Elucidating climate change adaptation potential of improved maize (Zea mays L.) varieties with crop modelling

The threats to crop yields are projected to increase under climate change and one of the most promising adaptation measures is for farmers to adjust their crop varieties over time to minimize climate risk. An improved or modern variety is a new variety of a plant species which produces higher yields, higher quality or provides better resistance to plant pests and diseases while minimizing the pressure on the natural environment. Selecting best maize varieties for various sites is also a good agricultural practice that can increase current yields in many low-productivity areas.  In this study, we aimed at identifying the climate change buffering potential of improved maize varieties using a spatialized DSSAT model using a case study across Uganda. We calibrate the model with observed weather data and then replace the weather files with climate projections from the ISIMIP3b. Model evaluation showed that the model performance was satisfactory with a correlation  coefficient (r) of 0.89, coefficient of determination (R2) of 0.79, index agreement (d) of 0.83 with observed yields. The impact of climate change on maize yield show spatial and temporal disparities with general trends showing that they worsen with time (2030 to 2090) and scenario (SSP1-RCP2.6 to SSP3-RCP7.0). At the national level, we project a yield loss of 6.2% (SSP1-RCP2.6) and 4.4% (SSP3-RCP7.0), by around 2030, 8.6% (SSP1-RCP2.6) and 14.3% (SSP3-RCP7.0) by around 2050, and 8.8% (SSP1-RCP2.6) and 26.8% (SSP1-RCP7.0) by around 2090. Switching to an improved variety results in at least double the maize yield under current climatic conditions (113.2%) compared to the current varieties, with maize yield exceeding 10 t/ha in the south-western, western and eastern parts of the country.  This positive yield effect was realized across all grids but substantially varied from around 10% to 500% yield change. Comparing the effect of climate change with an improved variety versus with a conventional variety shows it is always better to use an improved variety under climate change (positive effect), especially under worse case climatic conditions(2.9% and  8% yield buffering by 2090 under  SSP1:RCP2.6 and SSP3:RCP7.0 respectively) at national level. We therefore conclude that improved maize varieties offer a more durable solution to adapt to climate change and seed systems should therefore be strengthened to increase access to improved maize varieties for farmers.