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: 3.76). 06/2003; 117(1-2):23-37. DOI: 10.1016/S0168-1923(03)00037-6


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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    • "Different management techniques have been suggested to improve water productivity and produce " more crop per drop of rain " (Rockstrom et al., 2002). Water harvesting systems are among the technologies that have shown substantial productivity improvements in different regions in sub-Saharan Africa (Barron et al., 2003; Dile et al., 2013b; Fox and Rockstrom, 2003; Oweis and Hachum, 2006). Dile et al. (2013b) conceptually showed that water harvesting systems can build resilience and thereby result in sustainable agricultural intensification. "
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    ABSTRACT: Water harvesting systems have improved productivity in various regions in sub-Saharan Africa. Similarly, they can help retain water in landscapes, build resilience against droughts and dry spells, and thereby contribute to sustainable agricultural intensification. However, there is no strong empirical evidence that shows the effects of intensification of water harvesting on upstream–downstream social–ecological systems at a landscape scale. In this paper we develop a decision support system (DSS) for locating and sizing water harvesting ponds in a hydrological model, which enables assessments of water harvesting intensification on upstream–downstream ecosystem services in meso-scale watersheds. The DSS was used with the Soil and Water Assessment Tool (SWAT) for a case-study area located in the Lake Tana basin, Ethiopia. We found that supplementary irrigation in combination with nutrient application increased simulated teff (Eragrostis tef, staple crop in Ethiopia) production up to three times, compared to the current practice. Moreover, after supplemental irrigation of teff, the excess water was used for dry season onion production of 7.66 t/ha (median). Water harvesting, therefore, can play an important role in increasing local- to regional-scale food security through increased and more stable food production and generation of extra income from the sale of cash crops. The annual total irrigation water consumption was ~ 4%–30% of the annual water yield from the entire watershed. In general, water harvesting resulted in a reduction in peak flows and an increase in low flows. Water harvesting substantially reduced sediment yield leaving the watershed. The beneficiaries of water harvesting ponds may benefit from increases in agricultural production. The downstream social–ecological systems may benefit from reduced food prices, reduced flooding damages, and reduced sediment influxes, as well as enhancements in low flows and water quality. The benefits of water harvesting warrant economic feasibility studies and detailed analyses of its ecological impacts.
    Science of The Total Environment 10/2015; 542:22-35. DOI:10.1016/j.scitotenv.2015.10.065 · 4.10 Impact Factor
    • "There is only one main river crossing the catchment from north to south with a temporary water flow during rainy seasons. The high rainfall variability in time, space and altitude is also associated with long and frequent dry spells (Barron et al., 2003; Enfors & Gordon, 2007; Pachpute, 2010). The vegetation cover varies from forest to dense bushland in the highland and sparse bushland to degraded land in the lowlands. "
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    ABSTRACT: Land conversion in Sub-Saharan Africa has profound biophysical, ecological, political and social consequences for human wellbeing and ecosystems services. Understanding the process of land cover changes and transitions is essential for good ecosystem management policy that would lead to improved agricultural production, human wellbeing and ecosystems health. This study aimed to assess land cover transitions in a typical semi-arid degraded agro-ecosystems environment within the Pangani River Basin in northern Tanzania. Three Landsat images spanning over 30 years were used to detect random and systematic patterns of land cover transition in a landscape dominated by crop and livestock farming. Results revealed that current land cover transition is driven by a systematic process of change dominated by (i) transition from degraded land to sparse bushland (10.8%), (ii) conversion from sparse bushland to dense bushland in lowland areas (6.0%), (iii) conversion from bushland to forest (4.8%), and (iv) conversion from dense bushland to cropland in the highlands (4.5%). Agricultural lands under water harvesting technology adoption show a high degree of persistence (60-80%) between time slices. This suggests that there is a trend in land-use change towards vegetation improvement in the catchment with a continuous increase in the adoption of water harvesting technologies for crop and livestock farming. This can be interpreted as a sign of agricultural intensification and vegetation re-growth in the catchment. This article is protected by copyright. All rights reserved.
    Land Degradation and Development 10/2015; DOI:10.1002/ldr.2461 · 3.09 Impact Factor
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    • "Besides inter-annual variability, intra-seasonal variability also has a potential effect on crop yields (Cooper et al., 2008). Barron et al. (2003) noted high dry spells probabilities during maize flowering and grain filling at semi-arid sites in Kenya and Tanzania, resulting in substantial losses of final grain yields, especially on sandy soils. Araya and Stroosnijder (2011) demonstrated that in northern Ethiopia a short growing period or a total lack of rain were the main factors of crop failure, before dry spells occurrence and false starts of the rainy season. "
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    ABSTRACT: Mount Kenya is an equatorial mountain whose climatic setting is fairly simple (two rainy seasons in March – May, the Long Rains, and October – December, the Short Rains) though concealing significant spatial variations related to elevation and aspect (part I, Camberlin et al., 2014). This part II is dedicated to the sensitivity of sorghum yields to climate variability in space and time, with a focus on the intra-seasonal characteristics of the rainy seasons. To that aim we use the crop model SARRA-H calibrated for the region and fed with rainfall, temperature, wind speed, humidity and solar radiation data over the period 1973 – 2001 at three stations located on the eastern slopes of Mount Kenya. The crop model is run independently for the two rainy seasons. Four groups of simulations are conducted by varying the initialization date of the simulation, the sowing dates and the type of soil, in order to test sorghum sensitivity to water availability. Evidence is found that potential sorghum yields are dominantly controlled by variations in seasonal rainfall amounts: mean yields are higher at higher and wetter locations, and are higher during the wettest rainy season and years. However, beyond this apparent simplicity, more complex aspects emerge of the crop – climate relationships. First, the yield – elevation relationship is altered at high elevation due to lower temperature. Second, despite a strong link with the seasonal rainfall amounts, we evidence an underlying role of some intra-seasonal rainfall characteristics such as the number of rainy days (itself mainly determined by the rainy season duration) or the occurrence of long dry spells. Third, unseasonal rains occurring after the end of the rainy season, especially after the Short Rains, play a role in final crop yield. Fourth, variations of climate variables such as solar radiation by modulating the potential evapotranspiration concur to yield variations at the wettest locations.
    International Journal of Climatology 06/2015; DOI:10.1002/joc.4394 · 3.16 Impact Factor
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