Agricultural Water Management 197 (2018) 100–109 Contents lists available at ScienceDirect Agricultural Water Management journal homepage: www.elsevier.com/locate/agwat Winter wheat water requirement and utilization efficiency under simulated climate change conditions: A Penman-Monteith model evaluation Jianqing Wang, Xiaoyu Liu, Kun Cheng, Xuhui Zhang, Lianqing Li, Genxing Pan ∗ Institute of Resource, Ecosystem and Environment of Agriculture, and Center of Climate Change and Agriculture, Nanjing Agricultural University, 1 Weigang, Nanjing, Jiangsu 210095, China a r t i c l e i n f o Article history: Received 22 March 2017 Received in revised form 4 October 2017 Accepted 24 November 2017 Keywords: Climate change Free-Air CO2 enrichment (FACE) Elevated temperature Water utilization efficiency Winter wheat Crop water use a b s t r a c t Impact of climate change on water supply and use is a critical issue for dryland crop production. In this study is assessed the potential impact of atmospheric CO 2 enrichment (500 mol mol −1 , CE) and canopy warming (+2 ◦ C, WA) and their combination (CW) on crop water utilization efficiency (WUE) of winter wheat in an open-air field experiment from Southeast China. Micro-meteorological measurement and wheat growth under individual treatments over three executive years of 2012–2015 were used to esti- mate the crop water requirement (CWR) of wheat using an improved FAO Penman-Monteith equation. Overall, CO 2 enrichment slightly decreased the CWR by 8.3%, and increased the WUE of grain produc- tion (WUEg) by 23.1%, averaged over the three years. In contrast, warming increased CWR by 19.6% but decreased WUEg by 27.9% over the period. Under CW treatment, however, CWR was increased by 3.1–15.8% but WUEg was decreased by 3.5–18.2% throughout three years. Clearly, the positive impact of CO 2 enrichment on WUE was largely negated under canopy warming. Moreover, when assessing with individual year data, inter-annual variability of WUEg was insignificant under WA, smaller under CE but much higher under CW, compared to CK. These results indicated that an interaction by canopy warming overshadowed the potential increase in WUE with CO 2 enrichment and enforced yearly fluctuation of the crop production under simulated climate change conditions. Therefore, improving water supply and management in agriculture should thus be endeavored to address the potential constraints with future trends of concurrent atmospheric CO 2 enrichment and warming. © 2017 Published by Elsevier B.V. 1. Introduction World agriculture consumes about 70% of the world’s fresh- water and food security exerts a strong dependence on water resource availability (Bocchiola et al., 2013; Fader et al., 2011; Konar et al., 2011; Palazzoli et al., 2015). Water resource short- age has been increasingly constraining crop production (Piao et al., 2010; Wallace, 2000), challenged with the global climate change (Rosenzweig et al., 2014; Wheeler and von Braun, 2013). Increasing water utilization efficiency (WUE) would be a priority task among the key measures to sustaining global crop production in the com- ing decades (Elliott et al., 2014; Hoekstra and Mekonnen, 2012; Iglesias and Garrote, 2015; Ye et al., 2015). As one of most important non-irrigated staple crops (Ladha, 2003), winter wheat production ∗ Corresponding author. E-mail addresses: pangenxing@aliyun.com, gxpan1@njau.edu.cn (G. Pan). has been constrained by decline in water availability with increas- ing drought frequency in recent years. Therefore, technologies to increase WUE would be measures to enhance climate-smart agri- culture (Paustian et al., 2016). Global atmospheric CO 2 concentration is expected to increase over 500 mol mol −1 , while surface air temperature to elevate by about 2 ◦ C during the middle of 21st century (IPCC, 2013; Solomon et al., 2009). This climate change would have great impacts on crop production (Guo et al., 2010; O’Leary et al., 2015), potentially through decreasing WUE by plants (Wallace, 2000). However, the impacts on crop water utilization could vary with climatic factors that influence the evapotranspiration and plant physiological pro- cesses. Elevated CO 2 concentration tends to decrease transpiration and seasonal crop water requirement (CWR) owing to decreased stomatal conductance (Shimono et al., 2013; Yu et al., 2007). Being often addressed as CO 2 fertilization effect, CO 2 enrichment could increase plant biomass and grain production, resulting in an appar- ent increase in WUE (Bunce, 2013; Hunsaker et al., 2000; O’Leary https://doi.org/10.1016/j.agwat.2017.11.015 0378-3774/© 2017 Published by Elsevier B.V.