A Review of Extreme Air Temperature Analysis in Croatia

Abstract

A historical review of extreme air temperature analysis in Croatia is presented. Two capital works on the subject were published in the 1970s by the Croatian Meteorological and Hydrological Service (DHMZ) and Faculty of Science University of Zagreb (PMF-Zagreb), respectively. The first is a monography on extreme value theory or extreme value analysis (EVA) with an application on more than a century-long time series of annual minima air temperature for Zagreb Grič weather station (Croatia) for the period 1862–1969. It is just a case study, with a lot of instructions regarding how to estimate the generalized extreme value (GEV) distribution parameters. The second is a master’s thesis with an application of the EVA on maxima air temperature time series for 41 weather stations from Croatia for the period 1950–1969. The shortness of the time series of the presented data caused instability in the estimation of GEV distribution parameters in transition areas from continental to maritime climate, but in general, the results are acceptable after a reduction of the 1950–1969 time series data on a ‘normal climate period’ 1910–1969. Both works were pioneering for that time in the South-Eastern Europe scale. A routine application of GEV distribution on the extreme air temperature (both minimum and maximum) for ten representative weather stations from Croatia is represented in Climate atlas of Croatia for the period 1961–1990, published by DHMZ in 2008. Theoretically estimated results fit well with empirical data. A review of long-term “warm” and “cold” indices of extreme air temperature for 41 weather stations from Croatia for the period 1951–2010 is represented in the Sixth National Communication Report of Croatia under the UNFCCC published by the Ministry for Environment and Nature Protection of Croatia (MZOIP) in 2014, showing a positive trend of “warm” and a negative trend of “cold” indices during the period 1951–2010 which tackled the non-stationarity of extreme air temperature time series. That topic of non-stationarity is more extensively considered using the results of a series of scientific papers published in the international journals which conducted a study of extreme air temperature of the wider Western Europe territory, including Croatia and other countries close to Croatia. Some authors of these papers stated that the GEV distribution parameters have to be considered as a function of time rather than fixed in time using covariates like North Atlantic Oscillation (NAO), coherent atmospheric blocking regions, linear trends in data caused by global warming and others covariates. The EVA results, connected with the global climate warming, could contribute to the national Natural Disaster Risk Reduction (NDRR) efforts.