engleski

Trend analysis of mean and high river flows from stations in karstic Kupa catchment

Trends of mean and high river flows from three hydrological stations on watercourses of the Kupa River (Kupari, Kamanje), tributary Čabranka (Zamost 2) and one meteorological station (Parg) were analysed. The paper focuses on five indicators: annual mean flow, seasonal mean flows (winter and summer mean flows), instantaneous annual maximum flow and annual precipitation. Analysed time series range from 1951 to 2013, and the fixed period ranges from 1984 to 2013. Time series of each indicator was scaled to standardized flow anomaly and was analysed using the Mann-Kendall Z test for monotonic trend, after which it is smoothed using LOESS algorithm. The analysis was conducted for each indicator for full record, e.g. 1951-2013, then 1952-2013 and so on until 1984-2013. Thus, the sample size varies from 63 to 30 years. The smoothed standardized flow anomaly, expressed in standard deviations per year, is easily comparable among different hydrologic stations. The standardized flow anomaly on all analysed stations shows undisrupted periodicity of annual mean flow, instantaneous annual maximum flow and annual precipitation up until the mid-80s, after which the periodicity was disrupted. Further analysis of summer and winter seasonal mean flows revealed different deviation from long-term annual flow average. Negative trends of certain indicators were proven using Mann-Kendall Z test, by plotting Z values for each iteration of start year (1951 to 1984).

climate change; Mann-Kendall; precipitation; river flows; trend

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