Recent Tangible Natural Variability of Monsoonal Orographic Rainfall in the Eastern Himalayas

Abstract

Himalayas hydroclimate is a lifeline for South Asia's most densely populated region. Every year, flooding in the Himalayan rivers is usual during summer monsoon, which impacts millions of inhabitants of the Himalayas and downstream regions. Recent studies demonstrate the role of melting glaciers and snow in the context of global warming, along with monsoonal rain causing recurrent floods. Here, we highlight the natural variability in the eastern Himalayan hydroclimate over the last 43 years (1979–2021). We found extreme monsoonal rainy years with six dry years and seven wet years after removing the climate change signal. Monsoon rainfall is a significant contributor, and melting snow is not a potential contributor to these anomalous extreme years. The variability of Himalayan monsoonal rainfall is strongly regulated by local monsoonal Hadley circulation associated with tropical sea surface temperature. Our findings demonstrate mechanisms associated with Himalayan wet and dry monsoon. Atmospheric dynamics are attributed as the primary modulating factor, influencing local thermodynamics through moist processes. The insights provided in this study underscore the impact of natural variability‐driven challenging events that could be predictable. Thus, this mechanism could improve the predictability of the Himalayas floods.

Orographic effects on droughts in a monsoon climate with the world's highest rainfall

“…In particular, orographic barriers oriented perpendicular to the prevailing direction of air masses disrupt atmospheric stratification and enhance the spatial distribution of precipitation (Roe, 2005). While there is some overlap in the physical principles of orographic lift and rain shadow effects in all climate zones (Chao, 2012;Rotunno & Houze, 2007), the specific behaviour and effects of orography in monsoonal climates differ because of the unique seasonal and regional characteristics of monsoon (Anders et al, 2006;Bookhagen & Burbank, 2006;Kad & Ha, 2023;Kumari et al, 2017;Tawde & Singh, 2015;Xie et al, 2006). Orographic effects in monsoonal regions are closely linked to the reversal of prevailing wind patterns.…”