2.1 Data
In this work, Daily precipitation and temperature data were downloaded from 698 evenly distributed weather stations nationwide from the China Meteorological Data Network from 1961 to 2016 (https://data.cma.cn/), which covers a wide range of climate, ecological regions and landscapes throughout China. The temperature data was used to estimate the potential evaporation. Then abnormal data was excluded, and the research parameter changes and relationships in the middle and lower reaches of the Yangtze River were focused on. The 30 meter digital elevation model (DEM) was downloaded from the geospatial data cloud (http://www.gscloud.cn/) by using ArcGIS, and the corresponding watershed area of the hydrological station was extracted. According to the Hydrological Annual Report of the People’s Republic of China, daily runoff data was collected from 224 stations with records from 1970 to 1990 and from 2007 to 2016 for at least 20 years. Daily precipitation and temperature data were chosen from 267 weather stations in and near Yangtze river basin (YZRB). The observed precipitation and estimated potential evaporation were interpolated into the whole YZRB using the Thiessen polygon method (Meena et al., 2013). Then the interpolated precipitation and potential evaporation of the basin area corresponding to 224 hydrological stations were averaged to obtain the daily precipitation and potential evaporation data of each hydrological station.