Interacciones montaña-llanura frente al cambio global: desafíos y oportunidades en la gestión del territorio y de los recursos hídricos en Riegos del Alto Aragón

The transformation of rainfed agriculture lands into irrigated lands in the central sector of the Ebro Depression has represented a spectacular change in the cultivation conditions of a semi-arid territory affected by scarce and irregular precipitation. However, the new irrigation systems faced serious structural problems from the beginning due to the peculiar design of the irrigation system, the limitations of its objectives, the slow pace with which the infrastructures were built (reservoirs, canals and secondary ditches) and the conditioning of cultivated fields. This work focuses on the study of the limitations faced by Riegos del Alto Aragón due to the trend shown by water resources and their seasonal distribution as a result of the evolution of temperature and precipitation, the expansion of woody vegetation in mountain areas and the progressive silting up of the reservoirs. For this, the information available on Global Change in the Pyrenees has been reviewed and climatic and hydrological models have been applied. The necessary modernization has improved the irrigation systems and water use efficiency, and has allowed the expansion of much more productive and profitable crops. Paradoxically, modernization has also increased the water demand, and has made necessary to increase the system’s internal reserves through the construction of small reservoirs and ponds. This greater water demand coincides with a decreasing trend in water resources availability, due not only to the increase in average temperature, but also to changes in snowpack accumulation and melting dynamics in the Pyrenean headwaters and to forest expansion in old abandoned fields in the Pyrenean valleys, which reduces runoff generation and streamflow. It is foreseeable that most of these processes will continue or even accentuate in the medium- to long-term due to climate change. In addition, the progressive silting up of the reservoirs reduces the water storage capacity year after year. These processes, which highlight the interactions between mountain areas and the lowlands, will force in the medium term to reorganize the management of resources and irrigation procedures, as well as the progressive incorporation of crops with increasing added value that offset the rise in production costs linked to a stronger dependence of irrigation with respect to energy.