Effects on floods of recent afforestation and urbanisation in the Mella River (Italian Alps)

摘要

River floods areinfluenced by factors such as the duration, intensity and spacial distributionof precipitation and the land-use as well as the morphological characteristicsof the river basin. While the characteristics of the precipitation are tied tothe climatology of the region and can change only over the long term,anthropogenic land use changes exhibit a more pronounced dynamic. However, theconsequences of such changes on the increment in flood volumes and theirfrequency must be estimated objectively. To quantify the effects of theurbanisation on the flood volumes and peaks in the Mella river basin, 311 km2in size, changes in land use in the past 50 years have been compared using twoland use maps; the first was based on aerial photographs taken in 1954 and thesecond on photointerpretation and surveys in 1994. The comparison showed anincrease in the forested areas in the upper part of the basin as the use of woodfor fuel had declined and an increase in urban development in the valley bottom.Correspondingly, cultivated areas decreased in size. The consequence of thesechanges is that surface runoff, simulated with a distributed hydrological model,changes insignificantly at the catchment scale, but with slightly reduced floodpeaks and volumes in today’s conditions. style="line-height: 20px;">Keywords: floods, land use changes, afforestation, urbanisation