Abstract: Report on the catchment scale modelling of the Vansjø-Hobøl and Skuterud catchments, Norway.
Part 1: Vansjø-Hobøl catchment
A model network comprising climate models, a hydrological model, a catchment-scale model for phosphorus biogeochemistry and a lake stratification and plankton dynamic model was used to model phosphorus loadings in the Vansjø-Hobøl catchment, in southern Norway. The model network was automatically calibrated against time series of hydrological, chemical and biological observations in the catchment using a DREAM implementation of the Markov Chain Monte-Carlo (MCMC) algorithm. Climate predictions from 3 global climate models (HadRM3, ECHAM5r3 and BCM) were used to prepare present-day and future climate forcing for the model network: the GCM model predicting the highest increase in temperature and precipitation, HadRM3, yielded the highest increase in total phosphorus and chlorophyll concentration in the lake basin over the scenario period 2030-2052. Despite the significant impact of climate change on water quality, it is relatively minor when compared to the much larger impact of the increase in human activity, or conversely, the impact of the implementation of realistic abatement measures. Our results suggest that it will be challenging to reach the targets set for phosphorus by the Water Framework Directive in the Vansjø-Hobøl catchment, even under the management scenario focussing on water quality agreed upon by the stakeholders, though should more stringent P-load reduction measures be implemented, the model predicts that they should be effective under scenarios of future climate change.
Part 2. Skuterud catchment
Eutrophication is one of the most pervasive water quality problems in Europe and around the world. Reduced water quality due to eutrophication has negative consequences for many uses, including for drinking, for industrial use, adue to: (a) saturated overland flow caused by prolonged rainfall on a non-frozen soil, or (b) overland flow caused by snowmelt and/or rainfall events on a frozen or partly frozen soil. In the second case rainfall intensities can be higher than the infiltration capacity of frozen or partly frozen soils.
Land use and soil tillage methods can significantly influence soil loss during autumn and spring periods in Norwegian catchments. Often, the greatest erosion is measured in catchments where autumn tillage is predominant. The main soil management method to reduce erosion and losses of particulate P is reducing tillage operations in autumn and not leaving the soil surface bare during winter. Increasing grassland and forest areas is shown to decrease the risk of soil and P losses (Haygarth and Jarvis, 1999).
Climate change in Norway is expected to cause increase in precipitation amount and intensity. Additionally, increased temperatures in southeast Norway may lead to increased frequency of freeze-thaw events during winter. These changes may enhance the erosion and runoff processes and cause increased P losses, further increasing the demand for mitigation methods in agricultural production. Hence, we are facing an accelerating pressure on water resources to satisfy often conflicting environmental, food security and economic objectives. Optimised solutions are necessary to minimise the costs of improved water quality and at the same time to maintain food security.
Mathematical models incorporating physical background of the processes standing behind flow formation and particle and P losses are promising tools to solve optimisation problems and to simulate the effects of so far non existing climate and land use scenarios on water quality and freshwater ecosystems.
The main objectives of the work, carried out here were 1) to test the capability of the INCA-P model to describe the flow generation and soil and P losses from an agricultural-dominated catchment under S-E Norwegian conditions; 2) to evaluate the possible effects of the projected climate change on surface runoff, erosion processes and P losses and 3) to evaluate the combined effects of various land use and soil management strategies and climate change on stream water quality by fusion of available data, expert knowledge and a process-based mathematical model.
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