Comprehensive review of groundwater scarcity, stress and sustainability index-based assessment

Groundwater, the world's largest freshwater resource, is critically important for global food security. Excessive groundwater extraction has led to issues such as groundwater sustainability, scarcity, and stress; various indices have been developed for assessing them. The selection of the right index for the assessment is very important. Therefore, the existing index-based groundwater scarcity stress, and sustainability methods were reviewed to rank the indices based on scientific criteria, to identify the gaps in the literature, and propose a way to bridge them. Analysis of the review revealed that indices based on drivers pressures state impact response, and aggregation methods for groundwater sustainability were likely to yield more realistic outcomes and facilitated better planning of groundwater-related issues. Based on the criteria ranking, the groundwater stress index based on the groundwater footprint methodology secured the relatively uppermost rank. For future development, this study proposed an index by coupling two existing indices of the groundwater footprint family to get more realistic outcomes. One deals with the quantity and quality of groundwater and the other with quantity only but at a more detailed sub-system level. It combines the advantages of the two indices of which it is composed while minimizing their shortcomings.