VOL. 8, NO. 1, JANUARY 2013 ISSN 1819-6608 ARPN Journal of Engineering and Applied Sciences © 2006-2013 Asian Research Publishing Network (ARPN). All rights reserved. www.arpnjournals.com 9 MODELING INLAND VALLEY SUITABILITY FOR RICE CULTIVATION Masoud J. 1 , Agyare W. A. 1 , Forkuor G. 2 , Namara R. 2 and Ofori E. 1 1 Department of Agricultural Engineering, Kwame Nkrumah University of Science and Technology, Kumasi, Ghana 2 International Water Management Institute (IWMI), Accra, Ghana E-Mail: kuyinijalal@yahoo.com ABSTRACT The demand for rice (Oryza sativa) in Ghana is increasing at a rate of 11.8% from 939, 920 t in 2010. Though there has been some increase in production it does not match the increase in consumption. This study seeks to determine the most suitable areas for inland valley rice cultivation using computer based models for selected sites (15km by 15km) in the Brong Ahafo Region (BAR) and Western Region (WR) of Ghana. A sensitivity analysis was carried out by excluding the least contributing parameters and varying their weights to determine highly suitable areas. Finally, 12 most sensitive input parameters were identified from the original 22. These were used to model for five suitability classes (highly suitable, suitable, moderately suitable, marginally suitable and not suitable). The model results based on parameters having equal weights showed that 0.5% and 11.8% (BAR); and 1.4% and 21.4% (WR) of the area were highly suitable and suitable respectively. Using unequal weights, 0.8% and 7.6% (BAR); and 0.9% and 13.6% (WR) of the area were highly suitable and suitable, respectively. The study successfully mapped out suitable areas for rice cultivation using spatial models based on limited data set, which can be adopted for use elsewhere. Keywords: rice, inland valley, sensitivity analysis, suitable sites, model. 1. INTRODUCTION Rice has in recent years become an important source of food in Sub-Saharan Africa (SSA). It has been noted to be the most rapidly growing source of food (preferred staple) in SSA during the last decade (Sohl, 2005). This trend has drastically increased consumption of the commodity in the region. As a response to the rising demand, there’s been an increase in production. For instance, production in West Africa, which remains the hub of rice production in SSA, has more than doubled in the past 20 years, rising from 2.76 million tonnes in 1985 to 5.75 in 2005 (Africa Rice Center, 2007). Production for the whole of Africa was in excess of 20 million tonnes for the first time in 2006 while the annual rate of increase is expected to hit 7% in the future (Somado et al., 2005). Despite these increases, there still remains a production- consumption gap. For example, between 2001 and 2005, the annual average consumption rate in West Africa was 6.55% compared to a corresponding production growth rate of about 4.5% (Africa Rice Center, 2007). Reasons for the shortfall in rice production across SSA have been discussed in the literature (FAO, 1986; Somado et al., 2005). Prominent among these are: prevalence of small-scale subsistence farms, low level of mechanization, poor irrigation infrastructure, low yielding varieties, unreliable rainfall and predominance of farms on uplands. According to Lancon and Erenstein (2002), out of the 5 rice ecologies in West Africa, rainfed upland areas alone constitute 44%. In Ghana and Cote d’Ivoire, this figure is as high as 70% and 79%, respectively. However, problems such as droughts, erosion, weeds and termites, which are associated with upland cultivation, often lead to poor yields. Unlike upland areas which experiences water scarcity for most of the year (Thenkabail and Nolte, 2000), inland valleys have a favorable hydrological condition that ensure that water is at, or near, the surface for most of the year. Inland valleys are defined as the upper reaches of river systems in which river alluvial sedimentation processes are absent or imminent only (Windmeijer and Andriesse, 1993). They occur abundantly in the West African landscape, constituting an estimated 8-28% of the total land area in the sub-region (Thenkabail et al., 2000). They have a high potential for rice development due to a number of reasons including: (1) easy access to river water, (2) high soil fertility relative to uplands, (3) soil moisture availability during dry seasons, (4) high water availability in wet seasons relative to uplands, and (5) availability of groundwater through lateral inflow from higher parts of the landscape. Inland valley lowland rice cultivation greatly contributed to the success of the green revolution in east and south-east Asia. It is believed that intensifying inland valley lowland rice cultivation in West Africa is capable of improving the production volumes of rice to help bridge the consumption-production gap (Fashola et al., 2007). Identification of the most suitable inland valleys for rice cultivation is an important first step in promoting inland valley low land rice cultivation in West Africa. Suitability analysis involving the most critical factors in rice cultivation can lead to the selection of optimal areas within available inland valleys for rice cultivation and subsequent good yields. In this regard, Gumma et al. (2009) conducted suitability analysis to determine best areas for rice cultivation in the inland valley wetlands of Ghana. The study was conducted at local scale (15x15km) in two regions of Ghana - Ashanti and Northern regions. They developed a spatial model (using Erdas Imagine Model Maker) that combined spatial layers of influencing factors which were grouped into bio-physical, technical, socio-economic and eco-environmental factors. 22 and 16 (see Table-1) factors for Ashanti and Northern regions, respectively were combined in a multi-criteria evaluation to determine best areas for rice cultivation in the inland