On inclusion of water resource management in Earth System models – Part 2: Representation of water supply and allocation and opportunities for improved modeling
Abstract. Human water use has significantly increased during the recent past. Water allocation from surface and groundwater sources has altered terrestrial discharge and storage, with large variability in time and space. Water supply and allocation, therefore, should be considered with water demand and appropriately included in large-scale models to address various online and offline implications, with or without considering possible climate interactions. Here, we review the algorithms developed to represent the elements of water supply and allocation in large-scale models, in particular Land Surface Schemes and Global Hydrologic Models. We noted that some potentially-important online implications, such as the effects of large reservoirs on land-atmospheric feedbacks, have not yet been addressed. Regarding offline implications, we find that there are important elements, such as groundwater availability and withdrawals, and the representation of large reservoirs, which should be improved. Major sources of uncertainty in offline simulations include data support, water allocation algorithms and host large-scale models. Considering these findings with those highlighted in our companion paper, we note that advancements in computation, host models, system identification algorithms as well as remote sensing and data assimilation products can facilitate improved representations of water resource management at larger scales. We further propose a modular development framework to consider and test multiple datasets, algorithms and host models in a unified model diagnosis and uncertainty assessment framework. We suggest that such a framework is required to systematically improve current representations of water resource management in Earth System models. A key to this development is the availability of regional scale data. We argue that the time is right for a global initiative, based on regional case studies, to move this agenda forward.