Many studies have examined the role of mean climate change in agriculture, but an understanding of the influence of inter-annual climate variations on crop yields in different regions remains elusive. We use detailed crop statistics time series for ~13,500 political units to examine how recent climate variability led to variations in maize, rice, wheat and soybean crop yields worldwide. While some areas show no significant influence of climate variability, in substantial areas of the global breadbaskets, >60% of the yield variability can be explained by climate variability. Globally, climate variability accounts for roughly a third (~32-39%) of the observed yield variability. Our study uniquely illustrates spatial patterns in the relationship between climate variability and crop yield variability, highlighting where variations in temperature, precipitation or their interaction explain yield variability. We discuss key drivers for the observed variations to target further research and policy interventions geared towards buffering future crop production from climate variability.

/pdf/climate-variation-explains-a-third-of-global-crop-yield-49v478uhu9.pdf

Climate variation explains a third of global crop yield variability

Sub-Saharan Africa has been portrayed as the most vulnerable region to the impacts of global climate change because of its reliance on agriculture which is highly sensitive to weather and climate variables such as temperature, precipitation, and light and extreme events and low capacity for adaptation. This article reviews evidence on the scope and nature of the climate change challenge; and assesses the impact of climate change on agriculture and food security in Sub-Saharan Africa. From the review, it is apparent that the climate in Africa is already exhibiting significant changes, evident by changes in average temperature, change in amount of rainfall and patterns and the prevalence of frequency and intensity of weather extremes. The review also revealed that although uncertainties exist with regards to the magnitude of impacts, climate will negatively affect agricultural production in Sub-Saharan Africa. Specifically, as result of current and expected climate change, the area suitable for agriculture, the length of growing seasons and yield potential, particularly along the margins of semi-arid and arid areas, are expected to decrease. These impacts will affect all components of food security: food availability, food accessibility, food utilisation and food stability and hence increase the risk of hunger in the region. The review thus confirms the general consensus that Sub-Saharan Africa is the most vulnerable region to climate change. It suggests that, policymakers and development agencies should focus on formulating and implementing policies and programmes that promote farm level adaptation strategies currently being practiced by farmers across the region.

Climate change and variability in Sub-Saharan Africa: a review of current and future trends and impacts on agriculture and food security

The use of propensity scores in psychological and educational research has been steadily increasing in the last 2 to 3 years. However, there are some common misconceptions about the use of different estimation techniques and conditioning choices in the context of propensity score analysis. In addition, reporting practices for propensity score analyses often lack important details that allow other researchers to confidently judge the appropriateness of reported analyses and potentially to replicate published findings. In this article we conduct a systematic literature review of a large number of published articles in major areas of social science that used propensity scores up until the fall of 2009. We identify common errors in estimation, conditioning, and reporting of propensity score analyses and suggest possible solutions.

A Systematic Review of Propensity Score Methods in the Social Sciences.

In West Africa, agriculture, mainly rainfed, is a major economic sector and the one most vulnerable to climate change. A meta-database of future crop yields, built up from 16 recent studies, is used to provide an overall assessment of the potential impact of climate change on yields, and to analyze sources of uncertainty. Despite a large dispersion of yield changes ranging from -50% to +90%, the median is a yield loss near -11%. This negative impact is assessed by both empirical and process-based crop models whereas the Ricardian approach gives very contrasted results, even within a single study. The predicted impact is larger in northern West Africa (Sudano-Sahelian countries, -18% median response) than in southern West Africa (Guinean countries, -13%) which is likely due to drier and warmer projections in the northern part of West Africa. Moreover, negative impacts on crop productivity increase in severity as warming intensifies, with a median yield loss near -15% with most intense warming, highlighting the importance of global warming mitigation. The consistently negative impact of climate change results mainly from the temperature whose increase projected by climate models is much larger relative to precipitation change. However, rainfall changes, still uncertain in climate projections, have the potential to exacerbate or mitigate this impact depending on whether rainfall decreases or increases. Finally, results highlight the pivotal role that the carbon fertilization effect may have on the sign and amplitude of change in crop yields. This effect is particularly strong for a high carbon dioxide concentration scenario and for C3 crops (e.g. soybean, cassava). As staple crops are mainly C4 (e.g. maize, millet, sorghum) in WA, this positive effect is less significant for the region. (C) 2011 Elsevier Ltd. All rights reserved.

/pdf/the-impact-of-future-climate-change-on-west-african-crop-33uqq8e8n1.pdf

The impact of future climate change on West African crop yields: What does the recent literature say?

West Africa is known to be particularly vulnerable to climate change due to high climate variability, high reliance on rain-fed agriculture and limited economic and institutional capacity to respond to climate variability and change. In this context, better knowledge of how climate will change in West Africa and how such changes will impact crop productivity is crucial to inform policies that may counteract the adverse effects. This review paper provides a comprehensive overview of climate change impacts on agriculture in West Africa based on the recent scientific literature. West Africa is nowadays experiencing a rapid climate change, characterized by a widespread warming, a recovery of the monsoonal precipitation, and an increase in the occurrence of climate extremes. The observed climate tendencies are also projected to continue in the 21st century under moderate and high emission scenarios, although large uncertainties still affect simulations of the future West African climate, especially regarding the summer precipitation. However, despite diverging future projections of the monsoonal rainfall, which is essential for rain-fed agriculture, a robust evidence of yield loss in West Africa emerges. This yield loss is mainly driven by increased mean temperature while potential wetter or drier conditions as well as elevated CO2 concentrations can modulate this effect. Potential for adaptation is illustrated for major crops in West Africa through a selection of studies based on process-based crop models to adjust cropping systems (change in varieties, sowing dates and density, irrigation, fertilizer management) to future climate. Results of the cited studies are crop and region specific and no clear conclusions can be made regarding the most effective adaptation options difficult. Further efforts are needed to improve modelling of the monsoon system and to better quantify the uncertainty in its changes under a warmer climate, the response of the crops to such changes and in the potential for adaptation.

/pdf/agriculture-in-west-africa-in-the-twenty-first-century-39nke5sh8i.pdf

Agriculture in West Africa in the Twenty-First Century: Climate Change and Impacts Scenarios, and Potential for Adaptation

Two separate lines of investigation were adapted from the recommendations of the 1994 United States Country Studies Program (USCP). In one approach, arbitrary incremental scenarios were adopted to assess the response of crop yield to changes in the various elements of climate. Using the erosion productivity impact calculator (EPIC) crop model, tests were conducted to demonstrate how crop yield might respond to changes in rainfall, relative humidity (RH), temperature, solar radiation and CO2 concentration. The value of one element was altered incrementally while holding constant the values of the others. In the second approach, potential future changes in the yields of maize, sorghum, millet, rice and cassava were simulated based on a scenario specifying mean conditions for 1961-9190 as a baseline and general circulation model (GCM) projections from this for 3 periods: 2010-2039, 2040-2069 and 2070-2099. The results predicted a possible increase in crop yield during the first half of the 21st century to be followed by a decrease during the second half. Enhanced crop yield was explained by projected increases in rainfall, solar radiation, atmospheric humidity and CO2 concentrations. Lower yields were explained in terms of continued global warm- ing, as a result of which maximum and minimum temperatures approach the limits of tolerance for the modelled crops.

/pdf/food-crop-production-in-nigeria-ii-potential-effects-of-1bnix3nz3y.pdf

Food crop production in Nigeria. II. Potential effects of climate change

Climate and crop productivity are both characterised by inter-annual variability. The common understanding is that the co-variation is indicative of a simple cause and effect relationship. However, the relationship analysed in this paper is that of crops with complex phases of growth and development responding to a climate that is multivariate, dynamic and heterogeneous. Bivariate cor- relation, multiple correlation and regression analyses were employed to demonstrate the relationship between crop yield and climate. The crops studied were cowpeas, groundnut, millet, maize, sorghum and rice during the period 1983 to 1999 in the Nigerian Arid Zone. The predictive models generated for cowpeas, groundnut, millet and sorghum were statistically significant with α≤ 0.05. Among the more powerful determinants of crop yield were rainfall at the onset and at the cessation months of the growing season. Inter-annual changes in the yield of maize and rice were less sensitive to rainfall variability. In general, the linear models failed to incorporate the separation of crop yield variability from rainfall at higher levels of precipitation. During the long periods with normal and above normal rainfall, crop yield sensitivity tends to be weak. However, during the years with unusually low pre- cipitation, crop yield sensitivity becomes more pronounced. For purposes of developing the appropri- ate adaptation strategies, it is suggested that a distinction be made between drought with its associ- ated disasters and the less hazardous but more frequent inter-annual climate or rainfall variability.

/pdf/food-crop-production-in-nigeria-i-present-effects-of-climate-1sdgya8pf5.pdf

Food crop production in Nigeria. I. Present effects of climate variability

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Food crop production in Nigeria. II. Potential effects of climate change

Food crop production in Nigeria. I. Present effects of climate variability