Scientists have shown that warming global temperatures can lead to increases in extreme precipitation events—and therefore to increased surface runoff from soils unable to absorb heavy rainfall and snowmelt—as well as to aggravated droughts resulting from decreased precipitation and increased evapotranspiration. Understanding the likely timing and locations of future floods and droughts will be imperative in protecting people and managing risk.

In a new study, Zhai et al. use an established surface runoff model, called variable infiltration capacity, in combination with the latest climate projections from global circulation models to forecast global surface runoff and droughts and to compare differences in these forecasts between 1.5°C and 2°C warming scenarios, the targets for maximum warming established in the Paris Agreement.

The team reported that outcomes in their modeling are worse across the board for the 2°C scenario: Annual runoff is expected to be higher, water retention in terrestrial ecosystems is expected to be lower, and droughts and floods are expected to increase in frequency. The scientists identified Mexico, the western United States, western Europe, southeastern China, and the West Siberian Plain as likely candidates to experience increased droughts with the added warming. Meanwhile, Alaska, northern Canada, and much of Asia are expected to experience increased flooding hazards.

The researchers extended their analysis to determine how many more people would be affected under 2°C versus 1.5°C warming, as well as the added burden on gross domestic product (GDP). They calculated that globally, droughts would affect an additional 0.5% of the population, floods an additional 4.9%, and droughts and floods an additional 4.9% under 2°C warming relative to under 1.5°C warming. The scientists also found that the changes in runoff with 2°C warming versus 1.5°C warming would have widespread impacts on the affected economies, with droughts affecting an additional 4.6% of GDP globally, floods affecting an additional 2.4%, and both droughts and floods affecting an additional 5.7% of GDP.

Considering the severity of these projected human and economic impacts, the researchers pointed out the importance of trying to limit further warming of Earth’s climate. (Earth’s Future, https://doi.org/10.1029/2019EF001398, 2020)

—David Shultz, Freelance Writer