Dryness/wetness pattern over the Three-River Headwater Region: Variation characteristic, causes, and drought risks

摘要

The dryness/wetness patterns are a significant reference for stakeholders in developing reasonable strategies in regard to water resource management, prediction, prevention of extreme events, and management of agricultural activities; however, no attempts have been made to systematically quantify the dryness/wetness patterns and drought conditions over the Three-River Headwater Region (TRHR) of China, where the ecosystem is highly sensitive to climate change. The spatio-temporal characteristics of dryness/wetness for TRHR, as well as the reference evapotranspiration (ETr), precipitation (Pre), and drought risk, were all investigated for the period of 1961-2015. Using the methods of FAO-56 Penman-Monteith (FAO-56), standardized precipitation evapotranspiration index (SPEI), the Manner-Kendall (M-K) test, Pettitt test, factor contribution rate, and correlation analysis, the variation in the patterns of dryness/wetness, ETr, and Pre, and the causes behind dryness/wetness were discussed. Results indicated that the TRHR underwent a wetting tendency, which was characterized by decreasing ETr and increasing Pre based on the SPEI-12M during 1961-2015. Moreover, 1971-1980 was the driest period, while 2001-2015 was the wettest period. A significant difference between seasons was detected in the dryness/wetness patterns during all study periods, as well as in extreme droughts. The TRHR underwent an overall wetting trend with 85% of the stations' SPEI-3M showing increased variation during spring, in contrast with the north-south distribution pattern of the dryness/wetness with variation in the SPEI during summer. Moreover, it can be seen that droughts with higher longest drought duration (LDD) and total drought duration (TDD) were mostly located on the edge of the eastern and northern TRHR. The influencing factors demonstrate the vital roles of Pre and ETr in generating variation in the dryness/wetness patterns of the southern and northern parts of the TRHR, respectively. There is evidence indicating that Nino3.4, North Atlantic oscillation, and Arctic oscillation played more important roles in the variation of dryness/wetness patterns and Pre in TRHR.