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This study explores the implications of recent extreme rainfall and flood events in the Sahel and the wider West African region for climate change adaptation. Are these events merely a temporal nuisance as suggested by the lingering desertification discourse or will more climatic extremes characterize the region over the next century? After reviewing incidences of severe rainfall and projected future climate variability, the paper examines local flood knowledge and decision-making, drawing upon a case study in Ghana. The data demonstrate that a variety of response strategies to flooding exist; yet, knowledge of and access to climate forecasts and other learning tools are essentially absent. So far, floods have not triggered mass displacement although cumulative environmental deterioration is likely to cause environmental refugees. The paper recommends to lay to rest the desertification narrative, consider the possibility of both floods and droughts, and mobilize local memory for anticipatory learning and practical adaptation. [ABSTRACT FROM AUTHOR]

An introduction is presented in which the editors discuss articles in the issue on the topic of the Benefits of Reduced Anthropogenic Climate ChangE (BRACE) project including climate system outcomes, extreme weather events, and health impacts of climatic changes.

We perform CLMcrop simulations of the 20th and 21st centuries to assess potential avoided impacts in (a) crop yield losses and (b) water demand increases if humanity were to choose the representative concentration pathway (RCP) 4.5 instead of 8.5. RCP 8.5 imposes more extreme climatic changes on CLMcrop, while simultaneously exposing the crops to higher CO2 fertilization than RCP 4.5. As a result CLMcrop simulates global to regional scale changes in yield and water requirements for RCP 8.5 that exceed and sometimes more than double the RCP 4.5 changes relative to today. Under RCP 4.5 then, human societies may confront easier adaptation to changes in crop yields and water requirements. Under both RCPs, CLMcrop projects declining global yields for C3 crops (e.g., wheat, soybean, rice) without CO2 fertilization and C4 crops (corn, sugarcane) without irrigation. Yield declines of 3 t ha−1 stand out in parts of tropical and subtropical Africa and South America (presently areas of rapid agricultural expansion) and are due to increasing plant respiration and decreasing soil moisture, both due to rising temperatures. Irrigation and CO2 fertilization mitigate yield losses and in some cases lead to gains, so irrigation may help maintain or increase current yields through the 21st century. However, simulated global irrigation requirements increase: as much as 23 % for C4 crops without CO2 fertilization under RCP 8.5 and as little as 3 % for C4 crops with CO2 fertilization under RCP4.5. Nitrogen fertilized crops display greater vulnerability to climate and environmental change than unfertilized crops in our simulations; still relative to unfertilized crops, they deliver significantly higher yields and remain indispensable in supporting a more populous and affluent humanity. These CLMcrop results broadly agree with previously published outcomes for the 21st century. We describe in this article a new version of CLMcrop that represents prognostic crop behavior not only in the mid-latitudes but also the tropics. [ABSTRACT FROM AUTHOR]

Precipitation extremes are expected to increase in a warming climate, which may have serious societal impacts. This study uses two initial condition ensembles conducted with the Community Earth System Model (CESM) to investigate potential changes in extreme precipitation under two climate change scenarios over the contiguous United States. We fit non-stationary generalized extreme value (GEV) models to annual maximum daily precipitation simulated from a 30-member ensemble under the RCP8.5 scenario and a 15-member ensemble under the RCP4.5 scenario. We then compare impacts using the 1 % annual exceedance probability (AEP) level, which is the amount of daily rainfall with only a 1 % chance of being exceeded in a given year. Under RCP8.5 between 2005 and 2080, the 1 % AEP level is projected to increase by 17 % on average across the U.S., and up to 36 % for some grid cells. Compared to RCP8.5 in the year 2080, RCP4.5 is projected to reduce the 1 % AEP level by 7 % on average, with reductions as large as 18 % for some grid cells. We also investigate a pattern scaling approach in which we produce predictive GEV distributions of annual precipitation maxima under RCP4.5 given only global mean temperatures for this scenario. We compare results from this less computationally intensive method to those obtained from our GEV model fitted directly to the CESM RCP4.5 output and find that pattern scaling produces reasonable projections. [ABSTRACT FROM AUTHOR]

Using ensembles from the Community Earth System Model (CESM) under a high and a lower emission scenarios, we investigate changes in statistics of extreme daily temperature. The ensembles provide large samples for a robust application of extreme value theory. We estimate return values and return periods for annual maxima of the daily high and low temperatures as well as the 3-day averages of the same variables in current and future climate. Results indicate statistically significant increases (compared to the reference period of 1996–2005) in extreme temperatures over all land areas as early as 2025 under both scenarios, with statistically significant differences between them becoming pervasive over the globe by 2050. The substantially smaller changes, for all indices, produced under the lower emission case translate into sizeable benefits from emission mitigation: By 2075, in terms of reduced changes in 1-day heat extremes, about 95 % of land regions would see benefits of 1 °C or more under the lower emissions scenario, and 50 % or more of the land areas would benefit by at least 2 °C. 6 % of the land area would benefit by 3 °C or more in projected extreme minimum temperatures and 13 % would benefit by this amount for extreme maximum temperature. Benefits for 3-day metrics are similar. The future frequency of current extremes is also greatly reduced by mitigation: by the end of the century, under RCP8.5 more than half the land area experiences the current 20-year events every year while only between about 10 and 25 % of the area is affected by such severe changes under RCP4.5. [ABSTRACT FROM AUTHOR]

The probability that summer temperatures in the future will exceed the hottest on record during 1920–2014 is projected to increase at all land locations with global warming. Within the BRACE project framework we investigate the sensitivity of this projected change in probability to the choice of emissions scenario using two large ensembles of simulations with the Community Earth System Model. The large ensemble size allows for a robust assessment of the probability of record-breaking temperatures. Globally, the probability that any summer during the period 2061–2081 will be warmer than the hottest on record is 80 % for RCP 8.5 and 41 % for RCP 4.5. Hence, mitigation can reduce the risk of record-breaking temperatures by 39 %. The potential for risk reduction is greatest for some of the most populated regions of the globe. In Europe, for example, a potential risk reduction of over 50 % is projected. Model biases and future changes in temperature variance have only minor effects on the results, as their contribution stays well below 10 % for almost all locations. [ABSTRACT FROM AUTHOR]