Eco-Hydrological Requirements in Arid and Semiarid Regions: Case Study of the Yellow River in China

The eco-hydrological requirements of a river are related to the health of the river. In recent years, changing climate and intensifying human activities have further aggravated water problems in the Yellow River. Considering hydrological changes, this study addressed the ecological water requirements of the Yellow River basin, wherein the threshold ecological water requirement corresponded to the streamflow with the largest occurrence probability determined by the Pearson Type III distribution. Instream flow ± one standard deviation was adopted as the water resource management target and abrupt changes in streamflow were detected by using the Mann-Whitney U test. The results of the analysis indicated that: (1) the annual flow of the Yellow River substantially decreased after abrupt changes and the probability significantly dropped that the amount of annual streamflow satisfied the ecological instream flow requirement; and (2) the water resource management target was satisfied well after th echange point only at the Tangnaihai station, located in the upper Yellow River basin. From the upper to the lower Yellow River basins, the probability has dramatically decreased that the ecological water requirement target is satisfied. Therefore, the Yellow River basin will likely face increasingly serious water problems, particularly in the middle and lower parts.