The objective of this chapter is to highlight the seasonal statistical variability of rainfalls in Danube Delta and Dobrogea Tableland (Romania), considering the extreme and outliers values. The geomorphological and evaporimetric features of this region are also mentioned. Area of study is a complex geographical region, with two major units: the Dobrogea Tableland and the Danube Delta spread over 14,695 sq. km in the south-eastern part of Romania. The outcomes show that the minimum and maximum values of the lower quartile median and of the upper quartile median with the highest values occur in summer. The lowest values occur for all the indicators during winter and there are intermediate values for all indicators during autumn and spring. Regarding the seasonal variability of rainfalls, it has a mosaic distribution of the outliers and extreme values. The extreme values record a small number of values, both in autumn and summer. The maximum number of extreme values is during spring and winter. The drought is amplified by evaporation from water surface in summer.
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The aim of this paper is to highlight the seasonal statistical variability of rainfalls in Danube Delta and Dobrogea (is also known as Dobrudja - in English, Dobroudja in French), considering the extreme and outliers values. The geomorphologic and evaporimetric features are mentioned, too. Rainfalls are one of the main factors of the hydrological regime because they contribute to the emergence of water excess and hydrological drought (Haidu, Sorocovschi, & Imes, 2003; Sorocovschi, Tudose, Selagea, & Roman, 2010).
The importance of knowing the precipitations quantity comes from the utility of the resource, both as the main power source of the hydrographic arteries and as a necessary irrigation source. The hydrological effect of rainfalls on the water resources, especially on rivers, is strongly determined by the periodic variability of the rainfalls and evaporation. The hydrological elements of flow hydrograph (shape, timing and peak flow) are significantly influenced by spatial and temporal variability of rainfalls (Singh, 1997). Some studies investigated the effect of seasonal rainfalls variability on streamflow (Beven & Hornberger, 1982; Berndtsson & Niemcaynowicz, 1988; Krajewski, Lakshmi, Georgakakos, & Jain, 1991; Obled, Wendling, & Beven, 1994; Arnaud, Bouvier, Cisneros, & Dominguez, 2002; Arnaud, Lavabre, Fouchier, Diss, & Javelle, 2011).
Geographically, multiple and complex scientific studies, aimed at a deep knowledge, both monographic and applicable, were done on the region of Dobrogea. Among the relevant studies, we mention those of the following authors: Ionesi (1994); Zugrăvescu, Polonic, Horomnea, & Dragomir (1998) in geology; Conea (1970), Badea, Băcăuanu, & Posea, (1983), Posea & Badea (1984), Popescu & Ielenicz (2003), Ielenicz (1999), Panin (1989, 2003), Posea (2006), Vespremeanu-Stroe, Constantinescu, Tătui, & Giosan (2007) concerning the relief; Ciulache & Torică (2003); Păltineanu, Mihăilescu, Seceleanu, Dragotă, & Vasenciuc (2007), Tişcovschi, Manea, Cocoş, Vijulie, & Cuculici (2013), Şerban, Maftei, & Bărbulescu (2010) on climate; Ujvari (1972), Gâştescu (1971), Zaharia & Pişota (2003), Telteu, Stan, Brănescu, & Berghezan (2013) in the field of hydrology.