ADEFISAN ELIJAH ADESANYA
Publication
Agricultural practices and production in West Africa have become risky and unsustainable due to the persistent and disastrous drought which started in the early 70s and only began to abate towards the end of the last milleneum. In these circumstances, it is imperative that reliable methods for relating crop yield to climate variability be developed. This paper examines the variabilities in the climate parameters and identifies the environmental factors which influence the yield of two major staple food crops in West Africa – cowpea and rice. The study uses over 80 years of rainfall, 60 years of temperature and 19 years of crop yield data for cowpea and rice for Kano state, in the Sudano-Sahelian zone of Nigeria. Significant variations are found not only in the traditional climate parameters of rainfall amount and temperature, but also in the number of raindays, the onset and cessation and, hence, the length of the rainy season. Results show that rainfall amount and number of raindays of specific heaviness in September have strong influence on the yield of both rice and cowpea. However, while June minimum temperature (with other parameters) is important only for the latter, September maximum temperature affects the yield of both crops. The crop-climate models show high skill and demonstrate that reliable annual forecasts of the yield of the crops are possible if these climate parameters could be predicted.
With such crop yield models, governments would be able to plan and put in place pro-active food security measures for their people. The extremity and variability of climate and weather events has far reaching and grevious implications for agriculture and water resources and food security in the humid tropics. Although, models of soil-plant-atmosphere continuum (SPAC) integrate the influences of soil and micrometeorological conditions on plant processes, but have rarely been applied to tropical crops under rainfed agriculture. These
models present relevant options which may be applied in the development of technologies for irrigation and water resources management and to ameliorate environmental constraints to crop productivity in the tropics. In circumstances of the changing climate and weather variability and droughts of the future, it is imperative to raise the efficiency of rainfall and soil water use in agriculture. Adoption of water saving/conserving technologies and identification of crop species and species-specific traits that improves crop water use efficiency of crops under rainfed, irrigated and dryland farming systems. In the wake of the growing urgency surrounding drought and a drying climate, necessary to adapt crops and rooting systems to better perform under drought/water limited situations. Improved understanding of the bases of plant adaptation to insufficient-moisture environment will
offer possibilities for improving adaptation in crop plants. Therefore, the need is urgent, for tropical agriculture and farming systems to adapt and respond to the expected variable and warmer climates and droughts of the future. The conclusion emphasizes the need to strengthen knowledge and increase capacity building in soil, water and environmental management, and to develop soil, plant and agrometeorological based tools which integrate the influences of soil and micrometeorological conditions on plant processes. These tools present options useful in fine-tuning technological and agronomic interventions to protect farmers and agricultural systems from drought and consequences of extreme and hazardous climatic events. Soil, plant and agrometeorological based tools are relevant to the development of scientific base to build on sustainable agriculture and water resources management in the tropics.
The Coordinated Regional Downscaling Exercise (CORDEX-Africa) attempted to test some Regional Climate Models (RCMs) driven by the same initial and boundary conditions (ERA-Interim) in order to simulate African climate from 1998 to 2008. In this study, the ability of these RCMs to simulate West African rainfall distribution in addition to some useful agrometeorological information like rainfall onset and length of growing season were therefore evaluated over the entire West Africa and each of its three climatic zones. Data used for the study comprises of the daily precipitation from Global Precipitation Climatology Project (GPCP) form 1999 to 2007, monthly rainfall data from Climate Research Unit (CRU) from 1999 to 2006 were used with the models’ rainfall data.Comparison of CRU and the RCMs rainfall distribution shows that each of the ten RCMs simulated the patterns of monthly and annual rainfall distribution over Sahel and Savana very well by capturing the wet seasons though with some slight over-estimation in some RCMs. The over-estimation for five of the models was high over Guinea zone and most especially the leeward side of Cameroonians Mountain. The little dry season which is a common climatological feature over south of about 10oN was well captured by five of the RCMs while two RCMs barely captured it and three models were unable to capture it. Onset, Cessation and hence length of the rainy season as compared by GPCP and RCMs daily rainfall data from 1990 to 2008 shows that the onset and cessation of rainfall in Sahel and Savana zones were well captured by almost all the RCMs but some RCMs produced a huge errors in Guinea for the rainfall onset and hence length of rainy season. The problem with the Guinea zone might be due to firstly, the type of physics schemes used (most especially convection) by some models, secondly some RCMs are unable to properly resolve the land-ocean-atmospheric coupling very well and most importantly the unique shape of West African.
