A Numerical Model of the Surface Energy Balance and Ground Thermal Regime in Organic Permafrost Terrain
Measurements of the surface energy balance and ground thermal regime were carried out near Churchill, Manitoba at two sites in the summers of 1984 and 1985, and a third site in the summer of 1987. The sites represented unforested permafrost locations with a non-transpiring organic surface cover. After examining the microclimatic and ground thermal regimes, the measurements were used to develop a physically-based one-dimensional model capable of emulating the observed regimes. Sensitivity analysis of the model was carried out to determine the relative importance of processes and factors influencing ground temperatures at the study locations, and to assess the validity of using this modelling approach for prediction of changes in the microclimatic or ground thermal regimes.
The data collected in this study represent a complete, comprehensive, and accurate series of measurements of the summer microclimatic regimes at the study locations. On a descriptive basis, the data provides a strong knowledge base of microclimatic processes in this type of terrain. The major significance of the thesis lies in the results of the numerical modelling. Although the general modelling approach is similar to previous models in the literature, the model developed in this study uses a more comprehensive evaporation model which includes a thermal resistance factor acting in the surface layer. Changes in the thermal resistance factor completely reverse the sensitivity of the model to surface moisture changes: with a high thermal resistance the soil cools in response to surface drying, while low thermal resistance values lead to soil warming in response to surface drying. This result is very important in assessing the response of permafrost conditions to local or global climatic change.
In addition, the field data indicate that both surface moisture and surface temperature vary widely over horizontal distances of only a few metres. This result indicates that one-dimensional models may not be capable of treating the evaporation process in a physically-based manner. Evaporation models previously used in the literature may be misleading in their predicted response to climatic change. Further study is required into the nature of the surface evaporative layer, and the validity of one-dimensional evaporation models in non-homogeneous terrain.