title: Contrasting responses of water use efficiency to drought across global terrestrial ecosystems.
abstract: Drought is an intermittent disturbance of the water cycle that profoundly affects the terrestrial carbon cycle. However, the response of the coupled water and carbon cycles to drought and the underlying mechanisms remain unclear. Here we provide the first global synthesis of the drought effect on ecosystem water use efficiency (WUE = gross primary production (GPP)/evapotranspiration (ET)). Using two observational WUE datasets (i.e., eddy-covariance measurements at 95 sites (526 site-years) and global gridded diagnostic modelling based on existing observation and a data-adaptive machine learning approach), we find a contrasting response of WUE to drought between arid (WUE increases with drought) and semi-arid/sub-humid ecosystems (WUE decreases with drought), which is attributed to different sensitivities of ecosystem processes to changes in hydro-climatic conditions. WUE variability in arid ecosystems is primarily controlled by physical processes (i.e., evaporation), whereas WUE variability in semi-arid/sub-humid regions is mostly regulated by biological processes (i.e., assimilation). We also find that shifts in hydro-climatic conditions over years would intensify the drought effect on WUE. Our findings suggest that future drought events, when coupled with an increase in climate variability, will bring further threats to semi-arid/sub-humid ecosystems and potentially result in biome reorganization, starting with low-productivity and high water-sensitivity grassland.
authors.affiliation: School of the Environment, Flinders University, Adelaide, South Australia 5042, Australia.|CSIRO Land and Water, Canberra, ACT 2601, Australia.
authors.forename: Yuting
authors.initials: Y
authors.lastname: Yang
authors.affiliation: School of the Environment, Flinders University, Adelaide, South Australia 5042, Australia.|National Centre for Groundwater Research and Training, Adelaide, South Australia 5042, Australia.
authors.forename: Huade
authors.initials: H
authors.lastname: Guan
authors.affiliation: School of the Environment, Flinders University, Adelaide, South Australia 5042, Australia.|National Centre for Groundwater Research and Training, Adelaide, South Australia 5042, Australia.
authors.forename: Okke
authors.initials: O
authors.lastname: Batelaan
authors.affiliation: CSIRO Land and Water, Canberra, ACT 2601, Australia.|Australian Research Council Centre of Excellence for Climate System Science, Sydney, Australia.
authors.forename: Tim R
authors.initials: TR
authors.lastname: McVicar
authors.affiliation: State Key Laboratory of Hydroscience and Engineering, Department of Hydraulic Engineering, Tsinghua University, Beijing 100084, China.
authors.forename: Di
authors.initials: D
authors.lastname: Long
authors.affiliation: Sino-French Institute for Earth System Science, College of Urban and Environmental Sciences, Peking University, Beijing 100871, China.
authors.forename: Shilong
authors.initials: S
authors.lastname: Piao
authors.affiliation: College of Tourism and Environmental Sciences, Shaanxi Normal University, Xi'an 710062, China.
authors.forename: Wei
authors.initials: W
authors.lastname: Liang
authors.affiliation: Linze Inland River Basin Research Station, Laboratory of Heihe River Eco-Hydrology and Basin Science, Cold and Arid Regions Environmental and Engineering Research Institute, Chinese Academy of Sciences, Lanzhou 730000, China.
authors.forename: Bing
authors.initials: B
authors.lastname: Liu
authors.affiliation: College of Tourism and Environmental Sciences, Shaanxi Normal University, Xi'an 710062, China.
authors.forename: Zhao
authors.initials: Z
authors.lastname: Jin
authors.affiliation: School of the Environment, Flinders University, Adelaide, South Australia 5042, Australia.|National Centre for Groundwater Research and Training, Adelaide, South Australia 5042, Australia.
authors.forename: Craig T
authors.initials: CT
authors.lastname: Simmons
mesh_terms: D018533:Biomass; D057486:Carbon Cycle; D055864:Droughts; D017753:Ecosystem; D014867:Water / Q000378:metabolism*
chemical_list: D014867:Water