A simple tool for refining GCM water availability projections, applied to Chinese catchments
2018
Abstract. There is a growing desire for reliable 21st-century projections of water
availability at the regional scale. Global climate models (GCMs) are
typically used together with global hydrological models (GHMs) to generate
such projections. GCMs alone are unsuitable, especially if they have biased
representations of aridity. The Budyko framework represents how water
availability varies as a non-linear function of aridity and is used here to
constrain projections of runoff from GCMs, without the need for
computationally expensive GHMs. Considering a Chinese case study, we first
apply the framework to observations to show that the contribution of direct
human impacts (water consumption) to the significant decline in Yellow River
runoff was greater than the contribution of aridity change by a factor of
approximately 2, although we are unable to rule out a significant
contribution from the net effect of all other factors. We then show that the
Budyko framework can be used to narrow the range of Yellow River runoff
projections by 34 %, using a multi-model ensemble and the high-end Representative
Concentration Pathway (RCP8.5) emissions scenario. This increases confidence that the Yellow River will see
an increase in runoff due to aridity change by the end of the 21st century.
Yangtze River runoff projections change little, since aridity biases in GCMs
are less substantial. Our approach serves as a quick and inexpensive tool to
rapidly update and correct projections from GCMs alone. This could serve as a
valuable resource when determining the water management policies required to
alleviate water stress for future generations.
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