A study on production changes of steppic rangeland of Isfahan using the standard precipitation index

Rangeland ecosystems in semi-arid regions are vulnerable systems to climatic changes specially precipitation. In such conditions droughts are predictable. In this study the relationship between rangeland production and spatial and temporal changes of precipitation was investigated. Therefore، rangeland production through 10 years data set (1377-1387) in steppic bioclimatic of Esfahan province (Alavije، Muteh، Kalahrood and Gardaneshadian) using Standard Precipitation Index (SPI)، the relationship between SPI series of 3، 5 and 8 month time scales، and rangeland production of 10 years. Thus Anova and correlation matrix between production and SPI factors were formed. Results indicated that the most severe drought has occurred in 1387 simultaneously، with the least production. A harmony between change trend of production and SPI in the sites showed that in most cases maximum and minimum production have occurred simultaneously with maximum and minimum of SPI series. Also، the production correlated with SPI series of three، five and eight months'' time scales with correlation coefficients more than 63 percent which were significant in 1% and 5% level. Due to efficacy of production from spring precipitation and soil depth less than 30 cm in the sites، it is proposed to use SPI series of three months scale to evaluate drought in similar rangelands.