Science for All | What are flash droughts?

The Hindu’s weekly Science for All newsletter explains all things Science, without the jargon.

Updated - May 11, 2023 11:06 am IST

Published - May 10, 2023 05:15 pm IST

(This article forms a part of the Science for All newsletter that takes the jargon out of science and puts the fun in! Subscribe now!)

Droughts are periods of continuous water deficit, often caused by a lack of precipitation in a given area. They have a significant adverse impact on the regional environment and economy. A flash drought is a rapid onset or intensification of drought. 

Low rates of precipitation, along with abnormally high temperatures, winds, and solar radiation are factors that can rapidly alter local climate, leading to flash drought. It can also be linked to climatic patterns like La Niña. 

According to scientists, an early warning sign of flash droughts is evapotranspiration, which leads to a decrease in soil moisture. Evapotranspiration is the process of water transfer from land to atmosphere by evaporation from soil and transpiration from plants. 

A study, published in the journal Science on April 13, reported that climate change is intensifying flash droughts worldwide. In the last 64 years, more than 74% of the world’s regions identified by the U.N. Intergovernmental Panel on Climate Change’s ‘Special Report on Extreme Events’ have experienced flash droughts. This transition will only expand and the report calls for urgent adaptation to faster-onset droughts in a warmer future. 

The study divided sub-seasonal droughts into flash droughts and slow droughts. The onset speed of both is measured by declining soil moisture rate. Flash droughts usually last around 30-45 days while slow droughts last 40-60 days. Increasing drought onset speed is primarily due to intensifying rainfall deficit and increasing evapotranspiration caused by climate change, the study noted. Evapotranspiration quickly dries the soil, creating ideal conditions for heat waves, leading eventually to the rapid onset of drought conditions. 

Flash droughts may lead to irreversible changes in terrestrial ecosystems. In such conditions, ecosystems may not have enough time to adapt to a large water deficit and extreme heat, leading to lower productivity. Flash droughts can also significantly challenge drought monitoring and prediction.

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