The study aims to analyse the impact of the drought phenomenon on groundwater in Dobrogea Plateau, taking into account the specific climatic and hydrological factors and especially the geological and structural context in which it delineates the main hydrostructures. The groundwater is subject to climatic and anthropogenic impacts whose weight are difficult to assess, so until now, a hydrogeological drought index was not identified. The effects of climate change impact are reflected in the fluctuations of the piezometric surface of the shallow aquifers, the deepest aquifers being influenced rather by socio-economic issues. To achieve the objective of the research, the available data (climate, hydrological and hydrogeological) were processed using GIS and Excel softs and the results (maps, graphs, tables) were interpreted and correlated in some relevant conclusions.
TopBackground
In terms of climate it is remarkable that arid regions do not necessarily coincide with the dry ones and there is no natural altitudinal setting, which is a specific geographical feature in Romania. Arid regions can register very rainy intervals, with torrential that often lead to flood. Therefore, there is a clear difference between drought and aridity, although sometimes they are confused. Aridity is a permanent feature of reduced average precipitation, while the drought is a temporary feature of any region. This idea must be completed indicating that low rainfall of arid regions are associated with high evapotranspiration (Dragotă et al, 2007).
In terms of the distribution of aridity index, which highlights water scarcity by relating annual rainfall amounts to annual potential evapotranspiration, Dobrogea territory is characterized by aridity index values less than 0.7, as a large area along Danube valley and in the eastern part of the Romanian Plain. The lowest values of 0.5, is recorded in the eastern extremity of the Danube Delta (Sulina, 0.37), which marks the boundary between the dry sub-humid climate and semiarid climate (Clima României, 2008).
Also, the terms “drought event definition” and “drought index” are frequently being confused. A drought index is often a single number characterising the general drought behaviour at a measurement site, whereas a drought event definition is applied to select drought events in a time series including the beginning and end of the droughts (Hisdal & Tallaksen, 2000).
Regarding the drought definitions, a meteorological drought in terms of lack of precipitation is the primary cause of a drought. It usually first leads to an agricultural drought due to lack of soil water. If precipitation deficiencies continue a hydrological drought in terms of surface water deficits develops. The groundwater is usually the last to be affected, but also the last to return to normal water levels.
In the literature groundwater drought event definitions are rare. A conceptual definition is given by Calow et al. (1999): “We use the term ‘groundwater drought’ to describe a situation where groundwater sources fail as a direct consequence of drought” (p. 256).