Assessment of Damage to Vegetation in Belgium Based on an Ozone Flux Model Approach

Abstract

Elevated tropospheric ozone concentrations are not only harmful for human health, but they may also have detrimental effects on vegetation. Currently, an ozone exposure index (AOT40) and critical levels for the protection of vegetation have been agreed upon at European level based on the atmospheric ozone concentration and exposure time. Plants are however mainly affected by the ozone actually interacting with the plant tissue which could well be only a small part of the available ozone. Methods have therefore been developed for estimating ozone uptake by plants and to obtain reliable dose-response relationships based on the ozone flux. In this chapter we present a modelling procedure that integrates the DO3SE model for calculating the phytotoxic ozone dose with ECMWF meteorology and ground level ozone concentration maps to produce estimates of the ozone impact on yield and biomass accumulation of crops, forest trees and grassland. The procedure is applied to a Belgium for the year 2009 and compared with the results published for EMEP and used to quantify the impact of ozone on potato and wheat crop yields in 2009.

Questions and Answers

Questioner: Jon Pleim

Question: Another way to do this could be with coupled Met/AQ models that have land surface models with stomatal conductance and consistent calculations of O3 dry dep. So, O3 fluxes to vegetation are already computed accounting for soil moisture stress. Is this approach being pursued?

Answer: In this particular application we applied an existing O3flux calculation procedure, more specifically the DO3SE model as implemented in the EMEP model (Emberson et al. 2000) and as input for this model we used measured O₃ concentrations and the meteorology as calculated by the ECMWF model. Where it is true that by doing this it is quite unlikely that the vegetation exchange fluxes calculated in DO3SE and the ECMWF will be consistent we believe that the advantage of using measurements for the O₃ concentration, a very detailed O3flux calculation procedure in combination with high quality ECMWF meteorology is probably more accurate than using a code such as WRFCHEM to model meteorology and O₃ fluxes in a coupled way.

Questioner: Peter Builtjes

Question: Are you happy with the soil moisture index (SMI) of ECMWF? Especially since they are using their own land use (Author: shouldn’t this be soil types?) categories?

Answer: Since we ingest the SMI (= $\frac{{\theta - \theta_{WP} }}{{\theta_{FC} - \theta_{WP} }}$) directly to calculate the soil moisture factor in the DO3SE we don’t have to worry about the soil types that ECMWF is using. Initially we tried using the volumetric soil moisture, θ from ECMWF directly but that turned out to be the wrong way to do this precisely because of the unknown underlying soil map used by ECMWF. Off course one can also wonder how accurate the SMI calculated by ECMWF is and whether this is not more a tuning parameter in a model that is mainly used for wheather forecasting.