Northward shift of pre-monsoon winds exacerbating heatwaves over India

Abstract

India has observed increasingly persistent heat extremes in recent decades, that pose environmental, agricultural, and human health challenges. North-Central India, a highly populated region prone to heatwaves, has experienced record maximum temperatures (>48°C) during the pre-monsoon season. While studies have shown positive trends in heatwaves due to rising air temperature during pre-monsoon season, we identify a shift in pre-monsoon mean daily maximum temperature over North-Central India, resulting in an increase in seasonal mean maximum temperature by 0.7°C post-1998. The jump in temperature is associated with a weakening of mid-tropospheric zonal winds as a result of a northward migration of the subtropical jet since 1998. Further, comparing the two regimes before and after the shift, we find that the frequency and duration of heatwaves have accelerated in the latter regime. We also observe that the recent increase in heatwaves is associated with an increase in negative vorticity indicating increasing anticyclonic circulations over North-Central India. These findings highlight that the exacerbation of heatwaves in North-Central India is primarily driven by atmospheric dynamical changes triggered by a regime shift, further compounded by global warming.