Dry spell analysis and maize yields for two semi-arid locations in east Africa
ABSTRACT High variability in rainfall occurrence and amounts together with high evaporative demand create severe constraints for crop growth and yields in dry sub-humid and semi-arid farming areas in east Africa. Meteorological analyses on rainfall distribution are common, but generally focus on assessing drought occurrence on annual and seasonal basis. This paper presents two types of seasonal dry spell analysis, using easy accessible data on daily rainfall and evapotranspiration for two semi-arid locations in east Africa for 20–23 years. The meteorological dry spell analysis was obtained by Markov chain process, and the agricultural dry spell analysis used rainfall data in a simple water balance model also describing impact on maize (Zea mays L.) growth due to water availability on clay or sandy soil. The meteorological dry spell analysis showed a minimum probability of 20% of dry spells exceeding 10 days at both sites, increasing to 70% or more depending on onset of season, during approximate flowering and early grain filling stage. The agricultural dry spell analysis showed that maize was exposed to at least one dry spell of 10 days or longer in 74–80% of seasons at both sites. Maize on sandy soil experienced dry spells exceeding 10 days, three–four times more often than maize on clay soil during flowering and grain filling stages. In addition, the water balance analysis indicated substantial water losses by surface runoff and deep percolation as the crop utilised only 36–64% on average of seasonal rainfall. Such large proportion of non-productive water flow in the field water balance may provide scope for dry spell mitigation through improved water management strategies.
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ABSTRACT: This paper assesses the net welfare associated with the adoption of Bench Terraces (BT), Contour Bunds (CB), and Napier Grass Strips (NGS) in the Saba Saba sub-catchment of the Upper Tana catchment in Kenya. An agro-economic survey and informal interviews were conducted in the Saba Saba sub-catchment to elicit farm level quantitative data for the Cost Benefit Analysis (CBA). Financial functions in excel were used to analyze the on-site costs and benefits of adopting the identified SWC technologies on farms with crops such as maize, coffee, and tea. In this research CBA was used as a decision tool after the computation of all cost and benefits were valued in local currency to obtain the Net Present Value (NPV) or net welfare. The results show that investment in SWC measures may not be a feasible short-term option from farmers' perspective. There is, therefore, a strong case for intervention, especially in the initial years where SWC adoption yields negative returns. Again the maintenance cost was higher for all SWC technologies. This could be attributed to poor construction techniques. Considering the sub-catchment's erosion risk severity and slope stability, Bench Terrace was found to yield relatively higher on-site net welfare.International Journal of Scientific and Research Publication. 08/2014; 4(8):2250-3153.
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ABSTRACT: Sahelian rainfall has recorded a high variability during the last century with a significant decrease (more than 20 %) in the annual rainfall amount since 1970. Using a linear regression model, the fluctuations of the annual rainfall from the observations over Burkina Faso during 1961–2009 period are described through the changes in the characteristics of the rainy season. The methodology is then applied to simulated rainfall data produced by five regional climate models under A1B scenario over two periods: 1971–2000 as reference period and 2021–2050 as projection period. As found with other climate models, the projected change in annual rainfall for West Africa is very uncertain. However, the present study shows that some features of the impact of climate change on rainfall regime in the region are robust. The number of the low rainfall events (0.1–5 mm/d) is projected to decrease by 3 % and the number of strong rainfall events (>50 mm/d) is expected to increase by 15 % on average. In addition, the rainy season onset is projected by all models to be delayed by one week on average and a consensus exists on the lengthening of the dry spells at about 20 %. Furthermore, the simulated relationship between changed annual rainfall amounts and the number of rain days or their intensity varies strongly from one model to another and some changes do not correspond to what is observed for the rainfall variability over the last 50 years.Climate Dynamics 03/2014; 42(5):1363–1381. · 4.23 Impact Factor