Drought Frequency

In Ethiopia, an agricultural drought is assessed using the concept of the length of growing period (LGP). The growing period is defined as the period (in days) during a year when rainfall exceeds half the potential evapotranspiration (PET), plus a period required to evapotranspire water from excess rainfall stored in the soil profile (FAO, 1978). One-half of the PET has been considered sufficient to meet the crop water requirement (FAO, 1978; Doorenbos and Kassam, 1979). A year with an LGP less than 90 days is considered to be a drought year. Because most crops in Ethiopia, with the exception of some pulses and very low-yield varieties of tef (Eragrostis tef) and wheat, require a growing period of at least 90 days (Henricksen and Durkin, 1985). The number of this below-90 day-LGP-years divided by the total number of years gives the severity level of drought. Based on this ratio, Reddy (1990) classified drought severity as ranging from low to very high. There are two rainy seasons in Ethiopia: belg (the first rainy season, from February to May) and Kiremt (the second rainy season, from June to September), which do not apply equally for the whole country.

The results of assessing agricultural drought (figure 17.1) based on the above explanation indicates that during the first season the frequency of agricultural drought is low (below 15%) for most parts of the Amhara Regional State, with the exception of eastern and southern parts, western parts of Oromiya, Benshangul Gumuz; Southern Nations Nationalities Peoples Region (SNNPR) and, with the exception of parts of South Omo, Gambella Regional State, the highlands of Sidammo, Arsi, Bale, and Hararghie. The frequency of drought is between 15 and 40% (moderate) for northern parts of north Gonder, southwestern parts of south Tigrai, western parts of eastern Amhara, most parts of north Shoa, parts of east Shoa, parts of east and west Hararghie, northern parts of Bale, northern and western parts of Borena, and parts of South Omo. However, drought is very frequent in most parts of Tigrai, Afar, eastern Oromiya, Somali, and southern Borena. The area with high drought frequency has decreased and is limited to the eastern parts of Tigrai, most parts of Afar, most parts of Somali, southern Borena, and parts of South Omo during the second season. Most parts of Amhara, western parts of Tigrai, most parts of Oromiya, and SNNP have a low frequency of drought during the second season, as shown in figure 17.1. The other parts of the country that experience two rainy seasons experience medium drought risk (15-40% frequency) during the second season.

0 0

Post a comment