Analysis of Human Influence on Drought Conditions in the Upper Colorado River Basin (Texas)
Whittemore, Aaron Maitland
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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.
General Audience Abstract
It is expected that many arid climates around the globe will become even experience more frequent drought during the 21st century. Drought is a lack of water relative to normal levels and has important implications for agriculture, industry, fisheries, water managers, and the broader public. Drought is normally attributed to natural factors such as lack of rain or increases in temperature. Humans have affected these factors through global climate change, and many researchers have focused their efforts on understanding how global warming impacts drought conditions. However, humans can also affect drought conditions through water consumption. Despite the impact of human water consumption, it is rarely a topic of specific study in relation to the occurrence of drought. Here, conditions lacking human influence (i.e. no water consumption, land-use change, etc.) are simulated and compared to observed data from a stream gage downstream from human intervention, allowing for examination of human influences on drought. Public water usage and management data from the Colorado River Municipal Water District are also incorporated to allow for more specific understanding of how human influence affects drought conditions downstream of reservoir operation and groundwater pumping. Results show that drought occurred more often, persisted longer on average, and had a higher maximum duration due to human influence. Water usage and management by the Colorado River Municipal Water District are connected to and have a role in causing decreases in downstream flow and occurrence of drought. Results indicate that demand reductions will likely be needed to ensure sustainable water availability and that reducing demand during periods of low rainfall or during times of the year in which human water use accounts for larger portions of drought severity could be most helpful in lessening downstream drought.
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