The EUROSEM-GRIDSEM modeling system for erosion analyses under different natural and economic conditions

Within the research project, nutrient losses and erosion from agriculture are calculated. Calculations are done with an interdisciplinary modeling system capable of predicting the effect of various policy measures to reduce losses. This paper describes the application of the deterministic one event based erosion model EUROSEM in combination with a digital elevation model GRIDSEM, to analyze erosion at the catchment scale within the frame of the overall project. GRIDSEM uses a grid size of 30×30 m and includes a simple routine for adding up sediment losses in the watershed. For each day during a 20-year simulation period the soil erosion level is estimated for each cell, based on: (1) the permanent landscape related characteristics of slope and soil type; (2) parameters determined by the agricultural management system, including parameters for plant height, soil covered by plants, surface roughness and soil cohesion; and (3) actual weather data. A distinction is made between rainfall and snowmelt induced runoff events. Changes in erosion level could be estimated from the output of GRIDSEM and by analyses of the estimated erosion levels for the cells. Results show that this method is capable of: (1) estimating changes in overall erosion levels; (2) estimating the relative benefits of different agricultural management systems concerning total erosion; and (3) showing the unpredictability and importance of extreme erosion events, in both time and space.