Budyko framework based analysis of the effect of climate change on
watershed characteristics and their impact on discharge over Europe
Abstract
In a context of climate change, the stakes surrounding water
availability are getting higher. Decomposing and quantifying the effects
of climate on discharge allows to better understand their impact on
water resources. We propose a methodology to separate the effect of
change in annual mean of climate variables from the effect of
intra-annual distribution of precipitations. It combines the Budyko
framework with outputs from a Land Surface Model (LSM). The LSM is used
to reproduces the behavior of 2134 reconstructed watersheds over Europe
between 1902 and 2010, with climate inputs as the only source of change.
We fit to the LSM outputs a one parameter approximation to the Budyko
framework. It accounts for the evolution of annual mean in precipitation
(P) and potential evapotranspiration (PET). We introduce a time-varying
parameter in the equation which represents the effect of long-term
variations in the intra-annual distribution of P and PET. To better
assess the effects of changes in annual means or in intra-annual
distribution of P, we construct synthetic forcings fixing one or the
other. The results over Europe show that the changes in discharge due to
climate are dominated by the trends in the annual averages of P. The
second main climate driver is PET, except over the Mediterranean area
where changes in intra-annual variations of P have a higher impact on
discharge than trends in PET. Therefore the effects of changes in
intra-annual distribution of climate variables are not to be neglected
when looking at changes in annual discharge.