Spatio‐temporal patterns of grassland evapotranspiration and water use efficiency in arid areas

Abstract

Understanding spatio‐temporal patterns of grassland evapotranspiration (ET) and water use efficiency (WUE) in arid areas is important for livestock production and ecological conservation. Xinjiang, China, was used as an example in the Biome‐BGC model to explore spatio‐temporal patterns of grassland ET and WUE from 1979 to 2012 in arid areas. The ET ranked from high to low as follows: among seasons, summer (142.4 mm), spring (49.7 mm), autumn (45.9 mm) and winter (7.7 mm); among regions, the Tianshan Mountains (357.9 mm), northern Xinjiang (221.3 mm) and southern Xinjiang (183.2 mm); among grassland types, mid‐mountain meadow (387.7 mm), swamp meadow (358.3 mm), typical grassland (343.9 mm), desert grassland (236.2 mm), alpine meadow (229.7 mm), and saline meadow (154.7 mm). The WUE ranked from high to low as follows: among seasons, summer (0.60 g C kg H2O−1), autumn (0.48 g C kg H2O−1) and spring (0.43 g C kg H2O−1); among regions, northern Xinjiang (0.73 g C kg H2O−1), the Tianshan Mountains (0.69 g C kg H2O−1) and southern Xinjiang (0.26 g C kg H2O−1); among grassland types, mid‐mountain meadow (0.86 g C kg H2O−1), typical grassland (0.84 g C kg H2O−1), swamp meadow (0.77 g C kg H2O−1), saline meadow (0.52 g C kg H2O−1), alpine grassland (0.37 g C kg H2O−1) and desert grassland (0.34 g C kg H2O−1). In Xinjiang grasslands, the spatio‐temporal ET patterns were more strongly influenced by precipitation than by temperature, whereas most high WUE values occurred when precipitation and temperature were relatively conducive to grass growth.

Land–Atmosphere Exchange of Water and Heat in the Arid Mountainous Grasslands of Central Asia during the Growing Season

“…[39], the Le remained lower than the He. The Le and He values were similar from the beginning of May to mid-June.…”

“…In drought years, soil water deficits often occur, whereas in wet years, more water is received from the growing season P and Q. The differences between the above-mentioned water inputs and the ET in wet years were primarily caused by the formation of runoff and the storage of water in the soil [39,44]. A comparison of the soil VWC for 2013-2015 (Figure 5a) also provided strong evidence that soil water played a regulatory role in ET.…”

“…In April 2013, although snowmelt water resulted in relatively high soil moisture [39], the Le remained lower than the He. The Le and He values were similar from the beginning of May to mid-June.…”

“…Therefore, the ET was higher than the P (Figure 4), which was primarily due to the soil water and Q, as there was a severe drought in 2014 that resulted in a soil water deficit (Figure 5a and Table 1). In 2015, the ET in the growing season was 344.4 mm, while the P over the same period was 402.8 mm; thus, the ET was lower than the P, which was mainly caused by runoff and the storage of water in the soil [39,44]. The grassland ET exhibited significant variations among the different seasons; overall, the ET was relatively low in the autumn months, whereas high values were observed in the spring and summer.…”

“…However, the ET in the 2015 growing season was significantly lower than that in 2013, which was due to runoff. According to observations, the total P was high in 2015, and high-intensity P was relatively abundant, which increased the amount of runoff [39,44]. The soil VWC was relatively high in spring due to P infiltration, but the soil VWC showed an overall decreasing trend due to increased ET.…”