Rendimentos de água na cabeceira fluvial do rio DouroRelação com a variabilidade climática e as mudanças na cobertura vegetal

Abstract

This work analyses the changes in the evolution of river discharges and river regime in the Duero river headwaters over the past 5 decades. It further explores their relation with the tendencies observed for temperatures, precipitation, and forest cover extension. Results show significant losses on annual runoff, due to the notable decrease in river discharges during February - September. Moreover, the number of days with a flow lower than the third of the “mean annual daily flow” has clearly decreased. Linear regression developed shows a good correlation between annual precipitation and annual runoff (R = 0.72, p-value < 0.001) and the plot of residuals don’t show any significant tendency. These facts suggest that the forest growth undergone in the last few decades hasn’t had a clear influence on the reduction of river discharges. Nevertheless the absence of correlation between the monthly tendencies for precipitation and runoff, and the important increase in temperatures, indicate an increase in the volume of water consumed by the forest that will probably be perceptible in the evolution of runoff in a short/ middle term basis. Finally, the decrease in precipitation and the changes occurred in its monthly distribution have clearly affected the river regime. This has changed from having a maximum peak in winter during the first 2 decades of the studied period to a bimodal regime in the last 2 decades, with a principal peak in winter and a secondary peak in spring. This fact has to be considered by water administration to develop a responsible management in dams situated downstream.