www.ccsenet.org/jas Journal of Agricultural Science Vol. 2, No. 3; September 2010 Published by Canadian Center of Science and Education 3 Trends in Agriculturally-Relevant Rainfall Characteristics for Small-Scale Agriculture in Northern Ghana Genesis Tambang Yengoh Department of Earth & Ecosystem Sciences, Lund University Sölvegatan 12, SE-223 62 Lund, Sweden Tel: 46-46-222-222-8416 E-mail: yengoh.genesis@lucsus.lu.se Frederick Ato Armah Department of Environmental Science, University of Cape Coast, Ghana E-mail: atoarmah@yahoo.com Edward Ebo Onumah Department of Agricultural Economics and Agribusiness University of Ghana, Legon – Accra, Ghana E-mail: eonumah@gwdg.de Justice O. Odoi Ghana Nature Today, A 25 Standard Estates Sakumono, P.O. Box OS 1455, Osu, Accra, Ghana E-mail: justice20gh@gmail.com Abstract This study set out to investigate the trends of agriculturally-relevant rainfall characteristics among small-scale farmers in the rainfall-sensitive dry savanna agro-ecological zone of northern Ghana. Interviews are used to identify characteristics of rainfall which are deemed by the farmers as important in their food production. Time series daily rainfall data from 1960-2007 is then used to identify trends in these variables which include the amount and temporal distribution of rainfall, occurrence of extreme daily rainfall events, the onset of rains, risk of dry spells and coefficient of variability of rains. The risk of dry spells for varying number of days following the planting period is computed using first-order Markov chain modeling. We find that there is a significant increase in mean rainfall per rain day and the coefficient of variation or summer rainfall amounts. No significant change in the onset of rains, the annual rainfall amount or maximum rainfall days are established. However, a significant decrease in the number of rain days and the probability of dry spells of up to seven and eleven days in the first four weeks of the planting season is revealed. There is need for development of an agricultural policy framework designed to understand the growing risks associated with agricultural production among small-scale farmers, and to improve management practices to accommodate and adapt to the new challenges of varying rainfall. Keywords: Rainfall variability, Farming, Northern Ghana, Statistics, Risk of dry spells, Markov chain modeling 1. Introduction Climatic factors play an important role in determining the production of food crops in the semi-arid regions of Africa. This is a region characterized by a low and highly variable distribution of rainfall spatially and over time, which constitutes a limiting potential for crop yields (Tesfaye et al. 2004; Graef et al., 2001). The amount of rainfall and its distribution over the year (especially during the farming season) greatly affects the productivity of agriculture in these regions. It determines the types of crops to be grown, the presence or absence of support activities like irrigation and crop yields, as well as influences agricultural calendar. The start of rains marks the start of the main farming season in northern Ghana as well as most parts of the Guinea savanna and the Sudano-sahelian region of Africa. This is usually considered to be the planting period for some of the main