The D-A-R approach: a method for determining ecological flow based on the component structure of ecological protection objects and dynamic hierarchical adjustment to the annual flow process

Although regional and seasonal water scarcity occurs frequently in China, and the contradiction among domestic, production and ecological water is prominent in some watersheds, the Chinese government still attaches great importance to the determination and implementation of ecological flow of rivers or lakes. Practitioners have been seeking methods to determine the ecological flow of rivers or lakes and how to ensure its implementation. Taking the Dingnan River watershed as a case, drawing on the experience of ‘Hedging rule’, the ‘Determination-Assessment-Reduction’ for the ecological flow nexus approach (the D-A-R approach) is introduced, which includes the determination of the annual ecological flow process through the river section, the assessment of water scarcity degree of the watershed and various water reduction strategies, respectively, and respond to the three scenarios of ‘general type, saving type and constrained type’ during the gap period. The results show that it is possible to use the D-A-R approach to proactively and dynamically adjust the ecological flow according to the probability estimate of that amount of water inflow per month, which the adjusted ecological flow threshold can better adapt to water scarcity at different levels and alleviate the contradiction among domestic, production and ecological water in the watershed during the dry period.