Atmospheric precipitations, water discharge and inundations in the Moldavian plain

Abstract : One of the major challenges of this century is represented by climatic changes and their influence upon the environment. In the case of Romania, the orographic barrier plays the most important role in the delineation of surplus or deficient areas as refered to humidity. In the western and central regions of Romania, with oceanic influences, there is an surplus of humidity, while in the southern, south-eastern and eastern regions, with continental influences, there is a deficient humidity that generates dryness phenomena and drought. Non-the-less, we notice, in the last years, contrast situations with particularities in those regions affected by dryness and drought where there is an surplus of humidity. Climatic change at global or local level represent a major problem and induce concern among researchers from various disciplines (meteorology, climatology, geomorphology, ecology, hydrology, biology, medicine, sociology etc.) in consideration of change that might produce major setbacks in all the life domains and the socio-economic activities. In this respect, knowledge, research and investigation at detailed level of local and regional meteorological conditions that induce triggering situations for atmospheric hazards generating risks, human and economic losses, sometimes hard to estimate, develop in significant and full of concern attitudes in contemporary times. In the Moldavian Plain, due to the torrential character of most of the rivers, maximum discharge risk management is still difficult for the tributary/secondary streams. Even if the Jijia watershed, with the main stream of the Moldavian Plain, dispalys numerous water storages since 1960 to 1990, being one of the most systematized hydrographic basins, with tens of kilometers of dams and enbankments, the risks of maximum channel discharge and hillside discharge is still present. The intention of realizing a doctoral study on the Atmospheric precipitations, water discharge and inundations in the Moldavian Plain comes as a result of concerns in this respect and need to identify the natural risks and to evaluate the human activities as a perspective of risk – benefit for the efficient management of natural resources or in the attempt to favour sustainable development. Although floods are natural phenomena, with time repetability, as discharge processes along riverbeds, inundations represent, in modern times, one of the main causes of human and material losses. The analyses of the obtained maps regarding annual precipitations quantities in the Moldavian Plain reveal the decreasing trend from west to east, along with the decrease in overall altitudes and lower frequencies of humid air masses to the east (drier air masses), compared to more humid, Atlantic, air masses to the west. Torrential rains are atmospheric phenomena with short duration influence but with great intensity, upon the environment via erosion and flooding. They consist in increased precipitation quantities on short time intervals, sudden change of intensity along with extension of duration. As far as the vulnerability of the Moldavian Plain to the suumer rains we notice that the northern half displays an intermediate vulnerability while the southern half diplays a higher vulnerability. We also notice that for the whole space east, south-east and south of the Carpathians is vulnerable to an apreciable extent to torrential rains with intermediate and high intensities. In figure 5.32 we also observe that in those areas where oceanic influences predominate, rains have a less violent character and in those areas where continental influence pedominate (as the case of the Moldavian Plain) torrentail rains have a more violent character. In the Moldavian Plain the degree of vulnerability of torrential summer rains increases from WNW to SSE. Torrential rains bring a great pluviometric input that can reach a monthly quantity of 172.1 mm in July at Botosani and 277.2 mm in June 1985 at Iasi. The May-September interval remains the of the greates torrential rains with high and exceptional quantities of rain. The hydrological regime depends to a great extent on the hydrological network which constitutes an important assembly that limits the influence of the geographical factors. The dimensional characteristics of the rivers and of the source watersheds influence the volume of the received precipitations and the necessary time for main streams catchment and watershed output. These characteristics impose, finally, the volume of the liquid discharge. In order to determine the cyclic character of the discharge for the hydrometric stations in the Moldavian Plain we calculated the gliding averages on 5 years for the average values of the annual debits. By graphically transpose the results we observe that all the hydrometric stations present two periods of increase on rivers; the first period between 1965 and 1984 and the second period between 1995 and 2010, determined by the precipitations’ increase. Inside the first period we notice two important peaks in the rivers discharge corresponding to 1969 and 1982. The characterization of the variability of annual debits for a certain period, as reported to the multi-annual debit is suggestively expressed via the variation coefficient (Cv). For the rivers in NE Moldavia the values of Cv for the annual average debits oscillates between 0.07 on Bahlui, at Hârlau and 0.78 on Jijia, at Victoria. Comparing these results with the ones calculated by S. Dumitrescu (1964) for 38 characteristic points in Romania we infer that, in the main basins of the Moldavian Plain, the annual average debits are very unstable, mainly as a consequence of the excessive continental climate. Along the year, the maximum debits present larger or narrower variations from one month to another as a result of the pluviometric particularities. At the level of the Moldavian Plain, the maximum debits occur, more frequently, in the May-July interval (40% of the cases), followed by the March-April interval (30% of the cases). The month of June holds a percentage of 20 in the Upper Jijia Plain and 19 in the Lower Jijia Plain. The most important floods in the Moldavian Plain, between 1960-2011, appeared, in general in summer from June to July. In the above mentioned period, important floods appeared in: 1961, 1965, 1969, 1970, 1973, 1974, 1978, 1979, 1980, 1981, 1985, 1988, 1989, 1991, 1993, 1996, 2005, 2008 and 2010 with certain differences as a function of local conditions. Regarding the medium duration of the floods we notice that on the rivers of the Moldavian Plain they rarely exceed 4 days, in great majority one day or two. The most floods were registered on the interior rivers, respectively 62.9% and only 27.1% on Prut. In the Moldavian Plain the hydrologic risk is considerable and it manifests not only on the main streams but also on the affluents. The geographic position of the plain and the torrential rains determined by the cyclonical activity specificity of this zone creates favourable conditions for the appearance of flash floods in 73 basins. The increased precipitations quantities in short time produce very high debits, debits which, in the majority of occasions cannot be delivered by the minor river beds. In the case of the 49 localities that are directly exposed the maintaining of the transit capacity for the river bed is of maximum importance to prevent inundations. The climatic change and irregular territorial development that is insufficiently planned for inundations prevention and the increased erosion potential result in economical and social vulnerabilities as far as the floods risk in concerned is the Moldavian Plain.
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Marian-Daniel Buruiana. Atmospheric precipitations, water discharge and inundations in the Moldavian plain. Geography. Université de Lorraine, 2015. English. ⟨NNT : 2015LORR0251⟩. ⟨tel-01754603⟩

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