A framework for incorporating social processes in hydrological models Zhixiang Lu 1,2 , Yongping Wei 2 , Qi Feng 1 , Andrew W Western 3 and Sha Zhou 4 Earth’s surface has undergone dramatic changes due to the intensification of human activities. In turn, humans modify their behavior in response to environmental change. Conventional hydrological models do not represent such coupled human– water systems. This paper proposes a socio-hydrological water balance framework for analyzing the behavior of the sociohydrologic system in terms of water allocation between social system and ecological system. This proposed socio- hydrological framework will help develop a quantitative understanding of co-evolutionary processes in river basins from a social and ecological systems perspective. Addresses 1 Key Laboratory of Ecohydrology of Inland River Basin, Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences, Lanzhou 730000, China 2 School of Earth and Environmental Sciences, The University of Queensland, Brisbane 4067, Australia 3 School of Engineering, The University of Melbourne, Melbourne 3010, Australia 4 Department of Earth and Environmental Engineering, Columbia University, New York 10027, USA Corresponding author: Wei, Yongping (yongping.wei@uq.edu.au) Current Opinion in Environmental Sustainability 2018, 33:42–50 This review comes from a themed issue on System dynamics and sustainability Edited by Bojie Fu and Yongping Wei Received: 24-1-2018; Accepted: 17-4-2018 https://doi.org/10.1016/j.cosust.2018.04.011 1877-3435/ã 2018 Elsevier B.V. All rights reserved. Introduction Hydrology studies the earth’s water, its distribution and circulation, chemical and physical properties, and inter- action with the environment [1]. Hydrological models are simplified representations of the hydrologic cycle that typically extend from perceptual to numerical represen- tations of runoff and other hydrologic processes as a function of various parameters and inputs. Hydrologic models represent our understanding of hydrological pro- cesses and provide a basis to predict changes in basin behavior, making them an important tool for water resource management [2  ]. In the Anthropocene (the last 200 years), the global population has rapidly increased and human activities have altered water cycles to an unprecedented extent, for example through expansion of global irrigated areas for food production, and construction of tens of thou- sands of dams and reservoirs to boost water supply, to provide flood control, and to serve as a source of energy [3  ,4–6]. Water in many river basins has been increas- ingly transferred from the ecological system to the social system, which has led to worsening ecological degrada- tion. It is increasingly recognized that the biophysical focus of most hydrological models is no longer adequate. This is because multiple environmental subsystems have changed substantially during the Anthropocene as a direct or indirect result of human activity [7], and are expected to continue along a path of rapid change into the future [7,8]. Important changes include water abstraction, climatic change, land use and land cover change, and biogeochemical changes. Moreover, human activity is also likely to induce further changes over a range of physical, ecological and social processes as societies respond to environmental degradation [4–6]. Due to these dynamic changes in human and hydrologi- cal systems, the capacity of existing hydrological models in supporting sustainable water resources management is being seriously questioned. It is increasingly agreed that humans and their actions should be considered as part and parcel of water cycle dynamics and should be included in hydrological models. In essence, the hydrological changes and social changes in a river basin are co-evolutionary processes [9,10  ]. Socio- hydrology is an emerging discipline aiming to understand and predict the dynamics and co-evolution of coupled human–water systems that is attracting much scholarly attention [11  ,12  ,13]. There is a large diversity of emerging socio-hydrological models, in part, because they derive relationships and identify governing processes individually for each case study [14–16]. At present, there is no mechanistic understanding of how social drivers and social responses interact with the hydrological compo- nents of a co-evolving human–water system [4,17  ,18]. This paper aims to contribute to this understanding by providing a generic framework for representing the important components of the socio-hydrologic system and quantifying their interactions. Before doing so we Available online at www.sciencedirect.com ScienceDirect Current Opinion in Environmental Sustainability 2018, 33:42–50 www.sciencedirect.com