By the end of the 21st century, some parts of the world can expect as many as 30 more days a year without precipitation, according to a new study. Ongoing climate change caused by human influences will alter the nature of how rain and snow falls; areas that are prone to dry conditions will receive their precipitation in narrower windows of time. Computer model projections of future conditions indicate that regions such as the Amazon, Central America, Indonesia, and all Mediterranean climate regions around the world will likely see the greatest increase in the number of "dry days" per year, going without rain for as many as 30 days more every year. California, with its Mediterranean climate, is likely to have five to ten more dry days per year.
"Changes in intensity of precipitation events and duration of intervals between those events will have direct effects on vegetation and soil moisture," said Stephen Jackson, director of the U.S. Department of the Interior Southwest Climate Science Center, which co-funded the study. "(Study lead author Suraj) Polade and colleagues provide analyses that will be of considerable value to natural resource managers in climate adaptation and planning. Their study represents an important milestone in improving ecological and hydrological forecasting under climate change."
Polade, a postdoctoral researcher at Scripps, said that one of the implications of this finding is that annual rainfall could become less reliable in drying regions as annual averages will be calculated over a smaller number of days. The 28 models used by the team showed agreement in many parts of the world on the change in the number of dry days those regions will receive. They were in less agreement about how intense rain or snow will be when it does fall, although there is general consensus among models that the most extreme precipitation will become more frequent. Climate models agreed even less on how the conflicting daily changes affect annual mean rainfall.