Teemu Kokkonen

Snow processes in a forest clearing and in a coniferous forest

An energy balance approach is applied to simulate snow accumulation and melt in a forest clearing and in a coniferous forest. The study site is located in southern Finland (60.1°N) where the winters are mild considering the high latitude. For forest simulations the snow model is coupled with a procedure, which accounts for the effects of the canopy on the driving meteorological variables of the snow model. Model results are first validated against measured values of snow water equivalent and snow temperature in a forested site and in an adjacent clearing. Subsequently differences in snow accumulation, snowmelt, and energy components contributing to snowmelt in open and forested conditions are studied. Effect of the canopy on snow mass balance on the ground can be seen as higher accumulation and more intense snowmelt in the open. Due to these counteracting processes the results show little difference in the annual maximum of the snow water equivalent between the clearing and the forest. The model results suggest that in mid-winter the main source of energy for snowmelt is sensible heat in the open, whereas both sensible heat and net radiation contribute equally to snowmelt in the forest. Solar radiation intensity increases towards the spring, which causes net radiation to become dominant in both sites.

A comparison of metric and conceptual approaches in rainfall-runoff modeling and its implications

The aim of the present paper is to compare metric and conceptual approaches to rainfall-runoff modeling in terms of calibration and simulation performances and parameter invariance. This is investigated by applying two models of equal complexity (i.e., possessing the same number of parameters), but with different levels of conceptualization, to two catchments with different climatology. Level of conceptualization is understood as the degree to which the model structure and its parameters can be related to catchment-scale hydrological processes. The results suggest that the model with less conceptualization provides, in general, a more accurate reproduction of streamflow, even on independent data sets, but this difference only becomes clear when models are applied to the drier catchment. The paper corroborates that the more process complexity one wants to include in the model structure, the more types of data and higher information content are required to estimate the process parameters and to test the model performance. When only rainfall-runoff data are available, it is difficult to justify substantial conceptualization of complex processes.

Parameterisation and application of a hillslope hydrological model to assess impacts of a forest clear-cutting on runoff generation

Abstract This paper combines results of an empirical paired-catchment method and hydrological simulation techniques in quantifying and explaining the effect of a clear-cutting on runoff generation. The pair of catchments (56 and 24xa0ha) is located in the middle boreal zone in Eastern Finland. In the first part, measured runoff from the two catchments, of which one had been partly clear-cut (35%) and the other had not been treated (control), was analysed to detect differences in runoff preceding and following the cutting. In the next part, snow and canopy models were calibrated against snow water equivalent data in an open and forested environment, respectively. Output from the canopy and snow models provided an input to a hillslope hydrological model, which was parameterised for the two catchments and calibrated against runoff measurements. The hydrological model was applied to identify mechanisms that could explain the observed difference in the hydrological behaviour of the two catchments. According to the model results, both the decreased interception in the clear-cut catchment and the increased evapotranspiration in the young, growing forest in the control catchment contributed to the observed differences in spring flood volumes. During the growing season, most of the change in runoff generation between the catchments was attributed to the increased evapotranspiration in the young forest.

Interfacing environmental simulation models and databases using XML

Abstract Typically in environmental management tasks one needs to examine and explore data from several sources, use simulation models, develop scenarios, assess impacts, and provide support for decision makers. Here we consider the eXtensible Markup Language (XML) standard in developing information transfer techniques between databases and simulation models. Suitability of XML as the agreed data transfer format is studied in a sample application, where two snow models of different complexity are linked with input data extracted from a relational database. The simple case study demonstrated that with free and easily accessible tools it was relatively straightforward to develop an XML interface between a meteorological data set and simulation models. Based on the case study, a structure for a more comprehensive system comprising model and data resources, and a broker application that acts as an intermediate between the user and those resources, is presented. We believe that such an XML-based structure is worth exploring on the track towards an open modelling framework. Such a framework would allow models developed by various expert groups to connect easily to a common information system.

Dynamic mapping of nature values to support prioritization of coastal oil combating

Due to the continuing demand of oil for energy production and to manufacture various consumables the threat to coastal ecosystems by maritime oil transport remains at a high level. Clearly there is a need for tools that can be used in mitigating the environmental damage incurred by oil accidents. This paper presents a dynamic mapping application for comparing the ecological value of the shoreline of the Gulf of Finland to guide decisions on where to lay oil booms after an oil spill accident. The maps were required to combine conservational value of different species occurrences, the estimated level of oil exposure, the estimated recovery potential of the occurrences following the accident, and the efficiency of oil booms to safeguard the species inhabiting the occurrences. The mapping was tested in representative cases. The results indicate that the ranking of neighbouring shoreline streches changes depending on weather conditions and on choices made in developing the significance criteria. To the authors knowledge this work represents a unique effort in combining biological and geospatial expertise to provide decision support for oil combating. Such support is essential should ecological values truly be included in oil combating planning and management.

A semi-distributed approach to rainfall-runoff modelling—a case study in a snow affected catchment

Abstract A semi-distributed hydrological model was applied to a small forested catcment in southern Finland. The aim was to demonstrate how differences in terrain properties could be taken into account in modelling runoff generation, and to test how well the presented model simulated streamflow with only limited calibration. Modelling was based on subdivision of a catchment into topographically similar areas, which were identified from a digital elevation model. The water balance in each area was calculated using a hillslope-scale model. Discharges from the set of hillsope-scale models were combined with the aid of a routing procedure to yield the total streamflow at the catchment outlet. The catchment receives approximately 30% of the annual precipitation as snow, and thus a snow model was required in winter periods. The presented semi-distributed model was capable of reproducing fairly well the measured streamflow when only two model parameters were calibrated against streamflow. The results suggested that unlike the cumulative runoff, the temporal variability of runoff response was affected by terrain topography. Only minor differences were detected in reproduction of streamflow between the semi-distributed model and a simple lumped model IHACRES used as a reference.

Water protection and buffer zones: How much does it cost to reduce nitrogen load in a forest cutting?

Abstract Uncut buffer zones between clear-cuttings and water bodies can reduce export of nutrients to surface waters, but decrease in harvested stock volume result in losses of income for the landowner. Thinning in the buffer zones increases the income, but the effect of thinning on nutrient export is not well known. The FEMMA ecosystem model was applied to simulate nitrogen (N) export from a catchment with clear-cuttings and buffer zones. FEMMA is a spatially semi-distributed model calculating water and nitrogen fluxes in a scale of head-water catchments. The calibrated FEMMA model was applied to produce scenarios with different thinning intensities in buffer zones of varying dimensions. Reductions in N export achieved with buffer zones were computed for a 5-year period following the cutting. The economic current value of the stand left in the buffer zone represented an opportunity cost of the buffer zone. The unit cost of N reduction (€kg−1 N reduced) calculated from these simulations ranged from €219 to €1578 kg−1 N. A similar reduction in N export could be achieved with different combinations of buffer zone dimension and thinning intensity, but the unit costs of N reduction differed remarkably. The results indicate that cost-effective water protection can be achieved when the dimension of buffer zone and the intensity of thinning are optimized. Experimental research is warranted to verify these simulation results.

Impacts of logging residue and stump removal on nitrogen export to a stream: A modelling approach

Abstract The use of forest chips for energy can decrease net carbon emissions to the atmosphere, but harvesting logging residues and stumps may have adverse effects on the environment, including changes in nutrient export to water-bodies. The aim of this study was, with the aid of a computer model, to simulate the effects of logging residue and stump removal on nitrogen (N) export from a clear-cut area to a stream. A spatially semi-distributed FEMMA ecosystem model (tool for Forestry Environmental Management) was used to simulate N export from a catchment subject to clear-cutting and four different scenarios of logging residue and stump removal. These scenarios were compared with a conventional clear-cutting scenario, where the logging residues were left on site. Simulations suggested that the logging residue recovery does not decrease N export to the stream. In the model this was explained by a decrease in microbial immobilization, which in the case of conventional clear-cutting reduces net release of N in decomposition and mitigates the export of N. The decrease in immobilization is directly related to the removal of the woody debris from the site. Simulations suggested that harvesting of logging residues in low atmospheric N-deposition areas is not an effective strategy for reducing N loads in water-bodies.

Developing a Decision Support System for Assessing the Impact of Climate Change on Lakes

CLIME was a complex project where data from a variety of sources had to be summarized in a form that was readily accessible to stakeholders. The volume of data generated by the regional climate models, the catchment models, and the lake models was also very large and placed severe constraints on their direct examination. In situations such as this, Decision Support Systems (DSS), which employ databases, visualization, and models in an interactive way are usually the tools of choice (e.g., Loucks and da Costa, 1991; MacEachren et al., 2004). The Internet and the Web are increasingly being used as platforms for DSS, as systems implemented in this way are easy to access and to maintain (Jolma, 1999; Jolma et al., 1999). The analysis of causalities and the development of probabilistic models are issues that are central to any projections linked to climate change. Varis (1997), Ames (2002), Borsuk et al. (2004), and others have obtained encouraging results by applying Bayesian networks to environmental problems.