wAbstract
@From published runoff measurements in catchments with a wide
range of climatic conditions it is found that long-term mean annual
runoff (R) can be closely fitted (r2=0.94) to measured
climatic data by R = P * exp(-PET/P), where P is the mean annual
precipitation and PET is the mean annual potential evapotranspiration
(in mm) calculated via the Holland equation. PET = 1.2~1010*
exp(-4620/Tk), which is solely a function of the mean annual temperature
in Kelvin, Tk. Application of the chain rule for partial differentiation
to the combined equations gives the following equation for estimating
the change in runoff due to changes in P and Tk:
dR = exp(-PET/P) * [1 + PET/P] * dP - [5544~1010* exp(-PET/P)
* exp(-4620/Tk) * Tk-2] * dTk
@By setting dR equal to zero, this equation can be used to estimate
the increase in P required to maintain constant runoff for a small
increase in T. It can also be used to estimate the decrease in
runoff in a scenario with constant precipitation and increased
temperature. It is shown herein that predictions of annual runoff
changes for various climate change scenarios based on this simple
model compare favorably with those based on more complex, calibrated
hydrological models, as well as with those based on long-term
historical observations of runoff and climate change. Application
of the equation above also indicates that the IPCC projections
for climate change under the a1B emissions scenario may underestimate
the area of North America that is likely to suffer decreases in
runoff.
Keywords: Runoff; Evapotranspiration; Climate changex
Introduction
The models
Methods and data
Results
Effect of climate change on runoff
Climate elasticity
Runoff maintenance
Discussion
Acknowledgements
References