Abstract
Remotely sensed land surface temperature- (LST-) dependent evapotranspiration (ET) models and vegetation index- (VI-) LST methods may not be suitable for ET estimation in energy-limited cold areas. In this study, the relationship of ET to LST was simulated using the process-based Simultaneous Heat and Water (SHAW) model for energy- and water-limited conditions in Mongolia, to understand the differences in ET processes under these two limiting conditions in dry and cold climates. Simulation results from the SHAW model along with ground observational data showed that ET and LST have a positive relationship when air temperature (Ta) is less than or equal to the temperature (Ttra) above which plants transpire and have a negative relationship whenTais greater thanTtraunder the energy-limited condition. However, ET and LST maintain a negative relationship with changes inTaunder the water-limited condition. The differences in the relationship between ET and LST under the energy-limited and water-limited conditions could be attributed to plant transpiration and energy storage in moist/watered soil and plants. This study suggests that different strategies should be used to estimate ET under the energy-limited condition in dry and cold climates.
Highlights
Terrestrial evapotranspiration (ET), defined as the loss of water from the land surface to the atmosphere, is a key process in water cycles [1, 2]
A positive relationship between land surface temperature- (LST) and vegetation index (VI) has been observed in Alaska tundra ecosystems [21] and in North America above 45∘N [22]. These findings indicate that both land surface temperature- (LST-)dependent ET models and vegetation index- (VI-)LST methods may not be suitable for ET estimation in the energy-limited cold areas
These results suggest that some caution should be noted when ET is estimated from LSTdependent ET models and VI-LST methods
Summary
Terrestrial evapotranspiration (ET), defined as the loss of water from the land surface to the atmosphere, is a key process in water cycles [1, 2]. The VI-LST methods use the VI-LST triangle/trapezoidal feature space to derive an index, and this index is used to partition sensible heat and latent heat fluxes from available energy (net radiation minus soil heat flux) [16,17,18,19]. Both LSTdependent ET models and VI-LST methods assume that ET can cool land surfaces under the condition of homogeneous atmospheric forcing.
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