Modeling Climate Impacts on Agroforestry-Based Coffee Production of Small Growers in Mexico

Shaded coffee production in agroforestry systems, as opposed to full sun production, is a nature-based solution (NbS) that helps maintain soil water balance and reduce heat exposure of coffee plants. It is part of a range of NbS co-produced with stakeholders in the project SAbERES, which aims at supporting climate change adaptation for small-scale producers in Mexico. For this coffee production system, we analyze current and estimate future yields of small coffee growers in Mexico by employing a process-based coffee growth model CAF2014 adapted for geo-spatial applications and named CAF2014-Rhaobi. A range of climate projections reflecting the SSP5-8.5 scenario until 2100 is taken from an ensemble of five CMIP6 climate models to bracket climate ensemble response.

As NbS in agriculture are typically based on complex ecological interactions, a first crucial step in their modelling is the analysis of model sensitivity to its key inputs and validation of its ability to reflect reported yields. Particular attention was paid to the model’s sensitivity to adjustments in plot management such as shade trees pruning, projected changes in precipitation, hydrological soil parameters, and implications of using different soil datasets. The modeling of smallholders’ representative management was carried out based on parametrizations derived from literature. This informed key parameters of fertilizer application including nitrogen supply by litter from N-fixing shade trees and shading cover management, i.e., tree thinning and pruning frequency. Besides the quantification of crop yield changes per se, the project will analyze economic implications based on the spatial distribution of coffee yields and prices as reported by the Mexican Agri-Food and Fisheries Information Service (SIAP).

The modelled historical coffee yields are found to be in good agreement with the SIAP reported numbers, while there is a clear overestimation in the south-western part of the coffee producing region of Mexico. This is explained by a range of modeling assumptions and simplifications rendering the model less representative for this region. While shade trees provide some resilience, average drop in shaded coffee yields under present management estimated for the majority of the agro-environmentally diverse coffee producing regions in Mexico across all climate projections is about 25% at the end of the century. There are only few regions that are able to maintain their historical yields. These preliminary results underpin that shade trees as a single NbS do not suffice for climate adaptation in the long run under high warming conditions but will need to be combined with other measures. Future work may include refinement of modeling assumptions based on stakeholders input and analysis of economic implications driven by yield change estimates.