Rain during flowering outranks heat as the limit on cocoa yields

Somebody at a chocolate buyer reads a seasonal rainfall outlook in March and has to decide whether it changes the contract signed in April. The study makes that decision possible, and the work it implies happens on farms the buyer does not own.

Timing matters more than volume here. "Cocoa is not equally sensitive to rainfall throughout the year. Heavy rain during flowering or early pod development can be much more damaging than the same amount of rain at another time," Albright said ^[8]. Part of the damage is biological: "Very wet conditions can interfere with flowering and the development of young pods, and they can also create conditions that are favorable for fungal diseases," she said ^[21].

Ghana's other damage window runs November to February, when rain is short and pods are still developing ^[10]. Together the two windows cover seven of the twelve calendar months, and they run in opposite directions ^[23], so an insurance trigger or alert written only on heavy rain covers one of them.

Heat and drought have been the recognised threats to this crop for a long time ^[20]. Albright, who led the work as a postdoctoral fellow at the Harvard University Center for the Environment, argued for attention to rain on the grounds of what can be done with the information. "Heavy rainfall is potentially more actionable because it is an event that can be forecast," she told Gizmodo in an email ^[5][4]. She named the actions too: "If you know that a period of very heavy rain is expected during flowering or early pod development, there are actions that farmers can do to reduce the damage, particularly around drainage and disease management" ^[6].

Drainage and disease management are field operations, paid for and carried out by growers. Nearly 6 million smallholder farmers depend on cocoa ^[2]. A forecast reduces a loss only when it reaches one of those farmers early enough, and with enough cash behind it, for the ditch to get dug.

The near-term signal splits by origin. In West Africa, which grows about 70 percent of the world's cocoa ^[15], El Nino tends to reduce the risk of heavier rainfall while raising the risk of dry-season drought ^[17]. In Ecuador it usually brings a wetter wet season ^[18].

Each degree Celsius of warming lets the atmosphere hold about 7 percent more moisture ^[12], and the heaviest wet-season events in West Africa have already grown more intense over the past couple of decades ^[16]. "It loads the dice towards heavier rainfall," Albright said ^[14].

A forecastable risk gets planned around when the forecast arrives before the field work has to happen, and when the party doing that field work is funded for it. For cocoa the first condition looks satisfiable, since flowering sits on a calendar. The second is a purchasing decision: a buyer who wants April drainage done can pay for it in February, or can wait and read the size of the loss off next season's price.