Sandu-Valer TAHAS¹, Dumitru RISTOIU¹ & Constantin COSMA^1
1Babes-Bolyai University, Faculty of Environmental Science, 30 Fantanele Street, 400294, Cluj-Napoca, Romania
E-mail: alextahi@yahoo.com, dumitru.ristoiu@ubbcluj.ro

ANALYSIS OF GLOBAL SOLAR RADIATION AND PRECIPITATION TRENDS IN CLUJ-NAPOCA, ROMANIA, OVER THE PERIOD 1921-2009

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The evolution of annual global solar radiation (GSR) and precipitation trends in Cluj-Napoca, Romania, was analyzed for the period 1921 to 2009. In order to sustain the results from Cluj-Napoca, we had to add into analysis other two surroundings stations: Bistrita and Sibiu, because using only one meteorological station might be considered irrelevant. Also, we used into analysis the sunshine duration to make a good comparison with the evolution of global solar radiation. Four test methods have been performed on the data to test the series for homogeneity as follows: the Pettitt’s test, the standard normal homogeneity test (SNHT) for a single break, the Buishand range test and the Von Neumann’s ratio test. Different statistical procedures like regression models, Runs test and cumulative curve of the global solar radiation and precipitation standardized anomaly were used to find the most appropriate expression of the annual mean GSR and average amount of precipitation interannual evolution. The parametric analysis with regression models showed significant increasing trends for global solar radiation, sunshine duration and precipitation, the quadratic trend model providing a better fit than the linear and exponential models. To verify if the radiation, sunshine duration and precipitation variations were caused by trend or oscillation in the data, we used in the nonparametric analysis the Runs test. The results of Runs test detected significant trends for GSR and sunshine duration at Bistrita and Sibiu. Concerning to precipitation, the test didn’t clearly detect any trend or oscillation at the three stations. The shape of the cumulative curve suggests that in the last two decades the general tendency is towards increasing annual global solar radiation at all three stations and the observed fluctuations represent a microcycle or microcycles (for example, Sibiu), as a result of the normal variations of the climate, which in the last few years is/are reacting to the solar variations. The decreasing tendency of the annual precipitation could be ascribed to solar activity, which is known that plays an important role in influencing the precipitation on land, and the consequence of this fact is that precipitation is closely related to the variation of sunspot numbers. Therefore, it is the most probably that this increasing in GSR and increasing/decreasing in precipitation represents the ascensional or descensional parts of some natural micro-oscillations due to solar activity/variations and natural climate variability.