Improved standard precipitation index and drought characteristics

In many regions of the world, and particularly in the eastern Mediterranean region, there is a general precipitation decrease tendency according to the global circulation model (GCM) and the regional climate change models (RegCM). Dry spells and their temporal occurrences as droughts affect water resources, and hence, agriculture and food securities may be endangered in such region. It is, therefore, necessary to foresee the future drought characteristics based on the historical records. Although the Standard Precipitation Index (SPI) provides dryness classifications, it cannot reflect the basic drought characteristics in the original hydro-meteorological records. The main purpose of this paper is to propose improved SPI (ISPI) approach for quantitative drought characteristics calculations. In order to support the insufficiencies in the classical SPI, a comparative study is presented with the ISPI method on the bases of drought duration, amount and intensity concepts. It is shown that especially the risk calculations have wide discrepancies, but the ISPI provides actual results. The application with objective results is presented for Istanbul European side, Turkey, meteorology station monthly precipitation records.