Various scientific prospective climate studies have indicated in recent years that climate change will cause, in various parts of the planet, a significant increase in extreme events such as droughts or floods.
Blaming climate change for all kinds of local or regional episodes of lack of precipitation or intense rains is hardly a scientific approach, but the accumulation of this type of extreme events seems to indicate that the global increase in temperatures (as a synonym for climate change) is already is having the expected negative effects.
Two NASA experts have reviewed images and data captured by satellites in the last 20 years with the aim of analyzing the alterations in the water cycle and the recurrence of extreme phenomena (drought and rain), and they reach quite clear conclusions, according to They explain in an article published (March 13, 2023) in the journal Nature Water, from the Nature group.
The most notable result is that "The total intensity of extreme events in recent years has been strongly correlated with [rising] global mean temperature, rather than with the El Niño Southern Oscillation or other climate indicators, suggesting that the continued warming of the planet will cause more frequent, more severe, longer and/or greater droughts and rains".
Study authors Matthew Rodell and Bailing Li, researchers both at NASA's Goddard Space Flight Center in Greenbelt and at the University of Maryland, United States, reviewed data and images from the GRACE and GRACE-FO satellites of 1,056 episodes of droughts and floods registered between 2002 and 2021.
The scientists responsible for this study have discovered that "on a global scale, the intensity of these extreme wet and dry events - a metric that combines extent, duration and severity - is closely related to global warming," according to the summary published by NASA. .
The United States space agency recalls that "between 2015 and 2021, which were the seven of the nine warmest years in the modern record, the frequency of extreme wet and dry events was four per year, compared to three per year in the previous 13 years". This makes sense, the authors say, because warmer air causes more moisture to evaporate from Earth's surface during dry events; in the same way that warm air can also hold more moisture to fuel severe snowfall and rain.
“The idea of climate change can be abstract. A couple of degrees warmer doesn't sound like much, but the water cycle impacts are tangible," said Matt Rodell, study co-author and a hydrologist at NASA's Goddard Space Flight Center in Greenbelt, Maryland. “Global warming is going to cause more intense droughts and wet spells, which will affect people, the economy and agriculture around the world. The monitoring of hydrological extremes is important to prepare for future events, mitigate their impacts and adapt”, indicates this co-author.
To document the information, NASA has released a video (at the bottom) showing the extremes of the water cycle over a twenty-year period (2002-2021) based on observations from the GRACE and GRACE-FO satellites. . Dry events appear as red spheres and wet events as blue spheres; earlier years are shown in lighter tones and later years in darker tones. The volume of the sphere is proportional to the intensity of the event, quantity measured in cubic kilometers months. The graphs at the bottom of the figure show that the total intensity of extreme events increased as global temperatures increased.
Using the data from the GRACE satellites, “it's like looking at the water level in the bathtub,” Rodell said. "You can see how much it goes up and down without knowing the total amount of water in the tub." Because GRACE and GRACE-FO provide a new map of water storage anomalies around the world each month, they provide a comprehensive view of the severity of hydrological events and how they evolve over time.
NASA explains that Rodell and Li have applied an "intensity metric" that accounts for the severity, duration, and spatial extent of droughts and extreme wet events. They found that the global total intensity of extreme events increased from 2002 to 2021, reflecting rising Earth temperatures over the same period.
By far the most intense event identified in the study was a downpour that began in 2019 in central Africa and is still ongoing. It has caused the level of Lake Victoria to rise by more than one metre. A 2015-2016 drought in Brazil was the most intense dry event in the last two decades, leading to empty reservoirs and water rationing in some Brazilian cities.
“Both events were associated with climate variability, but the Brazilian drought occurred in the warmest year on record (2016), reflecting the impact of global warming,” said Bailing Li, a hydrologist at the University of Maryland at Goddard. “Recent droughts in the southwestern US and southern Europe were also some of the most intense events, in part, due to anthropogenic warming.”
"Global warming has had far-reaching and profound impacts on terrestrial water storage, such as reduced annual snowfall at high elevations and depletion of groundwater by people when surface water is scarce," Bailing Li explains. .