Global patterns and climate drivers of water‐use efficiency in terrestrial ecosystems deduced from satellite‐based datasets and carbon cycle models

Abstract

Aim To investigate how ecosystem water‐use efficiency (WUE) varies spatially under different climate conditions, and how spatial variations in WUE differ from those of transpiration‐based water‐use efficiency (WUEt) and transpiration‐based inherent water‐use efficiency (IWUEt). Location Global terrestrial ecosystems. Methods We investigated spatial patterns of WUE using two datasets of gross primary productivity (GPP) and evapotranspiration (ET) and four biosphere model estimates of GPP and ET. Spatial relationships between WUE and climate variables were further explored through regression analyses. Results Global WUE estimated by two satellite‐based datasets is 1.9 ± 0.1 and 1.8 ± 0.6 g C m−2 mm−1 lower than the simulations from four process‐based models (2.0 ± 0.3 g C m−2 mm−1) but comparable within the uncertainty of both approaches. In both satellite‐based datasets and process models, precipitation is more strongly associated with spatial gradients of WUE for temperate and tropical regions, but temperature dominates north of 50° N. WUE also increases with increasing solar radiation at high latitudes. The values of WUE from datasets and process‐based models are systematically higher in wet regions (with higher GPP) than in dry regions. WUEt shows a lower precipitation sensitivity than WUE, which is contrary to leaf‐ and plant‐level observations. IWUEt, the product of WUEt and water vapour deficit, is found to be rather conservative with spatially increasing precipitation, in agreement with leaf‐ and plant‐level measurements. Main conclusions WUE, WUEt and IWUEt produce different spatial relationships with climate variables. In dry ecosystems, water losses from evaporation from bare soil, uncorrelated with productivity, tend to make WUE lower than in wetter regions. Yet canopy conductance is intrinsically efficient in those ecosystems and maintains a higher IWUEt. This suggests that the responses of each component flux of evapotranspiration should be analysed separately when investigating regional gradients in WUE, its temporal variability and its trends.

Precipitation and carbon-water coupling jointly control the interannual variability of global land gross primary production

“…These regression slopes generally increase with aridity index and can also be regarded as an approximation of the ecosystem water use efficiency (WUE) as long as the ecosystem is water limited34. The increasing trend of β with aridity index (i.e., from hyper arid to humid) is consistent with the fact that WUE increasing with precipitation across spatial gradients as suggested by a recent study using an inter-comparison of multiple models35. β starts to decrease when the aridity index approaches 1, where GPP and ET become decoupled from each other (Supporting Information, Fig.…”

Assessment of ecosystem resilience to hydroclimatic disturbances in India

“…Water stress is one of the most important limiting factors, which directly or indirectly constrains the vegetation productivity (Mu, Zhao, & Running, ). The water loss from the ecosystem can be divided into two parts: (i) “physiologically productive water” which represents the transpiration during the growing season, and (ii) “nonproductive” water loss which includes the water loss from canopy interception and evaporation from bare soil (Sun et al., ). These two parts of ecosystem water use are controlled differently by the climatic factors.…”

“…In this work, we compared the functional response of WUE e to hydroclimatic disturbances (particularly droughts) to examine the ecosystem resilience, which is defined as the ability of the ecosystem to absorb the disturbances and sustain the same functioning under disturbed conditions (Ponce Campos et al., ; Walker, Holling, Carpenter, & Kinzig, ). The climate in most parts of India is tropical or temperate and hence, the vegetation productivity is controlled by the water/precipitation (Running et al., ; Sun et al., ). However, an increase in both drought severity and frequency has been reported both globally (Dai, , ) and in India (Mallya, Mishra, Niyogi, Tripathi, & Govindaraju, ).…”

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

“…Remote sensing and modeling methods allow for the characteristics of the land-atmosphere exchange of water and heat to be studied over large regions, but the results are often highly uncertain due to defects in computational methods and difficulty in determining initial parameter values [22,23]. In particular, there is a serious shortage of observational water and heat data for the arid mountainous grassland ecosystems in Central Asia, making it impossible to fully verify the findings obtained from remote sensing and modeling.…”