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- ItemAssessing the contribution of soil NOx emissions to European atmospheric pollution(Bristol : IOP Publ., 2021) Skiba, Ute; Medinets, Sergiy; Cardenas, Laura M.; Carnell, Edward John; Hutchings, Nick; Amon, BarbaraAtmospheric NOx concentrations are declining steadily due to successful abatement strategies predominantly targeting combustion sources. On the European continent, total NOx emissions fell by 55% between 1990 and 2017, but only modest reductions were achieved from the agricultural sector; with 7.8% from 20 Eastern European countries and 19.1% from 22 Western European countries. Consequently, the share of agricultural NOx emissions for these 42 European countries have increased from 3.6% to 7.2%. These values are highly uncertain due to serious lack of studies from agricultural soils and manure management. The emission factor (EFNO 1.33%), currently used for calculating soil NOx emissions from European agricultural categories ‘N applied to soils’ and ‘manure management’ was evaluated here by including recently published data from temperate climate zones. The newly calculated EFNO (average 0.60%, 0.0625th%/0.5475th%, n = 65 studies) is not notably different from the current value, given the large uncertainties associated with the small pool of studies, and therefore continued use of EFNO (1.33%) is recommended until more data become available. An assessment of the contribution of agricultural and non-agricultural NOx sources found that of the 42 European countries, the 8 most populated countries achieved considerable reductions (1990–2017) from categories ‘non-agricultural sources’ (55%), ‘N applied to soils’ (43%) and ‘manure management’ (1.2%), compared to small reductions from the remaining 34 countries. Forests are also large sources of soil NOx. On average, emissions from Eastern European forests were 4 times larger than from ‘N applied agricultural soil’, whereas Western European NOx emissions from ‘N applied agricultural soil’ were two times larger than from forest soils. Given that non-agricultural sources of NOx continue to decline, soil related emissions from agriculture, forests and manure management become more important, and require rigorous investigation in order to improve atmospheric pollution forecasts.
- ItemIs wetter better? Exploring agriculturally-relevant rainfall characteristics over four decades in the Sahel(Bristol : IOP Publ., 2021-2-11) Porkka, Miina; Wang-Erlandsson, Lan; Destouni, Georgia; Ekman, Annica M. L.; Rockström, Johan; Gordon, Line J.The semi-arid Sahel is a global hotspot for poverty and malnutrition. Rainfed agriculture is the main source of food and income, making the well-being of rural population highly sensitive to rainfall variability. Studies have reported an upward trend in annual precipitation in the Sahel since the drought of the 1970s and early ‘80s, yet farmers have questioned improvements in conditions for agriculture, suggesting that intraseasonal dynamics play a crucial role. Using high-resolution daily precipitation data spanning 1981–2017 and focusing on agriculturally-relevant areas of the Sahel, we re-examined the extent of rainfall increase and investigated whether the increases have been accompanied by changes in two aspects of intraseasonal variability that have relevance for agriculture: rainy season duration and occurrence of prolonged dry spells during vulnerable crop growth stages. We found that annual rainfall increased across 56% of the region, but remained largely the same elsewhere. Rainy season duration increased almost exclusively in areas with upward trends in annual precipitation (23% of them). Association between annual rain and dry spell occurrence was less clear: increasing and decreasing frequencies of false starts (dry spells after first rains) and post-floral dry spells (towards the end of the season) were found to almost equal extent both in areas with positive and those with no significant trend in annual precipitation. Overall, improvements in at least two of the three intraseasonal variables (and no declines in any) were found in 10% of the region, while over a half of the area experienced declines in at least one intraseasonal variable, or no improvement in any. We conclude that rainfall conditions for agriculture have improved overall only in scattered areas across the Sahel since the 1980s, and increased annual rainfall is only weakly, if at all, associated with changes in the agriculturally-relevant intraseasonal rainfall characteristics.
- ItemExploring uncertainties in global crop yield projections in a large ensemble of crop models and CMIP5 and CMIP6 climate scenarios(Bristol : IOP Publ., 2021) Mueller, Christoph; Franke, James; Jaegermeyr, Jonas; Ruane, Alex C.; Elliott, Joshua; Moyer, Elisabeth; Heinke, Jens; Falloon, Pete D.; Folberth, Christian; Francois, LouisConcerns over climate change are motivated in large part because of their impact on human society. Assessing the effect of that uncertainty on specific potential impacts is demanding, since it requires a systematic survey over both climate and impacts models. We provide a comprehensive evaluation of uncertainty in projected crop yields for maize, spring and winter wheat, rice, and soybean, using a suite of nine crop models and up to 45 CMIP5 and 34 CMIP6 climate projections for three different forcing scenarios. To make this task computationally tractable, we use a new set of statistical crop model emulators. We find that climate and crop models contribute about equally to overall uncertainty. While the ranges of yield uncertainties under CMIP5 and CMIP6 projections are similar, median impact in aggregate total caloric production is typically more negative for the CMIP6 projections (+1% to −19%) than for CMIP5 (+5% to −13%). In the first half of the 21st century and for individual crops is the spread across crop models typically wider than that across climate models, but we find distinct differences between crops: globally, wheat and maize uncertainties are dominated by the crop models, but soybean and rice are more sensitive to the climate projections. Climate models with very similar global mean warming can lead to very different aggregate impacts so that climate model uncertainties remain a significant contributor to agricultural impacts uncertainty. These results show the utility of large-ensemble methods that allow comprehensively evaluating factors affecting crop yields or other impacts under climate change. The crop model ensemble used here is unbalanced and pulls the assumption that all projections are equally plausible into question. Better methods for consistent model testing, also at the level of individual processes, will have to be developed and applied by the crop modeling community.