Some descriptive features and long - term changes of dry season over Iran

One of the important features of climate change is dry season persistence. Dry season continuing could effect the intensity and frequency of precipitation events as well as other climatic factors. Accordingly, the climatologists have recently been concentrating on this issue. According to the American Meteorological Society (AMS) a dry season is an annually recurring period of one or more months during which precipitation is at a minimum for that region. Changing in dry season length took a lot of expert's attention all over the world while it did not catch a lot of Iranian experts attention. In current study the changes in mean of length of dry season over Iran is considered. The objective of this research is to know and statistically analysis spatial pattern of length of dry season. Accordingly, daily database from 1961 to 2010 which have 15 15 km resolution are used. The spatial pattern of dry season follows the mountain chains pattern except in northwest and southeast of the country as well as some small parts of northern parts of Iran. Trend analysis showed that about 77.2 of the country experienced increasing in the length of dry season on average by 2 days per year. This event tends to pay a strong attention toward water resources managements.