Copyright © 2015 by the author(s). Published here under license by the Resilience Alliance. Cabello, V., B. Willaarts, M. Aguilar, and L. del Moral. 2015. River basins as social-ecological systems: linking levels of societal and ecosystem water metabolism in a semiarid watershed. Ecology and Society 20(3): 20. http://dx.doi.org/10.5751/ES-07778-200320 Research River basins as social-ecological systems: linking levels of societal and ecosystem water metabolism in a semiarid watershed Violeta Cabello 1 , Barbara A. Willaarts 2 , Monica Aguilar 3 and Leandro del Moral Ituarte 1 ABSTRACT. River basin modeling under complexity requires analytical frameworks capable of dealing with the multiple scales and dimensions of environmental problems as well as uncertainty in the evolution of social systems. Conceptual and methodological developments can now be framed using the wide socio-eco-hydrological approach. We add hierarchy theory into the mix to discuss the conceptualization of river basins as complex, holarchic social-ecological systems. We operationalize the social-ecological systems water metabolism framework in a semiarid watershed in Spain, and add the governance dimension that shapes human-environment reciprocity. To this purpose, we integrate an eco-hydrological model with the societal metabolism accounting scheme for land use, human activity, and water use. We explore four types of interactions: between societal organization and water uses/demands, between ecosystem organization and their water requirements/supplies, between societal metabolism and aquatic ecosystem health, and between water demand and availability. Our results reveal a metabolic pattern of a high mountain rural system striving to face exodus and agricultural land abandonment with a multifunctional economy. Centuries of social-ecological evolution shaping waterscapes through traditional water management practices have influenced the eco-hydrological functioning of the basin, enabling adaptation to aridity. We found a marked spatial gradient on water supply, use pattern, and impact on water bodies from the head to the mouth of the basin. Management challenges posed by the European water regulatory framework as a new driver of social-ecological change are highlighted. Key Words: holarchy; river basin; socio-eco-hydrology; social-ecological systems; water availability; water metabolism INTRODUCTION Water resources degradation is a complex environmental problem that involves multiple dimensions and scales of analysis. As the awareness over the human alteration of the global water system gained acceptance within the scientific community, the connections of local processes to global drivers and of human and environmental systems became key research objects (Vörösmarty et al. 2013). Watersheds have been the traditional observation system for hydrological studies focused on the reproducibility of water resources within the water cycle. Water basins are both a biophysical unit for hydrological modeling and a governance tool for water decision making in many countries (Cohen and Davison 2011, Del Moral and Do Ó 2014). As such, institutional performance and governance structures are drivers of change as much as biophysical and socioeconomic processes. Recent efforts of integrated river basin modeling strive to predict the effects of decision making on water allocation and land uses over the hydrological system under a range of scenarios (Jakeman and Letcher 2003, Henriques et al. 2008, Liu et al. 2008). Although these models are powerful in hydrological response forecasting, uncertainty in societal choice predictions is still a major challenge (Letcher et al. 2007). This is partially because of the local specificity of the complex organization of social systems as driver for environmental change, making extrapolation between contexts difficult. Nevertheless, water accounting methods, like virtual water (Allan 1998), water footprint (Hoekstra and Chapagain 2006), or social metabolism (Fischer-Kowalski 1998, Swyngedouw 2006) have engaged in trying to understand the socioeconomic and political drivers of water-use patterns, attempting to bridge scale mismatches with biophysical variables. Insights on the interactions between social, ecological, and hydrological processes have been proposed within analytical frameworks of social-ecological systems (SES; Madrid et al. 2013). Complexity theory deals with the epistemological implications of: (1) multiple scales and dimensions of analysis and (2) high stakes and uncertainty in decision making in coupled human- environmental systems (Liu et al. 2007). The representation and analysis of river basins as complex SES is still incipient, although some important works have been developed recently. Rathwell and Peterson 2012 addressed cross-scale interactions between water management and the provision of ecosystem services. Pahl- Wostl et al. (2010) proposed the management and transition framework for the analysis of water governance regimes, which they have later applied in at least 29 river basins all over the world (Pahl-Wostl et al. 2012). Mix et al. 2015 combined qualitative and quantitative methods to approach a diachronic analysis of multidimensional drivers of water-use change in an arid river basin. All these studies have two things in common: they depart from a networks approach to SES (Janssen et al. 2006), and they emphasize the role of policies and institutions shaping relations between social and ecological systems. However, none of them combine eco-hydrological modeling with socioeconomic quantitative analysis as integrated watershed modeling does, and none deal with the multiscale organization of SES. Hierarchy theory is another branch of complexity approaching the analysis of SES (Pattee 1973, Allen and Starr 1988, Giampietro 2003). Networks theory and hierarchy theory are not exclusive but rather complementary analytical lenses, each having strengths and purposes (Allen and Giampietro 2014). Although network approaches to SES gain analytical dynamism by focusing 1 Department of Human Geography, University of Seville, 2 Research Centre for the Management of Agricultural and Environmental Risks - CEIGRAM, Technical University of Madrid., 3 Department of Physical Geography, University of Seville