Quantifying the evolving role of intense precipitation runoff when calculating soil moisture trends in east Texas

Abstract

Eastern Texas straddles a precipitation zone that transitions from semi-arid grasslands to the humid, rainy conditions of the northern Gulf Coast. While several studies have quantified the changing magnitude and frequency of daily extreme events, the paucity of hourly datasets have limited insight into how the growing proportion of rainfall exceeding hourly soil infiltration capacity has and will exacerbate the state’s droughts. This paper builds on previous analysis, deploying algorithms with a temporal dimension to calculate soil moisture scarcity from evapotranspiration and precipitation data based on FAO-56 methodology and then introduces a daily estimate of the proportion of precipitation that flows off the ground surface rather than replenishing moisture deficits for soils with three different infiltrative capacities at 12 observation sites. The comparison of subsequent time series regression analyses showed that absorptive soils in east Texas have experienced modest, though mostly statistically insignificant, acceleration in drought trends after the incorporation of hourly rainfall intensity data: for the 24 soil samples (out of 36) with saturated hydraulic conductivity (Ksat) rates greater than 4.5 mm per hour, 14 had accelerated drying trends, five showed no change, and the remaining five displayed more gradual changes relative to their baseline trend magnitudes.