Chocolate's new climate threat: Too much rain

West African cocoa farmers struggle to protect their crops from unpredictable heavy rainfall, which now poses a major climate threat to the beloved chocolate ingredient. Researchers at Harvard and the University of Ghana have found that large-scale weather patterns could make the damaging effects of excess rain predictable months in advance. This gives farmers valuable time to prepare and protect their livelihoods.

Cocoa trees require a specific sequence of flowering, pollination, and pod development, and even slight changes in rainfall at critical stages can ruin a harvest. Excess rain during flowering or the spread of fungal diseases during this period can devastate the crop for the entire season. A study published in the journal Proceedings of the National Academy of Sciences reveals that heavy rain during the wet season and dry spells during the dry season explain about two-thirds of year-to-year cocoa yield swings in Ghana.

While drought has long been a concern for cocoa farmers, this study highlights that too much rain at the wrong time is equally damaging. The most destructive rains typically occur during the April–June wet season, when pods are beginning to form. Later in the dry season, insufficient rainfall can also harm the crop.

The researchers utilized two decades of district-level data from Ghana's Cocoa Board, removing long-term trends to isolate year-to-year variations. They compared these variations against daily weather records and potential factors, finding that heavy rainfall during the main wet season and too little rain during the dry season were the primary predictors of cocoa yield losses in Ghana.

Further analysis of other major cocoa-producing regions like Ecuador and Indonesia showed a similar pattern: Years with heavier rains during the wet season tended to yield worse results for cocoa. This suggests that forecasting rainfall patterns, such as those influenced by El Niño events, could provide farmers with crucial early warnings to adapt their strategies.

Adapting to these climate extremes is crucial, as the timing and intensity of rainfall significantly impact cocoa yield. While rainfall alone is not the only threat to Ghanaian cocoa farmers, this study emphasizes that understanding the climate threat—particularly the damaging effects of intense, short bursts of rain—can help protect the future of this essential agricultural product.