Its that time of the year when mobile phone screenshots increasingly lend themselves to Facebook posts grimly declaring regional temperatures from across the country — most on the wrong side of 40 and some hovering around 50 in degree celsius. It’s the time for the deadly heatwaves that kill thousands every year, close down schools and offices and, in general, make life miserable for millions.
The increasing intensity and number of these heatwaves between March and June every year have been a subject of concern for scientists for close to a decade now. In daily conversations, it is not unusual to encounter someone loosely blaming ‘global warming’ or ‘climate change’ for the phenomenon.
{credit}S. Priyadarshini{/credit}
Scientists from the Japan Agency for Marine-Earth Science and Technology in Yokohama and India’s ministry of earth sciences have now come together to analyse the anatomy of these heatwaves in a paper1 published in Scientific Reports last week. They tried to understand what causes these severe spells of heat. They looked at observed patterns and statistical analyses of the maximum temperature variability and have identified two types of heatwaves in the country — the first over north-central India and the second over coastal eastern India.
They associate the first one over north-central India with ‘blocking’ over faraway North Atlantic, which results in a cyclonic anomaly west of North Africa at upper atmospheric levels. All of this triggers a chain of events that eventually affects the Indian subcontinent causing heatwave conditions over India. The heatwave in coastal eastern India, on the other hand, is due to anomalous cooling in the Pacific which generates ‘northwesterly anomalies’ over the landmass reducing the land-sea breeze and resulting in heatwaves.
As several studies, including IPCC estimates, suggest that the frequency of heatwaves would only increase in near future, understanding the science behind India’s heatwaves would help policy makers design better strategies to tackle these annual extreme events.
In another related study2 in Scientific Reports last week, a group of international scientists, primarily from China and USA, have questioned earlier estimates of groundwater depletion in the Northwest India aquifer based on data from NASA’s Gravity Recovery and Climate Experiment (GRACE) satellites. Research in the past showed that groundwater levels in northern India have been declining very rapidly — by as much as a meter every three years — between 2002 and 2008. And also that the calamity was almost entirely man-made. In the hotbed of this unprecedented deletion are Rajasthan, Punjab, and Haryana — states with staggering population growth, rapid economic development, and water-hungry farms — accounting for about 95 percent of groundwater use in the region.
Last week’s study, however, says accurate ground water depletion estimation is challenging because of ‘uncertainties in GRACE data processing’ and that earlier studies might have overestimated the depletion over this region. This study highlights uncertainties in the estimates and the importance of incorporating a priori information to refine spatial patterns of GRACE signals that could be more useful in groundwater resource management.
- Ratnam, J. V. et al. Anatomy of Indian heatwaves. Sci. Rep. 6 (2016) doi: 10.1038/srep24395
- Long, D. et al. Have GRACE satellites overestimated groundwater depletion in the Northwest India Aquifer? Sci. Rep. 6 (2016) doi: 10.1038/srep24398