Human-induced biospheric change and the global carbon cycle: A spatial modeling approach and its application to tropical Asia.

摘要

I have developed a computer model, called GEOMOD, to simulate land use change and its consequences on biotic carbon exchanges between terrestrial ecosystems and the atmosphere, using a spatial modeling approach. Land use change is a most important part of the anthropogenic disturbance to the terrestrial biosphere. Its contribution to the atmospheric carbon dioxide accumulation is only second to fossil fuel combustion. Therefore modeling land use change has drawn great interest among the scientist community of global environmental change. Conventional models of land use change usually neglect the geographical heterogeneity within a region and thus cannot provide the spatial distribution of various land uses and their changes. We adopt a spatial modeling approach in this study. First, the input and output of the model are geographically-explicit. Spatial patterns of land use and factors that are related to land use change are represented with matrix-format raster data files. Each raster is dealt with independently; Second, the change of land use patterns are made driven by local features of geographical, ecological and societal variables.;In chapter 4, I have developed a method; called normalized distance method or RDM, for spatial pattern comparison and model validation. I analyzed the weakness of previous methods and construct a new index, normalized distance. The new index improves the previous methods by incorporating the locational information, as well as the number of matched grid cells.;I analyzed the effects of changing spatial scales on spatial pattern analysis, by computing the responses of four spatial autocorrelation coefficients to varying grid sizes. I found that all spatial autocorrelation coefficients are scale dependent for the data sets I used. This result suggests that scale effects be carefully incorporated when interpreting the results of spatial modeling.;The overall objective of the study is to explore approaches and tools for studying land use change and its impact on the global carbon cycle. However, we have found our results of model simulations could be used to feed e.g. three dimensional atmosphere transport models.;I first tested the model by applying it to Peninsular Malaysia and Chiang Mai, Thailand, two relatively small areas in tropical Asia. I found that a satisfactory accuracy can be obtained for simulating the changes in land use patterns, when using only one initial land use pattern, topography and land use change rates. This result suggests that land use pattern can be considered as a function of its initial pattern and topography in these cases. Then, I applied the model to thirteen countries in Tropical Asia, a much larger region than the test areas. In this application I made two model runs for comparison purpose. One is national level and the other sub-national. The national levels uses land use change rates for each country, while the sub-national run for each sub-national unit, or ecological zone. In addition, the spatial patterns of carbon content are also simulated.