Abstract
Abstract. Assessing the factors that have an impact on potential evapotranspiration (PET) sensitivity to changes in different climate variables is critical to understanding the possible implications of climatic changes on the catchment water balance. Using a global sensitivity analysis, this study assessed the implications of baseline climate conditions on the sensitivity of PET to a large range of plausible changes in temperature (T), relative humidity (RH), solar radiation (Rs) and wind speed (uz). The analysis was conducted at 30 Australian locations representing different climatic zones, using the Penman–Monteith and Priestley–Taylor PET models. Results from both models suggest that the baseline climate can have a substantial impact on overall PET sensitivity. In particular, approximately 2-fold greater changes in PET were observed in cool-climate energy-limited locations compared to other locations in Australia, indicating the potential for elevated water loss as a result of increasing actual evapotranspiration (AET) in these locations. The two PET models consistently indicated temperature to be the most important variable for PET, but showed large differences in the relative importance of the remaining climate variables. In particular for the Penman–Monteith model, wind and relative humidity were the second-most important variables for dry and humid catchments, respectively, whereas for the Priestley–Taylor model solar radiation was the second-most important variable, with the greatest influence in warmer catchments. This information can be useful to inform the selection of suitable PET models to estimate future PET for different climate conditions, providing evidence on both the structural plausibility and input uncertainty for the alternative models.
Highlights
Assessing changes to evapotranspiration (ET) is critical in understanding the impacts of anthropogenic climate change on the catchment water balance
We explore the relative importance of each climate variable on overall potential evapotranspiration (PET) sensitivity, by first visualizing the conditional responses of PET when holding each variable constant at its historical level while perturbing the remaining variables, and comparing this to the unconditional estimates of all potential responses in PET
We used a global sensitivity analysis to investigate the sensitivity of PET and the relative importance four climatic variables which influence PET (T, relative humidity (RH), Rs and uz) under plausible future changes in these variables
Summary
Assessing changes to evapotranspiration (ET) is critical in understanding the impacts of anthropogenic climate change on the catchment water balance. ET is affected by climate change through a cascade of processes that begins with the increasing concentration of greenhouse gases, followed by their attendant impacts on largescale circulation and changes to the global distribution of energy and moisture. These large-scale processes lead to localscale changes in the atmosphere, which in turn influence the catchment water balance through a set of terrestrial hydrological processes by which precipitation is converted into actual ET (AET), runoff and groundwater recharge (Oudin et al, 2005). The PET projections are combined with GCM projections of precipitation (P ), which together can be used to directly estimate the water deficit
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