The study watershed is located within the Idanha Irrigation Scheme, Portugal. A hydrological and water quality station was installed at the outlet of the catchment. The AnnAGNPS model was applied in this study, and afterwards it was calibrated and validated to the conditions in the study catchment. The antecedent soil moisture conditions play an important role for rapid runoff and flash flooding. Relative Water Supply (RWS) is always bellow the unity value and sometimes below the value 0.5. Sometimes in very dry years, like the year 2004-2005 (302 mm), a runoff coefficient is equal to 0.40. Spatial distribution of runoff was primarily influenced by topography and soil management, which is common in Mediterranean agricultural systems, namely in grain crop systems such as oats and wheat. The simulation of spatial distribution of nitrate load shows a dependence of the spatial distribution of runoff, due to its high solubility. Spatial distribution of soil erosion by water indicates that the process does not depend directly on the runoff distribution in the catchment. Therefore, soil erosion is greatly influenced by deficient land cover whenever erosivity of rainfall is strong. Phosphorus losses were less than nitrate losses, due to their lower water solubility and mobility in soil.
Part of the book: Mediterranean Identities
Climate change scenarios in Mediterranean basin point to a decrease in the amount of annual rainfall and the increased frequency of drought. In this framework of greater water scarcity, an increase in irrigation costs is expected, so its rational and efficient use is an unavoidable issue in modern irrigated agriculture. In the last 60 years in Portugal, it had a great increase in the efficiency of water use in agriculture, accompanied by a great increase in energy consumption, and the variation was 15,000 to 6000 m3/ha.year and 200 to 1500 kWh/ha, respectively. The rational application of fertilizers is a priority, to prevent the contamination of superficial and subterraneous waters, and the process of soil salinization in semi-arid conditions. The pressure of water demand by agriculture implies the use of other water sources. For example, in 2010, the volume of unconventional water resources in Spain rose to 4.540 hm3/year. Of the total used in agriculture, 450 hm3 of water comes from the reuse of treated water, and 690 hm3 comes from desalination. The use of modern/smart technologies in irrigated agriculture, like information and communication technologies, allows the rapid share of information between all the system components and can promote optimized answers at different scales.
Part of the book: Irrigation and Drainage