Seasonal Dependence and Variability of Rainfall Extremes in a Tropical River Basin, South Asia

In recent years, rainfall extremes have increased significantly and threatened the socio-economic development in Sri Lanka. This study investigates Mahaweli River Basin (MRB) of Lanka with daily station datasets from 1985 to 2015. The extreme indices recommended by Expert Team on Climate Change Detection Monitoring Indices (ETCCDMI) been used this study. Results showed a strong seasonal variation events over MRB significant interdecadal change between 1985–1999 2000–2015 wet region MRB, which is coherent decadal shift southwest monsoon (SWM) dry situations since year 2000. Based General Extreme Value distributions, long-term mean SWM (814 mm) moved leftward for period (704 rightward 1985–2000 period, suggesting that decreased late period. observed above-average (below-average) associated during can be ascribed strengthening (weakening) moisture flux Arabian Sea direction (weak) convergence domain. results further identified negative correlation Dipole Mode Index region, signifying Indian Ocean phase enhance MRB. Nino3.4 rain suggested high probability La Nina phase. findings understand precipitation context climate at river basin scale benefit policymakers building local adaptation strategies response change.