On the non-stationarity of hydrological response in anthropogenically unaffected catchments: an Australian perspective
2016
Increases in greenhouse gas concentrations are expected to impact the
terrestrial hydrologic cycle through changes in radiative forcings and plant
physiological and structural responses. Here, we investigate the nature and
frequency of non-stationary hydrological response as evidenced through water
balance studies over 166 anthropogenically unaffected catchments in
Australia. Non-stationarity of hydrologic response is investigated through
analysis of long-term trend in annual runoff ratio (1984–2005). Results
indicate that a significant trend (p < 0.01) in runoff ratio is
evident in 20 catchments located in three main ecoregions of the continent.
Runoff ratio decreased across the catchments with non-stationary hydrologic
response with the exception of one catchment in northern Australia. Annual
runoff ratio sensitivity to annual fractional vegetation cover was similar to or
greater than sensitivity to annual precipitation in most of the catchments
with non-stationary hydrologic response indicating vegetation impacts on
streamflow. We use precipitation–productivity relationships as the first-order
control for ecohydrologic catchment classification. A total of 12 out of 20
catchments present a positive precipitation–productivity relationship
possibly enhanced by CO2 fertilization effect. In the remaining
catchments, biogeochemical and edaphic factors may be impacting productivity.
Results suggest vegetation dynamics should be considered in exploring causes
of non-stationary hydrologic response.
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