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Ecosystem water use efficiency (WUE) and ecosystem photosynthetic efficiency (EPE) are key indicators in studies of the carbon–water cycle in terrestrial ecosystems. Analyses of WUE and EPE can enhance our understanding of the relationship between ecosystem light use efficiency and WUE. Although several studies of individual indexes (i.e., either WUE or EPE) have been conducted, analyses of variation in both WUE and EPE, as well as their relationships, have rarely been conducted. Here, we analyzed spatial and temporal variation in WUE and EPE in Central Asia. Specifically, time trend analysis was conducted to characterize temporal and spatial changes in WUE and EPE in Central Asia from 2001 to 2020 at different altitudes and latitudes. Pearson correlation analysis was used to characterize the effects of precipitation and temperature on WUE and EPE. WUE decreased and EPE increased in Central Asia over the 20-year study period; this might have been due to interannual variations in precipitation and temperature. WUE was highest in August, and EPE was highest in June and July. Substantial spatial heterogeneity in WUE and EPE was observed; WUE was highly variable in Central Asia as well as in western and southern Central Asia. Major changes in EPE were observed in northern, eastern, and southern Central Asia. We also found that both WUE and EPE decreased with the increase in altitude. WUE was positively correlated with temperature and negatively correlated with precipitation, whereas EPE was positively correlated with both temperature and precipitation. The increase in photosynthetic efficiency might be one of the main factors contributing to increases in ecosystem productivity in arid environments. The temporal and spatial variation in WUE and EPE observed in our study will aid ecosystem research, providing a reliable theoretical basis for ecosystem research in areas with scarce large-scale data, integrated water resources management, and ecosystem restoration efforts. Our findings also enhance our understanding of the terrestrial carbon–water cycle and have implications for predicting ecosystem responses to climate change. The results of this study provide insights that will aid studies of the terrestrial carbon–water cycle under the background of climate change. It is of great significance to further study the carbon water cycle in the future. [ABSTRACT FROM AUTHOR]

Although understanding the carbon and water cycles of dryland ecosystems in terms of water use efficiency (WUE) is important, WUE and its driving mechanisms are less understood in Central Asia. This study calculated Central Asian WUE for 2001–2021 based on the Google Earth Engine (GEE) platform and analyzed its spatial and temporal variability using temporal information entropy. The importance of atmospheric factors, hydrological factors, and biological factors in driving WUE in Central Asia was also explored using a geographic detector. The results show the following: (1) the average WUE in Central Asia from 2001–2021 is 2.584–3.607 gCkg−1H2O, with weak inter-annual variability and significant intra-annual variability and spatial distribution changes; (2) atmospheric and hydrological factors are strong drivers, with land surface temperature (LST) being the strongest driver of WUE, explaining 54.8% of variation; (3) the interaction of the driving factors can enhance the driving effect by more than 60% for the interaction between most atmospheric factors and vegetation factors, of which the effect of the interaction of temperature (TEM) with vegetation cover (FVC) is the greatest, explaining 68.1% of the change in WUE. Furthermore, the interaction of driving factors with very low explanatory power (e.g., water pressure (VAP), aerosol optical depth over land (AOD), and groundwater (GWS)) has a significant enhancement effect. Vegetation is an important link in driving WUE, and it is important to understand the mechanisms of WUE change to guide ecological restoration projects. [ABSTRACT FROM AUTHOR]

It is important to understand the carbon-water cycle, which accurately reflects the temporal and spatial variabilities in ecosystem water use efficiency (WUE). In this study, the Mann-Kendall (MK) test was used to study the variabilities in the spatial patterns of the gross primary production (GPP), evapotranspiration and WUE across Central Asia [the Xinjiang Uyghur Autonomous Region (XJ) in China (CHN), Kazakhstan (KAZ), Turkmenistan (TKM), Uzbekistan (UZB), Kyrgyzstan (KGZ), and Tajikistan (TJK)] from 2000 to 2014. We compared the change results by country, land cover type, population density, and human influence. In addition, the results of GPP, evapotranspiration (ET), and WUE parameter tests were combined and classified to analyse the causes of the changes in WUE. The results showed that (1) the time series of GPP, ET and WUE exhibited no significant changes. The spatial distribution of the WUE exhibited significant increases in the northern part of KAZ, the Ili Valley and the alpine region in KGZ and exhibited decreases in south Xinjiang and the irrigated area of UZB. (2) The main land cover types that exhibited changes in WUE were farmlands and grasslands, and areas with a medium population density exhibited large WUE changes. (3) The increased WUE resulted from an increased GPP and decreased ET. The increased GPP was because of increased precipitation and the Green for Grain Project, and the decreased ET was due to the response of vegetation to drought stress; the decreased WUE was mainly caused by changes in the crops planted and unreasonable water use practices in the irrigated agricultural areas in Central Asia. This study, which is based on the variabilities in WUE spatial patterns, should provide a theoretical basis for ecosystems in arid land areas. • The spatial-temporal pattern of WUE was examined in Central Asia using multiple remote sensing data. • A new WUE classification method using Mann-Kendall non-parametric estimation. • Farmland and grassland, and the medium population density areas had the great changes of WUE. • The decreased WUE were due to the shifts in crop type and unreasonable water use practices. [ABSTRACT FROM AUTHOR]