Detecting and attributing drought-induced changes in catchment
hydrological behaviors using data assimilation method
Abstract
It is widely recognized that multi-year drought can induce changes in
catchment hydrological behaviors. However, at present, our understanding
about multi-year, drought-induced changes in catchment hydrological
behaviors and its driving factors at the process level is still very
limited. This study proposed a new approach using a data assimilation
technique with a process-based hydrological model to detect multi-year
drought-induced changes in catchment hydrological behaviors and to
identify driving factors for the changes in an unimpaired Australian
catchment (Wee Jasper) which experienced prolonged drought from 1997 to
2009. Modelling experiments demonstrated that the multi-year drought
caused a significant change in the catchment rainfall-runoff
relationship, indicated by significant step changes in the estimated
time-variant hydrological parameters SC (indicating catchment active
water storage capacity) and C (reflecting catchment evapotranspiration
dynamics), whose average values increased 23.4% and 10.2%,
respectively, due to drought. The change in the rainfall-runoff
relationship identified by the data assimilation method is consistent
with that arrived at by a statistical examination. The proposed method
provides insights about the drivers of the changes in the
rainfall-runoff relationship at the processes level. Declining
groundwater and deep soil moisture depleted by persistent
evapotranspiration of deep-rooted woody vegetation during drought are
the main driving factors for the catchment behaviors change in the Wee
Jasper catchment. The new method proposed in this study was found to be
an effective technique for detecting both the change of hydrological
behaviors induced by prolonged drought and its driving factors at the
process level.