Impact of forest cover changes on annual streamflow and flow duration curves

The effect of forest cover changes on mean streamflow is well understood and worldwide data have shown that increasing forest cover decreases the total volume of flow at the catchment scale. However, due to the different methods used to assess the impact of forest cover at the annual and sub-annual timescale general conclusions can be difficult to draw. In this paper, consistent methods of analysing paired catchment data are used to assess the impact of forest cover change in afforestation and deforestation experiments on annual streamflow and flow duration curves (FDCs). The results indicate that in catchments undergoing a permanent change in forest cover it takes between 8 and 25 years for a catchment to reach a new equilibrium. Analysis of FDCs showed that three types of responses could be observed. These are: catchments with changes in the number of zero flow days (response group 1), catchments with proportionally larger changes in low flows compared to high flow (response group 2), and catchment with a uniform changes in all flows (response group 3).