Resumen de Evaluación del impacto del cambio climático (escenarios b1 y a2) en las aportaciones futuras generadas para el horizonte de proyección 2000-2050 en las cuencas del fluvià y la tordera en catalunya
The results presented in this doctoral thesis aims to evaluate the possible Climate Change effects on the water resources yield by the Fluvià river basin and the Tordera river basin, both located in the autonomous region of Catalonia. In order to carried out with the study, a climate change projection generated by the Global Circulation Model ECHAM5 for the scenarios B1 and A2 (IPCC, 2007) were applied. The projections were statistically downscaled at local level through a Markov’s chain of first order to determine the occurrence of rainfall and a Weibull distribution to evaluate the amount of it during that occurrence. The temperature was projected using an ARMA model (Autoregressive Moving Average). Both projections (rainfall and temperature) were obtained for the time horizon of 50 years (2000 – 2050). Historical data (1984 – 2008) were previously used as an input in the weather generators in the downscaling process.
The hydrological model of the case of study was developed using the software HEC-HMS 4.0 which through its Soil Moisture Accounting method (SMA) allows for long term simulations with a complete characterization of the hydrological process. The model was parametrized, calibrated and validated using discharge gages located at the outlet of each of the basins. The historical data for the rainfall and the temperature (evapotranspiration) were run in the hydrological model to evaluate the current condition of the basins to be finally compared with the future projections obtained from the downscaling process for the time horizon of 50 years for the Climate Change scenarios previously described.
When comparing the current situation (historical) with the future projections for the two scenarios analysed (B1 and A2), it is observed that in the Fluvià’s basin the annual average (2000 – 2050) for the water resources decrease 16.7% for the B1 scenario and 28.2% for the A2 scenario. For the Tordera’s basin the situation is similar, with reductions of 19.9% for the B1 scenario and 26.6% for the A2 scenario. It may also be observed that in both scenarios and both basins when the reductions of rainfall compared to the historical data goes from 2.5 to 11.2% the reductions on annual average for the water resources are larger, which would indicate that the basin amplifies the effect of the reductions of the rainfall in the yielded discharge.
Finally, it was also studied that carrying out modification to the downscaling process, new temporal distribution of the future rainfall may be obtained. This new time series were characterized by a more heterogenous distribution ungrouping rainfall event to a larger number of days. Once these new times series were input to the hydrological model it was observed the water resources increases in relation to the ones observed under the first downscaling carried out in the study. The increments observed were from 9 to 11% in both scenarios and both basins. This implies that it is important to evaluate the amount of future rainfall of the climate projections, but it is also very important to evaluate the temporal distribution of it due to the hydrological processes in a basin might be sensitive to this factor, affecting the water resource production in the long term.
