Long-Term Trends of Sunshine Durations in Relation with Cloudiness and Relative Humidity in GAP Area, Turkey

Long-term trends of monthly mean sunshine durations were analyzed utilizing non parametric tests for Southeastern Anatolian Project (GAP) region. Correlation coefficients between sunshine durations and relative humidity and cloudiness variable were determined over the years. Climatic data between 1970 and 2005 from nine meteorological stations scattered in the region were collected and used. The non-parametric test results revealed that an upward trend was dominant especially in the summer and early autumn months. Mann-Kendall test indicated that the strongest trend was in August at Gaziantep station with Z value of -6.63. Therefore, declining significant trends never observed in the months of January, February, March, November, and December. Although, the highest upward trend was observed in April at Mardin station, there was no significant rising trend in the whole region for the same month. Cloudiness and relative humidity data was satisfactorily explained the variation in sunshine durations. A common significant negative correlation was found using non parametric test between sunshine duration and relative humidity and cloudiness series. There were also a few positive correlations, but none of them was significant. Additionally, basic linear regression equation was employed in order to determine changes in sunshine duration that Gaziantep station showed the highest decrease in July with a value of 0.13 hours per year. Downward trends of sunshine duration could be attributed to air quality changes which could affect adversely the hydrological cycle and agricultural production. The overall findings support the view that there is a climate change regionally or globally.