Long-rains Season Research Articles

Regional climate projections for impact assessment studies in East Africa

In order to overcome limitations of climate projections from Global Climate Models (GCMs), such as coarse spatial resolution and biases, in this study, the Statistical Down-Scaling Model (SDSM) is used to downscale daily precipitation and maximum and minimum temperature (T-max and T-min) required by impact assessment models. We focus on East Africa, a region known to be highly vulnerable to climate change and at the same time facing challenges concerning availability and accessibility of climate data. SDSM is first calibrated and validated using observed daily precipitation, (T-max, and T-min) from 214 stations and predictors derived from the reanalysis data of the National Centers for Environmental Prediction. For projection (2006–2100), the same predictors derived from the second generation Canadian Earth System Model (CanESM2) are used. SDSM projections show an increase in precipitation during the short-rain season (October–December) in large parts of the region in the 2020s (2011–2040), 2050s (2041–2070), and 2080s (2071–2100). During the long-rain season (March–May (MAM)) precipitation is expected to increase (up to 680 mm) in Ethiopia, mainly in the western part, and Kenya and decrease (up to −500 mm) in Tanzania in the 2020s, 2050s, and 2080s. However, the western part of Ethiopia will be much drier than the baseline period (1961–1990) during June–September (JJAS) in the 2020s, 2050s, and 2080s, which indicates a shift in precipitation from JJAS to MAM. Annually, precipitation, T-max, and T-min will be higher than during the baseline period throughout the 21 century in large parts of the region. The projection based on SDSM is in line with the direction of CMIP5 GCMs but differs in magnitude, particularly for T-max and T-min. Overall, we conclude that the downscaled data allow for much more fine-scaled adaptation plans and ultimately better management of the impacts of projected climate in basins of Ethiopia, Kenya, and Tanzania.

Extreme Rainfall and Flooding over Central Kenya Including Nairobi City during the Long-Rains Season 2018: Causes, Predictability, and Potential for Early Warning and Actions

The Long-Rains wet season of March–May (MAM) over Kenya in 2018 was one of the wettest on record. This paper examines the nature, causes, impacts, and predictability of the rainfall events, and considers the implications for flood risk management. The exceptionally high monthly rainfall totals in March and April resulted from several multi-day heavy rainfall episodes, rather than from distinct extreme daily events. Three intra-seasonal rainfall events in particular resulted in extensive flooding with the loss of lives and livelihoods, a significant displacement of people, major disruption to essential services, and damage to infrastructure. The rainfall events appear to be associated with the combined effects of active Madden–Julian Oscillation (MJO) events in MJO phases 2–4, and at shorter timescales, tropical cyclone events over the southwest Indian Ocean. These combine to drive an anomalous westerly low-level circulation over Kenya and the surrounding region, which likely leads to moisture convergence and enhanced convection. We assessed how predictable such events over a range of forecast lead times. Long-lead seasonal forecast products for MAM 2018 showed little indication of an enhanced likelihood of heavy rain over most of Kenya, which is consistent with the low predictability of MAM Long-Rains at seasonal lead times. At shorter lead times of a few weeks, the seasonal and extended-range forecasts provided a clear signal of extreme rainfall, which is likely associated with skill in MJO prediction. Short lead weather forecasts from multiple models also highlighted enhanced risk. The flood response actions during the MAM 2018 events are reviewed. Implications of our results for forecasting and flood preparedness systems include: (i) Potential exists for the integration of sub-seasonal and short-term weather prediction to support flood risk management and preparedness action in Kenya, notwithstanding the particular challenge of forecasting at small scales. (ii) We suggest that forecasting agencies provide greater clarity on the difference in potentially useful forecast lead times between the two wet seasons in Kenya and East Africa. For the MAM Long-Rains, the utility of sub-seasonal to short-term forecasts should be emphasized; while at seasonal timescales, skill is currently low, and there is the challenge of exploiting new research identifying the primary drivers of variability. In contrast, greater seasonal predictability of the Short-Rains in the October–December season means that greater potential exists for early warning and preparedness over longer lead times. (iii) There is a need for well-developed and functional forecast-based action systems for heavy rain and flood risk management in Kenya, especially with the relatively short windows for anticipatory action during MAM.

Effect of nitrogen sources on the yield of common bean (Phaseolus vulgaris) in western Kenya

ABSTRACTDepletion of soil nutrients due to continuous cultivation without adequate external fertilization is one of the challenges facing many smallholder farmers in western Kenya. This study was conducted to assess the effects of organic (water hyacinth compost), inorganic (urea) nitrogen (N) sources, and commercial Rhizobia inoculant on the yield of common bean (Phaseolus vulgaris) for two consecutive seasons in the short rains (2013) and long rains (2014). The experiments were laid out in a randomized complete block design and replicated four times. Triple superphosphate was applied to all treatments except those with compost to ensure that the soil had adequate phosphorus (P). Yellow and Rose coco bean varieties grown with urea and inoculated with commercial Rhizobia inoculant gave significantly higher yield of 382 kg ha−1 and 341 kg ha−1, respectively in the short rains (SR) season. In the long rains (LR) season bean yield was high in water hyacinth compost (1526 kg ha−1) and control with non-limiting P (1300 kg ha−1) treatments. Commercial Rhizobia inoculant did not significantly increase in yield in the SR and LR seasons. There was no significant influence on soil properties after two seasons of continuous cultivation of common bean and application of organic and inorganic fertilizers. These results demonstrate that water hyacinth compost improved bean yield in the LR season. However, longer field testing and economic analysis are required for it to be recommended as a substitute for inorganic N source among smallholder farmers.

Combined Application of Biofertilizers and Inorganic Nutrients Improves Sweet Potato Yields.

Sweet potato [Ipomoea batatas (L) Lam] yields currently stand at 4.5 t ha−1 on smallholder farms in Uganda, despite the attainable yield (45–48 t ha−1) of NASPOT 11 cultivar comparable to the potential yield (45 t ha−1) in sub-Saharan Africa (SSA). On-farm field experiments were conducted for two seasons in the Mt Elgon High Farmlands and Lake Victoria Crescent agro-ecological zones in Uganda to determine the potential of biofertilizers, specifically arbuscular mycorrhizal fungi (AMF), to increase sweet potato yields (NASPOT 11 cultivar). Two kinds of biofertilizers were compared to different rates of phosphorus (P) fertilizer when applied with or without nitrogen (N) and potassium (K). The sweet potato response to treatments was variable across sites (soil types) and seasons, and significant tuber yield increase (p < 0.05) was promoted by biofertilizer and NPK treatments during the short-rain season in the Ferralsol. Tuber yields ranged from 12.8 to 20.1 t ha−1 in the Rhodic Nitisol (sandy-clay) compared to 7.6 to 14.9 t ha−1 in the Ferralsol (sandy-loam) during the same season. Root colonization was greater in the short-rain season compared to the long-rain season. Biofertilizers combined with N and K realized higher biomass and tuber yield than biofertilizers alone during the short-rain season indicating the need for starter nutrients for hyphal growth and root colonization of AMF. In this study, N0.25PK (34.6 t ha−1) and N0.5PK (32.9 t ha−1) resulted in the highest yield during the long and the short-rain season, respectively, but there was still a yield gap of 11.9 and 13.6 t ha−1 for the cultivar. Therefore, a combination of 90 kg N ha−1 and 100 kg K ha−1 with either 15 or 30 kg P ha−1 can increase sweet potato yield from 4.5 to >30 t ha−1. The results also show that to realize significance of AMF in nutrient depleted soils, starter nutrients should be included.

Simulating Soil Moisture under Different Tillage Practices, Cropping Systems and Organic Fertilizers Using CropSyst Model, in Matuu Division, Kenya

Soil moisture stress is a limiting factor in crop production particularly in arid and semi-arid lands (ASALs) as it affects many physiological and biochemical processes of plants. Research on moisture conservation measures is thus imperative. The current study used CropSyst model to simulate soil moisture under different tillage practices (oxen plough, tied ridges and furrows and ridges), cropping systems (monocropping, intercropping and crop-rotation) and organic fertilizers; farm yard manure, rock phosphate (RP) and Farmyard manure (FYM) combined with rock phosphate (RP+FYM). The study was conducted in Matuu Division, Kenya for two seasons; October 2012 to February 2013 short rain season (SRS) and March to August 2013 long rain season (LRS). The experiment was laid out in a Randomized Complete Block design with a split-split plot arrangement and replicated three times. The main plots were tillage practices whereas the split plots were cropping systems and split-split plots were organic fertilizers and a control (nothing applied). The test crops were sorghum ( Sorghum bicolor L.) and sweet potato ( Ipomea batatas L. lam ) rotated and/or intercropped with dolichos ( Lablab purpureus ) and chickpea ( Cicer arietinum ). The CropSyst model was calibrated using measured soil texture, permanent wilting point, bulk density and initial soil moisture at the experimental site. Model validation was done using Root Mean Square Error (RMSE), percentage differences (PD) and willmott index (WI) of agreement. CropSyst model was reasonably validated as indicated by the low RMSE (0.5 to 1.3), PD (less than ±15) and WI index (close to 1). In the first season and second season, simulated soil moisture (101.91 and 108.3 mm) was significantly (P < 0.05) high in sorghum/dolichos intercrop with RP+FYM application under tied ridges and least (13.52 and 15.4 mm) in control treatment of sorghum mono crop under oxen plough. In sweet potato plots, both individual treatment and treatment interaction significantly influenced simulated soil moisture. Sweet potato-dolichos rotation (75.32 and 79.63 mm), with application of RP+FYM (75.03 and 79.39 mm) under tield ridges (95 and 100.24 mm) had highest simulated soil moisture levels under oxen plough (32.49 and 34.36 mm), sweet potato monocrop (53.46 and 55.26 mm) and control (52.52 and 55.39 mm) having the least during the first and second season, respectively. In both sorghum and sweet potato based cropping systems, soil moisture was correspondingly highest in tied ridges, intercropping and rotation systems involving dolichos and application of FYM+RP and least in control of monocropping under oxen plough. Information on effects of tillage practices, cropping systems and organic inputs could be very useful for soil water conservation purposes. Thus, using simulation models to attain the same could be the ultimate solution. A good agreement between observed and simulated soil moisture implied that CropSyst model is capable of investigating sustainable alternatives of increasing soil moisture in the ASALs.

Influence of Selected Ecological Farming Practices on Soil Moisture Retention and Yield of Sorghum (Sorghum bicolor (L.) Moench) and Cassava (Manihot esculanta Crantz) in Semi-Arid Yatta Sub-County, Kenya

In this study, the influence of ecological farming practices on soil moisture and yield of cassava (Manihot esculanta Crantz) and sorghum (Sorghum bicolor (L.) Moench) was investigated. The study was conducted in semi-arid Katangi and Ikombe divisions of Yatta sub-county between October 2010 and August 2012. A randomised complete block design with a split plot arrangement was used. Main plots were three cropping systems: (i) Intercropping; (Dolichos [Lablab purpureus]/Cassava, Dolichos/Sorghum, Pigeon pea [Cajanus cajan (L.) Millsp.]/Sorghum, Pigeon pea/Cassava); (ii) Rotation; Dolichos-Cassava, Dolichos-Sorghum, Pigeon pea-Cassava, Pigeon pea-Sorghum and (iii) Monocrop (pure cassava and sorghum). Split plots were organic inputs; farm yard manure (FYM), compost and absolute control. Sorghum/pigeon pea intercrop+FYM treatment had high moisture levels during short rain season (SRS) of 2010 at Katangi (5.21%), SRS of 2011 at Ikombe (5.19%) and long rain season (LRS) of 2011 at both sites (5.83%, 12.30%). Grain yields were highest under sorghum/dolichos intercrop+ FYM during LRS of 2011 at Katangi (1.36 t ha-1) and Ikombe (1.48 t ha-1), and SRS of 2010 at Katangi (1.39 t ha-1) only. Cassava/dolichos intercrop recorded high soil moisture levels in both sites under sorghum/dolichos intercrop during SRS of 2010 (6.48%, 8.35%), LRS of 2011 (7.63%, 8.77%) and LRS of 2012 (6.41%, 3.65%) for Katangi and Ikombe, respectively. Tuber yields were higher under cassava/pigeon intercrop in Katangi (18.63 t ha-1) and Ikombe (28.73 t ha-1) during SRS of 2010 and LRS of 2011, and SRS of 2011 and LRS of 2012 at Katangi (20.86 t ha-1). Intercropping sorghum with dolichos and cassava with pigeon pea + FYM would be a viable strategy to boost crop yields in smallholder farming systems of Yatta sub-county.

Special issue “Adaptation to climate change: analysing capacities in Africa”

Adapting to climate change is a challenge in Africa considering the prevailing livelihood conditions, the widespread poverty and food insecurity, the varying adaptive capacities, the weak institutional frameworks and the exposure to multiple stressors, which range from volatile financial and commodity markets and violent conflicts to extreme weather events. Adaptation is made more difficult by the complex interaction of impacts across sectors, which produces ‘‘cascading effects that are largely unpredictable’’ (World Bank 2012: 62). Two sets of dynamics intertwine and affect adaptation: the interactions between different biophysical impacts of global warming on the one hand (i.e. higher temperatures, changes in precipitation patterns, impacts on biodiversity), and the processes triggered by weak social systems that may be unable to compensate for sudden ecological changes and uncertainties on the other hand. As the stabilization of greenhouse gas concentrations in the atmosphere continues to be elusive, the threats of climate change to ecosystems, food production and economic development are becoming more apparent. With the exception of areas in the northeast, drier conditions are projected for Africa. Sillmann et al. (2012) project significant increases in extreme precipitation in terms of the monthly or annual maximum of 5-day precipitation accumulations increasing by 20–30 % towards the end of the twenty-first century for Western and Eastern Africa. East Africa is projected to become generally wetter in the future, while dry conditions are to intensify significantly in Southern Africa with significant increases in consecutive dry days (Sillmann et al. 2012; cf. Batisani and Yarnal 2010). Much of Southern Africa will be affected by extreme droughts and particularly soil moisture decreases (Dai 2012). However, a simulation by Williams and Funk (2010) shows contrasting results for tropical Eastern Africa—during the twenty-first century, drier conditions, associated with warming in the Indian Ocean, are more likely than wetter conditions in the long-rains season (March–June). Thus, there is still uncertainty about how climate change will actually affect precipitation in the continent, but a varying range of impacts can be expected. The fundamental limits to climate predictability (Thornton et al. 2011) indicate the need for downscaled climate projections in Africa, yet the already projected unprecedented conditions have various implications for African social and ecological systems. Changes in climate variables will affect water availability. Gerten et al. (2011) show that many African regions such as North and East Africa are physically water scarce, being unable to meet the water requirements of their populations. With climate and population change, water availability per person is likely to decline in these regions. While population growth is a major driver of water stress, in a ?2 C and ?4 C world, climate change would be the dominant cause of water stress in African river basins (Fung et al. 2011). Sea level rise and saltwater intrusion also threaten parts of Africa (Nicholls and Cazenave 2010). Forests in Africa may expand in some regions while they might decline in others. In a ?2 C and ?4 C world, forest area is likely to increase in the Congo Basin, West Africa and Madagascar, although the risk of niche contraction remains mainly in the North and South of Africa (Zelazowski et al. 2011). While not all climate change C. Ifejika Speranza (&) I. Scholz Centre for Development and Environment/NCCR North–South/ Institute of Geography, University of Bern, Bern, Switzerland e-mail: chinwe.ifejika.speranza@cde.unibe.ch

Performance of a Number of NERICA Cultivars in Zanzibar, Tanzania: Yield, Yield Components and Grain Quality

The cultivars of NERICA (New Rice for Africa), which are characterized by early maturity and high yield potential under rainfed conditions, have the potential to increase rice production in Tanzania, where rice cultivation is greatly affected by a short rainy season. Trials were conducted in Zanzibar to examine the yield performances of 14 NERICA cultivars at five locations during the long-rains season (Masika) and at another five locations during the short-rains season (Vuli). The NERICA cultivars produced significantly higher yields than local cultivars at five locations. Yields of 12 NERICA cultivars were associated with rainfall (R2 = 0.367 to 0.732) such that they yielded well during Masika (109 to 343 g m-2) and poorly during Vuli (11 to 68 g m-2). Spikelet number per panicle and percentage of filled spikelets (% filled spikelets) accounted for 70 to 90% of the yield variation in all cultivars, suggesting that yield was determined mainly during the later part of the growth period. In some cultivars, yield was associated with rainfall during the later part of the growth period but the yield of the remainder was associated with rainfall during the early part. A selected group of farmers, extension workers and researchers evaluated grain quality. Some cultivars scored well, especially NERICA 1. We conclude that NERICAs are generally suitable for production during Masika and that NERICA 1 especially should be promoted due to its high grain quality. However, for double cropping of NERICAs, measures must be implemented for increasing or maintaining the water status of the soil during Vuli.

Supplemental irrigation effects on yield of two watermelon (Citrulus lanatus) cultivars under semi-arid climate in Kenya

The objectives of this study were to determine the effect of the supplemental irrigation using drip, sprinkler and furrow methods on two watermelon cultivars (Charleston grey, and Sugar baby) by studying their growth, yield and quality (Brix index) and economic feasibility under semi-arid climate in Kenya. Cultivars irrigated with drip produced significantly more fruits than those under either sprinkler or furrow. The highest total economic yield of 4.05 Mg/ha in the short rain season (SRS) and 4.95 mg/ha in the long rain season (LRS) was obtained in ‘Charleston grey’ irrigated by drip. The average fruit weight was 6.07 kg in the SRS and 7.42 kg in the LRS. The highest net benefit was US$ 493.3/ha in the SRS and 706.1/ha in the LRS. A 2 or 4-week starter irrigation, drip supplemental irrigation boosted ‘Charleston grey’ yields by 1.78-fold, if water stress occurred during the late vegetative growth. Supplemental irrigation during late vegetative growth decreased the total soluble solids in fruits. Total soluble solids concentration was 5.93°Brix in the SRS and 8.16°Brix in the LRS. The furrow irrigation supplied the most water to the crop resulting in the lowest total soluble solids of watermelons. Key words: Drought management, irrigation methods, watermelon cultivar.

Influence of improved fallow systems and phosphorus application on arbuscular mycorrhizal fungi symbiosis in maize grown in western Kenya

A field study was carried out on a six-year-old on-farm field trial during long-rains season (April–August) 2003 to investigate the effect of improved fallow systems and phosphorus application on arbuscular mycorrhiza fungi (AMF) symbiosis in maize. The trial comprised of maize rotated with a fast growing leguminous Crotalariagrahamiana fallow and a non-leguminous Tithonia diversifolia fallow for 3 years followed by continuous maize. The experiment was randomized complete block design with three cropping (continuous maize, Crotalaria fallow and Tithonia fallow) systems and two phosphorus levels (0 and 50 kg P/ha). AMF colonization in maize roots, maize yield and macro-nutrients uptake were recorded. Phosphorus applications improved (P < 0.05) early (<8 weeks old maize) AMF colonization, nutrient uptake and maize yield in improved fallow systems. Greater differences due to phosphorus application were noted in maize in Tithonia fallow than in Crotalaria fallow. Following phosphorus application, a positive relationship existed between early AMF colonization and maize yield (r = 0.38), and phosphorus and nitrogen uptake (r = 0.40 and r = 0.43, respectively), demonstrating the importance of phosphorus fertilization in enhancing low-input technologies (improved fallows systems) in phosphorus deficient and acidic soils of western Kenya.

Effect of legume-managed fallow on weeds and soil nitrogen in following maize (Zea mays L.) and wheat (Triticum aestivum L.) crops in the Rift Valley highlands of Kenya

The use of legume crops as alternatives to a fallow in wheat–maize rotations in the Rift Valley of Kenya may suppress weeds and add nitrogen to the system. A field study was set up in the Njoro and Rongai regions to evaluate the effect of managing the traditional fallow with chickpea (Cicer arietinum L.), field bean (Phaseolus vulgaris L.), soybean [Glycine max (L.) Merril], field pea (Pisum sativum L.) and dolichos [Lablab purpureus (L) Sweet] on the following wheat and maize crops. The objectives of this study were to assess the impact of improved fallow on weed control, soil nitrogen and performance of the following cereals in a bid to improve their yields. The legumes, along with wheat and maize, were grown as fallow-management treatments during the short-rains season, and their residues were incorporated into the soil before sowing the test cereal in the long-rains season. Weed biomass and species diversity reduced by 35–92% and 25–58% at Njoro, and 10–100% and 83–100% at Rongai, respectively, in the succeeding cereal against preceding traditional fallow. The perennial weeds, which included Digitaria scalarum, Pennisetum clandestinum and Conyza sp., were substantially reduced in the managed fallow. Legume-managed fallow significantly improved soil nitrogen status and the yield of the following cereals. Grain yield in managed fallow increased on average by about 39 and 17% over locations in maize and wheat, respectively. Despite yielding less soil-incorporated residue, the impact of legumes was greater than that of the traditional fallow yielding large amount of organic material. Among the legume species, dolichos showed outstanding positive effect on succeeding cereal crop, probably due to increased soil nitrate levels. Field bean and chickpea have a potential seed advantage, although the latter is susceptible to 100% loss by Helicoverpa armigera. Hence, managing the traditional short-rains fallow with legumes could reduce weed infestation, in addition to improving soil nitrogen for subsequent crops.

The influence of climate change on maize production in the semi-humid–semi-arid areas of Kenya

The effect of climate change on maize production in the semi-humid and semi-arid, agro-climatic zones III-IV of Kenya was evaluated using two General Circulation Models (GCMs): the Canadian Climate Center Model (CCCM) and the Geophysical Fluid Dynamics Laboratory (GFDL), as well as the CERES-Maize model. Long-term climate data was obtained from three meteorological stations situated in eastern, central and western regions of Kenya, while maize data was obtained from six sites within the regions. The climate scenarios were projected to the year 2030. Temperature increases of 2·29 and 2·89°C are predicted by the CCCM and GFDL, respectively. Rainfall levels are predicted to remain unchanged, but there are thought to be shifts in distribution. It is predicted that the short-rains season (October–January) will experience some increased rainfall, while the long-rains season (April–July) will show a decrease. Maize yields are predicted to decrease in zone III areas, while an increase is predicted in zone IV areas. However, the predicted changes in yields are low since they all fall below 500 kg ha−1, except the Homa Bay site. Thus, to counter the adverse effects of climate change on maize production, it may be necessary to use early maturing cultivars, practice early planting, and in eastern Kenya, shift to growing maize during the short-rains season.

A diagnostic study of the eastern Africa monsoon circulation during the northern hemisphere spring season

The eastern Africa monsoons during the Northern Hemisphere spring (NHS) season are described based on composites derived from various rainfall anomaly scenarios. The years 1981/1984 were delineated as some of the recent wettest/driest years over this region during the NHS season. Wet/dry spells within these anomalous years were further selected using PCA T-mode analysis. Both the anomalous years and the wet/dry spells identified from these years were used to create wind composites that were used to describe the eastern Africa Monsoon circulation. Composite wind analyses showed the dominance of the westerlies/easterlies in the lower/upper troposphere and their migration from the Southern Hemisphere to the Northern Hemisphere. Analysis of the individual wettest/driest years showed that before the start of the equatorial eastern Africa (EEA) long-rains season, easterlies are dominant near the Equator and westerlies near 15°S in the lower troposphere, while at the end of the rainy season the westerlies were located to the north of the Equator, near 5°N, with easterlies on their lateral sides. However, during the EEA long-rains season westerly/easterly wind events occurred in alternation over the region. These westerly/easterly episodes were associated with wet/dry rainfall spells. Vertical sections of zonal wind component showed that the wind alignment during wet spells was similar to that generally observed in other monsoonal regions, with lower tropospheric westerlies overlain by upper tropospheric easterlies. But the reduced frequency of lower tropospheric westerlies is suggested to be due to the barrier effect of the north–south mountain chains which allow only the most intense westerlies to cross the mountains into the EEA region. Copyright © 1999 Royal Meteorological Society

Seasonal variation of anti- Plasmodium falciparum antibodies directed against a repetitive peptide of gametocyte antigen Pfs2400 in inhabitants in the State of Amapá, Brazil

Antibodies to the Pfs2400 gametocyte antigen have been shown to inhibit the development of Plasmodium falciparum in anophelines and therefore this antigen is a candidate for a transmission-blocking vaccine. To test seasonal variation of these antibodies under field conditions, sera from 72 individuals were collected twice, first during the long-rains season with low malaria transmission and then, 6 months later, during the short-rains season, when transmission is high. This study was conducted in several localities in the State of Amapá, Brazil. All but three individuals had a positive indirect fluorescent antibody test (IFAT) with asexual forms of P. falciparum. Most of them did not report malaria attacks during the period between the first and second sampling. Their sera were tested by IFAT with P. falciparum gametocytes. The overall positivity of this test did not vary between seasons, and was 47.2 (34/72) and 48.6% (35/72), respectively. The sera were also tested by ELISA with the Pfs2400 repeat peptide. The positivity rate dropped from 29.2 (21/72) to 15.3% (11/72) and the mean absorbancies from 0.623 to 0.354, when we compared the results of the long-rains and short-rains seasons. Fifteen out of the 21 ELISA positive sera turned negative, with no change of geometric mean of titres (GMT) of asexual IFAT, while five negatives became ELISA positive on second sampling, with increase of GMT. Soon after the second sampling a malaria outbreak was reported in one of the localities. These results point toward a relatively short persistence of anti-Pfs2400 repeat peptide antibodies, under natural field conditions. A gametocyte antigen booster before a high transmission period might contribute towards lowering malaria incidence by eliciting a partially effective antibody response.