Dynamics and characteristics of monsoonal orographic rainfall variability over Eastern Himalaya

Abstract

The Himalayas are an essential driver of the monsoon and climate system. However, river flooding during the monsoon impacts the most densely populated region of Himalayan downstream regions annually. Previous studies also reported elevation-dependent warming, rainfall changes, ice-sheet melting, and extremes in the Himalayas. Nevertheless, due to complicated orography, Himalayan precipitation dynamics remain quantitatively limited on a spatial scale compared to other monsoon regions. In the context of climate change, recent studies show how melting glaciers and snow, along with monsoonal rains causing recurrent floods, play a role. This study examined the last 43 years (1979-2021) to emphasize the interannual variability. We found a robust signal over in the Eastern Himalayas, where the orographic features and process plays a dominant role. Further analysis indicates Monsoonal rainfall is the main factor, rather than melting snow for these unusually extreme years. Regional monsoonal circulation connected to Walker circulation controls the variability of Himalayan monsoonal rainfall via circulation linkages. Our findings illustrate the wet and dry response mechanisms in the eastern Himalayas. The conclusions are drawn from this work highlight the role of natural variability, which might help understand Himalayan floods and their predictability. Keywords – Himalayas, Interannual variability, Monsoon dynamics, Orographic features, River floods