Assessment of hydroclimatic trends in Southeast Europe – Examples from two adjacent countries (Bosnia & Herzegovina and Serbia)

Water quantity is often analyzed throughout mean annual and seasonal discharges in various studies worldwide. This paper aims to present water discharge trends in the lower parts of the Una, Sana, and Vrbanja rivers in Bosnia and Herzegovina and the largest Serbian national river Velika Morava and its tributaries Jasenica and Resava rivers in Serbia for the period 1961–2020. Also, the paper examines air temperature and precipitation trends and their connection with discharge trends. Mann-Kendall test was applied for the determination of trends in air temperature, precipitation, and discharges; the Sen's nonparametric estimator was utilized for establishing the magnitude of the trend, while the t-test was used for determining the statistical significance of the trend. In order to determine possible changes, two periods were observed: 1961–1990 and 1991–2020. Results showed statistically insignificant changes in discharges and precipitation trends on annual and seasonal levels. On the other hand, a significant air temperature increase was recorded in the period 1991–2020, with the highest increase during the summer. The most significant increase was observed in Banja Luka due to urban heat island effect in this city.