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Large‐scale hydrology: advances in understanding processes, dynamics and models from beyond river basin to global scale

This Special Issue stems from recent heightened research activity on the theme of large-scale hydrology, which we define as water science that encompasses spatial scales greater than a single river basin all the way up to the entire planet. Given increasing concern about climate change and human impacts on the hydrological cycle and water resources, it is critical to provide information on current and future hydrological dynamics and process understanding over large spatial domains (Döll, 2009; World Water Assessment Programme, 2009; Hannah et al., 2011). This knowledge is central to improving large-scale hydrological modelling approaches and predictions (Yang & Musiake, 2003; Bordi et al., 2009; Dankers & Feyen, 2008; Döll et al., 2008; Döll & Fiedler, 2008; Hagemann et al., 2008; Pappenberger et al., 2008; Getirana et al., 2010). In particular, it is important to conduct research that seeks to elucidate patterns and drivers of widespread hydrological response, to identify those regions and time periods most susceptible to climate change/variability and anthropogenic influences, and to use scientific findings to inform decision making so that water hazards and stress (e.g. floods and droughts) may be managed using better mitigation and adaptation strategies (Huang & Demuth, 2010). However, there remains high uncertainty over prediction of water-related variables (Dirmeyer et al., 2006; Beven, 2007; Kingston et al., 2009b; Kundzewicz et al., 2008) and a clear need for better integrated, quantitative understanding of the changes in all water cycle stores and fluxes, including precipitation, evapotranspiration, soil moisture, surface waters, groundwater, and snow and glaciers (e.g. Koster et al., 2004). The articles in this Special Issue aim to address these significant challenges facing large-scale hydrological research. To the best of our knowledge, there have been no recent major international journal volumes on large-scale hydrology that capture the present cuttingedge issues and debates. However, we recognize the Hydrology and Earth System Science special issue on the TIGER Initiative (Oliver et al., 1999) and that there have been several publications on regional hydrology by International Association of Hydrological Sciences (IAHS) Press, particularly as contributions to UNESCOInternational Hydrology Programme cross-cutting theme Flow Regimes from International Experimental and Network Data (FRIEND; e.g. most recently Servat et al., 2010). Hence, we believe that this Special Issue represents a useful and timely addition to the hydrological literature by providing a state-of-the art, interdisciplinary, thematic volume on a fast-moving topic area. This Special Issue contains 13 research articles and one HP-Today invited commentary that individually and collectively showcase recent advances, challenges, and perspectives on large-scale hydrology. The articles are arranged into the following thematic sections (with their key contributions summarized in brief below):