A Study of Anomalies and Trends of Sunshine Hours in Iran

Sunshine hours rate with its effect on determination of solar radiation rate is the main factor of controlling life, climate and other biological activities on the earth, especially in arid and semiarid zones. The purpose of this research is to offer an image about anomalies and trends of sunshine hours rate in Iran, and to estimate its values based on the latest data. For this purpose, the country area was zoned for annual and seasonal sunshine hours by using 87 synoptic stations data in a 20-years period (1986 to 2005) via cluster analysis and ArcGIS software capabilities. For confirming the zonation, Sidak and One-Way ANOVA parametric tests or Mann-Whitney and Kruskal-Wallis non-parametric tests were used. In addition, multivariate and simple linear regression equations were used for estimating sunshine hour’s numbers and recognizing their temporal trends respectively. The results of the research showed that the mean sunshine hours increase and their variability decrease from the north to the south and from the west to the east of country until the coefficient of variation (CV) values of annual sunshine hours, contrary to the spatial distribution of them reach to the highest rates in the Caspian sea coasts and the lowest ones in the central deserts. Sunshine hours rates show either significant increasing trends or essentially non-significant trends in the whole country. However, even one case of significant decreasing trend has not been observed in the country. The mean increasing amount of trends in the country is 16.6 hours per year. Statistical model shows that except in the summer, the rule of the latitude in spatial distribution of sunshine hours is salient. By using this model, sunshine hour’s values in the country were estimated with good precision based upon latitude and elevation values.