Risks of seasonal extreme rainfall events in Bangladesh under 1.5 and 2.0 °C warmer worlds – how anthropogenic aerosols change the story

Abstract

Abstract. Anthropogenic climate change is likely to increase the risk (probability of occurrence of a hazard) of extreme weather events in the 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 extreme rainfall events in Bangladesh under the Paris Agreement temperature goals of 1.5 and 2.0 ∘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; NAT), current (actual; ACT), 1.5 and 2.0 ∘C warmer, and greenhouse gas (GHG)-only (with pre-industrial levels of anthropogenic aerosols) conditions. Both GHGs and anthropogenic aerosols have an impact on seasonal mean rainfall over this region. In general, higher global mean temperature levels lead to higher rainfall and higher aerosol concentrations to lower rainfall, however the relative importance of the two factors varies between the regions. For extreme rainfall events, we find that the risk of a 1 in 100 year rainfall episode has already increased significantly compared with pre- industrial levels across parts of Bangladesh, with additional increases likely for 1.5 and 2.0 ∘C warming. Climate change impacts on the probabilities of extreme rainfall episodes are found during both pre-monsoon and monsoon seasons. Results show that reduction in anthropogenic aerosols will exacerbate the effects of GHG-induced warming and thereby increasing the rainfall intensity, which has otherwise attenuated the impacts. 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. While there is a substantial reduction in risk at 1.5 ∘C warming when compared to 2 ∘C warming, the difference is spatially and temporally variable too, specifically with respect to seasonal extreme rainfall events.

Climate change quadruples flood‐causing extreme monsoon rainfall events in Bangladesh and northeast India

“…Based on the HadRM3P model, Rimi et al (2019) attributed that a flash flood in northeastern Bangladesh driven by an extreme rainfall event in March 2017 was most likely due to anthropogenic forcing, instead of internal variability modes such as IOD or ENSO. Later, Rimi et al (2022) used a large ensemble regional climate model to investigate the influence of aerosols on the mean and extreme monsoon rainfall events, and found extreme rainfall events increase in the future due to global warming. The anthropogenic aerosols, however, suppress the increase of mean rainfall events during pre-monsoon and monsoon, whereas the increase of global mean surface temperature increases the rainfall (Rimi et al, 2022).…”

“…Later, Rimi et al (2022) used a large ensemble regional climate model to investigate the influence of aerosols on the mean and extreme monsoon rainfall events, and found extreme rainfall events increase in the future due to global warming. The anthropogenic aerosols, however, suppress the increase of mean rainfall events during pre-monsoon and monsoon, whereas the increase of global mean surface temperature increases the rainfall (Rimi et al, 2022). Tang et al (2022) analyzed the seasonal mean summer 2020 rainfall event over the northeast Indian subcontinent and found an anomalous anticyclone associated with the La Niña phase that contributed to the wettest summer rainfall event over this region since 1901.…”

Climate change research, capacity building and communication on climate extremes over South Asia

“…However, the coastal areas have shown a higher rate of warming over the last five decades (Abdullah et al, 2022). A study investigated the trends of climate extremes in Bangladesh and concluded that mean monsoon seasonal rainfall can alter, posing significant challenges to agriculture, hydropower and the ecosystem (Rimi et al, 2022). Nepal has experienced extreme events due to climate extremes in recent decades.…”