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

Abstract

Arid grassland ecosystems are widely distributed across Central Asia. However, there is a lack of research and observations of the land-atmosphere exchange of water and heat in the arid grasslands in this region, particularly over complex surfaces. In this study, systematic observations were conducted from 2013 to 2015 using an HL20 Bowen ratio and TDR300 and WatchDog1400 systems to determine the characteristics of these processes during the growing season (April-October) of the arid mountainous grasslands of this region. (1) The latent heat flux (Le) was lower than the sensible heat flux (He) overall, and a small transient decrease in Le was observed before its daytime maximum; daily comparative variations in both fluxes were closely related to vegetation growth. (2) Evapotranspiration (ET) showed substantial variation across different years, seasons and months, and monthly variations in ET were closely related to vegetation growth. Water condensation (Q) was low and relatively stable. Relatively high levels of soil water were measured in spring followed by a decreasing trend. The land-atmosphere exchange of water and heat during the growing season in this region was closely associated with phenology, available precipitation and terrain. This study provides data support for the scientific management of arid mountainous grasslands.

Aboveground Biomass Dynamics in the Low-Mountain Dry Grasslands of the Tianshan Mountains

“…Plants grew rapidly in spring, due to the high SVWC caused by snow melt water. As the soil water evaporated, SVWC decreased sharply in summer and autumn [10]. In addition to phenology, low SVWC was the most important factor that led to low AB in this region [11].…”

“…is representative of the LMDG region in the Tianshan Mountains, and is located in Fukang, Xinjiang, China. Because of the arid climate, plants suffer water stress in this region [4,10]. Precipitation is the only source of water, and is subject to considerable inter-annual variation [10].…”

“…Because of the arid climate, plants suffer water stress in this region [4,10]. Precipitation is the only source of water, and is subject to considerable inter-annual variation [10]. The temperature in summer (June -August) is high and was approximately 18.23°C from 2014 to 2017.…”

How precipitation and grazing influence the ecological functions of drought-prone grasslands on the northern slopes of the Tianshan Mountains, China?

“…The annual average air temperature is approximately 8°C . The average air temperature in summer is about 18°C, and it rises rapidly in spring and decreases rapidly in autumn (Liu et al, 2016;Huang et al, 2017b). The land surface is covered by snow throughout winter; in spring, snowmelt has a positive role in promoting plant growth.…”

“…Technological advances have led to major improvements in the availability and precision of experimental instruments. Field observations are more accurate than remote sensing and modelling (Huang et al, 2017b;Martí nez-Garcí a et al, 2017;Marshall et al, 2018). Therefore, we used field observations of AGB, SVWC, and precipitation data during the period of 2014-2017 to identify how precipitation and grazing influence the ecological functions of a drought-prone grassland on the northern slopes of the Tianshan Mountains.…”