Spatio-temporal analysis and zoning of probable occurrence of wet and dry years in North West of iran

North West of Iran consists of environmental، plant، and animal biodiversity due to its topographic conditions which have been adapted to the present climatic conditions. Long-time fluctuations and changes in climatic elements of the area can result in harmful impacts in environment، agriculture، economy، and even human properties. On this basis we attempted in this paper to evaluate susceptible sections to wet years and droughts in the north west of Iran for the statistical period of 1986-2005 (20 years)، by applying the data collected from 55 synoptic، climatic and rain gauging stations of the area. For so doing، we used SPI index in 12-month duration. For studying the wet years and droughts، we produced 240 maps containing all months of the study and applied Kriging interpolation method in 8 English Abstracts Surfer software. Afterwards، were converted to data and the calculations on descriptive statistics including mean، standard circle and oval shapes were accomplished over 4236 cells in ArcView software. The monthly review of the wet and dry years during 240 months having various intensities shows. heterogeneity in intense drought occurrence and weak wet years from the normal distribution and the probability of weak wet year’s occurrence are higher in eastern and central parts while intense droughts might occur in the southern parts. The calculation of central inclination and spatial indexes also indicated that the probability of weak wet year occurrence is higher in northern sections and the possibility of severe drought occurrence is more in the southern sections of the study area. In the meantime، the probability of severe drought occurrence is more stable in terms of the location.