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About 10-15 per cent areas under cultivation of rice and maize were affected by flash droughts during the monsoon seasons in India between 1951 and 2018, a recent study has found.
The study, Dominance of summer monsoon flash droughts in India, said flash droughts are mainly concentrated in the monsoon season in the majority of India, which can adversely affect maize and rice grown in the Kharif (June-September) season.
It has the potential to affect crop production and pose challenges in meeting increased irrigation demands, the study added.
Shanti Swarup Mahto and Vimal Mishra — researchers from the Indian Institute of Technology, Gandhinagar — identified 39 flash droughts during 1951-2018 and found that 82 per cent of those occurred during the monsoon season.
According to the research, published in journal Environmental Research Letters:
A considerably long dry spell with significantly low precipitation anomalies during the monsoon results in an increase in air temperature. Increased air temperature and precipitation deficit together cause a rapid depletion of soil moisture leading to flash drought. Therefore, flash droughts in the monsoon season are primarily caused by the monsoon breaks. However, flash droughts can also occur due to delayed onset of the summer.
Precipitation deficit and lack of soil moisture during a flash drought can lead to reduction in the yield of rice and maize. About 21.5 per cent of median area under rice and maize cultivation was affected by flash droughts during 1951-2018 monsoon season, the study stated.
Flash droughts primarily affected rice cultivation in eastern and peninsular India in 1976. In 1979, a large part of the rice-cultivated region of the Indo-Gangetic Plain and eastern India was severely affected; the 1982 flash drought during the monsoon season was widespread and affected the eastern and northeastern regions.
Similarly, the maize-cultivated area (mostly central and peninsular India) was influenced by major flash droughts in 1972, 1976 and 2015. “The spatial coverage of soil moisture conditions during the peak of flash droughts showed that the land was extremely dry due to anomalously low precipitation and high temperature,” said the paper.
These conditions rapidly depleted soil moisture in the rice- and maize-dominated regions during the monsoon season, which affected agriculture. This stressed already depleting groundwater levels, a major source for irrigation in north India.
The occurrence of flash droughts and their characteristics, however, have not been examined in India, the paper said.
“Moreover, the dominant seasons of flash drought occurrence in India are not known. Understanding the occurrence and their seasonal variability is vital as flash droughts can be more detrimental in India due to intensive agriculture primarily in the rain-fed regions,” it said.
The paper found that top all-India level flash droughts occurred during the monsoon season of 1979, 2001, 1958 and 1986. Except one (1958), all the other major flash droughts occurred in the mid to late monsoon season.
The researchers divided the Indian region into six regions — Central North East (CNE); Himalayan region (HR); North East (NE); North West (NW); Peninsular Region (PR); and West Central (WC) — based on the precipitation distribution to understand regional-scale variability of flash droughts.
A regional scale assessment of flash droughts showed that four regions — CNE, NE, NW, and WC — that fall in the core monsoon zone, witnessed a majority of flash droughts during 1951-2018. Two regions, HR and PR, experienced more flash droughts during the non-monsoon season than monsoon season during 1951-2018.
“The core monsoon region of central and eastern India witnessed the highest frequency of flash droughts. The regions that experience frequent flash droughts include CNE, NE and Western Ghats. In contrast, arid and semi-arid regions of western India, Deccan plateau, and the peninsular region experienced the least frequency of flash droughts during monsoon,” it said.