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

Long-term trends ofmonthly mean sunshine durations were analyzed utilizing non parametric testsfor Southeastern Anatolian Project (GAP) region. Correlation coefficientsbetween sunshine durations and relative humidity and cloudiness variable weredetermined over the years. Climatic data between 1970 and 2005 from ninemeteorological stations scattered in the region were collected and used. Thenon-parametric test results revealed that an upward trend was dominantespecially in the summer and early autumn months. Mann-Kendall test indicatedthat the strongest trend was in August at Gaziantep station with Z value of-6.63. Therefore, declining significant trends never observed in the months ofJanuary, February, March, November, and December. Although, the highest upwardtrend was observed in April at Mardin station, there was no significant risingtrend in the whole region for the same month. Cloudiness and relative humiditydata was satisfactorily explained the variation in sunshine durations. A commonsignificant negative correlation was found using non parametric test betweensunshine duration and relative humidity and cloudiness series. There were alsoa few positive correlations, but none of them was significant. Additionally,basic linear regression equation was employed in order to determine changes insunshine duration that Gaziantep station showed the highest decrease in Julywith a value of 0.13 hours per year. Downward trends of sunshine duration couldbe attributed to air quality changes which could affect adversely thehydrological cycle and agricultural production. The overall findings support theview that there is a climate change regionally or globally.