6. Conclusion
This study considered the environmental impact in low-flow recession
analysis, exploring the changes in low-flow characteristics, dynamic
storage, and storage-discharge relationships in order to understand the
effect of groundwater loss or gain on the catchment recession regime.
The results showed decreased low-flow characteristics in most catchments
which represent the lower flow variation owing to environmental change.
In addition, the regional distribution of low-flow characteristics and
dynamic storage showed regional differences in aquifer properties, which
is consistent with previous work. The majority of the dynamic storage
increased in the post-period, indicating that environmental change
ultimately led to increased groundwater consumption by increased
vegetation cover, groundwater pumping or other possible factors. It also
causes a decrease in storage-discharge sensitivities with lower
streamflow. This highlighted a critical problem where frequent drought
events may occur during dry periods due to a lower streamflow generated
from groundwater. To understand whether the quantifying environmental
change is consistent with changes in land use, this study calculated the
NDVI changes for comparison. As expected, both changes were the same,
and only a few catchments were inconsistent. These inconsistent cases
can be explained by the possible impact factors (including return flow
of agricultural irrigation, increase in industrial land use, surface
erosion by natural hazards, and others) from local land use. In
conclusion, this study demonstrated that quantifying environmental
impacts through the recession method can help to clarify current changes
in groundwater and related processes from environmental co-evolution.
Different from our previous research that focused on S-Qsensitivity and its change, this study can compare regional differences
and its changes over time by quantified environmental impact. Future
challenges lie in the development of methods or modeling for assessing
an impact of specific factor with a physics-based description.