Spanish National Research Council1, Pyrenean Institute of Ecology (CSIC)2, Oficina Catalana del Canvi Climàtic3, CREAF4, IRTA5
Changes in precipitation and temperature, but also in solar radiation, relative humidity and wind speed have affected recent water resources availability in the Mediterranean basin (García-Ruiz et al., 2011). Climate processes have a direct influence on the availability of water resources. Nevertheless, these processes converge with current land cover changes and human water management (SavÃ© et al. 2012), which may accentuate the decrease in river flows and reservoir storages. This is especially critical in areas with high water demand as a consequence of the increase of irrigated lands, urban consumptions, etc. as is the case of the Iberian Peninsula. Future climate and land cover scenarios for the Iberian Peninsula suggest important water stress as a consequence of increased water needs by natural forests and crops, but also given precipitation decrease and increased atmospheric water demand. Here we have studied the recent evolution of climate and streamflows in the past five decades in three basins of Catalonia (NE Spain): Muga, Ter and Segre. These basins are characterized by different water uses, land covers and management strategies and they include one of the main irrigated areas of Spain (the Segre basin), the Metropolitan Barcelona area in which there is large urban water demand (more than 4.5M people), and also high pressure tourism areas in the Mediterranean coastland. We have also modeled future availability of water resources by means of numerical models by means of the forcing by state-of-the art climate models and different land cover and water management scenarios. This study has been developed in the frame of the project: "LIFE12 ENV/ES/000536 Demonstration and validation of innovative methodology for regional climate change adaptation in the Mediterranean area (MEDACC)" financed by the LIFE Programme of the European Commission and focused on establishing adaptation strategies to mitigate the impacts of climate change on water resources in the three analyzed basins.
We have used the complete historical meteorological network maintained by the Spanish and Catalan meteorological agencies. We have focused on the period 1960-2013. Daily meteorological records were carefully reconstructed, quality controlled and homogenised. We also summarized the first available land cover map in the region representative of land conditions in the decade of 1960, and comparable in legend to the official land cover map of 2010. Daily streamflow records were also available from gauging stations in the three basins. We analyzed trends in climate and hydrological series and we analyzed the connection of trends with the change of land cover, streamflow regulation and water demand by means of different statistical techniques. To determine the possible availability of water resources in the future (scenario 2050-2080), we have used high resolution regional climate models (RCMs) developed by the Catalan Meteorological Agency and alternative land cover scenarios. These data were used to force two hydrological models (RHESys and SWAT) that were calibrated by means of streamflow and climate observations for the period 2000-2010.
Results and Discussion
The streamflow records in the last five decades show a clear negative trends in the three analyzed basins. Nevertheless, there are noticeable spatial differences that may be related to the land cover changes, water demands and the different water management strategies in the three basins. The observed decrease of precipitation and mainly the increase of the atmospheric water demand have affected streamflow evolution in the three basins. Nevertheless, the decrease in the water resources has been more important than that expected by the observed climate evolution. In the headwater of the three basins the observed growth of natural vegetation, as a consequence of land abandonment, has clearly affected the decrease of the streamflows. In the medium course of the rivers the creation of large dams, and the increased irrigation surface has had dramatic consequences on the streamflows of the river Segre. The same pattern has been observed in the Ter (as a consequence of the water demand by the Metropolitan Barcelona area) and the Muga (as a consequence of irrigation and water demand by tourism). In general, the climate trends, land transformations, water regulation (damming) and water demand are complementary to explain current trends in the water resources in the three basins. Negative evolution of water resources will accentuate in the future as a consequence of the climate scenarios predicted by the RCMs. The strong reduction of precipitation (10-15% in 2050-2080 regarding 1960-1990 average) and the increase of evapotranspiration rates as a consequence of warming, will cause a reduction of streamflow of about 15-20% regarding current observations. In addition, the most plausible land cover scenario, toward generalized forest regeneration in the slopes of the mountain headwaters, would also affect the streamflow decrease between 18-20%.
We have showed that evolution of water resources in three basins of Catalonia (NE Spain) have clearly decreased in the last five decades as a consequence of the combined influence of the climate evolution, land cover changes and water demands. Current water availability shows an unstable equilibrium to cope with increased water demand (irrigation, urban and tourism consumption and ecological uses). Future land cover and climate scenarios indicate that the most plausible evolution of water resources is a reduction that oscillated between 30-40% of current availability. Under these scenarios, it will be increasingly difficult or impossible to satisfy water demand using the current management strategy, and it is likely that new approaches will be needed. García-Ruiz, J.M. et al. (2011): Mediterranean water resources in a global change scenario. Earth Sciences Review 105, 121-139. Saví, R. et al. (2012): Potential changes in irrigation requirements and phenology of maize, apple trees and alfalfa under global change conditions in FluviÃ watershed during XXIst century: results from a modeling approximation to watershed-level water balance. Agricultural Water Management 114: 78-87.