Precipitation Concentration Changes
in Egypt during the Period (1947-2006)
Dr. Mohamed Mohamed Abdelaal Ibrahim
Lecturer of Physical Geography, Social Studies Department, Faculty of Education, Mansoura University, Egyp
ABSTRACT
Nowadays it is so crucial to understand and to analyze precipitation variability and its seasonality being the most climatic variable in time and space for the assessment of erosivity and its impacts on rain-fed agriculture and conservation measures. Hence, this study aimed to characterize Egypt in terms of spatio-temporal distribution of precipitation by means of the analysis of annual, seasonal (winter-spring-autumn) and supra-seasonal (wet and dry) Precipitation Concentration Index (PCI) during the period (1947 – 2006); also, it aimed to look for changes through the mean values of PCI concerning the two independent sub-periods (1947-1976) and (1977-2006) . This study used monthly precipitation dataset for 31 rain gauges as representative as possible for the whole region, and these data underwent some quality control, homogenization, and reconstruction procedures recommended by the World Meteorological Organization. The main results obtained for the seasonality of the precipitation over the year showed no strong evidence of PCI spatio-temporal changes between the two independent sub-periods (1947-1976) and (1977-2006), especially in the northern coast, and there were no definite clear patterns of changes in precipitation concentration.
Keywords: Precipitation Concentration, Spatio-temporal, Supra-seasonal, Egypt.
DISCUSSION AND CONCLUSION
This study showed that there is no strong evidence of PCI spatio-temporal change between 1947-1976 and 1977-2006 at annual, seasonal and supra-seasonal time scales, especially along the Egyptian coasts. Results were similar to many studies conducted in different parts of the world (e.g. Elagib, 2011; Gozzini, et al., 2012; Cortesi et al., 2012; Ngongondo et al., 2011; Daniela & Stelian, 2012) which revealed that there was no strong statistically significant change in precipitation in seasonality and concentration. Furthermore, there were no definite patterns for precipitation concentration during the second half of the twentieth century.
Furthermore, many studies in different parts of the Mediterranean basin (e.g. Zhang et al., 2005) showed that trends in precipitation indices, including the number of days of precipitation, the average precipitation intensity, and maximum daily precipitation events for the Middle East, were weak in general and did not show spatial coherence. Also, lack of trend and non-significant trends were greatly prevailing in many indices of precipitation at monthly and daily levels in the Mediterranean during period (1950–2000) (Norrant & Douguedroit, 2006). Ibrahim (2012) showed a statistically insignificant trend in monthly and daily rainfall for most of the observatories along the Egyptian coasts in majority of months and seasons. Also, Alpert, et al. (2002) noted that there was no paradoxical trend between extreme daily rainfall and total values in Israel and Cyprus. Equally important, no significant trends were found in the daily rainfall categories during (1951–1995). Conversely, a general future tendency was found towards drier Eastern Mediterranean, with reduced rainfall intensity (2070-2100) (Oikonomou, et al., 2008).
Moreover, Karl and Trenberth (2003) confirmed that even without any change in total precipitation, there was an increase in the frequency of intense daily precipitation in warmer climates owing to increased water vapor, a fact that would have led to an increase in precipitation concentration. Hasanean (2004) and Kenawy et al. (2010) concluded that a significant positive (warming) trend was observed in Egypt for mean, maximum and minimum temperature at annual and seasonal time scales during the second half of the twentieth century. According to these results, precipitation in Egypt should have been more concentrated in time during the last decades, but no clear signals of changes in precipitation concentration were found across Egypt between (1947-1976) and (1977-2006).
The absence of clear changes in precipitation concentration in Egypt can be ascribed to the absence of clear changes in atmospheric circulation, synoptic and local factors during the two independent sub-periods (1947-1976) and (1977-2006) (De Luis et al., 2010 & 2011). In fact, precipitation is one of the factors in the processes of creating landscape, and thus differences in temporal distribution of precipitation can lead to different precipitation regimes and various climatic conditions affecting landscapes processes, even if annual total amounts are similar (Cortesi et al., 2012).
Finally, the spatial coherence of the results of this study, and the absence of significant changes (except for some observatories) showed that no generalized changes have occurred in precipitation concentration across Egypt in the period examined (1947-2006) only using monthly precipitation data. Therefore, this study suggests studying the trend and changes of the daily precipitation concentration across Egypt during a longer period. Unfortunately, the data and information of daily precipitation would be scarce, especially in the developing countries. The PCI correlates with annual, seasonal and supra-seasonal precipitation amount (A significant negative correlation) within the territory studied.
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