Disrupting the continuity of soil properties and its hydrological functions: estimating and modelling soil hydraulic functions at regional scale with increasing soil sealing

Soil sealing is one of the major threats to soil, leading to a virtually permanent loss of soil functions. Beside the loss of fertile soils with a direct impact on food security, soil sealing strongly modifies the hydrological cycle. This causes an increased flooding risk, due to urban development in potential risk areas and to the increased volumes of runoff. Soil hydrological properties, their distribution and variability are then critical issues when adopting hydrological models at catchment scale. In a densely populated area of Northern Italy, the impact of soil sealing due to urban development has been assessed using a distributed infiltration model in different land use scenarios, representing the sealing conditions in 1976 and 2008. The soil hydrological properties have been derived from the Emilia Romagna soil data base (ca. 3300 soil sites) using a locally validated set of PTFs, The spatial variability has been explicitly taken into account adopting a SCORPAN kriging approach based on the soil mapping units at 1:50,000 scale and on major land use. The lower boundary conditions have been set assuming the depth of impermeable horizon within 100 cm or the 95th percentile of the shallow groundwater depth. Peak discharges have been considered for 20 and 200 yr rainfall events. The impact of land use changes under the different simulation scenarios is discussed in terms of their impact on soil hydrologic functions.