How Exceptional Was the 2015-2019 Central American Drought?

The Central American Dry Corridor experienced five consecutive years of drought from 2015 to 2019. Here, we find that the severity of this drought was driven primarily by rainfall deficits in July-August. To determine if the magnitude of this event was outside the range of natural variability, we apply a statistical resampling method to observations that emulates internal climate variability. Our analyses show that droughts similar to the 2015-2019 event are possible, although extremely rare, even without anthropogenic influences. Persistent droughts in our ensemble are consistently linked to stronger easterly winds associated with the Caribbean Low-Level Jet. We also examine the effects of temperature on soil moisture during this drought using the Palmer Drought Severity Index and show that anthropogenic warming increases the likelihood of severe deficits. Multi-year droughts are likely to worsen by the end of the 21st century due to the compound effects of anthropogenic climate change. Climate models project that Central America is one of the global hotspots for future decreases in precipitation as a result of human-caused climate change. This is particularly concerning for the Dry Corridor region, which is already prone to frequent droughts and high levels of food insecurity among households. Much of this region experienced severe rainfall deficits between 2015 and 2019, provoking the question of whether or not this drought was caused by climate change or if it could have occurred because of natural climate variability alone. Using a statistical model, we show that while 2015-2019 was the driest period in the observational record, droughts as bad as this one are possible even without the influence of human-caused climate change. We examine the additional role of temperature since it can modulate drought severity through its influence on soil moisture. We find warming temperatures increase the occurrences of greater soil moisture deficits. We also determine that the strength of the Caribbean Low-Level Jet, which transports moisture from the Caribbean Sea into Central America, is strongly associated with persistent dry conditions in the region. The 2015-2019 drought was severe, but it falls within the range of natural climate variabilityJuly-August deficits were the most significant drivers of overall droughtPositive easterly zonal wind anomalies associated with the Caribbean Low-Level Jet are strongly linked to regional precipitation deficits