Article

Dry spell analysis and maize yields for two semi-arid locations in East Africa

Natural Resources Management, Department of Systems Ecology, Stockholm University, 106 91 Stockholm, Sweden
Agricultural and Forest Meteorology (Impact Factor: 3.89). 06/2003; 117(1-2):23-37. DOI: 10.1016/S0168-1923(03)00037-6

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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    • "The use of seasonal amounts can be detrimental when the largest rainfall amounts near the seasonal peak are not spatially coherent and may hide potentially predictable signals, notably at the beginning and end of the rainy seasons, that can be important for crops (Sivakumar 1993; Barron et al. 2003; Sultan et al. 2005; Marteau et al. 2011). Our results demonstrate that the interannual variability of the long (FMAMJ) rains in Kenya and north Tanzania is consistent with such behavior, with the most spatially coherent signals confined to the early stage or at least the first half of the rainy season (Figs. 2, 6). "
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    • "For seasonal precipitation, we also include a quadratic term to account for non-linear relationships, and the differential response to precipitation changes in dry vs. wet regions of the country. Given that not just the total volume of precipitation is important, but also its timing and intensity (Barron et al., 2003; Biazin et al., 2012), we define a variable with the total number of dry days from planting to harvest, as we expect long dry spells to be associated with drought-related yield declines and losses. "
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    Agricultural and Forest Meteorology 11/2014; 200. DOI:10.1016/j.agrformet.2014.10.002 · 3.89 Impact Factor
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    • "Finally, in the Greater Horn, a region that is highly reliant on rain-fed agriculture, dry spells within any given rainy season can be as detrimental to crops as seasonal drought (e.g., Barron et al. 2003). Here it is simply noted that on subseasonal time scales, rainfall variations associated with the Madden–Julian oscillation (MJO) have been reported for both the short and long rains (e.g., Mutai and Ward 2000; Pohl and Camberlin 2006). "
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