Trends in high flows in the central Spanish Pyrenees: response to climatic factors or to land-use change?

This paper analyses the evolution of high flows in the central Spanish Pyrenees during the period 1955-1995. The method applied makes it possible to assess whether the contribution of the largest daily discharge and rainfall events to the total annual runoff and precipitation remains stationary or shows any temporal trend. The results show a general negative trend in flood intensity in the last decades, together with an increase in the importance of low flows in the total annual contribution. However, a change in the frequency distribution of precipitation events has not been detected. The different behaviour shown by runoff and precipitation could only be explained as being due to the increase in vegetation cover that is a consequence of the farmland abandonment and reforestation that occurred during the 20th century.