Study of Land Surface feedback in catalysing the intensity and duration of Heatwave over Indian subcontinent

Abstract

<p>Extreme heat events are rising in nature over the Indian subcontinent under the stressed environmental conditions. Unprecedented event of extreme heat is threatening our socio-economic and ecosystem. April marks the start of summer with a clear sky; agricultural harvesting exposes the large land surface to solar heating, so the drying up of the surface causing loss of soil moisture and vegetations. Temperature anomalies become high during May and June, signifying possible role play local land-surface-atmosphere feedbacks involving dried soils in driving the heat extreme. Thus, the study of extreme heat and surface feedback process is conducted using a combination of ERA5 reanalysis data, GLDAS Noah Land Surface Model data, satellite-based observations (TRMM and MODIS), and in-situ India Metrological Department datasets. To address the bias present in datasets, we make use of IMD Datasets for bias correction. We use 2m air temperature to define the extreme heat events as per the IMD definition for the heatwave from 2001 to 2019. Parameters like surface net solar and thermal radiation and (also, clear sky) heat flux, total precipitation, land surface temperature, land use type and vegetation cover, soil moisture used to study the details of land surface conditions during the heatwave events. The examination of the above datasets in space-time provided the general view of heatwaves and suggest that late April and early May with clear sky increased net solar radiation started drying up the surface. Late May and early June with a clear sky and positive net solar radiation anomaly with positive heat flux anomaly and lack of soil moisture and rainfall developed local forcing on air temperature that catalyzed the heatwave events in terms of intensity and duration. The above conclusion is supported by the satellite-derived land surface temperature and heat flux. The results obtained establish the link between the local surface feedback and extreme heat events during the summer over the Indian subcontinent and can enhance in a dry environment with the large agricultural field with no standing crop barren land or land with dead or no shrubs over India leaving northern Himalayan part.</p>