Measurement of the likely magnitude of the economic impact of climate change on African agriculture has been a challenge. Using data from a survey of more than 9,000 farmers across 11 African countries, a cross-sectional approach estimates how farm net revenues are affected by climate change compared with current mean temperature. Revenues fall with warming for dryland crops (temperature elasticity of -1.9) and livestock (-5.4), whereas revenues rise for irrigated crops (elasticity of 0.5), which are located in relatively cool parts of Africa and are buffered by irrigation from the effects of warming. At first, warming has little net aggregate effect as the gains for irrigated crops offset the losses for dryland crops and livestock. Warming, however, will likely reduce dryland farm income immediately. The final effects will also depend on changes in precipitation, because revenues from all farm types increase with precipitation. Because irrigated farms are less sensitive to climate, where water is available, irrigation is a practical adaptation to climate change in Africa.

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Global climate changes can alter the suitable geographical range of different crops, leading to possible changes in cropping pattern and its extent in some regions. For example, temperature changes can interact very closely with changes in availability of water and soil nutrients, and crop growth cycle. The consequences of the biophysical impacts of climate changes will be influenced by the human responses to these impacts. There is a strong link between soils and human health, and these soils per se are controlled by climate changes. The human health is very close to both selenium (Se) element and climate changes. It is estimated that about 37-40 % of the total Se emissions to the atmosphere are due to the anthropogenic activities.Those anthropogenic activities, which are sources of Se, include coal and oil combustion, mining activities, the utilization of rock phosphates as a fertilizer and the application of sewage sludge to agricultural land. It was thought that selenium was a toxicant for a long time due to inadequate analytical data. In the recent past, Se has become very important in environmental biogeochemistry because of its influence on human health. Although Se is an essential nutrient for animals and humans, it is also toxic at high doses. Furthermore, the range between Se deficiency, lower than 40 lg day -1 , and toxicity, higher than 400 lg day -1 , is narrow. Selenium deficiency has been linked to several human diseases including multiple sclerosis, muscular dystrophy, heart disease, immune system, cancer and reproductive disorders. On the other hand, Se toxicity can lead to hair and nail loss and disruption of the nervous and digestive systems in animals and humans. Despite the obvious connections between Se element and human health under climate changes, there has not been a great amount of research done in this area. So, more and more studies should be carried out to enhance and protect human health. Therefore, this article reviews the biological and economic dimensions of the effects of Se element on human health under climate changes.

The Policy Research Working Paper Series disseminates the findings of work in progress to encourage the exchange of ideas about development issues. An objective of the series is to get the findings out quickly, even if the presentations are less than fully polished. The papers carry the names of the authors and should be cited accordingly. The findings, interpretations, and conclusions expressed in this paper are entirely those of the authors. They do not necessarily represent the views of the International Bank for Reconstruction and Development/World Bank and its affiliated organizations, or those of the Executive Directors of the World Bank or the governments they represent.

Estimating crop water productivity (CWP) for spatially variable climatic conditions in Egypt is important for the redistribution of crop planting to optimize production per unit of water consumed. The current paper aims to estimate maximum CWP trends under conditions of the Northern Nile Delta over three decades to choose crops that exhibit a higher productivity per unit of water and positive trends in the CWP. The Kafr El Sheikh Governorate was selected to represent the Northern Nile Delta Region, and mean monthly weather data for the period of 1985 to 2015 were collected to calculate standardized reference evapotranspiration and crop water use for a wide array of crops grown in the region using the CROPWAT8.0 model. The CWP was then calculated by dividing crop yield by seasonal water consumption. The CWP data range from 0.69 to 13.79 kg·m−3 for winter field crops, 3.40 to 10.69 kg·m−3 for winter vegetables, 0.29 to 6.04 kg·m−3 for summer field crops, 2.38 to 7.65 kg·m−3 for summer vegetables, 1.00 to 5.38 kg·m−3 for nili season crops (short-season post summer), and 0.66 to 3.35 kg·m−3 for orchards. The crops with the highest CWP values (kg·m−3) over three decades in descending order are: sugar beet (13.79), potato (w2) (10.69), tomato (w) (10.58), eggplant (w) (10.05), potato (w1) (9.98), cucumber (w) (9.81), and cabbage (w) (9.59). There was an increase in CWP of 41% from the first to the second and 22% from the second to the third decade. The CWP increase is attributed to a small decrease in water consumption and to a considerable increase in crop yield. The yield increases are attributed mainly to the planting of higher yielding varieties and/or the application of better agronomic practices.