Severe floods and landslides in Eastern Northeast Brazil in May 2022 led to severe impacts with human losses and material damage. These disasters were a direct consequence of extremely heavy rainfall days. A rapid attribution study was performed to assess the role of anthropogenic climate change in 7 and 15-day mean rainfall over this region. A dense network of 389 weather stations was analysed resulting in 79 selected stations containing consistent and spatially well-distributed data over the study region with records starting in the 1970s. Daily rainfall from a multi-model ensemble of climate simulations were also examined to investigate the role of climate change in modifying the likelihood of such extreme events over the studied region. However, such an analysis was hindered by the fact that most investigated models have deficiencies in representing convection associated with warm rains, which are key for the manifestation of such extreme events associated with Easterly Wave Disturbances. From the observational analysis, both 7 and 15-day mean events in 2022 were found to be exceptionally rare, with an approximately 1-in-500 and 1-in-1000 chance of happening in any year in today's climate, respectively. Even though both events were located far outside the previously observed records, because of the short observational record and associated uncertainties it was not possible to quantify how much climate change made these events more likely to happen. The performed analysis also revealed that global warming increased the intensity of such extreme rainfall: rainfall events as rare as those investigated here occurring in a 1.2 °C cooler climate would have been approximately a fifth less intense. Combining observations with the physical understanding of the climate system, this study showed that human-induced climate change is, at least in part, responsible for the increase in likelihood and intensity of heavy rainfall events as observed in May 2022. Besides, the extreme nature, as a result of such events, made it so extraordinary that population exposure and vulnerability was identified as the main driver for the observed impacts, although long-term impacts and recovery will likely be mediated by socio-economic, demographic and governance factors.

中文翻译：

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巴西东北部东部特强降雨事件的归因研究


2022 年 5 月，巴西东北部东部发生严重洪水和山体滑坡，造成严重人员伤亡和物质损失。这些灾害是特大降雨的直接后果。进行了一项快速归因研究，以评估人为气候变化对该地区 7 天和 15 天平均降雨量的影响。对由 389 个气象站组成的密集网络进行了分析，最终选出 79 个气象站，其中包含研究区域一致且空间分布良好的数据，记录始于 20 世纪 70 年代。还检查了气候模拟的多模型集合的每日降雨量，以调查气候变化在改变研究区域发生此类极端事件的可能性方面的作用。然而，这样的分析受到了以下事实的阻碍：大多数研究的模型在表示与暖雨相关的对流方面存在缺陷，而这对于与东风波扰动相关的此类极端事件的表现至关重要。根据观测分析，2022 年平均 7 天和 15 天的事件都极其罕见，在当今气候下，任何一年发生的概率分别约为五百分之一和千分之一。尽管这两个事件都远远超出了之前观测到的记录，但由于观测记录较短和相关的不确定性，无法量化气候变化在多大程度上使这些事件更有可能发生。进行的分析还显示，全球变暖增加了这种极端降雨的强度：在气温降低 1.2°C 的气候下，像这里调查的那样罕见的降雨事件的强度大约会降低五分之一。 将观测结果与对气候系统的物理理解相结合，这项研究表明，人类引起的气候变化至少在一定程度上是造成 2022 年 5 月观测到的强降雨事件可能性和强度增加的原因。此外，极端自然条件由于这些事件，尽管长期影响和恢复可能受到社会经济、人口和治理因素的调节，但人口暴露和脆弱性被确定为造成所观察到的影响的主要驱动因素。