Assessment of Water Stresses in Southwest Louisiana: Effects of Uncertainties in Water Resources Availability

Hisham Eldardiry, Department of Civil Engineering, University of Louisiana at Lafayette, PO Box 40404, Lafayette, LA, 70504: hae5018@louisiana.edu; Emad Habib, Department of Civil Engineering, University of Louisiana at Lafayette, PO Box 42291, Lafayette, LA, 70504: habib@louisiana.edu; and David Borrok, School of Geosciences, University of Louisiana at Lafayette, Lafayette, LA, 70504: dmb5953@louisiana.edu

The current study evaluates stresses on the water system of southwest Louisiana based on the balance between availability of surface and groundwater resources, and the collective water withdrawals by public supply, industrial, power generation, and irrigation. Water use in southwest Louisiana has been dominated by groundwater withdrawals, while less surface water has been used despite abundant rainfall and surface water availability. Stresses on water systems are usually quantitatively assessed through indices that account for water demand relative to water availability, e.g., the Water Supply Stress Index (WaSSI). However, as a result of adopting deterministic supply-driven approaches, limited attention is paid to the potential impacts of climatic variability on water system balance. The focus of the current study is to adopt a probabilistic-based approach to evaluating water stress by modeling water supply as a stochastic variable to account for uncertainties in the availability of water resources. Under this probabilistic framework, we also evaluate the potential for drought conditions southwest Louisiana using the Threshold Level Method (TLM). Drought conditions result in periods of low surface flows and can adversely limit water resources availability.

The variability in water supply stresses under drought conditions is examined through sectoral-based analysis to characterize the potential impacts on the use of water for different sectors. Two different datasets are used for estimating surface water availability: the National Hydrography Dataset (NHDPlus), and the second phase of the North American Land Data Assimilation System (NLDAS-2). The NHDPlus dataset, which provides estimates of mean monthly and annual streamflow information (averaged over 1970-2000), will be used to assess water stresses under climatologically average conditions of water availability. The hourly streamflow estimates from NLDAS-2 dataset (available for 1979-present) will be used to incorporate intra-annual and inter-annual variability in surface water availability and the impact on water stress calculations at different temporal scales (seasonal and annual). The analysis is performed on a Hydrological Unit Code (HUC)-12 watershed scale. The results of the water stress indices suggest new opportunities for reallocation of surface water use to help determine how the existing water systems can be made more reliable, resilient and less vulnerable to climate variability. Furthermore, this study will also have large implications to applied water resource studies aiming to formulate water management policies and improve water system sustainability.

Keywords: water resources system; Water supply stress index; climate variability; drought

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