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.
Highlights
Water crises have been increasingly observed in various parts of the world including Thailand
The proposed two approaches for accounting Environmental Water Requirement (EWR) in the demand to availability (DTA) ratio of the WSIe are based on a human perspective and an environmental perspective (EWR is explicitly reserved by subtracting it from the water availability, WSIe2)
The annual water stress results revealed the same level of classification for both the approaches as the Bang Pakong watershed needs attention to monitor the stress situation; these annual results cannot be used to evaluate the implications of applying the different approaches
Summary
Water crises have been increasingly observed in various parts of the world including Thailand. All regions of Thailand are being affected by floods and droughts almost every year This issue is taken into consideration by assessing the impact of freshwater use on freshwater resources. Do humans need water for satisfying their demands, but water is required by the environment, especially a river or watershed system, to maintain its functions and ecosystem services. This environmental water is affected by the overuse of freshwater resources as well as water scarcity [1] and it requires concern at different scales of analysis from large to small [2]. Accounting for EWR in the characterization of freshwater resource impact has been strongly recommended by Fingerman et al [5]
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