Climate models predict a strengthening contrast between wet and dry regions in the tropics and subtropics (30°S-30°N), and data from the latest model intercomparison project (CMIP6) support this expectation. Rainfall in ascending regions increases, and in descending regions decreases in climate models, reanalyses, and observational data. This strengthening contrast can be captured by tracking the rainfall change each month in the wettest and driest third of the tropics and subtropics combined. Since wet and dry regions are selected individually every month for each model ensemble member, and the observations, this analysis is largely unaffected by biases in location of precipitation features. Blended satellite and in situ data from 1988-2019 support the CMIP6-model-simulated tendency of sharpening contrasts between wet and dry regions, with rainfall in wet regions increasing substantially opposed by a slight decrease in dry regions. We detect the effect of external forcings on tropical and subtropical observed precipitation in wet and dry regions combined, and attribute this change for the first time to anthropogenic and natural forcings separately. Our results show that most of the observed change has been caused by increasing greenhouse gases. Natural forcings also contribute, following the drop in wet-region precipitation after the 1991 eruption of Mount Pinatubo, while anthropogenic aerosol effects show only weak trends in tropic-wide wet and dry regions consistent with flat global aerosol forcing over the analysis period. The observed response to external forcing is significantly larger (p>0.95) than the multi-model mean simulated response. As expected from climate models, the observed signal strengthens further when focusing on the wet tail of spatial distributions in both models and data. Page 1 of 24 AUTHOR SUBMITTED MANUSCRIPT ERL-108080.R1 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 A cc ep t d M an us cr ip t

中文翻译：

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人类影响加强了热带干湿地区的对比

气候模型预测热带和亚热带 (30°S-30°N) 的干湿区域之间的对比会加强，来自最新模型比对项目 (CMIP6) 的数据支持这一预期。在气候模型、再分析和观测数据中，上升区域的降雨量增加，而下降区域的降雨量减少。通过跟踪热带和亚热带最潮湿和最干燥的三分之一地区每月的降雨量变化，可以捕捉到这种增强的对比。由于每个月为每个模型集合成员和观测单独选择湿区和干区，因此该分析在很大程度上不受降水特征位置偏差的影响。1988 年至 2019 年的混合卫星和原位数据支持 CMIP6 模型模拟的湿区和干区对比度增强趋势，潮湿地区的降雨量大幅增加，而干燥地区的降雨量则略有减少。我们检测了外强迫对干湿区热带和亚热带观测降水的影响，并首次将这种变化分别归因于人为强迫和自然强迫。我们的结果表明，大部分观察到的变化是由温室气体增加引起的。在 1991 年皮纳图博火山喷发后湿区降水下降之后，自然强迫也有贡献，而人为气溶胶效应仅在整个热带干湿地区表现出微弱的趋势，与分析期间全球气溶胶强迫的持平一致。观察到的对外部强迫的响应明显大于多模型平均模拟响应 (p>0.95)。正如气候模型所预期的那样，当关注模型和数据中空间分布的湿尾时，观测到的信号会进一步增强。第 1 页，共 24 页作者提交的手稿 ERL-108080.R1 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 263 3 3 3 2 3 3 2 3 3 3 7 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 A cc ep td M an us cr ip t