Assessment of Vegetation Condition Index Using Modified Standard Precipitation Index to Monitor and zoning Drought

Drought management is an essential task to exploit water resources. In this study, the monthly rainfall of 35 synoptic stations in Qazvin province during 30-year were considered for drought monitoring. In this study two drought monitoring indices including modified standard Precipitation index (MSPI) and Standardized Precipitation Index (SPI) are accomplished and compared to the reports of four indices in the study area. The obtained results showed that the MSPI is more accurate than the SPI and other indices. Having the drought conditions in the stations, zoning of drought were calculated by Interpolation methods such as IDW, Kriging, GPI, and RBF.The obtained results demonstrated that IDW method with first power is the best method in terms of average error. Moreover, zoning of the precipitation is conducted using Kriging interpolation then the MSPI value for each cell is computed for monthly precipitation. The results show that if the precipitation interpolation is conducted firstly, the drought index is calculated more accurately than the method that drought index calculated in the stations. In order to assess the drought condition more accurately, the vegetation condition index (VCI) is computed using monthly NDVI product of MODIS. The correlation between VCI and MSPI was calculated that the results illustrated that MSPI confirms the results obtained by VCI. As a result, VCI can be used to monitor drought in the watersheds which suffer from sufficient ground stations.