Spatio-temporal changes in daily extreme precipitation for the Lancang-Mekong River Basin

The Lancang-Mekong River Basin (LMRB) is one of the river basins most prone to floods and droughts induced by extreme precipitation (EP). Therefore, it is of great significance to characterize the spatio-temporal changes of EP in the LMRB. Based on the Multi-Source Weighted-Ensemble Precipitation dataset (MSWEP) Version 2.2 (V2.2) dataset from 1979 to 2016, all improved extreme precipitation indices (EPIs) at grid and national levels were computed and their changing trends were investigated by means of the trend-free pre-whitening Mann-Kendall significance test and the Sen's slope; the rationality of the improved EPIs was discussed. The results revealed: (1) The improved EPIs performed better than the original ones in describing the spatio-temporal variations of EP across LMRB; (2) R95p, R99p, SDII-10, SDII-25, SDII-50, Rx1day, Rx3day, and Rx7day showed a significant decreasing trend (p < 0.05) in the northeastern part of the upper, middle, and lower reaches of the Mekong River Basin (MRB), implying a probable reduction in flood risks; (3) Rx15day and Rx30day showed a significant increasing trends (p < 0.05) in the southeast upper MRB and the north middle MRB, indicating a probable increase in flood risks; (4) CDD4 and NDD4 manifested an probably increasing drought risk in the middle and lower reaches of the Lancang River Basin and the lower MRB with a probably reducing drought risk in Lancang River Headwater Region, the middle MRB and the Mekong Delta; (5) the decreasing trend exhibited by most flood-related indices in China, Laos, Thailand, Cambodia, and Vietnam signified a probable reduction in flood risks; (6) the increasing trend of both CDD4 and NDD4 in China and Cambodia indicated a probable increase in drought risks. The outputs of this paper could benefit a better understanding of evolution in daily extreme precipitation, and flood and drought risk in LMRB.