Droughts May Last Up to 10 Days Longer Than Predicted by 2100

In the coming decades, periods of droughts are expected to last longer and longer because of the effects of climate change.
By the year 2100, the average longest period of drought could be 10 days longer than scientists previously estimated, according to a new paper in the journal Nature. This may mean that these periods of drought could be more damaging than expected, the researchers suggest.
“At present, more than half of the global land area and about half of the world’s population (that is, around 3.2 billion people for 2020) experience LAD [longest annual dry spell] periods of at least 2 months or longer on average,” the researchers wrote.
Current models predict that about 50 percent of the global land surface will experience an increase in LAD of at least five days by the end of the century under the Shared Socioeconomic Pathway (SSP) 5-8.5 scenario.
“Although a global average increase of 5 days is expected, in some areas the increase could be up to 45 days,” the authors wrote.
The SSP scenarios are used by the U.N.’s Intergovernmental Panel on Climate Change (IPCC) to project the possible future impacts of climate change, based on different levels of greenhouse gas emissions.
SSP2-4.5 is a moderate emissions scenario where global efforts to mitigate climate change are somewhat successful. This scenario limits global warming to around 2.5 to 3 degrees Celsius by 2100, depending on the climate model used.
SSP5-8.5, on the other hand, is a high emissions, worst-case scenario, assuming continued heavy reliance on fossil fuels, rapid economic growth and minimal efforts to reduce greenhouse gas emissions. This scenario could lead to severe global warming, with temperatures rising by 4 to 5 degrees C by the end of the century.
The researchers examined possible biases in climate models of future drought conditions under the IPCC’s SSP2-4.5 and SSP5-8.5 scenarios. By comparing projections with the longest annual dry spell (the longest number of consecutive dry days each year) observed between 1998 and 2018, they estimated how much longer periods of drought may be compared with predictions.
They found that the longest annual dry spell length could be 42 to 44 percent higher on average than previously predicted by the end of the century.
“Here we show that constraining model projections with observations using a newly proposed emergent constraint (EC) reduces the uncertainty in predictions of a core drought indicator, the longest annual dry spell (LAD), by 10–26 percent globally,” the researchers wrote.
“Our EC-corrected projections reveal that the increase in LAD will be 42–44 percent greater, on average, than ‘mid-range’ or ‘high-end’ future forcing scenarios currently indicate. These results imply that by the end of this century, the global mean land-only LAD could be 10 days longer than currently expected,” they said.
In North America, Southern Africa and Madagascar, the longest annual dry spell length may be as much as twice as long as previously predicted.
Interestingly, the researchers found that decreases in the longest annual dry spell length may be up to three times greater in Central and East Asia. This may be because there is a risk of increased rainfall or flooding in some areas.
“Our findings reveal extensive regions where climate change may cause stronger and earlier aggravation of drought-associated risks than previously expected under both the mid-range and high-end scenarios, and they emphasize the importance of reducing systematic climate-model errors, which are still largely caused by rainfall biases,” the researchers said.
They continued: “Correcting these biases should be a priority and will increase the confidence of future projections of dry extremes, which is a prerequisite for effective reduction of drought risk in the near future, with direct benefits for human and natural systems.”
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Petrova, I.Y., Miralles, D.G., Brient, F., Donat, M.G., Min, S.-K., Kim, Y.-H., & Bador, M. (2024). Observation-constrained projections reveal longer-than-expected dry spells. Nature. https://doi.org/10.1038/s41586-024-07887-y