Abstract: Climate changes and human activities can lead to hydrological change. Distributions of the samples before and after hydrological change are significantly different. It means the local hydrological condition has changed, which breaks the ecological balance. We use moving rank sum test (Mann-Whitney U Test) to analyse hydrological changes and their causes. Then, L-moment is used to evaluate the parameters of generalized extreme value (GEV) distribution of the monthly flow series before hydrological change, and to calculate the maximum probability density flow, as the ecological instream flow. We use this method to calculate ecological instream flows of 7 hydrometric stations in the Yellow River Basin. The result shows that ecological calculating method which considers the hydrological change is practicable.

Key words: ecological instream flow, hydrological change, moving rank sum test, Mann-Whitney U Test, Yellow River