Water-deficit-based drought risk assessments in Taiwan

Taiwan is located in Western Pacific and receives approximate 2,500 mm rainfall per year. Suffered from inadequate water supply during prolonged and severe droughts, assessing drought risk becomes one of the key tasks of water-resources planning and management in Taiwan. Well-prepared drought mitigation measures require assimilation of physical environment of droughts and human socioeconomic factors. An index-based approach is presented in this study to evaluate drought risk at municipal scale in Taiwan for current status (2008) as well as future scenarios (2021). A multiplicative formula links drought hazard (frequency, duration, and severity of droughts), drought exposure (water use), and drought vulnerability (unreliable water supply) to determine drought risk. This approach quantifies the spatial distribution of drought risk and is able to deal with future changes of water use and water-supply source and to examine their influences on drought risk assessments. The results reveal that the regions that are at great risk in the future are those regions already threaten by drought currently. Changes of future water use and water-supply source would not significantly alter spatial distribution of drought risk and ranking order among regions. These results present a basis for future water-resources planning and economic developments for each municipal region.