Conclusions
A few previous studies using
statistical approaches have reported that multi-year drought can induce
a shift in the catchment rainfall-runoff relationship, but rarely have
studies provided process-level interpretation of such shifts. Consistent
with the results of previous research, the current study demonstrated
that a change in the rainfall-runoff relationship was detected after the
beginning of a prolonged drought period (1997) in the Wee Jasper
catchment in New South Wales, Australia. However, the new analysis
approach proposed in this study found that the change in the
rainfall-runoff relationship is induced by an increase of catchment
active storage capacity and a decrease in soil moisture resulting from
persistent evapotranspiration of deep-rooted woody vegetation during the
drought, leading to a decline in groundwater level and deep soil
moisture.
This study concluded that the combination of data assimilation and a
hydrological model was a suitable approach for detecting the
hydrological non-stationarity caused by prolonged drought. This approach
not only can detect changes in rainfall-runoff relationships, but also
can identify the driving factors for such changes at the process-level.
The method used in this study can provide assistance in developing
strategies and management practices to mitigate the negative effects of
prolonged drought, and in developing preparedness and adaptation
strategies for the challenges of climate change which will likely
increase the frequency and severity of drought in the future.