The fate of of hydrologic connectivity in the American Southwest

The American Southwest, already known for its arid environment and scarcity of water sources, may be headed for even drier conditions. In new research coming out in PNAS, Jaeger et al. examine hydrological connectivity and flow in a large tributary of the Colorado River in Arizona under projected climate change scenarios. Although dryland streams are already ephemeral and intermittent by nature, their results indicate dramatic shifts towards even greater disruption in streamflow through river networks. Simulations indicate probable changes such as reduction in flow, greater frequency of streamdrying events, extended lengths of channel reaches that undergo streamdrying, and decreased connectivity between portions of the channel that support streamflow. This loss of connectivity is likely to have strong effects on native fish populations, some of which are endangered. Many of these species have evolved spawning and dispersal behavior to cope with the harsh natural dynamic of stream drying, but will face additional pressures of a changing climate. This study represents the first of its kind to specifically detail the consequences of climate change on hydrological flow and connectivity in a region already under pressure from human development and use. When climate and anthropomorphic threats are combined, the fragmentation of hydrological systems in the region is likely to create huge challenges for local populations to adapt to in the coming years.