engleski

Trends in cooling degree-days for five locations in Croatia

The cooling degree-days (CDD) and number of cooling days (CD) over the period 1901-2008 are analyzed at five stations that represent different climatic regions in Croatia. The stations under consideration are: Osijek in the southern lowland of Pannonian Plain, Zagreb - Griˇc at the furthest south-eastern edge of the Julian Alps, Gospi´c in highland - hinterland of the Dinaric Alps, Crikvenica on the north-eastern Adriatic coast and Hvar on the mid - Adriatic island with the same name. Calculation of CDDs and counting of CDs are performed for the 18°C, 21°C and 23°C temperature thresholds that represent daily mean air temperature. Daily mean temperature (M) is calculated by using daily temperatures measured at 7 a.m. (t7), 2 p.m. (t14) and 9 p.m. (t21), in the following way: M=(t7+t14+2t21)/4. Linear trends over the period 1901-2008 are determined for each month as well as for the whole year (annual trend). Statistical significances of the trends are tested using the non-parametric Mann - Kendal test. For the months with the greatest potential cooling demands - June, July and August, the increasing trend is detected for almost all analyzed values at five locations. Namely, only for the August CD (threshold 18°C) for Hvar area and for the June and August CDDs (threshold 23°C) for Gospi´c area are detected slightly decreasing trends. Most slightly decreasing trends are discovered for September for both parameters at Osijek, Zagreb and Gospi´c area. Annual trends in both parameters for all locations are increasing, except the annual Gospi´c CDD (threshold 23°C) trend that is slightly decreasing. According to the Mann - Kendal test neither of the annual trends in CDD and CD for three temperature thresholds are statistically significant at 0.05 significance level in Gospi´c and Osijek. On the contrary, all of the mentioned annual trends are significant in Zagreb and Crikvenica, and almost all in Hvar (except trends in CD for the 21°C and 23°C thresholds). Months with the significant trends in most of analyzed values are: May and June in Osijek, May, June and July in Zagreb, June in Gospi´c, June, July and August in Crikvenica and July in Hvar.

cooling degree-day; number of cooling days; trend; Mann-Kendall rank test

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