Evapotranspiration on a greening Earth

Evapotranspiration (ET) — the distribution and partitioning of which is strongly mediated by vegetation — is central to the water, energy and carbon cycles. In this Review, we examine the spatiotemporal patterns of ET changes and their linkages with vegetation. A multi-decadal and accelerating rise in global ET is apparent since the 1980s. Diagnostic data sets indicate increases of 0.66 ± 0.38 mm year −2 (mean ± one standard deviation) over 1982–2011 and 1.19 ± 0.31 mm year −2 over 2001–2020. These changes are largely related to vegetation greening (increasing leaf area index (LAI)), hence large ET increases occur in northern high latitudes where greening predominates; increased precipitation and enhanced atmospheric evaporative demand have secondary roles. The impacts of specific drivers of vegetation change on ET, such as CO 2 fertilization, land use change and nitrogen deposition, are uncertain and difficult to quantify at the global scale but have strong impacts at local and/or regional scales. Owing to projected increases in LAI, global ET is expected to continue rising with future anthropogenic warming, although ET sensitivity to greening is lower than in the present climate. Enhanced model validation with respect to long-term trends and ET partitioning, improved mechanistic understanding of key processes and greater data-model fusion techniques are essential for improved understanding of ET characteristics.