Recasting catchment water balance for water allocation between human and environmental purposes
Abstract. Rebalancing water allocation between human consumptive uses and the environment in water catchments is a global challenge. The conventional water balance approach which partitions precipitation into evapotranspiration (ET) and surface runoff supports the optimization of water allocations among different human water use sectors under the cap of water supply. However, this approach is unable to support the emerging water management priority issue of allocating water between societal and ecological systems. This paper recast the catchment water balance by partitioning catchment total ET into ET for the society and ET for the natural ecological systems, and estimated the impacts of water allocation on the two systems in terms of gross primary productivity (GPP), in the Murray–Darling Basin (MDB) of Australia over the period 1900–2010. With the recast water balance, the more than 100 year water management in the MDB was divided into four periods corresponding to major changes in basin management: period 1 (1900–1956) expansion of water and land use by the societal system, period 2 (1956–1985) maximization of water and land use by the societal system, period 3 (1985–2002) maximization of water diversion for the societal system, and period 4 (2002–present) rebalancing of water and land use between the societal and ecological systems. The recast water balance provided new understandings of the water and land dynamics between societal and ecological systems in the MDB, and it highlighted the experiences and lessons of catchment water management in the MDB over the last more than 100 years. The recast water balance could serve as the theoretical foundation for water allocation to keep a dynamic balance between the societal and ecological systems within a basin for sustainable catchment development. It provides a new approach to advance the discipline of socio-hydrology.