840s, and the central government spent a huge amount of money to solve the problem of the river, which greatly aggravated the financial difficulties in that period. The large-scale flood in the lower Yellow River corresponds to the period of sudden change of runoff flow in Sanmenxia section revealed by this research, which indicates the sudden increase of rainfall in the Loess Plateau. Climate change was deeply involved in China's decline and depression during the reign of Daoguang. (4) Although some progress has been made in reconstruction of multi-site and long-time runoff series of the Yellow River based on different materials, further work is needed in data analysis so as to make clear the sequences of uncertainty, thus enabling the integration of data in the future to provide basic data for further research on long-time spatial and temporal change of runoff of the Yellow River.

Pan evaporation is the only long-term observation of potential evaporation around the world. In analyzing and predicting how droughts and hydrological cycles might change in a warming climate, change of pan evaporation is one crucial element to be understood. In this paper, we chose 416 sites with continuous monthly observations over 1960-2014 in China. We calibrated the wind function in the PenPan model to improve the estimation of pan evaporation. We developed a new approach, i.e., the experimental detrending (ED) approach, and made comparison with the traditional partial differential (PD) method in attributing changes of pan evaporation for the periods of 1960-2014, 1960-1993 (evaporation paradox) and 1993-2014 (evaporation paradox disappeared). The results first showed that improvement in estimating pan evaporation can be made when using the new calibrated wind function: f_q(u₂)=3.977×10^-8(1+0.505u₂). The comparison then showed that both methods can well attribute changes of pan evaporation, and the ED approach performs slightly better than the traditional PD method. In addition, the ED approach can help make effective adjustment for the PD method in attribution analysis so as to better understand the change of pan evaporation. Hence, the ED approach is recommended to assist a better understanding and prediction of water-energy cycles in a changing climate.

The abrupt change point detection is an important content in the research of current climate change problem. And many methods and achievements have already been proposed. The results of traditional methods are often considered to be unpersuasive due to the irrational structure of statistics, ideal assumptions and subjectivity. In this paper, a new method called moving mean difference method for abrupt change points detection is proposed. It is compared with four widely used methods via both hypothetic series and observed data. The results show that the moving mean difference method has three advantages: (1) The method has a simple structure and definite physical meaning; (2) It is more accurate to detect the mutation point; (3) It can simultaneously detect all the mutation points and calculate the corresponding intensity of the mutations. The sediment discharge abrupt changes in different reaches of the Yellow River are analyzed through the five methods, based on the annual data obtained from the main hydrological stations in the Yellow River Basin. The results indicate that the sediment discharge in the upper reaches the river mutated in 1986, while that in the middle reaches changed suddenly in 1979 and 1996. The mutations of sediment discharge at Huaxian and Tongguan stations occurred in 1979, 1996 and 2003. The main factors for the mutation are human activities, including hydraulic engineering construction and large-scale water and soil conservation measures.

Due to rapid urbanization and relevant impacts on precipitation in both space and time, effects of urbanization processes on precipitation changes have been widely discussed in recent years. Based on hourly precipitation dataset from 20 stations covering the period of 2011-2015 across Beijing city, statistical methods such as circular statistical method were applied to examine spatio-temporal characteristics of precipitation with respect to precipitation types, extreme precipitation events and so on. The results indicated that: (1) regions in the central Beijing city are dominated by higher rainstorm precipitation amount, duration and precipitation intensity. Compared with rainstorm events in suburbs, precipitation processes in the central city are characterized by long duration and larger precipitation amount. Urban Rain Island effects could contribute to the above-mentioned rainstorm changes in the central city. (2) Uneven daily distribution of precipitation can be found across Beijing with remarkable regional difference. Rainstorm events mostly occurred after noon, accounting for 47.53% of the total precipitation type. Rainstorms in mountainous regions, northern and southern Beijing occurred mostly after noon, at noon and even at night. However, due to valley wind circulation and heat island circulation, precipitation patterns in central Beijing are relatively complicated and storms in western-central part of the city occurred mainly at nighttime. (3) Peak value of precipitation intensity of rainstorms occurred mainly during 12:00-19:00 and delayed occurrence of peak rainstorm values was observed in central city when compared to that in suburbs. Meanwhile, altitude can further induce uncertainty in occurrence time of peak precipitation amount. (4) The extreme precipitation index and the continuous drought as well as moisture index showed the high value in the urban area. The high value of the frequency of extreme precipitation index was found in the downwind direction of the urban area. Urbanization may indirectly increase the risk of extreme precipitation by population growth and land-use change.

The transport of sediment by rivers to the oceans plays an important role in coastal stabilization. The Qidong foreland is located on the junction between Yangtze Estuary and Jiangsu coast, where strong land-ocean interactions are highly sensitive to environmental changes. In order to examine sediment sources and change, QDZ-1 core sediments were collected at Qidong foreland tidal flat. And the content of micro-elements was analyzed by ICP-MS, further, the source-indicating significance of micro-elements was discussed based on distribution and enrichment coefficient. The result showed that sediment sources derive from the Yangtze River and the south Yellow Sea. In addition, sediment sources were quantitatively evaluated by estimation of sedimentary end-members. The result showed that sediment sources could be divided into three stages. The sediment flew mainly from the sediment transport of the Yangtze River into the sea, with the contribution rate being 68.1%. Then, the contribution rate gradually decreased with the decline of the North Branch, down to 38.5% during the period of 1930-1972, and to 17.5% after 1972. Meanwhile, the suspended sediments from southern Yellow Sea moved mainly to the south by strong tide and Subei coastal current, and the contribution rate was 27.1% before 1930. Subsequently, the contribution rate gradually increased, up to 55.6% during the period of 1930-1972, and to 75.9% after 1972. The sediment sources of Qidong foreland tide flat mainly transformed from the Yangtze sediment to the south Yellow Sea sediment. The changes in stages of sediment source were consistent with the decline of the North Branch.