An application to which SVFlux / SVHeat was recently applied involves calculation of the change in soil suctions near the ground surface in a woodland area. The issue at stake was whether long term climate change will affect the forestry industry in Canada. If there is a change in average annual air temperature, how will this affect the distribution of water contents and soil suctions in the upper root zone? The danger is that increased temperatures could lead to less moisture being available in the root zones. Less moisture could then potentially affect the growth of trees. The intent of this study was to use the SVFlux software and model detailed climatic flows near the ground surface both in the present day and into the future. The potential impact of climate change on forestry could then be determined.
Why SVFlux / SVHeat?
The SVFlux and SVHeat software packages were used for this particular and analysis because of their ease of use and their ability to handle both water and heat flow in a coupled or uncoupled fashion. 1D versions of each package are available which simplifies this type of analysis such that it can be run quickly and easily. Both software packages implement climatic coupling and therefore can compute the influence of detailed climatic data on the soil profile. Coupled analysis is important for this profile as the flow and thermal processes are highly dependent upon each other. This is particularly true in the wintertime months.
A typical forest site profileClimate data was pulled from Environment Canada weather stations which existed near the study site. An analysis period of 15 years was selected and matching data was obtained. The data collected involved measurements of precipitation, net radiation, windspeed, and air temperature.
The methodology for this particular study utilized two different sites. One site consisted of a high water table and the other site consists of a low water table. The vegetation at each site and the resulting root depth were varied to reflect the changing vegetation. A typical profile analyzed may be seen in the diagram to the right.
In this particular modeling exercise, the lower boundary condition was assumed be constant. The variation in the numerical model was then entirely controlled by the upper climatic boundary condition. The SVFlux software makes use of the Wilson-Penman equation in order to calculate actual evaporation. Calculation of actual evaporation in these modeling situations is of paramount importance as it controls the results of the modeling. The Wilson-Penman equation then makes use of detailed climatic data in order to determine a net flux boundary condition on the upper surface of the model. Some of the precipitation data used in the numerical model can be seen in the figure below.
A range of soil properties which were representative of this region were utilized in the numerical model.
Results and Discussion
The numerical model was successfully able to calculate the influence of climate change on the near surface water content, so suction, and freezing front. Cumulative plots of the flows of precipitation, evaporation, and net flux into the ground could be produced. In particular, and the impact of climate change on the moisture conditions and their relative impact on the root zones of the forest vegetation could be calculated. The study therefore provided valuable information to the forestry industry regarding reasonable expectations of the impact of climate change.