1. Study site
This study was conducted between January, 2014 and May, 2014 at Dire Dawa Administration (DDA). DDA is located in the eastern part of Ethiopia and lies between 900 27' and 900 49'N latitudes and between 410 38' and 420 19'E longitudes, 515 Km from Addis Ababa, the capital city of Ethiopia. The total area of the administration is 128,802 hectare and the administration shares common boundaries with Somali National Regional States in the West, North and East and with the Oromia National Regional State in the South. Its altitude ranges from 960 meters above sea level (m.a.s.l) in the northeast to 2450 m.a.s.l in the South West. Using the 1500m contour as a line of separation, two agroclimatic Zones are known: the Kolla (below 1500m) and Woina Dega (above 1500m) (DDAEPA, 2011). The rainfall is bimodal and characterized by small rainy season from February to May and high rainy season from July to September. The dry season extends from October to January. The mean annual rainfall in the study area varies from 550mm in the lowland Northern part to 850mm in the Southern mountain ranges. The monthly mean maximum temperature ranges from 28.1°C, to 34.6°C. Likewise, the monthly mean minimum temperature varies from 14.5°C in December to 21.6°C in June (DDAC and Agricultural Bureau, 1998).