Water security, global change and land–atmosphere feedbacks

Abstract

Understanding the competing pressures on water resources requires a detailed knowledge of the future water balance under uncertain environmental change. The need for a robust, scientifically rigorous evidence base for effective policy planning and practice has never been greater. Environmental change includes, but is not limited to, climate change; it also includes land-use and land-cover change, including deforestation for agriculture, and occurs alongside changes in anthropogenic interventions that are used in natural resource management such as the regulation of river flows using dams, which can have impacts that frequently exceed those arising in the natural system. In this paper, we examine the role that land surface models can play in providing a robust scientific basis for making resource management decisions against a background of environmental change. We provide some perspectives on recent developments in modelling in land surface hydrology. Among the range of current land surface and hydrology models, there is a large range of variability, which indicates that the specification and parametrization of several basic processes in the models can be improved. Key areas that require improvement in order to address hydrological applications include (i)the representation of groundwater in models, particularly at the scales relevant to land surface modelling, (ii)the representation of human interventions such as dams and irrigation in the hydrological system, (iii)the quantification and communication of uncertainty, and (iv)improved understanding of the impact on water resources availability of multiple use through treatment, recycling and return flows (and the balance of consumptive and conservative uses). Through a series of examples, we demonstrate that changes in water use could have important reciprocal impacts on climate over a wide area. The effects of water management decisions on climate feedbacks are only beginning to be investigated-they are still only rarely included in climate impact assessments-and the links between the hydrological system and climate are rarely acknowledged in studies of ecosystem services. Nevertheless, because water is essential not only for its direct uses but also for the indirect functions that it serves (including food production, fisheries and industry), it is vital that these connected systems are studied. Building on the examples above, we highlight recent research showing that assessment of these trade-offs is particularly complex in wetland areas, especially in situations where these trade-offs play to the advantage of different communities.