Australian Journal of Basic and Applied Sciences, 5(12): 136-144, 2011 ISSN 1991-8178 Corresponding Author: O. Ghanem, Department of Soil Science, National Superior School of Agriculture (ENSA), El Harrach, Algiers Algeria. 136 Causes of Agricultural Terraces Degradation in Al-kimmah Watershed (Yemen) 1 O. Ghanem, 2 A. Jazem, 1 K. Djili 1 Department of Soil Science, National Superior School of Agriculture (ENSA), El Harrach, Algiers Algeria. 2 Faculty of Civil engineering, University of Dhamar, Yemen. Abstract: The agricultural terraces in north western Semi-arid highland in Yemen have always played an important role in social stability of rural population. However, since the second half of the twentieth century, these terraces have been subjected to continuous degradation that could endanger the fragile socio-economic development in these areas. This study aims at understanding and investigating the causes of the agricultural terraces degradation in Al-Kimmah Kuhlan Affar Hajjah region. The agricultural terraces of the representative watershed were divided into four groups mainly; salubrious (no degraded) terraces (group A), slightly degraded (group B), moderately degraded (group C) and highly degraded (Group D) based on the rate of destruction and collapse of stone walls. The study of socio-economic factors has been conducted on a sample of 40 farmers spreading across the watershed and covering the four groups of terraces. The study of environmental factors was conducted through observations and field measurements from 98 sites representing all forms of degradation. Statistical analysis of data revealed that 18 socio-economic and 12 environmental factors are statistically (p <0.05) linked to the agricultural terraces degradation. Altogether, the causes of the agricultural terraces degradation are social, economic and environmental in their nature. The most influential factors are the exodus of the local workforce, the low agricultural productivity, the lack of profitability and steep slopes. Moreover, it also appears from this study that the steep slopes, the mountainous landscape, the presence of rock outcrops, the spontaneous vegetation and the dark color of the soil are good indicators of land degradation in Al- Kimmah Kuhlan Affar area. Key words: agricultural terraces, Yemen, degradation, erosion, watershed. INTRODUCTION The agricultural terraces play an important role in social stability and economic development of highlands areas of Yemen. Indeed, some of these terraces were built about 5000 years ago (Wilkinson, 2008; Gibson and Wilkinson, 2008), thus, covering all the mountains, or about 60% of the country (F.A.O, 2000). The area of agricultural land in Yemen is quite limited since it is estimated about 1.66 million hectares of which 64% are actually cultivated. The agricultural terraces compose of 25% of the cultivated land (AW-Hassan et al., 2000). In addition, rain-fed agriculture accounts for 70% of the cultivated land consisting principally of terraced agricultural production, apart from livestock farming, 80% of cereals (AL-Mashreki, 2002). Indigenous individuals have found a solution for the exploitation of mountain slopes through enormous efforts and huge sums for the construction of millions of agricultural terraces (Vogel, 1987). This construction was made possible through the efforts of the family, cooperation of individuals and sometimes participation of the whole society (AL-Hebshi, 2005). FAO (1997) estimated the area occupied by agricultural terraces about 450 000 ha distributed mainly in the western and southern highlands of Yemen. However, ACSAD (2002), evaluates the amount of the agricultural terraces land approximately 662 000 ha. According to Al-Ghulaibi (2009), the length of the dry season and erratic rainfall during the year is the main constraint facing the agricultural cycle in arid and semi-arid regions. According to the same author, Yemeni farmers have solved this problem by valuing each parcel of mountainous land by building agricultural terraces that also act as a collector and water reservoir. The traditional irrigation system is designed so gently conveying runoff watershed from one terrace to another and then to the stream (Rappold, 2004). With these terraces during the medieval period, Yemen had one of the widest ranges of agricultural crops in the region (Varisco, 1991). In the 1950s, FAO (Varisco, 1991) classified the system of agricultural terraces of North Yemen among the most powerful systems in the world.