Understanding the role of land-based evapotranspiration on Indian Summer Monsoon Rainfall

Land plays an important role in influencing weather and climate due to its interaction with the atmosphere in the form of water and energy. The effect of land on precipitation has been a key concern to the hydrology community for years. To understand this, it is necessary to assess the influence of land surface feedbacks on evapotranspiration and, subsequently, precipitation. The Indian subcontinent houses various climatic zones ranging from arid to one of the wettest areas of the world, and from cold-dry regions of Tibet to the hot and humid peninsular India. With such large variations in the climate, this region hosts a large number of transitional zones, which are considered the hotspots for soil moisture-precipitation interactions. This work aims to study the evapotranspiration-precipitation feedback over the Indian subcontinent and quantify the recycled precipitation over different sub-regions using water vapor tagging technique incorporated in WRF model. For present study, WRF model with tagging capabilities developed by Arnault et al., (2016) is utilized which allows us to specify a source region for moisture originating in the form of evapotranspiration, which can be tagged and tracked throughout the atmosphere. This will enable us to quantify the tagged moisture accurately and facilitate understanding of recycled precipitation over India. Two experiments are set up to assess the feedbacks at continental and regional scales. For the first experiment, entire India is set as the source region. This essentially tags entire evapotranspiration originating from the Indian landmass and tracks it throughout the atmosphere for the monsoon season from 1st June to 30th September. In the second experiment, the Indian region is sub divided according to homogeneous rainfall regions. The evapotranspiration from each of these regions is tagged individually to quantify its recycled precipitation. The results show high recycling over the Indo-Gangetic plains and Central India and a general west to east increasing trend of precipitation recycling. The regional analysis showed the west-central and central northeast homogeneous monsoon regions as the highest contributor of evapotranspiration and also received the highest recycled precipitation.