Climate Change

Megadrought in Chile: Both natural climate factors, human-induced global warming to blame

A quarter of reduction of rainfall a direct result of sea-surface warming    

By Akshit Sangomla
Published: Tuesday 26 July 2022

The prolonged drought in central Chile is a result of a combination of climatic factors, both natural and human-induced global warming.  

The megadrought — the longest and most intense one in the region in the last millennium — has impacted lakes and glaciers, a report has found. This has led to water scarcity, food insecurity, loss of livelihoods and massively impacted biodiversity

The report by World Meteorological Organisation, called State of the Climate in Latin America and Caribbean, 2021, was released July 22, 2022. It highlighted the length and strength of the drought, which started in 2010 and is still ongoing. WMO is a specialised agency of the United Nations for meteorology. 

Central Chile experienced temperatures above normal (1981-2010) by 1-2°C in 2021. This is higher than the general warming of the continent by 0.36°C, WMO found.  

Most of Chile also experienced below-normal rainfall in 2021, a trend that has now held for 13 years. There was a rainfall deficit of 20-60 per cent over different regions of the country. 

Some research indicates that the drought began in 2007, which would push the drought period to 16 years.  

Between 2010 and 2018, Chile's rainfall deficit varied from 20-40 per cent. 

With further warming of the Earth's atmosphere and the oceans, the sea level pressure will further get enhanced and cause even more frequent and intense megadroughts in the decades to come.

Coquimbo and Araucania received 30 per cent less rain than average from 2010-2015, according to a report published by Centre for Climate and Resilience Research (CR2) in November 2015. CR2 is a research centre based in Chile. 

The WMO report has further found that Chile's Dry Andes and Central Andes glaciers lost 0.72 and 0.56 metres water equivalent (m we), respectively, in 2021. One m we is equivalent to around 1.1 metres loss in glacial ice thickness.

Read more: Oceans Great Dying 2.0: Earth’s climate moderator is warming, faster

The mountain lakes in central Chile, a major source of freshwater, also dried up between 2010 and 2020. There was a surface area reduction in the same period in 12 lakes from 7 per cent to 25 per cent, according to a research paper published in the Journal of Hydrology: Regional Studies in December 2021.

"The continuing drought (in Chile) and loss of surface and underground water resources severely affected dozens of rural communities, requiring water to be supplied by trucks," WMO said in a StoryMap on its website. 

The situation is also dire in urban areas. In April 2022, the Government of Chile announced an unprecedented water rationing plan for its capital city Santiago.

The plan included public service announcements, restrictions on water pressure and rotating water cuts for up to 24 hours.

The government estimated that the country's water availability had gone down to 37 per cent in the last 30 years and may further drop by 50 percentage points in northern and central Chile by 2060, according to a report by Reuters. Reuters is an international news agency. 

The water availability has impacted the region's flora, evidenced by the decline in vegetation productivity between the drought period of 2007-2008 and 2019-2020. This can be seen especially in forests, as per a research paper presented at the International Geoscience and Remote Sensing Symposium in October 2020.

The symposium was organised by the Institute of Electrical and Electronics Engineers, a professional association for electronic engineering and electrical engineering. 

The impact of the decrease in water availability and vegetation can be seen across sectors.

In January 2022, a group of beekeepers protested with 60 hives containing 10,000 bees in front of the presidential palace in Santiago. The beekeepers voiced their concerns about the impact of the megadrought on the bees' food sources, such as flowers and crops, according to a BBC report.

According to a research paper published in the journal Progress in Physical Geography: Earth and Environment in May 2022, 82 per cent of the surveyed beekeepers said that their honey production had declined. 

This happened even though around 80 per cent of them had taken adaptive measures and 74 per cent believed that these adaptive measures worked. 

Droughts lasting a couple of years have been common in Chile for a long time, but the current drought is unique and has global warming's imprint on it. 

The major reason for the drastic decrease in rainfall in the region is the reduced activity of storms, which generally bring most of the rainfall. Around 25 per cent of the reduction of rainfall in the region is a direct result of sea surface warming. 

The reduction in storms in Chile is because of a difference in pressure between two areas. The sub-tropical Pacific Ocean in the west between Chile and New Zealand is high-pressure. Whereas the Amundsen–Bellingshausen Sea in the south, close to the continent of Antarctica, is low-pressure. 

Read more: How not to solve the climate change problem

Usually, the El Nino Southern Oscillation (ENSO) towards the west of Chile in the equatorial Pacific Ocean modulates the difference in sea-level pressures.

However, most of the megadrought has occurred under ENSO-neutral conditions, according to a research paper published in the International Journal of Climatology published in July 2019. The difference in sea level pressure has existed for the past 40 years.

Half of the pressure difference is natural because of variability over decades and expansion of the Hadley cell, according to a research paper published in the Journal of Climate in September 2021. The other 50 per cent is because of enhanced warming of an extensive area of sea surface known as a blob in south-west Pacific Ocean.

The Hadley cell constitutes a westward movement of winds towards the equator at the surface and an eastwards movement of winds towards the poles in higher altitudes.

The warming excites the planetary waves of winds known as Rossby waves. 

The propagation of these waves causes intensification of the wind circulation pattern, which causes a further decrease in rainfall in central Chile. 

The region has seen several droughts. There have been three other multi-year droughts since 1945. 

The first drought was between 1945 and 1947, the second between 1967 and 1969, the third between 1988 and 1990 and finally, the current drought, which has been the longest.

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