بررسي تغيير اقليم گرگان طي چهل سال گذشته

Climatic change in Gorgan during past 40 years

The climatic changes especially global warming as a result of use of fossil fuels has taken many attentions during past years. In order to examine climatic change, 40 years weather data (1961-2000) of Gorgan Station were used. Simple linear regression (y=a+bx) was used to determine rate of change (b) in temperature and precipitation variables. The results showed that annual mean maximum and minimum temperatures have not increased (p=0.05) during past 40 years, but mean minimum temperature in May has decreased by 0.04°c per year (p=0.048). The number of days with a maximum temperature greater than 35°C has decreased by 0.05 day per month per year (p=0.019) for May and 0.13 day per month per year for June. Total annual precipitation has significantly decreased by 4.3 mm per year (p=0.00$). Total rainfall in March has also declined by 1.3 mm per year. On the other hand, total annual number of days with precipitation less than