NEW PROPOSALS FOR THE HYDROLOGY OF THE OMBLA KARST SPRING

The Ombla karst spring is probably the most abundant karst spring in the Dinaric karst. The paper focuses on the analysis of its water temperature. Available data were those of hourly measurements in the period from January 1, 2007 at 0 a.m. to December 31, 2021 at 11 p.m. The analyses were conducted at different time scales (a year, month, day and hour). It was determined that there were two sub-periods within this period, with different characteristic water temperatures (minimum, average and maximum). In the first sub-period from January 1, 2007 at 0 a.m. to January 24, 2012 at 8 a.m., the values of minimum, average and maximum water temperatures were 12.5 degrees C, 13.83 degrees C and 15.0 degrees C, respectively. In the second sub-period from January 24, 2012 at 9 a.m. to December 31, 2021 at 11 p.m., there was a sudden drop in characteristic temperatures of 10.9 degrees C, 12.91 degrees C and 14.0 degrees C, respectively. We attempted to determine the reasons for these sudden changes, i.e. a drop of about 1 degrees C by comparing them with air temperatures measured at the Dubrovnik station and the Ombla spring discharges. Unfortunately, the Ombla spring discharges have not been measured since January 1, 2015 onward. It was determined that the water temperatures reacted to air temperatures with approximately 1-month delay. Due to enormous importance of this karst spring, it is necessary to determine the reasons that lead to the sudden drop in the water temperatures at the end of January 2012.