Spatial distribution and temporal trend of pan evaporation in the three gorges reservoir area and its surroundings during 1952-2013

Abstract

Under climate warming and impoundment conditions of the Three Gorges Reservoir (TGR), spatial distribution and temporal trend of pan evaporation in the Three Gorges Reservoir Area (TGRA) and its surroundings offer valuable information about regional hydrology and ecosystem succession. In this study, pan evaporation measured by a pan of 20 cm diameter at 27 meteorological stations during 1952-2013 in the TGRA and its surroundings were calculated, compared and analyzed. Their spatial distribution and temporal trend were examined and the causes for the variations are discussed. The results show that: (1) The average annual pan evaporation in the TGRA and its surroundings is 1208.03 mm，and it appears an east–west downward gradient. (2) Examined by Mann-Kendall (MK) test, pan evaporation significantly declined at the rate of -40.8 mm/decade during 1952-2013. It shows upward trend in 1960s, 1970s, but downward trend in 1980s and 2000s. (3) The decreasing of pan evaporation is the results of comprehensive influences of air temperature (TEM), wind speed (WIN), sunshine duration (SSD) and relative humidity (RHU). Among them, SSD is the largest contributor.