Open access book on Prognosis of hydrological drought development in Slovakia

Prognosis of hydrological drought development in Slovakia (Miriam Fendeková and Lotta Blaškovičová Eds., 2018)

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The monograph is the contribution of the Slovak scientific community to the international UNESCO-IHP VIII FRIEND-Water programme, the EUROFRIEND – Low Flow and Drought group. The book is the condensed English version of the monograph which was published as the result of the research project financed by the Slovak Research and Development Agency No. APVV-0089-12 in Slovak language in 2017. The large team of authors from the Comenius University in Bratislava and the Slovak Hydrometeorological Institute in Bratislava took part in the research activities. Tobias Gauster from the BOKU Vienna and Pavla Pekárová from the Institute of Hydrology of the SAS in Bratislava also contributed to the research results.

The main goal of the research was to assess drought occurrence in Slovakia between 1981 and 2012 and to use models for drought development prediction to 2100. Research was based on daily discharge data from ten main river basins approximately equally distributed throughout Slovak territory in the differing climatic, hydrological and hydrogeological conditions which form the mutual interrelationship of the hydrological balance equation elements. The river basins were: the Myjava (western Slovakia), the upper Váh and the Kysuca (north-western Slovakia), the Poprad (northern Slovakia), the Hron and the Nitra (central Slovakia), the Ipeľ and the Rimava (southern Slovakia) and the Torysa and the Topľa (eastern Slovakia). The hydrological conditions and drought occurrence were evaluated in detail in daily, monthly and annual steps. Hydrological data were correlated with data on meteorological conditions in the evaluated river basins; and hence throughout Slovakia.

Detailed analysis of 1981–2012 meteorological and hydrological conditions established meteorological and hydrological drought occurrence. As the first step, the climatic scenarios data were prepared to be used in hydrological models. The Netherlands KNMI and German MPI regional climatic models (RCMs) were both used in two different scenarios. The latest observations have confirmed that predicted climate change progress presents quite realistic alternatives for future Slovak climate development. These have indicated that future climate development is not very favourable for Slovakia; with negative consequences outweighing the positive. Moreover, climate change scenarios anticipate further aridity in southern Slovakia and climate zone shift to higher altitudes in the north.

The FRIER spatially distributed physical model was the main tool used in prognosis of future drought development. FRIER model prediction of development of the hydrological balance elements provided the following results: (1) while we can anticipate less meteorological drought periods for 1981–2100, greater water deficits are predicted; (2) the future unsaturated zone drought should last longer with greater deficit volumes and (3) although the saturated zone droughts should last approximately as long as at present, the drought duration could also be much longer and deficit volumes much larger.

Both KNMI 2 and MPI 1 models gave similar seasonality change prognosis. They predict a general increase in precipitation amounts, shifts in the highest precipitation amounts from July to September and less precipitation from May to July. Air temperature should increase; mainly during the winter period and this could cause less snow accumulation and increased winter snow-melt runoff. While the onset of dry periods should be more frequent, with low precipitation, low runoff and less water storage, the most pronounced seasonality change is expected to evapotranspiration. The expectation of change to spatial distribution in hydrological balance elements from the 1981–2012 reference period to 2069–2100 was also done.

Groundwater drought occurrence evaluation showed that most dry years in the evaluated 1981–2012 period occurred before 1993; even allowing for the five-year drought between 1989 and 1993. The most intense droughts in these five years were in 1990 and 1993. The groundwater drought evaluation results correspond well with the established discharge trends, and this evaluation documents the important percentage of identified decreasing discharge trends before 2001. Finally, following the 1993 wet spell, droughts occurred only in 2003, 2004, 2007, and also in 2012 which was the most intense event. Detailed study was also performed on the seasonality of yields from 78 springs in mountainous Slovak areas; with emphasis on minimum yields. The average and minimum spring yield seasonality was evaluated by Burn vector and frequency histograms. These evaluations were followed by minimum spring yield regionalisation based on the combined physical-geographical factors of precipitation, air temperature, spring discharge area altitude, slope orientation and the rock hydraulic properties expressed as transmissivity coefficient. The regionalisation results for these minimum spring yield parameters were similar, thus reflecting the dominant influence of spring discharge area altitude and enabled to delineate three regions with different minimum spring yields seasonality.

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