Modelled average percentage yield loss due to ozone damage for four global staple crops (2010-2012)

A 1 degree by 1 degree grid was created using ArcMap. Crop production data (0.0833 degree resolution) from the Food and Agriculture Organisation’s (FAO) Global Agro-Ecological Zones (GAEZ) dataset (for the year 2000) was downloaded. Irrigated and non-irrigated production data was collected for each crop type. For each crop, total production was summed per 1 degree by 1 degree grid cell. Then average production for the period 2010-2012 for each grid cell was estimated using a conversion factor from FAO national crop production data, based on the difference between average production for the period 1999-2001 and 2010-2012. For each crop, only grid cells with greater than 500 tonnes crop production were included when mapping yield loss.

Each grid cell was classed as either irrigated (greater than 75 percent irrigated crop production) or non-irrigated. Grid cells were also assigned to a hemisphere (Northern or Southern) and a climatic zone. For each hemisphere/climatic zone combination, a 90-day growing period was set, based on the main growing season per year for each crop.

The EMEP MSC-W (European Monitoring and Evaluation Programme, Meteorological Synthesising Centre‐West) chemical transport model (version 4.16) was used to calculate daily ozone flux (POD3IAM; phytotoxic ozone dose above 3 nmol m−2 s−1, parameterized for integrated assessment modelling) for the years 2010 - 2012. For each crop, the accumulated 90-day POD3IAM was calculated per grid cell based on the climate specific growing period for the cell, and an average value calculated for the period 2010-2012.

Yield loss was calculated using the ozone dose-response relationship for wheat, following the most recent methodology adopted by the Convention for Long-Range Transboundary Air Pollution (CLRTAP) in 2017. First a reference value of POD3IAM = 0.1mmol/m2 (used to represent ozone uptake at pre-industrial or natural ozone levels) was subtracted before yield loss was calculated. This value was the mean POD3IAM for the experimental conditions included in the dose-response relationship, assuming constant 10 ppb ozone throughout the 90-day period.

The equation used to calculate percentage yield loss was as follows:
percentage Yield Loss = (POD3IAM – 0.1) * 0.64
where 0.64 is the slope of the relationship between POD3IAM and percentage yield reduction and represents the percentage reduction per mmol/m2 POD3IAM.

For maize, rice and soybean, the POD3IAM values per grid cell were first used to calculate percentage yield loss using the equation for wheat. Then the relative ozone sensitivity of each crop compared to wheat was calculated by dividing the slope of the M7 (7-hour mean ozone concentration) response function for the crop by that for wheat. For each grid cell, the percentage yield loss for wheat was multiplied by the relative ozone sensitivity value, to calculate the final estimated percentage yield loss for each crop.

Percentage yield loss values were added to the 1 degree by 1 degree grid and saved as GIS shapefiles, one per crop for ingestion into the EIDC.

An evaluation of EMEP model performance found a strong correlation between modelled and measured ozone data from Global Atmosphere Watch (GAW) sites. The EMEP model was found to capture spatial and temporal variations in ozone across regions.