Assessing the Effect of Incorporating Environmental Water Requirement in the Water Stress Index for Thailand

Abstract

Human and environmental demands for water are both important; therefore, two approaches are proposed for assessing water scarcity using the water stress index. In one of them, the human demand for water explicitly includes environmental water as one of the components (WSIe1), whereas in the other, environmental water is explicitly reserved by subtracting it from the water availability (WSIe2). The results obtained from using the two approaches in the case of Bang Pakong watershed correspondingly contribute to the explanation of the existing stress situation, especially in the dry season. The stressful results were noticed during December to February for both approaches as a result of less available water and higher environmental water requirement. The assessment of environmental water requirement (EWR) in this study was quantified according to low and high flow periods. The two approaches perform well for assessing water scarcity in the Bang Pakong watershed; however, the result interpretation using the WSIe1 approach is more serious than the WSIe2 approach in terms of water scarcity potential beyond the critical threshold. In conclusion, priority of water allocation is the key consideration for selecting the approach. Higher priority for the environment favors the use of WSIe2 for policy making whereas for a lower priority, the use of WSIe1. In case of Thailand, the WSIe2 approach would be recommended in order to put the EWR as the first priority. Then, water allocation priorities can be rearranged only for human demands for water while the EWR is already safeguarded by setting it aside.