Water use efficiency (WUE; gross primary production [GPP]/evapotranspiration [ET])
estimates the tradeoff between carbon gain and water loss during photosynthesis and is an important
link of the carbon and water cycles. Understanding the spatiotemporal patterns and drivers of WUE is
helpful for projecting the responses of ecosystems to climate change. Here we examine the spatiotemporal
patterns, trends, and drivers of WUE at the global scale from 2000 to 2013 using the gridded GPP and ET
data derived from the Moderate Resolution Imaging Spectroradiometer (MODIS). Our results show that
the global WUE has an average value of 1.70 g C/kg H2O with large spatial variability during the 14-year
period. WUE exhibits large variability with latitude. WUE also varies much with elevation: it first remains
relatively constant as the elevation varies from 0 to 1000 m and then decreases dramatically. WUE generally
increases as precipitation and specific humidity increase; whereas it decreases after reaching maxima as
temperature and solar radiation increases. In most land areas, the temporal trend of WUE is positively
correlated with precipitation and specific humidity over the 14-year period; while it has a negative
relationship with temperature and solar radiation related to global warming and dimming. On average,
WUE shows an increasing trend of 0.0025 g Ckg1 H2Oyr1 globally. Our global-scale assessment of WUE
has implications for improving our understanding of the linkages between the water and carbon cycles and
for better projecting the responses of ecosystems to climate change.
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