Surface soil moisture has a direct impact on food security, human health and ecosystem function. It also plays a key role in the climate system, and the development and persistence of extreme weather events such as droughts, floods and heatwaves. However, sparse and uneven observations have made it difficult to quantify the global distribution and dynamics of surface soil moisture. Here we introduce a metric of soil moisture memory and use a full year of global observations from NASA's Soil Moisture Active Passive mission to show that surface soil moisture-a storage believed to make up less than 0.001% of the global freshwater budget by volume, and equivalent to an, on average, 8-mm thin layer of water covering all land surfaces-plays a significant role in the water cycle. Specifically, we find that surface soil moisture retains a median 14% of precipitation falling on land after three days. Furthermore, the retained fraction of the surface soil moisture storage after three days is highest over arid regions, and in regions where drainage to groundwater storage is lowest. We conclude that lower groundwater storage in these regions is due not only to lower precipitation, but also to the complex partitioning of the water cycle by the surface soil moisture storage layer at the land surface.

Drought is one of the most catastrophic natural hazards which have severe impacts on human society and yet it is the least understood hazard. Monitoring drought in a reliable way plays a critical role in the early warning as well as the mitigation of drought hazard. Generally, the integrated agro-meteorological drought monitoring is one of the most popular drought monitoring methods and it is the key step to mitigate droughts effectively. However, the originally developed integrated drought monitoring index included nothing about evapotranspiration, and it does perform not well in reflecting impacts of evapotranspiration on occurrence of droughts. In this case, this study attempted to propose an improved version of the multivariate standardized drought index (MSDI) using standardized precipitation evapotranspiration index (SPEI) and standardized soil moisture index (SSI), i.e. modified multivariate standardized drought index (MMSDI). Based on the statistical records of drought-affected crop area in 7 geographical zones across China, this study tests the applicability of MMSDI in drought monitoring across China in 3-month and 6-month time scales, with comparison to the meteorological drought monitored by SPEI, agricultural drought monitored by SSI and integrated agro-meteorological drought monitored by MSDI. The result indicates that MMSDI can monitor meteorological drought and agricultural drought simultaneously. Furthermore, MMSDI has greater superiority than SPEI, SSI and MSDI in the veracity of drought monitoring. Besides, MMSDI can monitor droughts in bad conditions where meteorological drought and agricultural drought monitoring technique cannot be applied. Moreover, MSDI tends to overestimate the drought intensity and the size of drought-affected regions across China. In sum, MMSDI proposed in this study can be used to monitor and detect drought conditions in a more accurate way from perspectives of meteorological drought and agricultural drought. Meanwhile, drought conditions monitored by MMSDI are very close to in-situ observations and to the real-world observations of droughts in terms of drought-affected regions and related losses. In this sense, this study provides a theoretical foundation for large-scale drought monitoring across China, and provides practical regional case studies for related research in other regions of the world.

旱灾是对人类社会影响以及致损最大的灾种之一,如何进行可靠的旱灾监测是旱灾预警与旱灾防灾减灾的关键。气象干旱与农业干旱的综合干旱方法是目前干旱监测的主要方法之一。本文对多变量标准化干旱指数（MSDI）方法进行改进,以非参数化的方法计算标准化降水蒸散指数（SPEI）、标准化土壤湿度指数（SSI）,提出改进的MSDI,即气象农业综合干旱指标（MMSDI）。在此基础上,用1979-2015年中国降水资料、蒸散发资料以及土壤湿度数据对不同时间尺度（3月尺度与6月尺度）分别研究气象干旱、农业干旱、气象农业综合干旱,用气象农业综合干旱分别与气象干旱、农业干旱和改进之前的气象农业综合干旱对比,并结合实际记录的干旱事件时空特征验证,结果证实MMSDI指数可以同时监测气象与农业干旱,且其监测结果准确度高于单一变量的气象（SPEI）或农业（SSI）干旱监测,MMSDI指数对气象农业综合干旱具有更好的监测效果,可考虑作为中国气象农业综合干旱监测及旱灾预警的重要理论依据。

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.

以全国653个农业气象站1993-2013年耕地的土壤相对湿度数据为基础,运用地统计方法,分析中国耕地土壤相对湿度时空分异特征与规律。结果表明：自1993年以来全国耕地的土壤相对湿度呈现波动上升趋势。全国耕地的土壤相对湿度普遍大于60%,分布区域自4月中旬开始随夏季风推移不断向北向西扩大,自10月下旬开始向东、南方向缩小。耕地土壤相对湿度值随土壤深度的增加而增加。年际尺度上,耕地的土壤相对湿度在夏秋季上升速度最快,变化幅度随土层深度增加而变小。土壤相对湿度与降水量存在较强的正相关关系,与潜在蒸发量、气温普遍存在较强的负相关关系。土壤相对湿度与各气象要素的相关性随深度加深而减弱。春、夏、秋季气象因素对旱地土壤相对湿度影响较大,冬季气象因素对水田影响更大。

Previous estimates of land-atmosphere interaction (the impact of soil moisture on precipitation) have been limited by a lack of observational data and by the model dependence of computational estimates. To counter the second limitation, a dozen climate-modeling groups have recently performed the same highly controlled numerical experiment as part of a coordinated comparison project. This allows a multimodel estimation of the regions on Earth where precipitation is affected by soil moisture anomalies during Northern Hemisphere summer. Potential benefits of this estimation may include improved seasonal rainfall forecasts.

<p>The ratio of transpiration to evapotranspiration (T/ET) is a key parameter for quantifying water use efficiency of ecosystems and understanding the interaction between ecosystem carbon uptake and water cycling in the context of global change. The estimation of T/ET has been paid increasing attention from the scientific community in recent years globally. In this paper, we used the Priestly-Taylor Jet Propulsion Laboratory Model (PT-JPL) driven by regional remote sensing data and gridded meteorological data, to simulate the T/ET in forest ecosystems along the North-South Transect of Eastern China (NSTEC) during 2001-2010, and to analyze the spatial distribution and temporal variation of T/ET, as well as the factors influencing the variation in T/ET. The results show that: (1) The PT-JPL model is suitable for the simulation of evapotranspiration and its components of forest ecosystems in Eastern China, and has relatively good stability and reliability. (2) Spatial distribution of T/ET in forest ecosystems along NSTEC was heterogeneous, i.e., T/ET was higher in the north and lower in the south, with an averaged value of 0.69; and the inter-annual variation of T/ET showed a significantly increasing trend, with an increment of 0.007/yr (<i>p </i>< 0.01). (3) Seasonal and inter-annual variations of T/ET had different dominant factors. Temperature and EVI can explain around 90% (<i>p </i>< 0.01) of the seasonal variation in T/ET, while the inter-annual variation in T/ET was mainly controlled by EVI (53%, <i>p </i>< 0.05).</p>

植被蒸腾与蒸散的比值（transpiration/evapotranspiration, T/ET）表征了植被蒸腾对生态系统蒸散的贡献率,是准确量化生态系统水分利用效率的关键参数,对研究植被水分运移的生理生态机理以及碳水循环关系具有重要意义。基于站点数据验证PT-JPL模型（Priestly-Taylor Jet Propulsion Laboratory Model）模拟精度,集成遥感数据和气象栅格数据模拟中国东部南北样带森林生态系统2001-2010年T/ET,并分析其时空变化及影响因子。结果表明：① PT-JPL模型适用于中国东部森林生态系统蒸散及其组分模拟,具有较高的稳定性和可靠性;② 中国东部南北样带森林生态系统T/ET空间差异显著,整体呈南部低、北部高,主要由夏季T/ET空间格局主导;样带整体T/ET均值为0.69,2001-2010年呈显著缓慢上升趋势,增幅为0.007/yr（p p p

Using actual observed soil moisture data of 155 agro-meteorological stations across China, at dekadal scale from 1981 to 2010, this paper examined the spatial and temporal characteristics of soil moisture at each 10 cm depth from 0 to 50 cm, at regional and national scales. Annual trend and significant change point were detected through tendency analysis and Cramér-von Mises test methods. Since soil texture and crop types were approximately homogeneous in each climatic region, regional average variation of soil moisture could be observed in the analysis. Mean soil moisture was between 15% and 25% in most regions while it was above 25% in the northern part of Northeast China and southern part of Southwest China. At each depth, larger soil moisture was detected in Southwest China, Jianghuai, Northeast China, Jiangnan, Jianghan, Huanghuai and South China, while the smallest value was observed in Inner Mongolia. As soil deepening, except in Tibetan Plateau, increases in soil moisture were apparent, being a maximal magnitude in Southwest China. Obviously, as well as periodical characteristics, annual and seasonal difference of soil moisture emerged at each depth, corresponding well to regional precipitation, temperature, and water demand for planting crops. An obvious freezing-increasing-deceasing-increasing trend existed in Northeast China, Inner Mongolia and Xinjiang, a variation of deceasing-increasing-fluctuating in North China, Huanghuai, and eastern Northwest China, a multiple fluctuation in Jianghuai, Jianghan and Jiangnan, and a deceasing-increasing-deceasing trend in South China and Southwest China, while an increasing-deceasing trend was found in the Tibetan Plateau. Soil moisture at a greater depth was higher than that at superficial layers. Annual soil moisture varied at each depth, but the mean value decreased from 1981 to 2010. Such annual variation could be well explained by corresponding temperature and precipitation. Consequently, soil moisture tended to decrease in response to temperature increase, following climate change. Apart from climatic factors, soil texture and crop type, as well as human activity, can have influence on soil moisture, which is needed to be studied further. Soil moisture decreased in Xinjiang, South China, North China, Tibetan Plateau, Northeast China and Huanghuai among which Xinjiang was most remarkable with a velocity above -2.3%?(10a)-1. Except in Jianghuai, a significant change of soil moisture was detected, mainly during two periods, i.e. from the late 1980s to early 1990s, and late 1990s.

基于中国155个农业气象观测站1981-2010年逐旬土壤湿度资料,分析了全国和12个气候区域0~50 cm逐层的土壤湿度时空分布规律,采用趋势分析和Cramér-von Mises（CVM）方法探究了土壤湿度的变化趋势及突变性。结果表明：西南、江淮、东北、江南、江汉、黄淮和华南地区各层土壤湿度均高于全国平均值,内蒙古地区最低;随着深度增加,西南地区土壤湿度增加最明显,仅青藏高原地区土壤湿度减小。不同区域0~50 cm各层土壤湿度年变化和季节变化差异明显,并具有阶段性特征,大部地区深层土壤湿度高于浅层;总体上,新疆、华南、华北、青藏高原、东北、黄淮地区1981-2010年土壤湿度减小趋势显著,其中新疆地区减小最为明显。除江淮地区外,各区域土壤湿度均存在较为明显的年际差异,突变时段主要集中在20世纪80年代后期至90年代初期、90年代后期两个时间段。

Little measurement-based soil moisture information is available for the humid to semi-humid transitional zones in China. Anhui Province is a representative area of these zones and spans several hydroclimatic and geomorphological zones. To overcome shortage of observational soil moisture information in this area, we collected and compiled a multi-layer daily soil moisture record from 2012 to 2016 across Anhui Province based on the observations of a soil moisture-observing network composed of 85 sites. We then analyzed the vertical and spatiotemporal variability of soil moisture across this region. Primary findings are: (a) soil moisture in this region has apparent vertical gradients and increases with soil depth; (b) substantial soil moisture spatial variability appears in the shallow soil layers (depth <= 40 cm) with the highest values in the middle part of this region, but soil moisture in the deep layers (depth > 40 cm) shows low spatial variability; (c) seasonality of soil moisture across this region is complicated and has fluctuations with July as the wettest month in most of the province; (d) inter-monthly fluctuation of soil moisture is larger in the upper soil layers than in the lower layers; and (e) antecedent accumulated rainfall is a major factor influencing soil moisture throughout this region with soil moisture in the upper layers more sensitive to immediate weather conditions and soil moisture in the lower layers showing lagged responses to the weather conditions. This study can not only reveal the spatiotemporal and vertical characteristics of soil moisture across this region, but also provide a useful reference dataset for the other soil moisture modeling and retrieval studies.

It is important to quantitatively analyze the effects of protecting important ecological spaces in China to ensure national ecological security. By considering changes in the ecological land, this study examines the effects of protecting three types of important natural ecological spaces in China. The results show that: (1) In 2018, the ratio of ecological land to important natural ecological spaces accounted for 92.64%. This land had a good ecological background that reflects the developmental orientation of important ecological spaces. (2) From 1980 to 2018, the area of ecological land in important ecological spaces shrank but the rate of reduction was lower than the national average, which shows the positive effect of regulating construction in natural ecological spaces. The restorative effects of ecological projects to convert farmland into forests and grasslands have been prominent. The expanded ecological land is mainly distributed in areas where such projects have been implemented, and the reduced area is concentrated in grain-producing regions of the Northeast China Plain and agricultural oases of Xinjiang. In the future, the government should focus on strengthening the management and control of these areas. (3) The area ratio of ecological land was the highest in national nature reserves. The rate of reduction in its area was the lowest and the trend of reduction was the smallest in national nature reserves, which reflects differences in the status of ecological protection among different spaces. (4) The ratio of ecological land to important ecological spaces was higher than that in the surrounding external space, and the rate of reduction in it was lower. Thus, the effects of internal and external protection had clear differences in terms of gradient.

定量分析重要生态空间建立前后的生态保护成效,对于保障国家生态安全具有重要意义。本文以生态用地为切入点,从时间和空间双重角度,评估了中国重要生态空间构建的生态保护效果,以期能为国土空间分类分区管控提供科学依据。结果表明：① 2018年重要生态空间以生态用地为主导,具有良好的生态本底,体现了重要生态空间的发展定位和重要地位; ② 1980&#x02014;2018年,重要生态空间内生态用地呈收缩趋势,但面积减少率低于全国平均水平,定量反映了重要生态空间的构建对生态的积极保护成效,总体来说生态用地变化基本处于稳定状态,扩大区域主要分布在退耕还林还草生态保护工程实施区,缩小区域集中在东北平原的粮食主产区和新疆绿洲农业地区,今后要重点加强管控;③ 3类重要生态空间内部生态保护成效有差异,国家级自然保护区生态用地面积比例最高,生态用地面积减少率最小、减少趋势最不明显、变化最为稳定,生态保护效果最好;④ 重要生态空间内生态用地面积比例高于周边外部区域,面积减少率低于外部区域,内、外保护成效具有明显梯度差异,说明重要生态空间的构建对生态保护的意义重大。