Spatio-Temporal Variability Of Drought Characteristics In The Eastern Watershed Entering Lake In Inner Mongolia During The Past 30 Years

Drought is a key factor to restrict the development of the ecological environment and the social economy, especially for the watersheds entering lake in arid and semi-arid regions, its knock-on effect on watershed per se and downstream lake should not be ignored. In this paper, based on daily precipitation data collected at 11 stations in the eastern watershed of Lake Wuliangsuhai from 1986 to 2014, the multi-period Universal Kriging method was used to build the precipitation data sets. The Mann-Kendall test, Spearman’s Rho test and R/S methods were employed to analyze the trend and mutation test. Standardized Precipitation Index (SPI) was adopted to evaluate the drought level, and two drought characteristic values, such as drought duration and drought severity, were used to discuss the temporal-spatial distribution and clarified the impact of drought on the eastern watershed and downstream Lake Wuliangsuhai. The main conclusions are as follows:(1) The precipitation in the Lake Wuliangsuhai is characterized by obvious seasonal changes, great variability and concentrating rainstorm. Three persistent drought periods were found during 1999-2001a,2005-2007a and 2009-2011a in the last 29years.(2) The Mann-Kendall test showed that the precipitation in spring was not significant, presented decreasing trend in summer and winter and performed increasing trend in autumn. The trend of annual precipitation was same as that in summer, with the increasing rate of -4.77mm/10a. The results from R/S test showed that the variations of seasonal and annual precipitation in the future were in accordance with the previous period. In addition, the Mann-Kendall mutation test showed that the breakpoint of precipitation occurred in 2004, and then it began to decrease.(3) The results of spatial distributions of seasonal and annual precipitation presented a decreasing trend from the east to the west in the eastern watershed of Lake Wuliangsuhai. The precipitation in the plain area was less than that in the mountainous area. The short time-scale drought was mainly concentrated on the central part named as downstream of Wusutule River and southeastern part named as upstream of Heishuihao River and Huangtuyaozi River. The long time-scale drought primarily occurred in the northern parts of watershed named as upstream of Wusutule River and upstream of Jialage River. In addition, drought process had an increasing trend in northern watershed and the upstream of southeastern mountainous regions. The phenomenon of drought was not serious near the wetland of Lake Wuliangsuhai and Dashetai Reservoirs.(4) The precipitation and water evaporation had decreased slightly in Lake Wuliangsuhai, while the water supplement from the eastern watershed performed an obvious decreasing trend. In order to meet the ecological water requirement of Lake Wuliangsuhai, governments have to increase the water supplement from Yellow River, and even provide more discharge to make up the water absence to alleviate eutrophication and control the growth of yellow algae. Therefore, from the global perspective, rational usage of water conservancy facilities in the eastern watershed and optimal allocation of water resources in Hetao irrigation area simultaneously should be adopted to ensure the cleaning water source of Lake Wuliangsuhai which has a great significance for the sustainable exploitation and development of Lake Wuliangsuhai.