Abstract
AbstractThe climate modeling techniques of event attribution enable systematic assessments of the extent that anthropogenic climate change may be altering the probability or magnitude of extreme events. In the consecutive years of 2018, 2019, and 2020, rainfalls caused repeated flooding impacts in the lower Parnaíba River in Northeastern Brazil. We studied the effect that alterations in precipitation resulting from human influences on the climate had on the likelihood of flooding using two ensembles of the HadGEM3‐GA6 atmospheric model: one driven by both natural and anthropogenic forcings; and the other driven only by natural atmospheric forcings, with anthropogenic changes removed from sea surface temperatures and sea ice patterns. We performed hydrological modeling to base our assessments on the peak annual streamflow. The change in the likelihood of flooding was expressed in terms of the ratio between probabilities of threshold exceedance estimated for each model ensemble. With uncertainty estimates at the 90% confidence level, the median (5% 95%) probability ratio at the threshold for flooding impacts in the historical period (1982–2013) was 1.12 (0.97 1.26), pointing to a marginal contribution of anthropogenic emissions by about 12%. For the 2018, 2019, and 2020 events, the median (5% 95%) probability ratios at the threshold for flooding impacts were higher at 1.25 (1.07 1.46), 1.27 (1.12 1.445), and 1.37 (1.19 1.59), respectively; indicating that precipitation change driven by anthropogenic emissions has contributed to the increase of likelihood of these events by about 30%. However, there are other intricate hydrometeorological and anthropogenic processes undergoing long‐term changes that affect the flood hazard in the lower Parnaíba River. Trend and flood frequency analyses performed on observations showed a nonsignificant long‐term reduction of annual peak flow, likely due to decreasing precipitation from natural climate variability and increasing evapotranspiration and flow regulation.
Highlights
Climate change may be altering the frequency of hazards from extreme weather events such as heatwave, wildfire, drought, and flood at different rates across the globe (IPCC, 2014)
Our study focuses on the lower reach of the Parnaíba River, near Luziândia, Piauí (Figure 1), which drains a catchment area of about 325,000 kmš in a tropical savanna climate with annual precipitation of about 980 mm
We analyzed flood trend and frequency based on annual peak streamflow observations available between 1982 and 2020 at the gauge operated by the National Water Agency (ANA) in Luzilândia (ID: 34879500)
Summary
Climate change may be altering the frequency of hazards from extreme weather events such as heatwave, wildfire, drought, and flood at different rates across the globe (IPCC, 2014). Following an impactful extreme event, public awareness of the risk of natural disasters increases, intensifying questions about the role of climate change. While the evidence of human influence on climate change is increasingly clear, tracing its effects on climate variability and extreme weather events needs more understanding (Stott, 2015; Easterling et al, 2016). The change in the likelihood of an extreme event resulting from human influences on the climate is usually expressed in terms of the ratio between probabilities of threshold exceedance in ensembles of atmospheric model simulations performed with and without the forcings of human influence on climate change (National Academies of Sciences, Engineering, and Medicine, 2016)
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