Montana streams are running lower in late summer
Late-summer stream flows in seven Montana rivers have dropped 20 to 30% since 1950, according to research in a lab run by Steve Running at the University of Montana. The scientists’ tentative interpretation is that changes in climate and the increasing withdrawal of water for irrigation are driving these decreases in flow (the data underpinning this research come from the US Geological Survey). This interpretation is consistent with research showing that late-summer stream flow has diminished across the American West.
A primary cause of this late-summer stream flow reduction is the earlier melting of winter snowpack in the West generally, and in Montana specifically. Among the consequences of reduced flow are more drought stress on trees which in turn raises the risk of harmful forest insect epidemics and an increase in wildfires. Reductions in streamflow, along with the consequences that result, are likely to increase over coming decades with the projected rise in temperatures.