New research about drought impacts on wildlife can inform conservation strategies

New research predicts that many wildlife species in the continental United States will experience year-long droughts nearly five times as often in the coming decades (2050-2080) than they did historically (1950-2005). In an even more dramatic turn of events, three-year droughts may become nearly seven times more frequent.

"The degree of increased drought exposure for each species in our analysis strongly depends on future greenhouse gas concentrations," said Dr. Merijn van den Bosch, the lead author of the study. "But even under a lower-concentration scenario, virtually all vertebrates face increased year-long and multi-year droughts in the second half of this century. The implications will depend on the species and the length of the drought."

For example, the endangered giant kangaroo rat, which is native to dry habitats in California, has adapted to occasional short droughts. However, populations can plummet after multi-year droughts, compounding existing threats, including a loss of nearly all their historic habitat. This study shows that much of the remaining giant kangaroo rat range soon could face these longer droughts much more often. "That does not bode well for this already-endangered species," said van den Bosch.

Likewise, the ranges of many game species whose populations are not currently at risk -- including certain ducks and other waterfowl and ungulates like elks -- also will face more frequent year-long and three-year droughts in the future. This trend could have implications for wildlife and game management.

Scientists aimed to identify areas with both high biodiversity and large predicted increases in drought to provide information about places where adaptive water management or habitat restoration could benefit the most wildlife species. They used state-of-the-art modeling techniques to predict future scenarios based on six different projections of temperature and moisture conditions. Then, they compared the frequency of observed and projected drought exposure to the range maps of 349 birds, 339 mammals, 280 amphibians, and 253 reptile species and created regional summaries.

It turned out, after they adjusted for land area, that the southwestern United States had the highest number of different species, the highest number of drought-threatened species, and the highest predicted change in drought exposure. "Some of the areas expected to see the greatest increase in drought, such as the southwestern U.S., are already quite dry," said Dr. Zack Steel. "Many species living in these regions are adapted to periodic droughts, but the concern is that if they are already near the limit of what they can tolerate, the large increase in drought we're expecting can have grave consequences for these ecosystems and the wildlife that depend on them."

This research was led by Dr. Merijn van den Bosch, post-doctoral scientist at Colorado State University and the Rocky Mountain Research Station, along with senior author, Dr. Zack Steel, a research ecologist with the Rocky Mountain Research Station. Additional coauthors of this research include Dr. Jennifer Costanza from the USDA Forest Service's Southern Research Station, Dr. Ryan Peek from California Department of Fish and Wildlife, and Dr. John Mola from Colorado State University. For more information, please visit the scientific publication in Communications Earth & Environment.