Seasonality of the Transpiration Fraction and Its Controls Across Typical Ecosystems Within the Heihe River Basin

Abstract

Understanding the seasonality of the transpiration fraction (T/ET) of total terrestrial evapotranspiration (ET) is vital for coupling ecological and hydrological systems and quantifying the heterogeneity among various ecosystems. In this study, a two‐source model was used to estimate T/ET in five ecosystems over the Heihe River Basin. In situ measurements of daily energy flux, sap flow, and surface soil temperature were compared with model outputs for 2014 and 2015. Agreement between model predictions and observations demonstrates good performance in capturing the ecosystem seasonality of T/ET. In addition, sensitivity analysis indicated that the model is insensitive to errors in measured input variables and parameters. T/ET among the five sites showed only slight interannual fluctuations while exhibited significant seasonality. All the ecosystems presented a single‐peak trend, reaching the maximum value in July and fluctuating day to day. During the growing season, average T/ET was the highest for the cropland ecosystem (0.80 ± 0.13), followed by the alpine meadow ecosystem (0.79 ± 0.12), the desert riparian forest Populus euphratica (0.67 ± 0.07), the Tamarix ramosissima Ledeb desert riparian shrub ecosystem (0.67 ± 0.06), and the alpine swamp meadow (0.55 ± 0.23). Leaf area index exerted a first‐order control on T/ET and showed divergence among the five ecosystems because of different vegetation dynamics and environmental conditions (e.g., water availability or vapor pressure deficits). This study quantified transpiration fraction across diverse ecosystems within the same water basin and emphasized the biotic controls on the seasonality of the transpiration fraction.

Irrigation‐Induced Potential Evapotranspiration Decrease in the Heihe River Basin, Northwest China, as Simulated by the WRF Model

“…In the upper reaches, ET 0 is approximately 2 mm d − 1 ; in the middle reaches, ET 0 reaches up to approximately 4 mm d − 1 ; in the lower reaches, ET 0 reaches as high as approximately 8 mm d − 1 . Such a spatial pattern matches the spatial variabilities in temperature and surface net radiation, both of which increase from the upper reaches to the lower reaches (Tong et al, ).…”

A Novel Approach for the Simulation of Reference Evapotranspiration and Its Partitioning

“…Originally, the SPAC model were used to simulate the actual evapotranspiration (ET a ) and partition ET a into transpiration (T) and evaporation (E). The existing SPAC model achieved good performance in partitioning ET in the humid grasslands of Japan [28], arid and semiarid grassland in Inner Mongolia [21], the typical ecosystem of the Heihe River Basin [25], and Alpine Meadow in Tibetan Plateau [29]. Therefore, we used the main equations of the SPAC model [28] and applied it on the reference land surface in this study.…”

“…Many multi-source models have been developed to understand energy partitioning between sources and the routing of sensible and latent heat [7,[18][19][20][21]. Two-source models have been shown to be capable of reasonably estimating ET and its components under different climate and vegetation conditions [22][23][24][25]. The FAO PM and updated Shuttle Worth-Wallace dualsource models [18] have been shown to be capable of estimating ET 0 and its components.…”

Effects of Urbanization on Watershed Evapotranspiration and Its Components in Southern China

“…Our study showed that forests had the highest T rate (656 mm/year), followed by rice-wheat rotation field (460 mm/year) and dry land (190 mm/year) ( Figure 8). T was sensitive to changes in plant types and temporal vegetation dynamics [21]. Urbanization may result in the expansion of impervious surfaces with no vegetation, resulting in reduction of T and ET.…”