Temperature change in India from 1875 to 2023. Credit: Ed Hawkins/CC BY SA 4.0
Most pre-monsoon heatwaves emerge in northwest India1. Heatwaves moving southwards are larger and last longer than those heading northeast, and are linked to El Niño.
Scientists at the Indian Institute of Technology in Kanpur say there is a good chance of predicting heatwaves in south India based on El Niño conditions from the previous winter.
To analyse spatial patterns of where heatwaves originate and how they spread, the team used India Meteorological Department daily maximum temperature data from 1950 to 2020 covering March to May.
They applied the 3-D connected components (CC3D) algorithm to track heatwave trajectories. The study also looked at physical drivers using reanalysis data from the ERA5-Land data set, which includes variables like air temperature, radiation, heat fluxes and soil moisture.
After originating in the northwest, heatwaves follow two main trajectories: northeastward and southeastward. Heatwaves in northern and central India are shorter and more intense because of higher solar radiation and heat being absorbed and trapped in the lower part of the atmosphere close to the Earth's surface.
These findings highlight the importance of validating reanalysis data sets with available observations for extreme event studies, the researchers say.
