TRENDS IN TEMPERATURE AND PRECIPITATION IN THE MISSOURI RIVER BASIN FROM 1957 TO 2008

The U.S. Global Change Research Program reported that global temperatures have increased 1.5°F since 1900 and are projected to rise from 2 to 11.5°F by 2100 with regional variations. Average temperatures have increased about 1.5°F for the Great Plains over the last 30 years relative to a 1961-1979 baseline. Precipitation has increased up to 25% in the eastern Great Plains and decreased up to 15% in the western Great Plains and northern Rocky Mountains since 1958. Here, we explore climate change and its relationship to streamflow trends in the Missouri River Basin (MRB) which covers much of the northern Great Plains. We examine temperature and precipitation records from climate stations and gridded climate datasets (PRISM; ~4 km grid resolution) and compare these data to observed trends in the streamflow record for the MRB from 1957-2008. We used the Kendall Tau non-parametric test to identify significant trends. Significant increases in annual average of minimum temperatures at climate stations largely coincide with shifts toward earlier spring runoff over the MRB. Montana, northwestern Wyoming, and western North Dakota exhibit significant upward trends in the annual average of minimum and maximum temperature, significant downward trends in annual precipitation at climate stations, and significant downward trends in streamflow. PRISM data, however, indicate no trend in precipitation in the western MRB for this period. Eastern North and South Dakota exhibit upward trends in annual precipitation, annual average of minimum temperature at climate stations, and streamflow over the period of record. Southern Nebraska and northern Kansas exhibit significant upward trends in both annual average of minimum and maximum temperature, downward trends in annual precipitation, and streamflow. These data suggest that climate change plays a significant role in the nature of streamflow in the Missouri River Basin, and the nature of this role varies across the basin.