Spatial variation in annual actual evapotranspiration of terrestrial ecosystems in China: Results from eddy covariance measurements

Abstract

Abstract:Understanding the spatial variation in annual actual evapotranspiration (AET) and its influencing factors is crucial for a better understanding of hydrological processes and water resources management. By synthesizing ecosystem-level observations of eddy-covariance flux sites in China (a total of 61 sites), we constructed the most complete AET dataset in China up to now. Based on this dataset, we quantified the statistic characteristics of AET and water budgets (defined as the ratio of AET to annual mean precipitation (MAP), AET/MAP) of terrestrial ecosystems in China. Results showed that AET differed significantly among both different vegetation types and climate types in China, with overall mean AET of 534.7±232.8 mm yr -1 . AET/MAP also differed significantly among different climate types, but there were no distinct differences in AET/MAP values across vegetation types, with mean AET/MAP of 0.82±0.28 for non-irrigated ecosystems. We further investigated how the main climatic factors and vegetation attributes control the spatial variation in AET. Our findings revealed that the spatial variation of AET in China was closely correlated with the geographical patterns of climate and vegetation, in which the effects of total annual net radiation (R n ), MAP and mean annual air temperature (MAT) were dominant. Thus, we proposed an empirical equation to describe the spatial patterns of AET in China, which could explain about 84% of the spatial variation in AET of terrestrial ecosystems in China. Based on the constructed dataset, we also evaluated the uncertainties of five published global evapotranspiration products in simulating 1392 Journal of Geographical Sciences site-specific AET in China. Results showed that large biases in site-specific AET values existed for all five global evapotranspiration products, which indicated that it is necessary to involve more observation data of China in their parameterization or validation, while our AET dataset would provide a data source for it.

Net radiation rather than surface moisture limits evapotranspiration over a humid alpine meadow on the northeastern Qinghai‐Tibetan Plateau

“…Meanwhile, annual values of the Priestley–Taylor coefficient ( a = ET/ET eq , 1.08–1.14, 1.37 in the growing season) and annual decoupling coefficient Ω (0.43–0.48, 0.61 in the growing season) evidently showed that the alpine meadow was under strongly energy‐limited condition (Li et al, ; Obojes et al, ; Priestley & Taylor, ). This finding is consistent with radiation energy availability ( Rn – G ) being the dominant factor controlling summer ET in alpine regions (Knowles et al, ; Yang et al, ; Zheng et al, ). Additionally, the much greater actual ET than reference ET in the growing season (Figure b) also suggested that ET was mainly controlled by the availability of evaporative energy (Sun et al, ; Williams et al, ).…”

“…Leaf area index (LAI) is an important variable affecting root zone soil water content and consequently ecosystem ET (Gu et al, ; Hurtalová, Usowicz, Kossowski, & Matejka, ; Shen et al, ) or may just be a proxy for the partitioning of ET into more plant transpiration and canopy interception than soil water evaporation under a dense canopy (Hu et al, ; McFadden et al, ; Zhu, Su, Li, Zhang, & Li, ). Moreover, the magnitudes of these controls vary with respect to vegetation types and timescales (Brümmer et al, ; Williams et al, ; Zheng et al, ). Therefore, understanding the interrelations of these covarying climatic and biotic determinants on ET variability remains challenging (Knowles et al, ; Ljungqvist et al, ; Obojes et al, ).…”

Construction and progress of Chinese terrestrial ecosystem carbon, nitrogen and water fluxes coordinated observation

“…The results indicated that annual net radiation, annual precipitation and annual mean temperature shaped the spatial pattern of ET, which provides a basis for assessing the spatial distribution of ET (Zheng et al, 2016). Network measured ET was also used to optimize the ET remote sensing model and to assess the spatial distribution of ET in China .…”

“…Investigating the spatio-temporal variations of ET and their influencing factors is of great significance for water resource management and assessment (Zheng et al, 2016). Eddy covariance technique can directly measure water vapor fluxes between atmosphere and biosphere Baldocchi, 2008), which plays an important role in exploring ET spatio-temporal variations and their affecting factors.…”

Drought and irrigation affect transpiration rate and morning tree water status of a mature European beech (Fagus sylvatica L.) forest in Central Europe

“…Evapotranspiration is the major component of water balance of the environment. In most terrestrial ecosystems, evapotranspiration is responsible for over 50% of the total water loss (Lu, Sun, McNulty, & Amatya, ; Zheng et al, ). During drought years or in regions where water is considerably limited, evapotranspiration is the most important component of the local water cycle and can comprise an even greater percentage of the total water loss (Jonard, André, Ponette, Vincke, & Jonard, ), which can equal or exceed precipitation (Wang et al, ).…”