A warming climate is expected to have an impact on the magnitude and timing of river floods; however, no consistent large-scale climate change signal in observed flood magnitudes has been identified so far. We analyzed the timing of river floods in Europe over the past five decades, using a pan-European database from 4262 observational hydrometric stations, and found clear patterns of change in flood timing. Warmer temperatures have led to earlier spring snowmelt floods throughout northeastern Europe; delayed winter storms associated with polar warming have led to later winter floods around the North Sea and some sectors of the Mediterranean coast; and earlier soil moisture maxima have led to earlier winter floods in western Europe. Our results highlight the existence of a clear climate signal in flood observations at the continental scale.

Climate change has led to concerns about increasing river floods resulting from the greater water-holding capacity of a warmer atmosphere 1 . These concerns are reinforced by evidence of increasing economic losses associated with flooding in many parts of the world, including Europe 2 . Any changes in river floods would have lasting implications for the design of flood protection measures and flood risk zoning. However, existing studies have been unable to identify a consistent continental-scale climatic-change signal in flood discharge observations in Europe 3 , because of the limited spatial coverage and number of hydrometric stations. Here we demonstrate clear regional patterns of both increases and decreases in observed river flood discharges in the past five decades in Europe, which are manifestations of a changing climate. Our results-arising from the most complete database of European flooding so farsuggest that: increasing autumn and winter rainfall has resulted in increasing floods in northwestern Europe; decreasing precipitation and increasing evaporation have led to decreasing floods in medium and large catchments in southern Europe; and decreasing snow cover and snowmelt, resulting from warmer temperatures, have led to decreasing floods in eastern Europe. Regional flood discharge trends in Europe range from an increase of about 11 per cent per decade to a decrease of 23 per cent. Notwithstanding the spatial and temporal heterogeneity of the observational record, the flood changes identified here are broadly consistent with climate model projections for the next century 4,5 , suggesting that climatedriven changes are already happening and supporting calls for the consideration of climate change in flood risk management.River floods are among the most costly natural hazards. Global annual average losses are estimated at US$104 billion 6 and are expected to increase with economic growth, urbanization and climatic change 2,7 . Physical arguments of increased heavy precipitation resulting from the enhanced water-holding capacity of a warmer atmosphere and

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This paper presents the fi rst 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 (fl ow). 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.Key words: discharge, trends, Croatia, rivers, hydrology, geography Novije promjene srednjih godišnjih i sezonskih protoka rijeka u Hrvatskoj 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 godiš-njoj 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).

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