Sensitivity of runoff and soil erosion to climate change in two Mediterranean watersheds. Part II: Assessing impacts from changes in storm rainfall, soil moisture and vegetation cover

The impacts of climate change on storm runoff and erosion in Mediterranean watersheds are difficult to assess due to the expected increase in storm frequency coupled with a decrease in total rainfall and soil moisture, added to positive or negative changes to different types of vegetation cover. This report, the second part of a two-part article, addresses this issue by analysing the sensitivity of runoff and erosion to incremental degrees of change (from a20 to C20%) to storm rainfall, pre-storm soil moisture, and vegetation cover, in two Mediterranean watersheds, using the MEFIDIS model. The main results point to the high sensitivity of storm runoff and peak runoff rates to changes in storm rainfall (2D2% per 1% change) and, to a lesser degree, to soil water content (a1D2% per 1% change). Catchment sediment yield shows a greater sensitivity than within-watershed erosion rates to both parameters: 7D8 versus 4D0% per 1% change for storm rainfall, and a4D9 versus a2D3% per 1% change for soil water content, indicating an increase in sensitivity with spatial scale due to changes to sediment connectivity within the catchment. Runoff and erosion showed a relatively low sensitivity to changes in vegetation cover. Finally, the shallow soils in one of the catchments led to a greater sensitivity to changes in storm rainfall and soil moisture. Overall, the results indicate that decreasing soil moisture levels caused by climate change could be sufficient to offset the impact of greater storm intensity in Mediterranean watersheds.