采用青海省1965—2018年50个气象站月降水资料和同时段太阳黑子相对数资料,将青海省划分为长江和澜沧江源区、黄河源区、东部低海拔区和柴达木盆地区,运用集中度和集中期、线性倾向估计、M-K检验法和Morlet小波分析法对青海省时空降水变化特征进行分析.结果表明:青海省降水量在空间分布上呈现由西北向东南增加的特征,在年际变化上,青海省和4个分区年降水量都具有上升趋势,其中青海省平均上升0.81 mm/a;青海省降水年内分配不均,降水集中度具有逐渐趋向均匀的趋势;青海省出现微弱的降水突变信号,青海省主体和东部低海拔区突变始于2006年前后,长江和澜沧江源区突变始于2003年前后,柴达木盆地区突变于2001年前后,而黄河源区存在4个可能突变点;柴达木盆地降水变化具有22～23 a的主周期,青海省和其他3个分区都具有28～30 a的主周期,在28 a尺度上青海省和4个分区降水量与太阳黑子相对数的小波系数都分别达到了0.95、0.86、0.91、0.93和0.75的正相关性,且显著性水平均为0.01.

The Yarlung Zangbo River is the largest river on the Tibetan Plateau and a major international river in South Asia. Changes in the blue and green water resources in its basin are of great importance to the surrounding local and Asian regions in the context of global warming. This research used the Soil and Water Assessment Tool model to estimate blue and green flows (BWF and GWF) and analyze the spatial-temporal distribution characteristics under different hypothetical climate change scenarios. The results show that (1) the multi-year average BWF in the middle and upper reaches of the Yarlung Zangbo River Basin is 176.2 mm, the GWF is 213.1 mm, and the difference between precipitation and total water resources is only 5.4 mm; (2) both BWF and GWF in this basin showed a slightly increasing trend from 1980 to 2010, but the distribution of subbasins from upstream to downstream is decreasing; and (3) GWF has a positive correlation with both precipitation and temperature, but BWF only increases with precipitation and decreases with increasing temperature. Moreover, the change in blue and green water resources is more sensitive to the changes in precipitation than to changes in the temperature.

Monitoring runoff is critical for water resources management. Remote sensing can be an effective technique to investigate changes in runoff on data-scarce regions. This study used Calibrated Passive Microwave Daily EASE-Grid 2.0 Brightness Temperature Earth System Data Record (CETB) and M/C signal method to simulate runoff in Lhasa River Basin. This satellite-derived runoff was compared with gauge observations and Soil and Water Assessment Tool (SWAT) model simulations. The results show that (1) the well-correlated satellite-derived M/C signals are able to detect the runoff process in the selected river channels. For most gauges, the runoff generated by M/C signals fit well with observation, giving a Pearson correlation coefficient greater than 0.9, Nash-Sutcliffe efficiency coefficient greater than 0.8, and relative error less than 15%; (2) When compared to the SWAT model, the M/C signal method has advantages in flood season runoff simulation. These two simulation methods are nearly equal for the entire runoff process; (3) For runoff simulation influenced by the underlying surface and the shape of the river channel, the M/C signal method is better suited in areas with a low fraction vegetation cover and channels with a typical inverted trapezoid shape. Overall, we conclude that M/C signal method simulation is a valuable source of surface water information and could be used for runoff monitoring in data-scarce areas.

Under the background of global climate change, drought is causing devastating impacts on the balance of the regional water resources system. Hydrological drought assessment is critical for drought prevention and water resources management. However, in China to assess hydrological drought at national scale is still challenging basically because of the difficulty of obtaining runoff data. In this study, we used the state-of-the-art passive microwave remote sensing techniques in river runoff modelling and thus assessed hydrological drought in Mainland China in 1996–2016. Specifically, 79 typical hydrological stations in 9 major basins were selected to simulate river runoff using the M/C signal method based on a high-resolution passive microwave bright temperature dataset. The standardized runoff index (SRI) was calculated for the spatial and temporal patterns of hydrological drought. Results show that passive microwave remote sensing can provide an effective way for runoff modelling as 92.4% and 59.5% of the selected 79 stations had the Pearson correlation coefficient (R) and the Nash-Sutcliffe efficiency coefficient (NS) scores greater than 0.5. Especially in areas located on Qinghai-Tibet Plateau in the Inland and the Southwest River Basin, the performance of the M/C signal method is quite outstanding. Further analysis indicates that stations with small rivers in the plateau areas with sparse vegetation tend to have better simulated results, which are usually located in drought-prone regions. Hydrological drought assessment shows that 30 out of the 79 stations present significant increasing trends in SRI-3 and 18 indicate significant decreasing trends. The duration and severity of droughts in the non-permanent dry areas of the Hai River Basin, the middle reaches of the Yangtze River Basin and the Southwest of China were found out to be more frequent and severe than other regions. This work can provide guidance for extending the applications of remote sensing data in drought assessment and other hydrological research.

: The Jinsha River Basin (JRB) is the most important tributary of the Changjiang River and the most ecological vulnerable region to climate change. Therefore, to better understand the hydro-meteorology characteristics of JRB and enhance hydrological forecasts, a temporal-spatial analysis of historical hydro-meteorological elements and drought characteristics is required. In this study, 45 meteorological stations and 5 hydrologic stations in JRB for the last 60 years of historical data were utilized for analyze the temporal-spatial distribution and trends of hydro-meteorological elements, while drought characteristics in this basin were assessed using SPI values at six-month scales (SPI-6). The results show that: (1) the three daily temperature types (minimum, mean and maximum) and precipitation of the JRB all show an increase from the upper to lower reaches. (2) the Mann-Kendall test analysis of hydro-meteorological elements’ annual values reveals that the mean temperature of 42 stations is rising, while precipitation is rising at 25 stations. The runoff at all five hydrologic stations is increasing. The temperature and precipitation in the upper reaches are the areas with the greatest increase in the JRB, while the precipitation in the lower reaches is the only one that is on a downward trend. (3) In the drought analysis based on SPI-6, the downstream of JRB, which is located in Sichuan and Yunnan provinces, is the region with the most severe drought. There is no visible trend in drought duration at most stations, and the drought magnitude analysis is dominated by a decreasing trend. However, the drought intensity analysis is dominated by an uptrend, especially in the mid- and lower streams.

Accurate river runoff simulation is of great importance for basin hydrological simulation, water resources plan and sustainable management, hydrological disaster prevention and control. With the rapid development of the earth observation satellite remote sensing techniques, microwave remote sensing monitoring can provide a new method for river runoff simulation. To date, for river runoff simulation, further exploration is needed based on passive microwave remote sensing brightness temperature observations. This paper applied the M/C signal method to river runoff simulation in typical river basins in China based on a high-resolution passive microwave remote sensing brightness temperature dataset. The usability of this method was discussed. To analyze the influence factors of the simulation results, 7 geomorphologic and hydrometeorological factors were chosen, including river width, mean observed discharge, control area, vegetation percentage, elevation, land use/cover and climate type. Results of the monthly runoff simulation show that among the 61 typical sites in 7 river basins in China, R2 of 59.0% of them exceeded 0.5 and more than 41.0% reached an ENS larger than 0.5. Performance for the sites in basins of the rivers in Southwest China is obviously better, especially for the sites on the Tibetan Plateau; elevation, mean observed discharge, climate type and width of the river cross section are found out to be the dominated factors; and the M/C method is more suitable for sites on small rivers of high elevation under mountain plateau climate. Generally, this paper can inspire research ideas for river runoff simulation, thus providing reliable guidance for extending the hydrological application of microwave remote sensing in China.