Evapotranspiration and water yield over China's landmass from 2000 to 2010

Abstract

Abstract. Terrestrial carbon and water cycles are interactively linked at various spatial and temporal scales. Evapotranspiration (ET) plays a key role in the terrestrial water cycle, altering carbon sequestration of terrestrial ecosystems. The study of ET and its response to climate and vegetation changes is critical in China because water availability is a limiting factor for the functioning of terrestrial ecosystems in vast arid and semiarid regions. To constrain uncertainties in ET estimation, the process-based Boreal Ecosystem Productivity Simulator (BEPS) model was employed in conjunction with a newly developed leaf area index (LAI) data set, MODIS land cover, meteorological, and soil data to simulate daily ET and water yield at a spatial resolution of 500 m over China for the period from 2000 to 2010. The spatial and temporal variations of ET and water yield were analyzed. The influences of climatic factors (temperature and precipitation) and vegetation (land cover types and LAI) on these variations were assessed.Validations against ET measured at five ChinaFLUX sites showed that the BEPS model was able to simulate daily and annual ET well at site scales. Simulated annual ET exhibited a distinguishable southeast to northwest decreasing gradient, corresponding to climate conditions and vegetation types. It increased with the increase of LAI in 74 % of China's landmass and was positively correlated with temperature in most areas of southwest, south, east, and central China. The correlation between annual ET and precipitation was positive in the arid and semiarid areas of northwest and north China, but negative in the Tibetan Plateau and humid southeast China. The national annual ET varied from 345.5 mm in 2001 to 387.8 mm in 2005, with an average of 369.8 mm during the study period. The overall rate of increase, 1.7 mm yr −1 (R 2 = 0.18, p = 0.19), was mainly driven by the increase of total ET in forests. During 2006During -2009 and LAI decreased widely and consequently caused a detectable decrease in national total ET. Annual ET increased over 62.2 % of China's landmass, especially in the cropland areas of the southern Haihe River basin, most of the Huaihe River basin, and the southeastern Yangtze River basin. It decreased in parts of northeast, north, northwest, south China, especially in eastern Qinghai-Tibetan Plateau, the south of Yunnan Province, and Hainan Province. Reduction in precipitation and increase in ET caused vast regions in China, especially the regions south of Yangtze River, to experience significant decreases in water yield, while some sporadically distributed areas experienced increases in water yield. This study shows that the terrestrial water cycles in China's terrestrial ecosystems appear to have been intensified by recent climatic variability and human induced vegetation changes.

Hydrological Effects of Vegetation Cover Degradation and Environmental Implications in a Semiarid Temperate Steppe, China

“…In this study, we specified three grassland types in the land use/cover database of the SWAT model according to the vegetation LAI in XLRB [24]. High cover grassland (Pasture with high cover, PSTH) means that its cover is more than 50% with LAI of 4.70; the moderate cover grassland (Pasture with moderate cover, PSTM) is from 20% to 50% with LAI of 1.63; and the low cover grassland (Pasture with low cover, PSTL) is from 5% to 20% with an LAI of 0.65 (Table 1).…”

Simulation of Forest Evapotranspiration Using Time-Series Parameterization of the Surface Energy Balance System (SEBS) over the Qilian Mountains

“…In situ measurements using weighing lysimeters, Bowen ratios, sap flow meters, eddy covariance (EC), and scintillometers are considered reliable for quantifying ET at individual sites or for small footprints [4,20,21]. However, these types of measurements are unsuitable at large scales.…”

“…As the principle component of terrestrial hydrology, evapotranspiration (ET), which is composed of evaporation and transpiration, is affected by both biophysical and environmental processes at the interface of soils, vegetation, and the atmosphere, thereby linking hydrological, energy, and carbon processes [2][3][4]. Globally, ET returns approximately 60% of land-based precipitation to the atmosphere [5,6] and consumes more than 50% of the solar radiation absorbed by the land's surface [7].…”

“…Although they have been applied over a number of study areas, uncertainties related to the disadvantage of these models and their inputs, and parameterization and scaling schemes still exist [4,[35][36][37][38]. As far as remote sensing techniques are concerned, the availability of measurements and estimations of land surface and atmospheric parameters have increased over time, and the improvement of model performance through the integration of various techniques and data sources has received renewed global interest.…”

Modeling of forest above-ground biomass and evapotransportation dynamics

“…As the principle component of terrestrial hydrology, evapotranspiration (ET) is affected by both biophysical and environmental processes at the interface of soils, vegetation, and the atmosphere, thereby linking hydrological, energy and carbon processes (Fisher et al, 2008;Jung et al, 2010;Liu et al, 2013). Globally, ET returns approximately 60% of landbased precipitation to the atmosphere (Oki and Kanae, 2006;Trenberth et al, 2007) and consumes more than 50% of the solar radiation absorbed by the land surface (Trenberth et al, 2009).…”