Role of Terrestrial Moisture Source Transport on Summer Monsoon Rainfall Variability over Ganga River Basin

Abstract:

Ganga river basin, which is one of the most agricultural intensified and densely populated in the world, receives moisture from different terrestrial sources, other than oceanic sources. The modeling of Indian Summer Monsoon Rainfall (ISMR) over Ganga Basin, especially its variability, is very crucial as most of the agro-economical practices depend on it. The monsoon rainfall over the core monsoon zone in India which covers the large amount of area of Ganga basin is significantly correlated with the rainfall over Ganga basin. Therefore, the atmospheric moisture transport from different terrestrial sources to the sink over Ganga basin is studied for better understanding of ISMR variability (both inter–annual, and intraseasonal timescale) over Ganga Basin and core monsoon zone. We use extended version of the dynamic recycling model, which is based on Lagrangian trajectory approach to study the impact of moisture source variability on ISMR over Ganga basin during 1979–2013. The intraseasonal variation of ISMR is also observed to be significantly associated with the moisture source variability. The regions with dense vegetation cover such as Ganga basin and south-central forest region in India, manifest substantial role of land surface feedback with high recycling ratios (15-20%). It is also observed that the peak monsoon rainfall occurs during a period when all the oceanic and terrestrial sources altogether contribute significantly to the ISMR. The novelty of present work lies in understanding the role of different terrestrial sources on ISMR variability at different timescale viz., intra–seasonal to interannual. Our findings also highlight the importance of land surface feedback through evapotranspiration, in order to accurately model ISMR variability for better planning and management of the crop calendar.

Key words: Atmospheric moisture transport, Dynamic precipitation recycling, Indian summer monsoon rainfall variability, Ganga River Basin.