A model-based approach to assessing the balance between groundwater recharge and use in Kumamoto Area, southern Japan

For sustainable use of groundwater, it is important to know the water balance of groundwater as land and water use changes for working with stakeholder collectively.

In order to understand these issues, a distributed hydrological model that includes the key processes of the regional hydrological system is considered to be a powerful tool, as it enables us to understand the impact of human activities at any given site.

In the Kumamoto region, which is almost 100% dependent on groundwater for drinking water, there have been attempts to understand groundwater flow and water balance qualitatively and quantitatively (Ministry of Land, Infrastructure, Transport and Tourism (2011), Rahman et al. (2021)), and uncertainty quantification of model parameters (Kawasaki et al.(2022)).

These models are expected to be applied to understanding the impacts of changes in land and water use, but it is not easy to conduct an evaluation of impacts to derive practical actions, as it requires a large number of calculations with many possible combinations of scenarios, including the area to be changed and the degree of change.

Therefore, in this study, with the objective of understanding the impact of possible anthropogenic and environmental changes on the groundwater balance, the areas that are important for the assessment target were first identified by sensitivity analysis. Then, based on confirmation that no extreme phenomena occur in the identified important areas and in combination with each parameter, an evaluation of the impact was attempted by using what-if simulations, and the results of these simulations are reported.