SCIENCE CHINA Earth Sciences © Science China Press and Springer-Verlag Berlin Heidelberg 2014 earth.scichina.com link.springer.com *Corresponding author (email: lenggy.11b@igsnrr.ac.cn)  RESEARCH PAPER  doi: 10.1007/s11430-014-4987-0 Projected changes in mean and interannual variability of surface water over continental China LENG GuoYong 1,4* , TANG QiuHong 1 , HUANG MaoYi 2 , HONG Yang 3 & Leung L RUBY 2 1 Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing 100101, China; 2 Atmospheric Sciences and Global Change Division, Pacific Northwest National Laboratory, Richland, WA 99352, USA; 3 School of Civil Engineering and Environmental Sciences, University of Oklahoma, Norman 73019, USA; 4 University of Chinese Academy of Sciences, Beijing 100049, China Received March 28, 2014; accepted June 30, 2014 Five General Circulation Model (GCM) climate projections under the RCP8.5 emission scenario were used to drive the Varia- ble Infiltration Capacity (VIC) hydrologic model to investigate the impacts of climate change on hydrologic cycle over conti- nental China in the 21st century. The bias-corrected climatic variables were generated for the Fifth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC AR5) by the Inter-Sectoral Impact Model Intercomparison Project (ISI- MIP). Results showed much larger fractional changes of annual mean Evapotranspiration (ET) per unit warming than the cor- responding fractional changes of Precipitation (P) per unit warming across the country, especially for South China, which led to a notable decrease of surface water variability (PE). Specifically, negative trends for annual mean runoff up to 0.33%/ year and soil moisture trends varying between 0.02% to 0.13%/year were found for most river basins across China. Coinci- dentally, interannual variability for both runoff and soil moisture exhibited significant positive trends for almost all river basins across China, implying an increase in extremes relative to the mean conditions. Noticeably, the largest positive trends for run- off variability and soil moisture variability, which were up to 0.41%/year and 0.90%/year, both occurred in Southwest China. In addition to the regional contrast, intra-seasonal variation was also large for the runoff mean and runoff variability changes, but small for the soil moisture mean and variability changes. Our results suggest that future climate change could further exac- erbate existing water-related risks (e.g., floods and droughts) across China as indicated by the marked decrease of surface wa- ter amounts combined with a steady increase of interannual variability throughout the 21st century. This study highlights the regional contrast and intra-seasonal variations for the projected hydrologic changes and could provide a multi-scale guidance for assessing effective adaptation strategies for China on a river basin, regional, or as a whole. climate change, surface water, interannual variability, China Citation: Leng G Y, Tang Q H, Huang M Y, et al. 2014. Projected changes in mean and interannual variability of surface water over continental China. Sci- ence China: Earth Sciences, doi: 10.1007/s11430-014-4987-0 Global warming is projected to increase rainfall variability (O’Gorman and Schneider, 2009) and substantially intensify the global water cycle (Durack, 2012), with notable effects on the water availability for ecosystems and agriculture (Arnell, 2003). Most Asian countries are facing challenges in adapting to social and environmental problems associated with climate changes (Zhai et al., 2005; Fujibe et al., 2006; Yao et al., 2008; Kranz et al., 2010). China is one of the most vulnerable countries around the world to future climate changes with water being one of the sectors most directly affected (Piao et al., 2010). Such vulnerabilities are further exacerbated by its incomplete or not-so-well-designed water infrastructure. A robust response to future climate change is