LONG–TERM PRECIPITATION ANALYSES FOR THE CENTRAL TEXAS BLACKLAND PRAIRIE

Continuous records of intensively monitored precipitation data are rare, but where available they provide valuable regional information on hydrologic structure design and on other water supply and water quality management and modeling issues. One such long–term precipitation record exists for the Texas Blackland Prairie region. Beginning in 1937 and continuing to the present, hydrologic data have been collected at the USDA–ARS Grassland Soil and Water Research Laboratory watershed facility near Riesel, Texas. The objectives of this article are to present long–term analyses and to publicize the availability of that precipitation database. Long–term analyses included examination of general precipitation properties, depth–duration–frequency relationships, and trends in rainfall amount and occurrence. Annual rainfall for the region averages about 890 mm, with relatively wet springs and falls and drier summer and winter months. Depth–duration–frequency results emphasize the need for engineers to use the most current and extensive data sets and/or proven relationships in the design of hydrologic structures. Several significant temporal trends that can affect water resource management were also determined. These trends include increases in October rainfall, non–spring rainfall, and the number of summer, fall, and annual rainy days. These increases, however, are offset to some degree by decreases in April rainfall, in the number of extreme events in the spring, and in the magnitude of extreme fall rain events.