Local irrigation systems, regional hydrological problems and the demand for overarching solutions at the example of an irrigation system in the P.R. of China

Abstract. The utilization of groundwater for irrigation purposes becomes problematic if groundwater recharge decreases through climate variability. Nevertheless, the degree of groundwater utilization for irrigation increases significantly in dry periods, when the amount of green water is strongly limited. With an increasing gap between water demand and supply, new water management activities are started, which are mostly directed to increase the supply, often by overuse of local resources. In many cases such local activities results in their summarization in side-effects, which worsen the hydrological conditions throughout a region. Step by step the spatial scale of water management measures has to be extended in such cases by implementation of water transfer systems. In this contribution this general scale problem of water management is discussed at the example of an agricultural region in the Province of Shandong (P.R. of China). The local irrigation systems and the options to increase the water supply at the local scale (e.g. by waste water reuse) are discussed as well as regional measures e.g. reservoirs or barrages in rivers to increase the groundwater recharge. For this purpose, several socio-economic and hydrological models were combined. It is shown how a change of water policy towards a demand management requires a new approach to spatial aspects. Here the question arises, how hydrological most effective measures can be allocated within a region. In the case study, a reduction of agricultural irrigation and a change of the crop structure would be essential to improve the groundwater conditions, which are impaired by ongoing sea-water intrusions. A model hierarchy, which is needed to answer such problems not only from the hydrological point of view, but also considering their socio-economic feasibility, are presented.