Novije promjene srednjih godišnjih i sezonskih protoka rijeka u Hrvatskoj

This paper presents the first comprehensive nationwide trend detection of mean discharges in Croatia. Over the last 30 years, global climate change has manifested itself largely in the rise of the average annual temperature, which has resulted in the changes of evapotranspiration and precipitation patterns. The consequences of those changes have been varied spatial impacts on river discharge (flow). We analysed the changes in mean river discharges in Croatia at 53 gauging hydrological stations over the most recent period from 1990 to 2009. To assess the trend, the Kendall-Theil (Sen) non parametric trend test was carried out for the yearly and seasonal mean discharge values. We found evidence of redistribution of discharge throughout the year, an increase in autumn and winter discharges (especially on the rivers dominantly fed by snowmelt) and a decrease in summer discharge values. Furthermore, we detected a change in the month of the appearance of mean discharge maxima and minima. In most cases the changes can be explained by the changes in the regime of climate elements (temperature, precipitation, evapotranspiration) although that information should be treated with care because of the shortness of the time-series. The results are consistent with the ones from the upstream countries, i.e. Slovenia and Austria.U radu se iznose rezultati prve sveobuhvatne analize suvremenih promjena srednjih mjesečnih protoka rijeka u Hrvatskoj. U posljednjih tridesetak godina globalne promjene klime uglavnom se očituju kroz porast srednje godišnje temperature zraka, što za posljedicu ima promjene u prostornoj i vremenskoj distribuciji padalina i vrijednosti evapotranspiracije. Te promjene imaju različite prostorne posljedice na protoke i protočne (riječne) režime rijeka. U ovom istraživanju analizirane su promjene srednjih protoka rijeka u Hrvatskoj na 53 hidrološke stanice od 1990. do 2009. Za analizu trenda na godišnjoj i sezonskoj razini upotrijebljen je Kendall-Theilov (odnosno Senov) test. Utvrđeno je postojanje preraspodjele protoka unutar godine, povećanje jesenskih i zimskih srednjih protoka (osobito na rijekama sa značajnijim udjelom sniježnice) i smanjenje ljetnih protoka. Uočene su i promjene u mjesecu javljanja maksimuma i minimum srednjih protoka, koje se u većini slučajeva mogu objasniti promjenama u režimu klimatskih elemenata (temperature, padalina i evapotranspiracije) iako rezultate treba uzimati s dozom opreza zbog kratkoće analiziranog niza. Rezultati istraživanja uglavnom se poklapaju s rezultatima sličnih istraživanja u nama uzvodnim zemljama (Slovenija i Austrija)

Changes in discharge regimes of rivers in Croatia

This paper presents the results of the first comprehensive national analysis of changes in discharge regimes of rivers in Croatia. Seven types of discharge regimes have been defined for rivers in Croatia. We analyzed the changes in discharge regimes of all types, comparing the standard period from 1961 to 1990 with the most recent period from 1990 to 2009. We found evidence of a redistribution of discharge throughout the year, an increase in autumn and winter discharges (especially for rivers dominantly fed by snowmelt), and a decrease in summer discharge values. Furthermore, we detected a change in the month of the appearance of mean discharge maxima and minima. In most cases, the changes can be explained by changes in the regime of climate elements (temperature, precipitation, and evapotranspiration). The results are consistent with those from upstream countries; that is, Slovenia, Austria, and Bosnia and Herzegovina