An examination of the trends in sunshine hours over Iran

For the purpose of assessing solar energy resources in different parts of Iran, this article provides a synopsis of the spatial and temporal variability of sunshine hours at 37 first‐order synoptic stations during the period 1981–2007. Annual and seasonal variations of sunshine duration were determined for four distinct regions within the country. By averaging the time series of sunshine hours in each subregion and standardizing them, four regional representative time series were developed. The results indicate, over all regions, the annual pattern of sunshine duration exhibited large sinusoidal increases and decreases, with minima occurring in 1990 and 2003. The trends of sunshine duration indicated that the sign of the seasonal and annual trends for the vast majority stations has been positive. The maximum positive trend was found across the western parts of the country for all seasons. The spring was found to have a negative trend in sunshine hours at only 2 of the 37 stations. On the annual scale, the change rates in sunshine hours from western to eastern part of Iran have gradually declined over time. The highest positive annual trend was found at Sanandaj station on the west side of Zagross Mountain, with of rate 253 h per decade. Given the increasing trends observed at many stations in Iran over the last 25 years, and recognizing the natural high sunshine duration experienced across the region, a strong case can be made for the introduction of solar energy across the country. Copyright © 2012 Royal Meteorological Society