Analysis of Human Influence on Drought Conditions in the Upper Colorado River Basin (Texas)

Globally, it is expected that arid and semi-arid areas will face increasing frequency of drought through the 21st century. Drought is normally attributed to climatic factors. However, humans constantly alter hydrologic systems through manipulating and consuming water, which can also cause drought. However, human influence on drought, outside of influences on warming-driven climate change, is rarely studied. Here, the upper Colorado River Basin (Texas) is studied to assess the human influence on drought conditions in a semi-arid basin. An observation-modeling framework is used to simulate naturalized runoff conditions which are compared to observed data in an undisturbed (little human influence) and disturbed (much human influence) period to elucidate human influences on drought. Further, public water storage and supply data are incorporated to analyze how human water management may be specifically affecting downstream hydrologic drought in the upper Colorado River Basin. Results show that according to observed data, drought occurred more often, persisted longer on average, and had a higher maximum duration during the disturbed period. Naturalized model output did not predict such increases, indicating that human influence is responsible. Water deliveries in the study area were found to significantly affect downstream flow and are connected to instances of human-influenced drought. Results suggest that in order to reduce downstream drought conditions, deliveries will likely have to be reduced and that reducing deliveries during periods of low rainfall, or during months in which deliveries constitute a large portion of human influenced drought severity could be especially helpful in alleviating downstream drought.