Climate Change- Runoff and Erosion From Agricultural Cathments Under Northern Winter Conditions.

Climate change will affect runoff, erosion and transport pathways and  nutrient load to environment. In Norway, erosion and nutrient losses have been monitored in ten catchments in the National Agricultural Environmental Programme (JOVA) since 1991. A special study  was performed  to investigate effects of climate change and extreme weather conditions on runoff, nutrient and soil loss from  4 selected catchments  (1- 28 km2) in the monitoring programme. Selected catchments include cereal production with erosion and gras production and phosphorous losses from animal husbandry.

Downscaled scenarioes were used for studying effects of change in runoff and soil erosion and nutrient losses.  In all catchments climate change will lead to increase in runoff, change in seasonality of runoff and most likely erosion and nutrient losses.  Increase in average runoff intensities outside growing season increase erosion risk. Milder winters combined with extreme runoff conditions can increase erosion caused by a combination of frozen soil, snowmelt and intense rainfall. Especially erosion in waterways and around hydrotechnical equipment can increase. Examples of such extreme events occurring in the monitoring period are included. Characterization of runoff processes in agricultural catchments based on average daily discharge may be improper, ignoring the large diurnal variations in discharge.

Increased runoff and erosion will increase the need of efficient measures in agricultural landscapes, both control with surface runoff, tillage methods and the need of buffer zones and sedimentation ponds.  One expected positive effect of climate effect is increase in length of growing season (1- 3 months) and farmers see new possibilities in growing winter wheat with higher yield. If climate change gives higher rainfall and runoff especially during autumn period this can increase erosion from areas with winter wheat. The study gives examples of such dilemmas and the need of new measures and maybe more restrictions in farming practices.