The risk of drought is set to increase significantly across many regions of the world, even when global warming is limited to 1.5°C, according to a new study by climate change researchers at the National Center for Atmospheric Research, Colorado.
The Paris Agreement aims to keep global warming well below 2°C and to pursue efforts to limit it to 1.5°C above pre-industrial temperatures. Global changes in drought risk under the 1.5°C and 2°C warming targets were assessed using model simulations based on these two scenarios.
The study focused on key drought-prone regions in North and South America, Europe, Africa, Asia, and Australia. The future period of 1.5°C and 2°C warming refers to the second half of this century. Changes were compared with the present-day reference period 1967-2016.
Higher risk in Mediterranean, central Europe, the Amazon, and southern Africa
Drought risk increases significantly for both warming targets in the Mediterranean, central Europe, the Amazon, and southern Africa, the researchers found. Moreover, for these four regions, the additional 0.5°C of warming from 1.5°C to 2°C leads to significantly drier mean conditions and higher risk of consecutive drought years. Southern Australia has a comparable increase in drought risk between 1.5°C and 2°C, while Southeast Asia sees no significant change in drought risk under any future scenario.
Drought events that last for several years
The risk of a drought event that lasts for four consecutive years, roughly similar to the recent 2012-2015 drought in California, substantially increases for the Mediterranean under the 1.5°C and 2°C warming targets. For central Europe, this risk of consecutive years of drought is lower but also increases for a warming of 2°C relative to 1.5°C. The Amazon experiences the strongest increase of the risk of such a drought event, while the response for Southern Africa is similar to the Mediterranean. Southern Australia also experiences an increase in risk of consecutive drought years under both 1.5°C and 2°C scenarios relative to present day. No major changes are simulated for the US Southwest and Central Plains, and Southeast Asia.
A high-end scenario of climate change
What if global warming exceeds the 2°C warming target? Simulations with a high-end scenario of climate change show that the risk of consecutive drought years increases substantially in all regions, including the US Southwest and Central Plains but except Southeast Asia. In Southeast Asia, evaporation strongly increases but this increase is balanced by a more-or-less comparable increase of precipitation. The latter is also shown in simulations for the US Southwest and Central Plains under the 1.5°C and 2°C warming targets, but this balance does not hold for stronger warming, causing the US Southwest and Central Plains to dry under a high-end scenario of climate change.
The article first appeared on Climate Change Post and is a digest of a scientific paper by Lehner et al., 2017. Geophysical Research Letters 44: 7419-7428.