Periodic Reporting for period 1 - IDIOM2 (Unravelling the role of water stress in Mediterranean isoprene emissions to better project future regional climate-air quality interactions)
Período documentado: 2018-12-03 hasta 2020-12-02
In response to changes in environmental conditions (e.g. temperature, radiation, water availability), plants emit reactive chemical compounds known as volatile organic compounds (BVOCs), which play an important role in atmospheric chemistry. In the large family of BVOCs, isoprene is the most abundant compound and influences the levels of ozone, a powerful greenhouse gas and air pollutant. Isoprene thus affects climate and air quality. In turn, climate change may alter isoprene emissions by increasing the occurrence and intensity of stresses that alter plant functioning (e.g. rising temperature, changing precipitation regimes).
While increasing temperatures may exacerbate ozone production by enhancing isoprene emissions, the effect of water availability on isoprene emissions is more controversial and may depend on water stress intensity. Field campaigns, in-situ and laboratory experiments investigated the effect of different water stress (short- vs. long-term) on isoprene emissions. However, these studies provided geographically scattered and uneven results. To explore the relationship between isoprene emissions and water stress at larger scales, the IDIOM2 project applied: (a) global observations of climatic drivers of isoprene and of an intermediate by-product of its oxidation, (b) statistical techniques to jointly analyse observations, and (c) regional climate modelling to assess the effect of soil moisture on isoprene emissions and ozone pollution.
As schematised in the figure, current air quality strategies pursue the reduction of anthropogenic emissions contributing to ozone production. In the future, benefits from air quality regulations may be offset by the evolution of isoprene and other BVOCs under climate changes that intensify favourable atmospheric conditions for ozone production and isoprene emissions (i.e. sunny, warm and stagnant days). To provide reliable projections of future air quality and design effective mitigation strategies, it is thus essential to reduce uncertainties in estimates of isoprene emissions both under present and future climates.
To answer scientific and societal questions related to the relationship between isoprene emissions and water stress, the IDIOM2 project has three objectives:
1. Elucidate the effect of water stress and other drivers on isoprene emissions at a large spatio-temporal scale
2. Assess the spread in future isoprene emissions in an ensemble of regional climate projections over Europe
3. Estimate surface ozone pollution resulting from climate-driven changes in isoprene emissions
The analysis of global observations confirmed the important role of temperature in modulating isoprene emissions and highlighted the contrasting effect of water stress in altering isoprene emissions in different regions. In parallel, numerical experiments performed at the European scale with a BVOC emission model, which assumes water stress reduces isoprene emissions, showed that large reductions in isoprene emissions slightly decrease surface ozone levels.
While increasing temperatures may exacerbate ozone production by enhancing isoprene emissions, the effect of water availability on isoprene emissions is more controversial and may depend on water stress intensity. Field campaigns, in-situ and laboratory experiments investigated the effect of different water stress (short- vs. long-term) on isoprene emissions. However, these studies provided geographically scattered and uneven results. To explore the relationship between isoprene emissions and water stress at larger scales, the IDIOM2 project applied: (a) global observations of climatic drivers of isoprene and of an intermediate by-product of its oxidation, (b) statistical techniques to jointly analyse observations, and (c) regional climate modelling to assess the effect of soil moisture on isoprene emissions and ozone pollution.
As schematised in the figure, current air quality strategies pursue the reduction of anthropogenic emissions contributing to ozone production. In the future, benefits from air quality regulations may be offset by the evolution of isoprene and other BVOCs under climate changes that intensify favourable atmospheric conditions for ozone production and isoprene emissions (i.e. sunny, warm and stagnant days). To provide reliable projections of future air quality and design effective mitigation strategies, it is thus essential to reduce uncertainties in estimates of isoprene emissions both under present and future climates.
To answer scientific and societal questions related to the relationship between isoprene emissions and water stress, the IDIOM2 project has three objectives:
1. Elucidate the effect of water stress and other drivers on isoprene emissions at a large spatio-temporal scale
2. Assess the spread in future isoprene emissions in an ensemble of regional climate projections over Europe
3. Estimate surface ozone pollution resulting from climate-driven changes in isoprene emissions
The analysis of global observations confirmed the important role of temperature in modulating isoprene emissions and highlighted the contrasting effect of water stress in altering isoprene emissions in different regions. In parallel, numerical experiments performed at the European scale with a BVOC emission model, which assumes water stress reduces isoprene emissions, showed that large reductions in isoprene emissions slightly decrease surface ozone levels.
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.
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.
The outcomes of the IDIOM2 project have highlighted the contrasting role of water stress in altering isoprene emissions in different regions of the world. If water availability sustains isoprene emissions over Australia, drier conditions enhance isoprene emissions over Europe. However, numerical schemes linking isoprene emissions and water stress assume that water stress reduces isoprene emissions everywhere. These findings may provide new insights in the relationship between isoprene emissions and water stress and may help in improving schemes that link soil moisture to isoprene emissions in numerical models, with potential impacts on air quality projections and design of future air quality strategies.