Geophysics for managing Norwegian agrohydrological threats

Norwegian agriculture is challenged by increased production demand and climate change while being faced with tight restrictions to its environmental impact. Due to climate change, an increase in extreme weather events is expected. High intensity rainfall events lead to flooding and water-logged conditions, which have negative impacts on yield and operational conditions related to tillage and transport (trafficability of the soil). Two thirds of Norway's agricultural area is drained to prevent water logging, but at times these drained soils have problems with too high water content, leading to delayed tillage in spring time resulting in lower yields. About 10% of the cultivated land is considered poorly drained.

Saturation and infiltration excess overland flow leads to sheet erosion. Erosion rates often follow a seasonal pattern with the highest soil losses during late autumn and early spring. For most of the total soil loss only a few runoff events are responsible each year. Soil loss from agricultural areas in Norway is not only harmful because of the loss of nutrient rich topsoil, but also because of off-site effects, especially in freshwater systems.

Poorly drained soils are prone to deterioration of its structure. In areas where overland flow concentrates, this may lead to the development of gullies. Ephemeral gullies make up a considerable part of the sediment losses from agricultural areas. In addition, they are shortcuts for sediment transport, forming a connection between the hillslope and the surface water system.

Seasonal saturation excess because of snow melt and rain also leads to high flow rates in Norway’s stream and river network. Flooding problems at the intersection between streams and roads occur even in first order streams.

While many soil conservation and water retention measures complement each other, they sometimes affect each other adversely. Intensification of tile drainage, for example, may reduce sheet and gully erosion risk levels, but will have an adverse effect on peak flow rates and flood risk. Other measures, like buffer zones, serve both purposes. But when, how and under which circumstances water retention and soil conservation measures function remains a complex question.

Understanding the spatio-temporal dynamics of water in the vadose and groundwater zones therefore is a key component of integrated agro-ecological management strategy at low (farm) and high (regional) levels. While the mechanics of overland water movement and infiltration are generally well understood, there are many significant challenges for system understanding at larger spatial scales, especially under increasingly non-normal weather conditions.

NIBIO endeavors to reconcile measurements and observations with agrohydrological system understanding. Complexity and scale (time and space) are the main challenges in this endeavor. In this presentation we will present how NIBIO uses geophysics for understanding agrohydrological threats and solutions, with focus on drainage, erosion and buffer zones.