To pursue its objectives, IDIOM2 included three phases:
Phase 1: Generalised Linear Mixed-Effects Models allowed to study spatial and temporal interactions between space retrievals of formaldehyde (used as a proxy of isoprene emissions) and observations of soil moisture, drought index, temperature, precipitation, biomass, particulate matter and burned fraction at the global and regional scales, over 2005–2016. In agreement with previous studies, formaldehyde concentrations show a robust negative trend over central Europe, Amazon, southern Africa and southern Australia, while a robust positive trend was found over India and China. Among the predictors, temperature, biomass, and particulate matter significantly contribute over time to the observed trends in formaldehyde. By accounting for interactions, statistical models revealed that, at the global scale, over the Amazon Basin and India-China, the formaldehyde concentrations locally increase with temperature even under low precipitation conditions, if there is enough soil moisture to sustain vegetation functioning and isoprene emissions. Over a dry region such as Australia, water availability may become a critical condition for isoprene emissions and, lastly, formaldehyde production. However, at both the global and European scale, trends in formaldehyde present a negative relationship with trends in a selected drought index (i.e. drier conditions correspond to higher formaldehyde), indicating that temperature is still a more important factor in determining emissions. This work was presented in May 2020 at the European Geosciences Union (EGU). A manuscript is in preparation for Global Change Biology.
Phase 2: The statistical model built in Phase 1, combined with temperature and precipitation projections from regional climate models, allowed the extrapolation of future formaldehyde concentrations under “business-as-usual” and “low carbon” climatic scenarios. Results show that future formaldehyde concentrations follow a decreasing trend, most likely driven by the prescribed decreasing trend in pollution. Compared to a “low carbon” scenario, a “business-as-usual” scenario leads to higher future formaldehyde concentrations. Temperature strongly influences projections of formaldehyde: higher temperatures correspond to higher formaldehyde concentrations.
Phase 3: A state-of-the-art regional climate model, which describes the interactions between climate conditions, vegetation processes, atmospheric chemistry and isoprene emissions, allowed to quantify the impact of soil moisture on isoprene emissions and surface ozone levels under present-day and future climates. The numerical model includes two formulations of a soil moisture activity factor linking soil moisture to isoprene emissions and assuming that water stress reduces isoprene emissions. Under present-day climate, when soil moisture and plant physiology are accounted for, isoprene emissions decrease during summer by 10-20% over the Euro-Mediterranean region, while surface ozone levels decrease by less than 1%. By adopting a mechanistic formulation that only connects isoprene emissions to soil moisture, reductions in isoprene emissions and surface ozone are larger and less localised. Under a “business-as-usual” scenario, by the mid 21st century the decrease in soil moisture is projected to lead to stronger and more extensive reductions in isoprene emissions (from -10% to -40%) and surface ozone levels (up to -2%). This work was presented in April 2021 at the EGU. Two manuscripts are in preparation for Atmospheric Physics and Chemistry.
