Assessment of Emergency Backup Water Sources: A Case of the Record-breaking Drought in Taiwan in 2021

The average annual rainfall in Taiwan is approximately 2,502 millimeters, far exceeding the global average of 973 millimeters. However, the rainfall is unevenly distributed, with approximately 78% occurring during the wet season. Over the past decade, the average annual rainfall has been about 91.5 billion cubic meters, but more than 50 billion cubic meters flow directly into the sea. In terms of the overall water resource utilization framework in Taiwan, it is influenced by hydrological environmental factors, coupled with the impacts of global climate change and the normalization of extreme weather events, water resources are expected to be increasingly affected by droughts.

Between June 2020 and February 2021, the cumulative rainfall in the catchment areas of Taiwan's major reservoirs reached a historic low, decreasing by approximately 1,000 millimeters compared to the historical average of 1,780 millimeters for the same period. This severe drought presented significant challenges to Taiwan's water supply. Securing water availability during the drought, the government improved regional water resource allocation and evaluated suitable locations for developing emergency groundwater wells. This assessment was based on factors such as groundwater levels, geological profiles, aquifer thickness, and groundwater recharge conditions. Priority was given to gravel aquifers with higher recharge potential, aquifer thickness exceeding 50 meters, and proximity to water treatment facilities within the public water supply system. According to the factors, it selects appropriate locations to drill emergency water wells, ensuring that the extracted groundwater can be integrated directly into the public water supply system.

The government completed 195 drought relief groundwater wells with the approach in main metropolitan areas affected by water shortages. These wells provided approximately 75,000 cubic meters in totality per day, effectively assisting Taiwan in overcoming the drought crisis. The paper uses Taiwan's century drought event and methods for assessing emergency backup water sources as a case. Additionally, it compares techniques for evaluating groundwater development potential with other countries, such as utilizing remote sensing, Geographic Information Systems (GIS), and the Modified Impact Factor (MIF). Through case studies and literature reviews, the paper examines the feasibility of the proposed methods for practical application in emergencies.

Keywords: Drought; Groundwater; Emergency Backup Water Sources