Smart licensing and environmental flows: Modeling framework and sensitivity testing

Adapting to climate change is just one among many challenges facing river managers. The response will involve balancing the long‐term water demands of society with the changing needs of the environment in sustainable and cost effective ways. This paper describes a modeling framework for evaluating the sensitivity of low river flows to different configurations of ion licensing under both historical climate variability and expected climate change. A rainfall‐runoff model is used to quantify trade‐offs among environmental flow (e‐flow) requirements, potential surface and groundwater ion volumes, and the frequency of harmful low‐flow conditions. Using the River Itchen in southern England as a case study it is shown that the ion volume is more sensitive to uncertainty in the regional climate change projection than to the e‐flow target. It is also found that “smarter” licensing arrangements (involving a mix of hands off flows and “rising block” ion rules) could achieve e‐flow targets more frequently than conventional seasonal ion limits, with only modest reductions in average annual yield, even under a hotter, drier climate change scenario. Key Points Smarter licensing of withdrawals could deliver benefits to the environment Smarter licensing can give better water yields under climate change Withdrawals are more sensitive to climate than e‐flow standards