Longterm Precipitation Analyses for the Central Texas Blackland Prairie

Continuous records of intensively monitored precipitation data are rare, but where available they provide valuableregional information on hydrologic structure design and on other water supply and water quality management and modelingissues. One such longterm precipitation record exists for the Texas Blackland Prairie region. Beginning in 1937 andcontinuing to the present, hydrologic data have been collected at the USDAARS Grassland Soil and Water ResearchLaboratory watershed facility near Riesel, Texas. The objectives of this article are to present longterm analyses and topublicize the availability of that precipitation database. Longterm analyses included examination of general precipitationproperties, depthdurationfrequency relationships, and trends in rainfall amount and occurrence. Annual rainfall for theregion averages about 890 mm, with relatively wet springs and falls and drier summer and winter months.Depthdurationfrequency results emphasize the need for engineers to use the most current and extensive data sets and/orproven relationships in the design of hydrologic structures. Several significant temporal trends that can affect water resourcemanagement were also determined. These trends include increases in October rainfall, nonspring rainfall, and the numberof 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.