Upland contribution of sediment and runoff during extreme drought: A study of the 1947-1956 drought in the Blackland Prairie, Texas

摘要

The 1950s drought severely impacted a 1.1millionkm~2 area in the central US. This drought, along with the famous 1930s drought, was among the most severe of the 20th century for large areas and is the drought of record for water supply planning in Texas. At the USDA-ARS Riesel Watersheds during the drought, average annual rainfall was reduced 27%, which produced 75% less runoff and 35% less sediment yield. Rainfall intensity during the drought was, however, typically greater than for the non-drought period. Based on long-term data from the Riesel Watersheds, the mean, 75th, 90th, and 95th percentile values of sediment yields on days with measureable soil loss were larger for the drought than non-drought periods. These results reflect the increase in rainfall intensity during the drought but more importantly the increased efficiency of drought rainfall to dislodge and transport sediment, which is attributed to the combined effects of reduced vegetative cover and increased soil erodibility. The potential for high sediment yields during drought periods illustrates the need to consider this landscape vulnerability in long-term planning and assessment and the importance of long-term monitoring to predict water supply impacts. This is especially evident in Texas, which is expected to experience a dramatic increase in population and water demand this century, with a corresponding decrease in reservoir storage capacity due to sedimentation.