The investigation of relations between large scale atmospheric parameters and drought indices

Drought indices are methods that quantify severity of drought and how long it will last. Various drought indices have been developed which can be calculated with different input parameters. In this study, drought indices have been calculated and drought of basin have been evaluated for stations data sets and NCEP/NCAR reanalyze data sets which use observed data to create low resolution grid data sets such as rainfall, temperature, evaporation all around the world. In this thesis, Percentage Normal Precipitation Index (PNPI), Reconnaissance Drought Index (RDI), Standardised Precipitation Index (SPI) and Standardised Precipitation Evapotranspiration Index (SPEI) drought definiton methods are calculated for the station based and NCEP/NCAR datasets in Lower North Aegean basin. The spatial distribution of the drought within the low resolution grid of Global Climate Models used to predict the future climate conditions, can be very variable. Therefore, drought indices obtained from atmospheric estimates of GCMs do not reflect the exact situation within the computation grid. Because of this, the relationship between Standardized Precipitation Index (SPI) values obtained from low resolution NCEP/NCAR reanalysis data and station based SPI values of the same region was investigated by quantile regression method and quantities of drought indices at stations under specific atmospheric conditions.