By 2050, the Verde River Basin in Arizona will have up to one-fifth more streams dry up each season and at least a quarter more days with no water flow.
The conditions will pose problems for fish already threatened by extinction that are trying to reach spawning habitats and refuges where water still remains.
The findings provide a grim snapshot of what could happen to watersheds and fish in arid areas around the world as climate warming occurs, researchers say.
The changes will diminish what scientists call “hydrologic connectivity” and reduce the ability of desert fish to use the entire watershed to obtain food, spawn, and raise offspring.
“By linking habitat patches within stream corridors and facilitating the ebb and flow of organisms across the landscape, hydrologic connectivity is fundamental to the persistence of desert fishes,” says Julian Olden, associate professor of aquatic and fishery sciences at University of Washington.
“Our study suggests that even modest changes in temperature and precipitation regimes in the future may lead to potentially large decreases in stream flow with associated habitat loss and reduced hydrologic connectivity.”
Fish forced out
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If water is flowing throughout the network, fish are able to access all parts of it and make use of whatever resources are there, says lead author Kristin Jaeger of Ohio State University, who conducted the work as a postdoctoral researcher in Olden’s lab.
When systems dry out, temporary fragmented systems develop that force fish into smaller, sometimes isolated channel reaches or pools until dry channels “wet up” again.
“Climate change, stream drying, and loss of habitat for threatened fish has implications for the streams and waterways that wind their way through arid and semi-arid landscapes that dominate the Earth’s surface,” Olden says.
The Verde River Basin is a network of waterways in Arizona that is characteristic of many desert watersheds.
Conservative estimates
For the study, published in the Proceeedings of the National Academy of Sciences, researchers used a rainfall runoff model that incorporates the basin’s elevation, terrain, soil, land use, vegetation coverage, and both current and future climate data, including precipitation and temperature.
The model revealed a mosaic of wet and dry patches that shifted seasonally and varied over time. By mid- to late-century, the model shows that a warming climate will reduce connectivity for fish by up to 9 percent over the course of a year and double that during the critical spring spawning months.
“Our study is the first to predict local habitat loss from stream drying events, and explore how these patterns scale up to shape habitat fragmentation through changes in hydrologic connectivity and affect population persistence of endemic fishes,” Olden says.
Quite telling is that the outlook from this study should be considered conservative, the co-authors say. Difficulties in projecting groundwater supplies and withdrawals needed to support a growing Arizona population precluded such information from being incorporated into the models. Many other areas of the Southwest US and other countries face similar situations.
“The prediction of more frequent and longer duration periods of stream drying in already fragmented systems will further fuel the need for ecologically sustainable water resource development,” the authors conclude.
Noel Pelland, a graduate student in oceanography at the University of Washington, is also a coauthor of the study. The Department of Defense’s Strategic Environmental Research and Development Program funded the work.
Source: University of Washington
