where x represents the groundwater storage flux under
environmental change [mm-1], named the ‘impact
parameter’. An increase in x indicates that the groundwater
rapidly decreased, and a decrease in x indicated a slower
groundwater decrease, as shown in Figure 2.
Groundwater discharge into the river channel during the recession period
can be expressed as a function of catchment groundwater storage (Sugita
& Brutsaert, 2009):