Global warming could bring flash flooding to dry regions

Flash flooding is likely to become a more frequent problem in both wet and dry regions of the globe as global warming brings intensified precipitation, new research shows.

The research, conducted by climate change scientists at the University of New South Wales and published in the journal Nature Climate Change, challenges previous thinking that higher temperatures would intensify current climate patterns, making dry areas of the world even drier and wet regions even wetter.

"The most significant finding actually was that the extremes are increasing in both the dry and the wet regions, and precipitation totals are also increasing in the dry regions," said Markus Donat, a climate scientist at the University of New South Wales in Sydney, who is the study’s lead author of the study.

To simplify the analysis, the researchers established two categories – dry and wet regions of the world. The team analyzed 60 years of weather observations in the wettest and driest regions, concluding that increases in heavy rainfall events matched simulations made by climate models. Future projections indicate that incidence of flooding will likely increase in dry regions more quickly than elsewhere.

Their results suggest that both annual precipitation and extreme precipitation increased by 1–2 percent per decade in dry regions, including western North America, Australia, and parts of Asia. Wet areas, including eastern North America, and southeast Asia, show similar increases in the size of extreme precipitation and smaller increases for annual totals. The increase in precipitation is projected to continue until 2100.

The researchers noted, however, that the expected increase in rainfall over dry areas doesn’t mean that more water will become available in the dry areas. The heat caused by global warming will likely lead to increased evaporation, which means that more frequent flooding events will have little impact on overall water storage rates.

“By deriving a robust and socially relevant result from a recently expanded observational dataset, this study reminds us how vital it is to continue making, sharing and recovering actual measurements of climate-monitoring quality, especially where they are currently sparse and where long series of data already exist,” writes William Ingram, of Oxford University, in a companion commentary in Nature Climate Change.

The coverage remains poor in the tropics, however, which means that the researchers conclusions may not be valid in the tropics, “precisely where the changes are likely to be greatest, where complex physical interactions make prediction hardest, and where the ecosystems and societies might be most sensitive to these changes,” Dr. Ingram notes.

“Given the intrinsic rarity of extreme events, these results do not tell us what will actually happen in any particular location, but rather how risks will change – which is precisely the information needed by emergency planners,” he writes.

This report contains material from Reuters.