Many climatologists expect that with global warming, wet regions of the world will get wetter and dry regions will get drier. As a result, more rain is expected to fall in the humid tropics, for example, whereas less rain is expected to fall in the arid subtropics. However, in a new study, Wills et al. suggest that the relationship between global warming and precipitation patterns is not always so straightforward.
The authors used data from 23 models in the Coupled Model Intercomparison Project phase 5 (CMIP5) from historical simulations (1976–2005) and simulations of the climate at the end of the century (2070–2099). The end of century simulations assume that greenhouse gases will continue to rise. The team looked at changes in net precipitation (precipitation minus evaporation) in wet regions, such as the South Asian and East Asian monsoon regions and the South Pacific Convergence Zone, and in dry regions, such as the Mediterranean, the boreal forests, and the eastern equatorial Pacific.
The analysis found that changes in persistent wind patterns can lead to large changes in net precipitation that can overwhelm the “wet gets wetter, dry gets drier” response.
The authors also report that contrasts in net precipitation between regions increase by 2% to 5% with each 1°C warming of global temperature. This increase is weaker than that which would result without changes in wind patterns. Changes in stationary eddy circulations—wind patterns due to the presence of continents and warm ocean regions—dominate regional precipitation changes. Transient eddies, such as extratropical cyclones, are also an important influence on precipitation changes at high latitudes.
These changes in atmospheric circulation can lead to large departures from the wet gets wetter, dry gets drier paradigm by introducing regional variations. The results suggest that it is important to understand how stationary eddies will change in the future if we are ever to accurately predict how precipitation in different regions will respond to climate change. (Geophysical Research Letters, doi:10.1002/2016GL068418, 2016)
—Wudan Yan, Freelance Writer