Role of land surface conditions on the evolution and spatial propagation of heatwaves in northwest India

Abstract

Land surface conditions are known to exert a significant influence on the frequency, intensity and propagation of heatwaves. In this study, we analyze the role of land surface conditions in the evolution and spatial propagation of pre-monsoon heatwaves in northwest and central India, a major hotspot for heatwaves in India, during 1950-2023. Heatwaves in northwest India (NWI) typically have low surface wind speeds in the development phase resulting in heat accumulation. The heating of land surface during the development phase creates thermally induced surface low pressure over NWI, which establishes zonal pressure gradient and intensifies westerly winds, facilitating heat dissipation through advection. The heat advected from the upwind NWI contributes to heatwave occurrence in the downwind regions of north and central India (NCI). We find a strong influence of initial land surface temperature (LST) in NWI on the spatial propagation of heatwaves. Heatwaves with higher initial LST in NWI are associated with stronger westerly winds during the termination phase as the negative surface pressure anomalies induced by land surface heating are stronger in such events. As a result, the propagation of heatwaves from NWI to NCI is faster and has a higher likelihood if the upwind heatwaves have a higher initial LST. Our study demonstrates significant potential of using initial LST of upwind regions of NWI for predicting heatwave occurrence in downwind NCI.