Investigating temporal and spatial changes of meteorological drought (SPI) in Karun watershed

Drought is one of the main and repeated features of different climates and also one of the environmental events and an integral part of climate fluctuations. Monitoring systems are very important in developing plans to deal with drought and its management, and for this reason, available quantitative indicators are used to express this phenomenon. Since these indices are calculated pointwise, it is necessary to process them spatially. In this regard, mediation methods including geostatistics are used. The analysis and how the meteorological drought changes over time, as well as the ability of kriging, cokriging, image distance weighted (IDW) and radial function (RBF) methods, were evaluated in the spatial analysis of meteorological drought in the entire Karun large watershed. Drought analysis was done using rainfall data from 58 rain gauge stations and 11 synoptic stations with a statistical period of 30 years in the period from 1987 to 2016 using the standardized precipitation index (SPI). Then drought maps were prepared and evaluated. The obtained results showed that the lowest value of the root mean square error (RMSE) related to the cokriging method with a value of (0.32), and the radial function method with a value of (0.34), and this method is considered the best method for the year 2013 is Also, in the year 2008 most stations were involved in very severe drought and year 2000, most stations were involved in severe drought. The results showed that the Cokriging method has higher accuracy than other methods in drought zoning.