Climate change projections predict a rise in temperatures which may result in a reduction in water resource availability. Irrigation is both the most demanding water use and that which is the lowest priority. Consequently, adaptation measures regarding irrigation demands are required in coping with such a resource decrease. As improvement in water efficiency use could not be enough to counteract strong stream flow reductions, management actions regarding demands may be implemented. This paper proposes a methodology for identifying the required reductions and sequence in which water allocation is to be reduced in order to meet satisfactory system behaviour. Such a methodology could help basin managers in decision making in meeting irrigation demands which, accordingly, could offer better performance in terms of both reliability and productivity. The methodology is applied at the Guadalquivir Basin in Spain, under eight hydrological projections which represent future climate change scenarios. The results show that it is possible to reduce future water scarcity problems and, hence, improve system performance. In addition to this, it is found that optimal reduction sequence is not only affected by water productivity, but also by the system topology which influences reliability. In the case study, the most sensitive demands are those located at the river head. As such demands have no alternative sources, they typically offer the lowest degree of reliability.