Facts about Ethiopia

The record showing the mean annual water deficit broadly indicates the regional variation in the magnitude of the mean annual moisture deficiency for plant growth and development.

The amount of moisture deficit is the excess of potential evapotranspiration over rainfall when soil moisture storage is assumed to be nil. The calculations are made on a monthly basis and totaled for the year.

While the amounts show the relative magnitudes of stress placed on plants during the dry seasons, they do not show the duration of the dry season.

Thus two places can have about the same amount of mean annual moisture deficit but vary greatly in the duration of the dry season.

For example, Gambela and Bati have about the same mean annual water deficit, 687mm and 689mm respectively. However, Gambela has moisture deficiency for six months while at Bati the dry season lasts for nine months Both Gambela and Bati, on the other hand, can at best support only scanty woodland vegetation although their mean annual rainfalls are 1,327 and 810mm respectively.

Similarly, two places can have about the same mean annual moisture surplus but vary widely in the amount of moisture deficit and the duration of the dry season.

Thus, at Jimma, the mean annual moisture deficit is 122mm and the dry season lasts for three months, while at Addis Zemen the mean annual moisture deficit is 779mm and the dry season lasts for seven months.

The mean annual moisture surplus at Jima and Addis Zemen however, is about the same 463mm and 492mm respectively. Because of the difference between the two places in the amount of moisture deficit and the duration of the dry season, Jima area can support much more luxuriant forest vegetation than Addis Zemen region.

The amounts of moisture deficit also show the relative magnitudes of the annual amount of water which needs to be supplied artificially through irrigation at various localities for optimum crop growth.

However, this does not mean irrigation requirements in absolute terms since the figures only indicate annual rather than seasonal amounts, and also since irrigation water requirements are affected by many other factors.

The map shows that the highest moisture deficits of over 900mm a year occur in most of the northern, northeastern, southeastern and southern parts of the country where potential evapotranspiration amounts are high and the rainfall amounts are low. At Gode the deficit is 1,546mm, at Gewane 1,216mm and at Humera 1,149mm.

In parts of the southern, southwestern and southeastern highlands of Ethiopia there is practically no moisture deficit (less than 100mm).

These are the highlands of Ilubabor, Kefa, Gamo Gofa, northern Sidamo, central Bale and central Arsi. At Wushwush the deficit is zero, at Gore 76, at Chencha 42, at Yirga Chefe 58, at Goba 89 and at Ticho 15.

(Source: National Atlas of Ethiopia)