Trend of humidity (specific and relative) in synoptic stations in Iran in period 1976-2005

In the last decades as a result of global warming climate change has been one of the fundamental discussions among scientists. As the atmospheric water vapor plays an important role in energy balance of the planet, so it is an important factor for explaining climate change. In this study, air pressure, vapor pressure and relative humidity and dew point temperature over 46 synoptic stations are obtained. The specific humidity is calculated for the statistic period (1976 till 2005). The amount of the relative and specific humidity trend is calculated by least square method. The Mann-Kendall test is used for determining the significance level of trend. The results showed that the annual of the mean relative humidity in north    and North West of Iran was greater than other areas. Relative humidity in winter was greater than other seasons. In coasts of Caspian Sea and Persian Gulf annual mean of specific humidity was greater than other areas; also summer specific humidity is greater than other seasons ().Relative humidity trend in most of stations except the stations which are in coasts of Caspian Sea and Persian Gulf and some of the western stations were negative. Annual specific humidity trends were positive in Caspian Sea and Persian Gulf stations and were negative in other stations. In winter most of stations had significant negative trend in relative humidity (28%). Specific humidity was reduced in most of stations in spring, but it increased for some of stations in coastal lines. Over all negative trends of investigated parameters was more than positive one.