Evaluation of methods for estimating daily reference crop
evapotranspiration at a site in the humid alpine meadow, northeastern
Qinghai-Tibetan Plateau
Abstract
Evapotranspiration as the key component of the terrestrial water cycle,
an accurate estimates of evapotranspiration are of great importance for
water irrigation management. Although many applicable ET models have
been developed, these are largely focused on low altitude regions, with
little attention to alpine ecosystem. In this paper, we evaluate the
performance of 14 evapotranspiration (ET0) models by comparison with
large weigh lysimeter measurements. Specifically, we use Bowen
ratio-energy balance method, three combination models, seven
radiation-based models and three temperature-based models driven with
data from June 2017 to December 2018 in a humid alpine meadow,
northeastern Qinghai-Tibetan Plateau. The daily actual
evapotranspiration was obtained by large weighing lysimeters located in
an alpine Kobresia meadow. We found that the performances of the 14 ET0
models, ranked on the basis of their RMSE (root mean square error),
decreased in the order: Bowen>
Priestley-Taylor> DeBruin-Keijman> 1963
Penman> FAO-24 Penman> FAO-56 Penman-Monteith
> IRMAK1> Makkink (1957) >
Makkink(1967)>Makkink> IRMAK2 >
Hargreaves>Hargreaves1>Hargreaves2. For the
combination models, FAO24 Penman yielded the highest correlation,
followed by Pen-63 and FAO-56 PM. For radiation-based models, PT and DK
obtained the highest correlation, followed by Makkink, Makkink(1967) and
Makkink (1957), IRMAK1 and IRMAK2. For temperature-based models, HAR,
HAR1 and HAR2 obtained the same correlation. Overall, the Bowen
performed best, with RMSEs 0.98, followed by radiation-based models,
combination models and temperature-based models. Furthermore, all models
tended to underestimate measured ETa during periods of larger
evaporative demand (i.e. growing season) and overestimate measured ETa
during lower evaporative demand (i.e. non-growing season). Our results
could provide a new sight for the accurate assessment of
evapotranspiration in an alpine ecosystem.