Quantification of Evaporative Sources of Precipitation and Its Changes in the Southeastern Tibetan Plateau and Middle Yangtze River Basin

The Southeastern Tibetan Plateau (SETP) and the Middle Yangtze River Basin (MYRB) show a large difference in their levels of precipitation, despite the fact that they are located within the same latitude band. The annual precipitation in the MYRB is much higher than in the SETP. Precipitation has decreased in the past three decades in both regions. To clarify the difference in precipitation and its changes between these two regions in recent decades, a quasi-isentropic backward trajectory (QIBT) model is used to track the evaporative source with the ERA-Interim reanalysis as the baseline. The wet seasons (from April to September) over the period of 1982–2011 were analyzed. Evaporative sources were divided into an oceanic portion and a terrestrial portion, in which local recycling was included. Our conclusions are as follows. A terrestrial evaporative source, including a neighboring terrestrial land source and local source, dominates both regions, although the summer monsoon regulates precipitation in the wet season. The local precipitation recycling ratio is 35% in the SETP and 29% in the MYRB. The oceanic evaporative source in the MYRB is five times larger than that in the SETP. The decrease in the oceanic evaporative source in the Indian Ocean is responsible for the decrease in precipitation in the SETP. In the MYRB, decreases in neighboring terrestrial sources dominate the precipitation decline. Regardless of the decreases in the remote oceanic or neighboring terrestrial evaporative sources, the local recycling ratio increased in both regions.