Rainfall Variability

Myriam Traboulsi

Rainfall varies considerably from year to year depending on the frequency of disturbed weather types generating rain, which in turn are characterized by great irregularity. Both "dry" and "wet" years, 1972-73 and 1966-67 respectively, illustrate the fluctuations in rainfall in the region (Fig. 2. During the years 1966-67, the Orontes valley received more than 500 mm in Syria and less than 200 mm in 1972-73

The ratio between the extreme "dry" and "wet" years varies between 3 in Jisr ash Shughur and 9 in the Beqaa: The variation coefficient of annual rainfall is at 24 in the Al Ghab Valley and increases toward the east and south of the basin (31.1 in Salamiyah, 31.9 in Furqlus and 34.5 in Qusayr). Variability is much more marked on a monthly scale -- a very rainy month one year may be dry the following one. Monthly variation coefficients in the four stations, in Fekehe, Hermel Salamiyah and Homs (Table 1) show that the months in-between seasons, experience the strongest variability, whereas it is relatively low at the heart of the rainy season. (Traboulsi 2004).

Table 1: Coefficients of monthly variations