3.1.3. Precipitation

The National Meteorological Information Centre of China provides daily precipitation data (meteorology station) from 1961 to present [47]. There are 2472 meteorology stations in China, and there are 7 meteorological stations in this study area. Daily precipitation data were collected from March 2015 to December 2018. Since precipitation data must be coordinated with SMAP data for irrigation information monitoring, the spatiotemporal resolution of the precipitation data must be processed. The daily precipitation data include statistical results for two periods (20:00–8:00 and 8:00–20:00) in Beijing time. The current method for the L3\_SM product is to use the nearest 6:00 AM local solar time criterion to perform Level 3 compositing [38]. The precipitation from 8:00–8:00 is summed as the daily precipitation, and the station data are interpolated into the grid data using the inverse distance weighting (IDW) method based on python 2.7.
