Hidrológiai Közlöny, 2017 (97. évfolyam)
2017 / 3. szám - MANAGING WATER QUALITY (ONGOING PROJECTS AND FUTURE CHALLENGES) - Rehák, Štefan - Vranovská, Andrea - Adam, Štefan - Kopčová, Ľubica: Hydrological balance of water resources for agriculture in the Slovakian part of the Danube Region
54 Hidrológiai Közlöny (Hungarian Journal of Hydrology) 2017. 97. évf. 3. sz. Hydrological balance of water resources for agriculture in the Slovakian part of the Danube Region Stefan Rehák2, Andrea Vranovská2, Stefan Adam1, Cubica Kopcová2 1 Ministry of Foreign Affairs of the Slovak Republic 2 Water Research Institute Abstract According to climate scenarios and outputs of models of general circulation of atmosphere, what can be expected is an extraordinary increase in precipitation totals as well as an increase in the number of days without any precipitation. These facts will impact the stability of agricultural production, especially in lowland areas. The area of land with water deficit has increased and the moisture demand of crops has also increased. However, the disposable resources of irrigation water are decreasing, whichwill limit the extension of irrigation. The areas with water deficit have been determined according to the ratio of actual and potential evapotranspiration E/Eo. The irrigation demand of crops was calculated with the help of model Daisy. Disposable resources of irrigation water were evaluated with the help of hydrological balance according to scenarios CCCM for time horizons 2030 and 2075. Keywords Evapotranspiration, moisture demand of crops, water deficit, disposable water resources INTRODUCTION The necessary amount of water in the soil and its proper distribution during the vegetation period is an indispensable condition for successful soil management. Irrigation optimizes the moisture regime of the soil through the demands of plants and therefore it is a significant part of production-cultivation technologies of field crops and production of fruit and vegetables. Analyses have proved that several river basins will have a tense hydrological balance in the near future and some of them will even have a passive hydrological balance, which will limit water abstraction for agriculture including water abstraction for irrigation. MATERIAL AND METHODS High intensity agricultural production in lowlands is conditioned by high solar radiation and natural soil fertility and requires corresponding levels of inputs and further production factors (fertilizers, pesticides and the most efficient seeds). Growing the main crops requires irrigation in lowlands because permanent dry vegetation periods are regularly repeated. Water as a non-alternative production factor significantly affects the stability and production of agro-ecosystems in agricultural production areas. The areas with moisture deficit were identified on the basis of climate regions and soil parameters of agricultural production areas (Buday and Vilcek 2013). However, evapotranspiration was chosen as the determining factor: the ratio of actual (E) and potential evapotranspiration (Eo) during a representative period, so-called relative evapotranspiration (E/Eo). DISTRIBUTION OF RELATIVE EVAPOTRANSPIRATION IN SLOVAKIA It has been shown by several studies that the optimal growth conditions of field crops mean that the actual evapotranspiration (E) only slightly differs from potential evapotranspiration (Eo), which is understood as the maximum possible evapotranspiration in given climate conditions if the surface root soil layer contains enough water for the normal growth of field crops (Rehák 1994, Sátor et al. 2007). Relative evapotranspiration and evapotranspiration deficit (Eo-E) make it possible to quantify the lack of water in the soil for the optimal growth of crops, which means that the amount of water needed for irrigation can be determined. The background for the assessment of relative evapotranspiration in the territory of Slovakia was a model calculation of monthly totals of potential and actual evapotranspiration during vegetation period at 32 meteorological stations in the period between 1981 and 2010. Annual values E/ Eo were used as supplementary data for the period between 1951 and 1980 at 54 stations. E and Eo monthly totals were calculated by the application of a method based on a common solution of the equations of energetic and water surface balance. A mathematical model was designed at the Department of Meteorology and Climatology of the Faculty of Mathematics and Physics at the Comenius University in Bratislava. On average, the smallest annual values E/ Eo during the period between 1981 and 2010 were recorded in the Danube Lowland (E/ Eo < 60 %), which is the warmest and driest area in Slovakia. The Western part of Záhorie Lowland, Southern Slovakia and the Southern part of the Eastern Slovakia Lowland are characterized by a relative evapotranspiration smaller than 65% on average annually. In the Southern part of Kosice Basin, South-Western Slovakia, the Eastern part of the Záhorie Lowland, Pov- azie South of Trencin, middle Ponitrie, the central part of Eastern Slovakia Lowland South of Michalovce and in the South-Eastern part of the Zvolen Basin, the average annual value E/Eo is smaller than 70%. In the north of Slovakia, mainly in the mountains, there is enough precipitation the whole year round and therefore annual values of relative evapotranspiration are higher than 90%.
