Meteorological Drought Zonation in Northwestern Iran by Using Rainfall Anomaly Index

Drought is one of the natural disasters which happen in different parts of the earth every year and bring direct and indirect losses. This phenomenon occur more often in arid region of the world، like Iran، due to high variability of rainfall. In this study، for assessing of meteorological drought in northwestern Iran، the statistical data in 22 selected stations of this region were analysed during 26 years (1985-2010) as the base of this study. To achieve this objective، the rainfall anomaly index (RAI) with respect to its capabilities and benefits was selected for drought assessment. Also، monthly and annual drought zonation maps was prepared using inverse distance weighting interpolation (IDW) and Arc GIS software. Then، extent، intensity، spread and spatial dispersion of droughts was analysed in the study area. The annual map showed that the effect of fluctuations due to very large and very small data and the resulting values of them will be decreased in long term، so that the most stations had a poor drought according to average annual values of statistical period. Moreover results showed that under normal conditions except summer season، the southern regions were more vulnerable to drought in the rest seasons، but in the time of drought، all regions of the study area severely affected by this phenomenon with different intensity.