|Abstract:||This study evaluates the performance of four evapotranspiration
methods (Priestley-Taylor, Penman-Monteith,
Hargreaves and Makkink) of differing complexity in a semiarid
environment in north China. The results are compared
to observed water vapour fluxes derived from eddy flux measurements.
The analysis became necessary after discharge
simulations using an automatically calibrated version of the
Soil and Water Assessment Tool (SWAT) failed to reproduce
runoff measurements. Although the study area receives most
of the annual rainfall during the vegetation period, high temperatures
can cause water scarcity. We investigate which
evapotranspiration method is most suitable for this environment
and whether the model performance of SWAT can be
improved with the most adequate evapotranspiration method.
The evapotranspiration models were tested in two consecutive
years with different rainfall amounts. In general,
the simple Hargreaves and Makkink equations outmatch the
more complex Priestley-Taylor and Penman-Monteith methods,
although their performance depended on water availability.
Effects on the quality of SWAT runoff simulations, however,
remained minor. Although evapotranspiration is an important
process in the hydrology of this steppe environment,
our analysis indicates that other driving factors still need to
be identified to improve SWAT simulations. |