Changing pattern of heavy rainstorms in the Indus basin of India under global warming scenarios

Abstract

Estimation of extremely high rainfall (point or areal) is one of the major components of design storm derivation. The estimation of Probable Maximum Precipitation (PMP) involves selection of heavy rainstorms and its maximization for the moisture content during the rainstorm period. These heavy rainstorms are nothing but the widespread heavy rainfall exceeding a certain threshold value. The present study examines the characteristics of heavy rainstorms in the Indus basin selected from present climate and future scenarios simulated by the regional climate model. Such information on heavy rainfall forms the basis for the hydrologic design projects and also for the water management of a river basin. Emphasis is given to severe rainstorms of 1-day duration covering an area of at least 40,000 km 2 with spatial average rainfall of at least 5cm. This analysis also provides the information on the temporal changes in the storm factors such as shape, orientation, and movement, and shows that the model can well simulate the rainstorm pattern in terms of its intensity, orientation, and shape of the rainstorm, but overestimates the frequency of such heavy rainstorms. The future scenario indicates increase in rainfall intensity at the center of the rainstorm with decreasing areal spread. Decrease in the frequency of rainstorms is projected under the global warming conditions.