Determining of Dryness Index According to the Demartonne Method

Salt Lake Basin of Iran which is situated on the arid and semi-arid climatic region and located at central Alborz southern slopes, covers an area of 92750 sq km and lies between 33º till 37° northern latitude and 48° till 52° 30´ easthern longitude. Salt Lake Basin of Iran according to “Country Water Comprehensive project” Classification, has been specified under the title: “The seventh Basin”. This basin consisted of 7 provinces: Tehran, Qazvin, Zanjan, Qom, Hamadan, Markazi province and some parts of Isfahan Province. In order to analyze of meteorological data, the statistics of one long-term time series past 40 for the years, from 1957 to 1996, were extracted for the 35 stations on this basin, for the climatic parameters which was studied in selected meteorological stations, consist of monthly precipitation, maximum daily precipitation, monthly maximum temperature average, monthly minimum temperature average, absolute maximum temperature, absolute minimum temperature. Meteorological data calculatefor one long-term time series 40 years indicates, rainfall average of Salt Lake Basin, is 256.5 mm and rainfall variability average is 35.11%. The Rainfall variability average of Salt Lake Basin, during 40 years differs between 22.1% in Malayer and 62.4% in Doozaj and annual precipitation disorder coefficient differs between 8.3% in Zanjan and 38.9% in Kavir. Annual mean temperature during 40 years is 13.9 °C. Absolute maximum and Absolute minimum temperature are 48°C and –35°C. Temperature variability average, during 40 years is 11.49°C. Aridity coefficient average during 40 years has been calculated to 11.092 and the regional climate average is Semi-Arid according to the method of Demartonne.