Contrasting drivers of consecutive pre-monsoon South Asian heatwaves in 2022: waveguide interaction and soil moisture depletion

South Asian countries including India, Pakistan, and Afghanistan experienced consecutive heatwave episodes in 2022, with the first episode in March, followed by an equally intense event in April of the same year. Here, we use diagnostics of local wave activity, waveguidability, and soil moisture-temperature coupling to gain insights into the previously underexplored dynamic and land drivers underlying these early pre-monsoon heatwave episodes. Our findings reveal a sudden surge in wave activity in the upper troposphere over the heatwave region during the first episode of the heatwave. The intensified wave activity results from strong transient waves, due to transfer of energy from the extratropical to the subtropical waveguide, leading to strong anticyclonic circulation. The April heatwave event, in contrast to the first episode, is found to be the result of a strong soil moisture-temperature coupling over the heatwave region. Further, the low-level winds revealed an advection of heat from highly coupled regions (Pakistan and Afghanistan) to the Indian landmass during the heatwave episode in April. Our findings indicate that waveguide interaction together with equatorward energy transfer drives early heat in March, subsequently setting the stage for further heat in the following weeks by depleting soil moisture levels.