Amendment of Climate Zones of the Northeastern Iran Based On a Combination of Changes in Aridity Index

The purpose of research is to rezoning the climate zones of the north east of Iran- located between 30° 35' to 38° 41'N and 56° 19' to 61° 16'E- based on the analysis of changes in the aridity index, in combination with other climatic parameters changes. Air temperature and precipitation parameters were provided in the scale of monthly average and annual over period time of 1990-2017. At first, the climate classification of the north east of Iran was revised by studying variations in precipitation, evapotranspiration and temperature and results were compared with the De Martonne and Köppen-Geiger climate classification. For analyzing the aridity status, trend of the above parameters in the form of UNEP index was tested using Mann-Kendall non-parametric method and Sen's slope estimator. Results indicated that applying of the aridity index, as a factor in improvement of the used pattern, caused the zoning of this method to be more precise than the previous methods. Therefore, the study area was classified into seven climatic groups, the zone Ac14 (Arid zone with cold winter and hot summer) with 39% and 9 stations, and Ec14 (Extremely-arid zone with cold winter and hot summer) with one station were the largest and smallest climate zones, respectively. Results of the Mann-Kendall test and trend line slope, for UNEP aridity index showed that the aridity and desertification intensity have increased in different parts of the area during 28 years.