Assessing Causes of Hydrologic Climate Extremes in the Upper Missouri Basin

Observations reveal a sharp increase in the Upper Missouri River Basin's year-to-year streamflow variability. The coefficient of variation of annual streamflow in the 20-year period 1993-2012 has doubled relative to the 20th century, with a disproportionate number of high streamflow years observed after 1993. Yet comparable changes in the variability of precipitation and temperature have not been observed. Here we present results that address causes of the streamflow changes, focusing on a clearer understanding of the relationship between the land surface physics and the evolving characteristics of the meteorological forcings. Results for regional hydrologic model experiments are presented that address the roles of changes in weather statistics, land-cover change, and changes in seasonality. Outcomes are expected to be broadly relevant as extreme global precipitation events have been projected to increase in the future and rising flood risks are of widespread concern.