Spatiotemporal Changes in Evapotranspiration from an Overexploited Water Resources Basin in Arid Northern China and Their Implications for Ecosystem Management

Abstract

Evapotranspiration (ET), including evaporation from soil and water surfaces and transpiration from vegetation, influences water distribution in the soil-plant-atmosphere continuum, especially in arid areas where water is a key limiting factor. Therefore, understanding the spatiotemporal dynamics of ET, including its two components of soil evaporation (Es) and vegetation transpiration (Ec), can be useful for water resource management and ecological restoration in arid regions. Based on ET data from 2002 to 2012, the spatiotemporal variations in ET were evaluated in the Shiyang River Basin in arid Northwest China. The results showed the following: (1) spatially, ET decreased from upstream of the Qilian Mountains to the middle and downstream, with a mean annual value of 316 mm; (2) temporally, ET showed a single peak curve throughout the year, with the highest value occurring in summer; (3) ET showed a downward trend (from 350 to 265 mm) before 2009 and thereafter increased (from 265 to 345 mm); and (4) water use efficiency, indicated by the ratio of Ec to ET, was low in the cropland, with a mean value of 50.9%. Further analysis indicates that decreases in ET are mainly caused by vegetation decreases; in contrast, ecological restriction measures and strict water resource management policies in the middle reaches of the basin led to ET increases. It is concluded that understanding ET and its two components can elucidate the connections between water and human society.Sustainability 2019, 11, 445 2 of 13 flow, is dynamic in nature. In addition, the hydrologic process is intimately linked with energy exchanges between the atmosphere, ocean, and land, and the hydrologic system determines the spatiotemporal distribution of water resources [3,4], which are necessary for sustaining life on Earth. Under such conditions, quantifying the key hydrologic variables in space is required to provide a deep understanding and a detailed analysis of land surface processes; in turn, this knowledge provides crucial information for water resource management and informs policy decisions to enhance sustainable development [5,6].Arid regions, accounting for one-third of the Earth's terrestrial area [7], are particularly short of water. Water is a major limiting factor for the growth and development of vegetation in arid regions [2,8]. As such, sustainable development in arid regions unquestionably requires sustainable water resource management [2,5,[8][9][10]. Precipitation and ET, the two vertical water fluxes, dominate arid hydrologic systems; the former is relatively low, whereas the latter, including evaporation from soil and water surfaces and transpiration from vegetation, is potentially high. Studies have revealed that land surface ET typically consumes approximately 60-90% of precipitation [11][12][13]. Therefore, an accurate assessment of the characteristics of the spatiotemporal distribution of ET can provide fundamental information for studying the feedback mechanism between vegetation and water [5,8,14].The Shiyang River Basin, ...

Estimating the Actual Evapotranspiration Using Remote Sensing and SEBAL Model in an Arid Environment of Northwest China

“…During the growing season, the ET d distribution in the Shiyang River Basin showed a unimodal variation, with the maximum value occurring in mid-July. The same conclusion was reported by Liu et al [29] using the MOD16 ET product, who suggested that the distribution trend of ET d was related to changes in irrigation water, temperature, precipitation, and vegetation within the Shiyang River Basin. Spatially, ET in the study area decreased from the southwest to northeast.…”

“…However, relatively few studies have spatially quantified the actual ET in this region. Liu et al [29] and Tian et al [30] assessed the distribution characteristics and dynamics of actual ET in the Shiyang River Basin using MOD16 ET products. However, it is important to note that the MOD16 ET products excluded the ET in barren/desert areas from the model calculations and set the ET value to 0.…”

Geobotanical Study of the Microforests of Juniperus oxycedrus subsp. badia in the Central and Southern Iberian Peninsula

“…Soil water in semiarid areas plays an important role in evapotranspiration [57]. The significance of evapotranspiration is confirmed as a tool for improving our understanding of environmental changes, and according to Liu et al [58], has a direct connection with society. Another important aspect is that the phytosociological approach and statistical analysis are fundamental for the study and greater knowledge of plant communities; several authors consider all these data (plus others such as phytotoponims) to be crucial to their conservation and/or restoration [20,56,[59][60][61][62][63].…”

Cryosphere Water Resources Simulation and Service Function Evaluation in the Shiyang River Basin of Northwest China

“…The average ET of each catchment was 387.6 mm. Liu et al [45] analyzed the long-term ET data (MOD16, version 5) from 2002 to 2012, and found that the annual ET gradually declined from southwest to northeast, with the highest values in the upper Qilian Mountain area in the south (>450 mm year −1 ), followed by the middle plain area (250-400 mm year −1 ) and the lower reaches (<250 mm year −1 ). We compared the simulation ET results with MOD16/ET monthly product data (Figure 3b).…”