The intensity of extreme droughts and rainfall has increased “sharp” over the past 20 years, according to a study published Monday in the journal Nature Water. These are not just extreme weather events, they lead to extremes such as crop failures, damage to infrastructure, even humanitarian crises and conflicts.
The big picture on water comes from data from a pair of satellites called GRACE, or Gravity Recovery and Climate Experiment, which were used to measure changes in the Earth’s water storage – the sum of all water on and in the land, including groundwater, surface water, ice and snow .
“It’s incredible that we can now monitor the pulse of continental water from space,” said Park Williams, a bioclimatologist at the University of California, Los Angeles, who was not involved in the study.
“I have a feeling that when future generations look back and try to determine when humanity really began to understand the planet as a whole, this will be one of the highlighted studies,” he said.
The researchers say the data confirms that both the frequency and intensity of rainfall and droughts are increasing due to the burning of fossil fuels and other human activities that release greenhouse gases.
“I was surprised to see how well global intensity correlated with global mean temperatures,” said Matthew Rodell, study author and associate director of Earth Sciences for Hydrosphere, Biosphere and Geophysics at NASA Goddard Space Flight Center.
The strong connection between these climate extremes and rising global average temperatures means that ongoing global warming will lead to more droughts and rainstorms that are worse in many ways – more frequent, more severe, longer and bigger.
Researchers looked at 1,056 events from 2002 to 2021 using a novel algorithm that identifies where land is much wetter or drier than normal.
This showed that the most extreme rains in sub-Saharan Africa would continue to occur at least until December 2021, when the data ended. The precipitation extremes also occurred in central and eastern North America in 2018–2021 and in Australia in 2011–2012.
The most intense droughts were record-breaking in northeastern South America from 2015-2016; an event in the Cerrado region of Brazil that started in 2019 and is ongoing; and the ongoing drought in the American Southwest, which has caused dangerously low water levels in two of the largest US reservoirs, Lake Mead and Lake Powell. These remain low despite heavy rainfall this year.
Drought events exceeded heavy rain events by 10%. Their geographic extent and duration were similar.
A warmer atmosphere increases the rate at which water evaporates during dry periods. It also holds more water vapor, leading to heavy rains.
The study found that infrastructures such as airports and sewage treatment plants, which are designed to withstand events that occur once every 100 years, are increasingly challenged as these extremes occur more frequently and with greater intensity.
“As we look ahead, in terms of water resource management and flood control, we should expect the wetter extremes to get wetter and the dry extremes to get drier,” said Richard Seager, a climate scientist at the Lamont Doherty Earth Observatory at Columbia University who was not involved in the study.
Seager said it’s a mistake to assume that future wet and dry extremes can be managed just as they have in the past because “everything on both ends of the dry-wet spectrum is amplified.”
According to the US National Integrated Drought Information System, 20% of annual economic losses from extreme weather events in the US are due to floods and droughts.
A drastic alternation between extreme drought and unprecedented flooding, dubbed “whiplash,” is becoming increasingly common in some regions.
Water scarcity is expected to severely impact poor, disenfranchised communities, as well as ecosystems that have been underfunded and exploited.
For example, the United Nations has said Somalia is experiencing its longest and most severe drought, an event that has caused the deaths of millions of livestock and widespread starvation. Venezuela, a country grappling with political and economic crises for years, resorted to nationwide power outages in April 2016 due to drought conditions affecting the water levels of the Guri Dam.
As solutions, using flood waters to replenish depleted aquifers and improving the health of agricultural soils so they can better absorb water and store more carbon are just a few methods that could improve water resilience in a warming world, states in the study.
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