Trends in Yellowstone River Basin Water Supply as Interpreted Through Hydrologic Analysis, 1898-2007

Abstract

The Yellowstone River and its tributaries provide an important case study in the changes in magnitude and timing of discharge. As part of a review of water demands on the river and potential effects on fish and other aquatic biota, we assessed long term trends (1898-2007) and more recent changes (1970-2007) in the hydrographs of the Yellowstone River and its tributaries using data from 18 USGS Hydro-Climatic Data Network Stations. We evaluated seven variables used to characterize the discharge: 1) annual discharge, 2) magnitude of discharge, 3) absolute annual minimum discharge, 4) monthly discharge, 5) date when half of annual volume passed station, 6) date when maximum daily mean occurred, and 7) date when discharge returned to baseflow. Declines in volume and magnitude of annual and seasonal discharges are present in the basin, more so in areas where there are no water storage facilities. Timing of flow events are occurring earlier in the year throughout the basin, leaving less water in the summer and fall when water demands are the greatest. The appearances of significant trends have increased over the period 1970-2007, and it is expected that they will continue without serious changes in the basin. Lessened flows and altered timing stands to greatly affect all users of water in the basin, as is occurring in the rest of western North America. Effects on the native biota inhabiting the river can also be expected.