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: Nicaragua has already experienced substantial climate change, in part due to a loss of one half of its forest cover in the last half-century. In this study, we assess the extent to which historical climate trends have contributed to stagnating yields for maize (Zea mays) and bean (Phaseolus vulgaris), the two main staple crops in the country. We first analyze 40 years of historical weather data throughout Nicaragua to estimate trends, and assess the extent to which these trends correlate with spatial deforestation patterns. Then, we create a regression model linking department-level maize and bean yields with seasonal weather conditions, and use the model to estimate the impact of historical climate trends on yields. Regressions are run for yields on both harvested and sown area, with the latter accounting for the effect of complete crop losses. Results confirm strong warming trends throughout the country, with daytime temperatures in deforested areas warming at more than double the rate of global averages in the tropics. Decreases in rainfall frequency are also seen almost everywhere, along with an earlier end to the rainy season. Regression model results show, as expected, that red bean is a highly temperature-sensitive crop, and that maize is more water-limited than bean due to its longer seasonal duration. Warming temperatures and less frequent rainfall have led to drought-related losses for both crops in the main commercial production areas, while heavier rains at planting and harvest have also negatively affected yields, especially for bean. Moreover, reduced precipitation in December and January has negatively impacted production for bean in the commercially important apante, or dry season, on the humid Atlantic side of the country. In these areas, however, substantial model uncertainty remains for maize, with an alternative model formulation showing substantial benefits from drier and sunnier conditions. At an annual, national scale, beans have been more affected by climate trends since 1970 than maize, with −5% yield declines per decade on harvested area for bean and −4% for maize, and −12% and −7% yield declines respectively on sown area (with the alternative model showing gains for maize). Climate adaptation responses include government efforts to limit bean exports to control consumer prices, a switch from red to black bean for commercial sales and export, and area expansion and migration for bean in order to maintain production levels.Agricultural and Forest Meteorology 11/2014; · 3.89 Impact Factor
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ABSTRACT: Climate variability is the major cause of in food production in the semi-arid tropical (SAT) regions of India leading to food insecurity, malnutrition and poverty. Although the total amount of rainfall in the SAT regions is adequate to meet the water requirements of the crops and cropping systems, its erratic distribution results in periods of excess and de water availability, leading to low productivity and degradation of natural resources. Therefore, an integrated water resources management approach comprising in-situ water conservation, harvesting of excess water in ponds and groundwater recharging and its e use through appropriate supplemental irrigation methods, improved crop varieties and cropping systems, balanced nutrition of crops, crop diversiication and intensi with high value crops and crop protection is needed to produce more food and income per unit of rainfall. The paper describes the achievements made by ICRISAT in collaboration with its partners in enhancing crop productivity and rainfall use e by implementing improved technologies in on-station and on-farm community watersheds in India.11/2014;
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ABSTRACT: The aim of this work is to determine to what extent precipitation modulated by the Madden–Julian Oscillation (MJO) over East Africa can be forecast by the operational global Met Office Unified Model (MetUM). Observed patterns of rainfall were analysed over Kenya, Tanzania and Uganda and used to validate MetUM forecasts made over the period 2005–2012. It was found that there is a large seasonal dependence on the MJO for episodes of enhancement and suppression of rainfall over the inland highlands and the coastal lowlands, particularly from March to May and October to December, when the Intertropical Convergence Zone is located directly over the region. In phases 2–4 of the MJO lifecycle, there is an enhancement of precipitation over the highland regions and suppression over the coast. This dipole is reversed throughout phases 6–8. These findings corroborate previous studies undertaken over the region. The observed patterns were replicated well by the MetUM global model, even up to a forecast lead time of 5 days (T + 120 h), though some minor drift is apparent and convective and suppressed centres tend to stray from those of the observed rainfall. Model resolution is thought to be a key component of this difference. The systematic errors will likely improve with further plans for model resolution and physics upgrades, although the overall quality of the MetUM's ability to forecast the MJO over this region is sound.Meteorological Applications 10/2014; · 1.52 Impact Factor