Abstract
The frequency and intensity of drought are expected to increase worldwide in the future. However, it is still unclear how ecosystems respond to drought. Ecosystem water use efficiency (WUE) is an essential ecological index used to measure the global carbon–water cycles, and is defined as the carbon absorbed per unit of water lost by the ecosystem. In this study, we applied gross primary productivity (GPP), evapotranspiration (ET), land surface temperature (LST), and normalized difference vegetation index (NDVI) data to calculate the WUE and drought index (temperature vegetation dryness index (TVDI)), all of which were retrieved from moderate resolution imaging spectroradiometer (MODIS) data. We compared the mean WUE across different vegetation types, drought classifications, and countries. The temporal and spatial changes in WUE and drought were analyzed. The correlation between drought and WUE was calculated and compared across different vegetation types, and the differences in WUE between drought and post-drought periods were compared. The results showed that (1) ecosystems with a low (high) productivity had a high (low) WUE, and the mean ecosystem WUE of Central Asia showed vast differences across various drought levels, countries, and vegetation types. (2) The WUE in Central Asia exhibited an increasing trend from 2000 to 2014, and Central Asia experienced both drought (from 2000 to 2010) and post-drought (from 2011 to 2014) periods. (3) The WUE showed a negative correlation with drought during the drought period, and an obvious drought legacy effect was found, in which severe drought affected the ecosystem WUE over the following two years, while a positive correlation between WUE and drought was found in the post-drought period. (4) A significant increase in ecosystem WUE was found after drought, which revealed that arid ecosystems exhibit high resilience to drought stress. Our results can provide a specific reference for understanding how ecosystems will respond to climate change.
Highlights
Drought is a natural event characterized by a supply of natural water that does not meet existing needs, or water that is below normal water levels for a long time [1]
(4) A significant increase in ecosystem water use efficiency (WUE) was found after drought, which revealed that arid ecosystems exhibit high resilience to drought stress
There are two possible reasons for this finding, namely: (1) The areas with high WUE are mainly distributed are two possible reasons for this finding, namely: (1) The areas with high WUE are mainly distributed in Turkmenistan and Uzbekistan, where the vegetation is characterized by relatively low gross primary productivity (GPP) growth in arid regions, and many studies have shown that plant leaf stomatal conductance in arid areas is more sensitive to drought than that in humid areas
Summary
Drought is a natural event characterized by a supply of natural water that does not meet existing needs, or water that is below normal water levels for a long time [1]. As an important part of the global carbon–water cycle, ecosystem plants absorb carbon dioxide from the atmosphere through. Sensors 2020, 20, 581 photosynthesis and lose water through transpiration, and these plants are important drivers of the energy and water cycles between the atmosphere and terrestrial ecosystems [2]. Drought is the main factor affecting the carbon–water cycle of terrestrial ecosystems, as it increases the individual mortality of vegetation; inhibits vegetation growth; and triggers forest fires, forest pests, and biological invasions [3,4,5,6]. Ecosystem water use efficiency (WUE) is an important indicator of the coupling of carbon and water cycles, and WUE is often employed to characterize ecosystem carbon and water cycle indicators
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