Looking back into history to understand droughts

The 2015­-2018 drought, the longest, but less severe of droughts experienced by India raises alarm on the negative effects of future droughts on water security in the country.
4 Dec 2019
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India will see more droughts in the future. (Image Source: Wikimedia Commons)
India will see more droughts in the future. (Image Source: Wikimedia Commons)

Droughts in India: types, causes and effects

Droughts are greatly feared in India, impacting food production, the economy and the livelihoods of millions of farmers. 60% of India’s population is engaged in agriculture.

So what is a drought? A drought can be defined as “An extended period—a season, a year, or several years - of deficient precipitation compared to the statistical multi-year average for a region, that results in water shortage for some activity, group or sector.”

Droughts can be classified into the following categories:

  • Meteorological droughts occur when there are long gaps in normal rainfall. These are measured based on the degree of dryness and the duration of the dry period.
  • Agricultural droughts occur when there is insufficient soil moisture to meet the needs of a crop at a particular time. Agricultural drought usually follows meteorological drought and occurs before a hydrological drought. Agricultural drought can be measured through indicators such as lack of rainfall, changes in evapotranspiration, soil water deficits, reduced groundwater or reservoir levels etc.
  • Hydrological droughts are the result of surface and subsurface water supplies from streams, rivers and lakes becoming scarce due to scanty rainfall. The frequency and severity of hydrological droughts are defined at the watershed or river basin scale and are influenced by factors such as land degradation or land use changes, construction of dams etc.
  • Socioeconomic droughts occur when water shortage starts to affect people’s lives, individually and collectively.

Droughts not new to India

India has a long history of droughts. There were 26 major droughts from 1870 to 2018, when the All India Summer Monsoon Rainfall (AISMR) was found to be lesser than the mean rainfall for the country. Even the most recent drought  was disastrous for India, affecting agriculture and water resources across the country. While recurring droughts are becoming increasingly common in India, with predictions for more frequent droughts in the future, is there anything to be learned from past droughts? If so, what?

A peek into history

A paper “Long-term (1870–2018) drought reconstruction in context of surface water security in India” published in the Journal of Hydrology argues that a comparison of the droughts that occurred over the years could help us in predicting the severity and causes of future droughts. The paper presents the findings of a study that aims at:

  • Identifying major meteorological and hydrological droughts in India during 1870–2018 and comparing the recent 2015–2018 drought with these
  • Exploring the causes behind major droughts in India and their impacts on surface and groundwater storage in the country

The study uses standardised precipitation index (SPI), an indicator used for measuring meteorological drought based only on precipitation or rainfall and standardised runoff index (SRI), an indicator used to measure hydrological drought based on runoff accumulated over a specific duration. Droughts are classified according to severity based on characteristics such as drought duration, intensity, and spread throughout the country.

The study finds that:

18 meteorological and 16 hydrological droughts occurred in India in the time span of 1870 to 2018.

The most severe meteorological droughts were in the years 1876, 1899, 1918, 1965 and 2000,  while the five worst hydrological droughts occurred in the years 1876, 1899, 1918, 1965 and 2000. The drought of 1899 can be classified as meteorological as well as hydrological and was the most severe documented drought India has ever experienced to date.

All the severe meteorological and hydrological droughts were found to be caused due to the positive phase of ENSO (El Nino Southern Oscillation).

ENSO is a recurring climate pattern involving changes in the temperature of waters in the central and eastern tropical Pacific Ocean. On periods ranging from about three to seven years, the surface waters across a large swath of the tropical Pacific Ocean warm or cool by anywhere from 1°C to 3°C, compared to normal. ENSO in turn is known to have a negative impact on the Indian monsoon.

The 1876 drought was a result of the combined impact of ENSO and the Indian Ocean Dipole effect (IOD)

IOD, also known as the Indian Nino is an irregular oscillation of sea-surface temperature, in which the Western Indian Ocean becomes alternately warmer and then colder than the eastern part of the ocean, affecting the Indian monsoon. When the eastern equatorial Indian Ocean off Sumatra in Indonesia becomes abnormally warm while the western tropical part of the ocean near the African coast becomes relatively colder, the progression of the monsoon over India is obstructed.

Recent droughts are found to be associated with ENSO and SST conditions over the Indian and Atlantic oceans.

Along with the impact of ENSO, this study shows that sea surface temperatures of the Indian and Atlantic oceans increasingly influence the monsoon in the country. While the 2015–2018 drought was found to be less severe as compared to other meteorological and hydrological droughts, it was the longest in the last 150 years. It was caused by the impact of ENSO in 2015 and IOD in 2017, affecting north and south India.

The 2015–2018 drought had a significant impact on reservoir and groundwater storage

This suggests that long term droughts can greatly influence water availability in India. While groundwater depletion has already reached dangerous levels in the country, the impact of future droughts could be disastrous for India, that continues to heavily depend on groundwater to meet its agriculture and drinking water needs.

Narrow approach to drought management hinders progress

Drought management continues to be inadequately addressed in India, not due to lack of policies and institutional framework, but because of of improper planning, coordination between different functioning units and implementation at the ground level. The approach to drought management has limitations too, focussing more on quick-fix solutions and not considering the long-term sustainability and livelihood issues of farmers themselves. Declaring drought is also riddled with problems and the new norms have been blamed for being too strict, making it difficult for the states to prove "severe" drought and thus get relief from the Centre.

Scanty rainfall and depleting water tables are a warning signal for India, that we clearly need to be better prepared to mitigate the impacts of future droughts. Concerted action at the policy level and urgent adaptation strategies are the need of the hour.

View the full paper here

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