ASSESSMENT OF RAINFALL SEASONALITY, CONCENTRATION AND EROSIVITY INDICES FOR THREE DIFFERENT CLIMATIC ZONES IN SUDAN.

This study was based on rainfall meteorological data (1960-2010) from three meteorological stations namely: Dongola, Khartoum and Al-damazine represented different climatic zones of Sudan, hyper-arid, arid and semi-arid respectively. The main objectives of this study conducted in the targeted areas to show data on rainfall indices such as, seasonality (SI), concentration (PCI) and erosivity (MFI), beside investigation the changes in annually and monthly rainfall, also comparing the total rain gauge in two temporal periods 1960-1984 and rain gauge 1985-2009. In addition to generate empirical relationship between rainfall and erosivity (MFI) index. The data subjected to statistical analysis by using SPSS and regression done by “Excel, 2000”. The results showed that the variation due to month was much higher than the annually. The monthly coefficient of variation for three meteorological stations, Dongola, Khartoum and Al-damazine were 1.3, 1.1 and 1.04 fold that measured annually. The highest contribution of the monthly rainfall in the three meteorological stations during 1960-2010 recorded in July and Aug. whereas absolutely lowest contribution of the monthly rainfall in Aldamazin, Khartoum and Dongola recorded in Dec. Annual overall means of the three meteorological stations significantly decreased in following order: Aldamazine> Khartoum> Dongola. The results revealed that Dongola, Khartoum and Aldamazine stations, the seasonality index accounted about 0.85, 0.99 and 0.90 mm respectively, so seasonality index in studied areas can be described as markedly seasonal with a long drier season. PCI in studied areas can be described as highly seasonal in Khartoum and Aldamazine but in Dongola gave irregular pattern of PCI. MFI in studied areas can be described as very low, low and high for Dongola, Khartoum and Aldamazine respectively. According to this finding the susceptibility of water erosion can flow the same order. The results for Dongola and Khartoum stations showed that the total rain gauge in two successive periods 1960-1984 (first period) and 1985-2009 (second period), decreased from first period to second by 30.2% and 11.9% respectively, but Aldamazin station gave very meager increasing accounted about 0.35. Eventually, since MFI for Dongola area gave higher correlation coefficient with annual total rainfall and the differences not exceeds plus or minus 4.5, thus it is recommended to predict MFI using the following equation: Y = -0.0003x3+0.0268x2+0.2958x+0.7752.