Increased Frequency of Humid Heat Extremes during El Niño events (Invited Presentation)

During an El Niño, there are often large circulation anomalies caused by the shifted convection in the central tropical Pacific and leading to not only surface climate anomalies like temperature and precipitation, but also agricultural yields and droughts and floods. In this study, we report a less known phenomenon that an El Niño event can lead to increases in global humid heat extreme events, particularly in the tropics and in the summer warm season. This increase in humid heat extremes significantly increased the risk of outdoor workers, particularly agricultural workers, during the extreme heat events. We further explore the mechanisms of the increase in humid heat extremes and found that it is mainly caused by increases in specific humidity over tropical land regions. We found that the increase in specific humidity is a result of the tropical-wide temperature increases resulting from the El Niño conditions, particularly in the summer season following the peak El Niño. The CMIP6 model ensembles show a remarkable similarity as observations based on ERA5, both in terms of the increases in humid heat extremes and the mechanisms for the increases. The implication for the future is that the additive effect of an El Niño and global warming will make the conditions much worse for outdoor workers in the regions affected, particularly for the agricultural intensive tropical regions.