the relationship between the satellite-based index and standard precipitation index, on different land covers

the normalized difference vegetation index (ndvi) derived from the spot 4 satellite has been widely used to monitor moisture-related vegetation condition. the relationship between vegetation and climate index, however, is complex and has not been adequately studied with satellite sensor data. to better understand this relationship, an analysis was conducted on time series of monthly ndvi (1999–2009) during the growing season in the semnan province. the ndvi was correlated to the standardized precipitation index (spi), a multiple-time scale meteorological-drought index based on precipitation. the 3 and 24 month spi were found to have the best correlation with ndvi, indicating lag and cumulative effects of precipitation on vegetation, but the correlation between ndvi and spi varies significantly between months. results show that combining ndvi and a climatic index is a suitable method for estimating land cover changes. steppe range land or class 7 in all stations had a higher correlation between ndvi and spi. land covers with vegetation have significant correlations in spring and summer months. the highest correlations occurred during the middle of the growing season, and lower correlations were noted at the beginning and end of the growing season in most of the area. a stepwise regression model showed that the relationship between the ndvi and spi was significant in both rangelands and forest.