Long-Term Water Balance in a Semiarid Shrubland

Abstract

Baseline information on the water balance is essential for adequately understanding ecohydrological relationships on rangelands. Unfortunately, such information is not always available, because insufficient data have been collected and/or the data do not represent relevant temporal or spatial scales. In particular, for many rangelands long-term records of runoff at the small catchment or larger scales are relatively rare. In this study, we used catchment-scale data, collected over nearly a decade, to estimate the long-term water balance for mesquite-juniper rangelands in the Rolling Plains of Texas. The data include precipitation, surface runoff, soil water, and vegetation cover; these were measured on 9 microcatchments, each about 1.4 ha in size. Soil water was determined by neutron-probe measurements to a depth of 120 cm. Surface runoff was, surprisingly, a very small component (<1%) of the water budget and occurred only during extraordinary precipitation events. Soil-water recharge resulted mainly from winter precipitation. Evapotranspiration, which took place during the entire year, ranged from less than 1 mm day-1 during the winter to almost 8 mm day-1 during the summer. This study is important because it clearly documents how water is allocated on these rangelands at spatial and temporal scales that are relevant to management. The results from this study, in conjunction with other work in the Rolling Plains, suggests that there is little potential for increasing water yield via brush control in these landscapes.