The WOFOST crop model -as implemented in the BioMA modelling framework- was extended with algorithms to account for the effects of ground-level ozone on crop growth and yield. The additional algorithms implemented concern: - Effect of water stress on stomatal conductance - Reduction of carboxylation rate of Rubisco - Ability of plants to partly recover from ozone damage - Acceleration of leaf senesce due to O3 exposure Meteorological datasets, with a consistent hourly-daily temporal resolution, were selected for two locations in Germany (Bremen) and Spain (Jerez), encompassing different climatic conditions. The sensitivity of two types of crops was assessed: wheat, which is relatively sensitive to O3 damage, and barley, which is less sensitive. These two crops were exposed to a range of hypothetical O3 mixing ratios of 20, 40, and 60 ppb during the entire crop growth cycle, as well as during specific months. Two agro-managements options were analysed: a potential yield case (i.e. no water stress by mimicking a full crop irrigation case), and a rain-fed case. Irrespective of ozone, rainfed wheat and barley yields are lower by only 12 % in Bremen compared to fully irrigated crops, while strongly reduced by 55 % in Jerez. Additionally, wheat yield losses, up to 30 % are calculated for ozone concentrations of 60 ppb, and only half of these for barley. Yield losses are substantially smaller in Jerez for rain-fed crops, when stomatal closure is limiting gas exchange, and thus impeding photosynthesis, crop growth and yields, but also reducing ozone uptake. General findings are: - Crop damages due to O3 exposure increase with O3 concentration - Effects of high O3 concentrations are very heterogeneous depending on month, site, crop and the simulated variable considered - The highest impact is obtained when the month with high O3 concentration coincides with the anthesis/grain filling stage (June for Bremen, April for Jerez) - Rain-fed crop damage is more marked in Bremen than Jerez and irrigation practice exacerbates O3 damages, especially in Jerez - Barley is less affected by O3 impact according to the lower sensitivity of the crop. The algorithms developed can easily be implemented in other (generic or crop-specific) models of similar complexity. Compare model results against field data under diverse conditions will be the next phase of this work, and further model developments are needed to simulate so-called "stomatal sluggishness" (i.e. damage to the stomata due to ozone).
