Determining the climate of Ardabil plain, its variation in past 25 years and agronomical strategies for system adjustments

The study was carried out based on the data collected in Ardabil Synoptic Station, Iran (Lat. 48°17´ E., Long. 38°15´ N., Alt. 1314 m from sea level) for 26 years (1976-2001). To determine the climate of Ardabil, the components hydro-climate curve, Ambrothermic diagram (Walter and Gusen methods), Kupen method, Ivanov moisture coefficient, Ambergeh precipitation coefficient, Dumarthone drought coefficient and hytrograph curve were used. In addition, the variations of 12 meteorological variables were compared by simple linear regression. Ardabil hydroclimate curve showed that precipitation exceeds evapotranspiration by about mid-March and stored moisture can be used by about May 1st. From May to mid-October, during which precipitation exceeds evapotranspiration again, the crops are dependent on irrigation for their moisture requirement. Walter method (P = 2T) identified four months i.e. June, July, August and September as dry months of Ardabil and Gusen method (P = T/2) identified July and August as dry months. The number of dry months decreased using Gusen, Walter and Thorntwhite methods, respectively. Different methods for determining Ardabil climate had different results. The climatic coefficients of Kupen, Ivanov (0.3186), Ambergeh and Dumarthone (16.07) identified the region as drier, respectively. In total, Ardabil region is on the border of dry and humid zones. Variation trends of climatic parameters showed that sunshine hours (0.754**) and average annual maximum relative humidity (0.548*) are increasing and soil surface temperature (-0.424*) is decreasing.