Application of Reanalysis and Observational Data for Comparison of Drought indices(Case Study: Esfarayen Sabzevar Region)

In present paper,Standard Precipitation Index SPI and SPEI indices were compared in order to assessment of drought conditions in the Esfarayen-Sabzevar region.As the aforementioned region does not have sufficient long-term data to assess the drought, reanalysis data of ERA-Interim were used to combine with the observed data.For this purpose,climatic data of precipitation and temperature were extracted for each station in the statistical period of 1979-2016 using the web interfaces,Python script,ECMWF WebAPI and ArcGIS software. After correcting the bias of the data based on observational data,combined data of precipitation and temperature were obtained for the aforementioned period that was basis for calculating the drought.Finally,drought assessment and estimating the correlation of SPI and SPEI of three stations of Sarcheshmeh,Ghasemabad,andJoghtay in the time scales of3,6,12,18,and24months were done.After generating data combination, the Root mean square error(RMSE)and Bias were decreased from0.39and6.69to0.32and0.24 respectively;therefore,these data can be used for drought assessment in areas with not available data.Results showed that in the short time scales,the frequency of dry and wet periods is high which decreases with increasing the time scale,but their continuity increases.In the stations,in most of the cases,coordination in the dry and wet periods was observed in both indices.Based on the provided results regarding the correlation between SPIand SPEI indices, there is a positive and significant correlation between above indices and the correlation is higher in the humid regions.As a result,the SPI index can be used in the regions without temperature data and with a precession similar to the SPEI index.