A Physiological Model to Quantify Impacts of Climate Change Variables on Cocoa Productivity

Climate change has the potential to alter cocoa production through, for example, changes in rainfall patterns (more intense droughts and/or more intense wet seasons), higher temperatures and increased carbon dioxide concentrations. A crop modelling approach allows prediction of yield changes in relation to climate events and quantification of interventions designed to ameliorate such changes (e.g. use of overhead shade or planting of different cocoa varieties more adapted to climate change). 

A physiological model is described that is parameterised using experimental data collected under controlled environment conditions. The model is compartmentalised into interacting modules that include assimilation of carbohydrates through canopy photosynthesis, respiration, partitioning of assimilates between vegetative and reproductive growth, partitioning of assimilates within the pod and the dynamics of pod-setting and wilting. Canopy photosynthesis is calculated from the parameters of photosynthetic light response curves of genotypes, specified by the user, and the properties of the canopy (leaf area index and light attenuation through the canopy, quantified as the extinction coefficient). Environmental parameters that can be modulated in the model include carbon dioxide concentration, soil water content, air temperature, vapour pressure deficit and solar radiation. These parameters then influence the outputs of the different modules, for example temperature impacts on photosynthetic rate and also on the amount of cherelle wilt.

A range of model simulations are presented on the impacts of elevated CO2 concentration, increases in temperature, water deficit and their interaction on productivity and yield. The potential impact of interventions such as changing variety and use of overhead shade in ameliorating the effects of climate change is also discussed.

Keywords: Climate change; crop model; adaptation