Performance Comparison of MODIS and Landsat Data in Estimating of NPP in Arid Regions of Isfahan Province

Net primary production (NPP) is one of the most important factors in ecosystem's function, which is affected by biological and climatic factors. The main objective of the current research was to investigate the potential of the CASA (carnegie-ames-stanford approach) model in determining the spatial and temporal distribution of NPP in rangland types of arid regions of Isfahan province using MODIS and Landsat. For this purpose, satellite and climatic data such as rainfall, temperature, monthly and sunny hours, were used. The NPP was modeled on two Landsat and MODIS scales and correlations between field measurements and CASA model were investigated based on rangeland conditions and vegetation types. Results showed that the highest plant production in the region was during the March-May months. Crrelation between CASA model with field data occurred in MODIS was higher than Landsat data. Based on the relations, the values of NPP and LUE (light use efficiency) were investigated in the region. The NPP spatial distribution and LUE values indicated that the amount of annual production and photosynthesis efficiency were decreased in degraded rangelands (poor and very poor conditions) compared to fair rangeland condition. The highest and lowest amount of NPP observed in Artemisia sieberi – Zygophyllum Spp (9.35 g C/m2 y-1) and Annual grasses - Annual forbs (0.2 g C/m2 y-1), respectively. The amount of NPP and LUE in shrublands and annual plant types were higher than bushlands.Results of this research probes the importance of biological classification, climate and scale of study in NPP modeling. Moreover, the stratification of rangelands based on life forms and range conditions has principal role in accuracy of the NPP estimation.