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Accueil du site → Doctorat → Espagne → 2016 → Spatial and Temporal Characteristics of Precipitation Variability and Drought Patterns in the Eastern Mediterranean.

Universitat de Barcelona (2016)

Spatial and Temporal Characteristics of Precipitation Variability and Drought Patterns in the Eastern Mediterranean.

Mathbout, Shifa

Titre : Spatial and Temporal Characteristics of Precipitation Variability and Drought Patterns in the Eastern Mediterranean.

Auteur : Mathbout, Shifa

Université de soutenance : Universitat de Barcelona

Grade : Doctor of Geography 2016

Résumé
As precipitation is a very important parameter of climate and hydrology, exploring spatial and temporal distribution and variation of this variable can give an idea about climate conditions and water resources in the future. Therefore accurate mapping of the temporal and spatial distributions of precipitation is important for many applications in hydrology, climatology, agronomy, ecology and other environmental sciences. In this thesis, spatiotemporal distributions and variations of total annual, seasonal and monthly precipitation of the Eastern Mediterranean (EM) are analysed. The Eastern Mediterranean is one of the most prominent hot spot of climate change in the world further ; extreme climatic events such as drought are expected to become more frequent and intense in this region. Main data source is instrumental data of monthly and daily precipitation at 103 and 70 meteorological stations, respectively. Spatial coherence analysis, coefficient of variation (CV), rainfall seasonality index (SI), incomplete gamma distribution and precipitation concentration index (PCI) are applied to evaluate the seasonality and variability of annual, seasonal and monthly precipitation amounts and their distribution. Daily precipitation concentration index (CI) is used as an important index for specifying daily rainfall characteristics. Additionally, rainfall entropy is also calculated for monthly and daily data for finding the most suitable probability distribution under the available information. High to moderate irregularity and rainfall concentration are the two very characteristic features of rainfall in the EM. Highest values of daily CI are detected in the southern parts of the EM. Distribution of annual precipitation CI trends indicate a statistically significant increase in the northern and northwestern regions of the EM. Four meteorological drought indices (DIs) are calculated at monthly time scale, the Standardized Precipitation Index (SPI), the Modified China Z Index (MCZI), the Statistical Z -scores and the Rainfall Decile based Drought Index (DI) while the Effective Drought Index (EDI) is calculated at daily time scale. All selected DIs with multiple time steps are applied to compute the severity for five time steps of 3, 6, 9, 12 and 24-month, and compared with each other and EDI. The most significant factor affecting the spatial accuracy of drought indices is seasonality. Study of DIs shows that the DIs are highly correlated at same time steps and can alternatively be used and the DIs computed for 6 and 9-month time step are best correlated with each other. SPI and MCZI are more consistent in detecting droughts for different time steps. EDI is found to be best correlated with other DIs when considering all time steps. The investigation shows that the use of an appropriate time step is as important as the type of DI used to identify drought severities. Principal Component Analysis (PCA) is employed and reveals the main modes and spatiotemporal variability of seasonal and annual precipitation and droughts over the EM. The preliminary analysis indicated tendencies towards a drier climate due to a statistically significant decrease in annual precipitation over the EM. The analysis of indicators of extreme events reveals a much more complex transformation of the climatic pattern with strong regional and seasonal variation. The results demonstrated that an extreme wet spells in the EM will shorten in all seasons, except autumn. Precipitation extremes are projected to become more pronounced in the northern parts of the EM than in southern ones and tend to be more significant during autumn. Extreme and heavy precipitation events showed a statistically significant decrease in whole parts of the EM and in the southern ones, respectively with a significant decreasing in total precipitation amount. A significant increase in daily intense precipitation events in the northern parts of the EM. In addition, climate extreme indices recommended by the joint World Meteorological Organization (CCL/CLIVAR/JCOMM) Expert Team on Climate Change Detection and Indices (ETCCDI) are also calculated for daily precipitation data. Finally, Mann- Kendall test, cumulative sum chart (CUSUM), regime shift index (RSI) calculated by a sequential algorithm are applied for detecting the shifts in the means of seasonal and annual precipitations. Mann-Kendall test and the linear slopes of trends are calculated using Sen’s slope estimator to determine the trend magnitude for SPI, CI, extreme precipitation indices, dry and drought periods. The highest decreasing of rainfall amounts is found in spring and winter and these seasons are the overall driving factor of trends in annual precipitation. Overall results of the trend analysis on the reconstructed shows that over last 52 years the drought events are more sever and frequent after 1990s over the EM which reflects negative effects on socio- economic sectors as well as water resources in this region. The findings of this study could be used or extended in further studies in the future to gain insights regarding the precipitation variability, drought patterns and extreme events over the domain of the EM

Mots Clés :  : Precipitacions (Meteorologia) ; Precipitaciones atmosféricas ; Precipitations (Meteorology) ; Climatologia ; Climatología ; Climatology ; Sequeres ; Sequía ; Droughts ; Mediterrània (Regió) ; Mediterráneo (Región) ; Mediterranean Region

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