Modelling the impact of land-use change due to anthropogenic activity on hydrodynamics in an aquifer in Southern Spain

Land use changes increases availability of necessities, but there is also a risk of damaging or depleting natural resources. Groundwater, which is one of the most important natural resources, is dependent on having a balance between the inputs and outputs to avoid changes in the water levels. Water shortage and salt water intrusion resulting from lowered water levels, are becoming a more and more serious problem along the Mediterranean coast in southern Spain, and also in other arid places around the world. One of the few coastal aquifers in southern Spain that still do not suffer from saltwater intrusion is the aquifer in the coastal area of Motril, south of Granada, but now the aquifer is undergoing hydrodynamic changes due to a shift in land use. Using a combination of recharge calculations and a groundwater flow model the impact of land use changes on groundwater resources is studied. Changes in land use from the 1950's to 2012 have been categorized using satellite images. The excess water from precipitation and irrigation recharging the aquifer was calculated for the different categories of as deep percolation return flow using the FAO Penman-Monteith method. In the 1950's, sugarcane was covering 70 % of the aquifer surface. By 2007 all sugarcane fields had been replaced by other crops in need of less irrigation, like subtropical trees, vegetables and crops in greenhouses. In the same period the urban areas was also expanding. The water used for irrigation in the area of Motril have been reduced by 28 Mm3/year from 1956 to 2012 due to land use changes. This decrease in irrigation have caused an estimated 65 % reduction in surface recharge. Scenarios of the past have been modelled to better understand how the changes on the surface have altered the dynamics in the groundwater. Following the reductions in surface recharge, the water levels have been reduced by 1 - 2 meters in the lowlands and in vicinity of the river, while the levels in the eastern sector of the aquifer have decreased by up to 10 m. The change in water levels affects the flow in the aquifer surrounding the river, From 1959 to 2012 the stretch that is gaining water has decreased to from approximately 3000 to 1000 m