100 Years of Changing Hydrologic Conditions in the Mississippi River Basin: Precipitation and Water Yield

Many parts of the Mississippi River Basin are experiencing vastly different hydrologic conditions than they did 100 years ago as a result of changes in the magnitude of hydrologic inputs and withdrawals. These changes can be attributed to factors such as altered amounts and timing (seasonality) of precipitation, changes in rainfall-runoff relations due to altered land use, and anthropogenic disturbances to streams and river systems. Data from thousands of NOAA precipitation gages and USGS flow stations in the basin were used. This study uses HUC4 basin boundaries within the major river systems (i.e., Missouri, Ohio, etc.) draining to the Mississippi River to spatially subdivide the approximately 100-year data set. Results show that in general, although most of the Mississippi River Basin is receiving more rainfall than it did 100 years ago that there are vast areas where water yields have decreased significantly, particularly in the western part of the basin and particularly in spring. Parts of the western basin are experiencing 25 to more than 50% less discharge per unit area than they did 100 years ago. Precipitation has also shifted temporally such that winter precipitation has significantly decreased in many areas while spring and autumn precipitation has generally increased. The anthropogenic influence on water yield, appears to be large over vast areas, with values of water yield per unit precipitation also decreasing between 25 to more than 50% throughout much of this area. Not all areas of the basin, however, are experiencing decreases in water yield.