Decision making model is a way to assess environmental impact. Decision making model physically and mathematically shows the relationship between quantities and qualities in a part of the existing world, ,as it is a reflection of an entity or a present event in the real world. Therefore, models explain relations between data to predict circumstances of events in the real world. Degradation model (Makhdoum,2002) is one of The mathematical models used through this research to assess environmental impacts of development in Hamedan province. In order to indicate degradation in impact units (which may be a set of areas, suburbs, factories,arbitary ecosystems or sets of the grid system depending on the level of decision making) the degradation coefficients were computed according to the following model:
H =( ?I+ Dp)/ V0
Where I is Intensity of degradation impact, Dp is Physiological density of population(Miller 1979), V is Ecological vulnerability, and H is Degradation coefficient of the habitat.
‘To achieve this , first the boundry of study area (political boundry) was depicted on 2 sheets of topographics map (1 :250000).Then the whole area was divided into 849 impact units (2x 2 cm grids, 2500 ha).Ecological vulnerability was calculated and classified by using maps of slope, elevation, climate, geology, earthquake risk,soil,flora,habitat & hydrological sensivity. Then degradation impacts were detected in study area by field works, experts opinion, documentations and land use maps, as well as, their intensity.
Physiological density was also obtained by dividing the population in every grid by the area of farming lands. Result of the model for every grid is a degradation coefficient. Finally according to the fuzzy theory, resulted degradation coefficients for all grids were classified into 6 classes and 3 categories. Further more the province was divided into 3 areas including prone to further development, noncritically impacted areas( need rehabilitation), critically impacted areas(need conservation measures).
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