The Quantification of Rainfall Needed to Overcome Drought: A Study in North Texas

The year of 2011 was the driest year ever on record in the state of Texas. All reservoirs in North Texas were below maximum conservation level by September. Although there was measurable rainfall in North Texas, it was not enough to refill the lakes. So, how much rainfall is needed to overcome a drought-induced soil moisture deficit so that runoff occurs? We answer this question based on the drought that occurred during the years of 2011 through 2015 over Texas, specifically North Texas within the domain of 31.35°N - 34.11°N and 95.41°W - 98.56°W. The study focused on the evolution of soil moisture anomalies and associated streamflow conditions and reservoir levels. Monthly soil moisture anomalies within the study domain were compared with monthly rainfall accumulations, as well as with reservoir lake levels and streamflow. The soil moisture data was obtained from the MOSAIC model output of the North American Land Data Assimilation System (NLDAS). Monthly rainfall data was derived over the same domain as the soil moisture from the Precipitation Reconstruction over Land dataset from the Climate Prediction Center. The comparison of soil moisture with rainfall revealed that it took about ten to fifteen inches of rain within a period of thirty days to bring a complete end to the drought in 2015. This research is quite significant because the methodology to study the evolution of soil moisture deficits, and the assessment of how much rainfall is needed to overcome the deficit, can be applied to any location where drought characteristics are similar, as long as there is data for the time period.