Zoning of Iran Based on Minimum Temperatures

  Abstract   Minimum temperatures in Iran were studied based on a forty years period data of 44 synoptic stations using statistical methods and techniques such as one-way ANOVA, Bonferroni’s multi comparison test and multivariate regression equations. Then the surface of Iran was classified annually and seasonally using GIS software capabilities and cluster analysis. Also kriging interpolation method was used for interpolating and estimating of temperature and it’s spatial variations in isotherm maps and CV (coefficient of variation) maps. The results of research specified four annual mean minimum temperature zones in Iran. Analyzing of annual and seasonal zoning maps obviously shows the role of latitude in distribution of minimum temperatures especially in the south coastal zone. But in other regions, especially in northwest region and Zagros Chain, the role of elevation is more important. Statistical tests such as one-way ANOVA and Bonferroni’s multi comparison test confirm the accuracy of zonings. On the other hand, standard deviations and CV values of matinal temperatures are more in high-elevation regions than low-elevation regions. Comparison of β standard coefficients of multivariate regression equations shows that the role of elevation in controlling of matinal temperatures is more than latitude in all seasons and also through the year. Also reviewing r2 coefficients reveals that the incorporate role of these two factors, whilst is very salient, has more importance in justification of winter matinal temperatures than summer ones. In other words, local factors (latitude and elevation) have more importance in controlling minimum temperatures of cold period of year. Inverse relations between elevation and latitude values of stations from one hand and annual and seasonal mean and absolute minimum temperatures on the other hand, are significant at 0. 01 level. Regression coefficients show that annual mean minimum temperatures gradient in the country is 5. 9˚C /1000m and the most seasonal gradient is 6. 7˚C /1000 m in autumn.