10 Sep 2018

10 Sep 2018

Review status: this preprint is currently under review for the journal HESS.

Risks of seasonal extreme rainfall events in Bangladesh under 1.5 and 2.0 degrees’ warmer worlds – How anthropogenic aerosols change the story

Ruksana H. Rimi1, Karsten Haustein1, Emily J. Barbour1,2, Sarah N. Sparrow3, Sihan Li1,3, David C. H. Wallom3, and Myles R. Allen1 Ruksana H. Rimi et al.
  • 1Environmental Change Institute, School of Geography and the Environment, University of Oxford, Oxford, OX1 3QY, UK
  • 2Commonwealth Scientific and Industrial Research Organisation, Land and Water, Canberra, ACT 2601, Australia
  • 3Oxford e-Research Centre, Department of Engineering Science, University of Oxford, Oxford, OX1 3QG, UK

Abstract. Anthropogenic climate change is likely to increase the frequency of extreme weather events in future. Previous studies have robustly shown how and where climate change has already changed the risks of weather extremes. However, developing countries have been somewhat underrepresented in these studies, despite high vulnerability and limited capacities to adapt. How additional global warming would affect the future risks of extreme rainfall events in Bangladesh needs to be addressed to limit adverse impacts. Our study focuses on understanding and quantifying the relative risks of seasonal extreme rainfall events in Bangladesh under the Paris Agreement temperature goals of 1.5 °C and 2 °C warming above pre-industrial levels. In particular, we investigate the influence of anthropogenic aerosols on these risks given their likely future reduction and resulting amplification of global warming. Using large ensemble regional climate model simulations from weather@home under different forcing scenarios, we compare the risks of rainfall events under pre-industrial (natural), current (actual), 1.5 °C, and 2.0 °C warmer and greenhouse gas only (anthropogenic aerosols removed) conditions. We find that the risk of a 1 in 100 year rainfall event has already increased significantly compared with pre-industrial levels across parts of Bangladesh, with additional increases likely for 1.5 and 2.0 degree warming (of up to 5.5 times higher, with an uncertainty range of 3.5 to 7.8 times). Impacts were observed during both the pre-monsoon and monsoon periods, but were spatially variable across the country in terms of the level of impact. Results also show that reduction in anthropogenic aerosols plays an important role in determining the overall future climate change impacts; by exacerbating the effects of GHG induced global warming and thereby increasing the rainfall intensity. We highlight that the net aerosol effect varies from region to region within Bangladesh, which leads to different outcomes of aerosol reduction on extreme rainfall statistics, and must therefore be considered in future risk assessments. Whilst there is a substantial reduction in the impacts resulting from 1.5 °C compared with 2 °C warming, the difference is spatially and temporally variable, specifically with respect to seasonal extreme rainfall events.

Ruksana H. Rimi et al.

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Ruksana H. Rimi et al.

Ruksana H. Rimi et al.


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Short summary
Extreme rainfall events are major concerns in Bangladesh because such events can cause flash floods and damage nearly harvestable crops in pre-monsoon season; whereas, in monsoon season, the impacts can range from widespread agricultural loss, huge property damage to loss of lives and livelihoods. This paper reveals the role of anthropogenic climate change drivers in changing the risks of extreme rainfall events during pre-monsoon and monsoon seasons at local sub-regional scale within Bangladesh.