TY - JOUR

T1 - Modelling the effect of the 2018 summer heatwave and drought on isoprene emissions in a UK woodland

T2 - Modelling isoprene emissions during heatwave-drought

AU - Otu-Larbi, Frederick

AU - Bolas, Conor

AU - Ferracci, Valerio

AU - Staniaszek, Zosia

AU - Jones, Roderic

AU - Mahli, Yadvinder

AU - Harris, Neil

AU - Wild, Oliver

AU - Ashworth, Kirsti

N1 - This is the peer reviewed version of the following article: Otu‐Larbi, F, Bolas, CG, Ferracci, V, et al. Modelling the effect of the 2018 summer heatwave and drought on isoprene emissions in a UK woodland. Glob Change Biol. 2020; 26: 2320-2335. https://doi.org/10.1111/gcb.14963 which has been published in final form at https://onlinelibrary.wiley.com/doi/full/10.1111/gcb.14963 This article may be used for non-commercial purposes in accordance With Wiley Terms and Conditions for self-archiving.

PY - 2020/4/1

Y1 - 2020/4/1

N2 - Projected future climatic extremes such as heatwaves and droughts are expected to have major impacts on emissions and concentrations of biogenic volatile organic compounds (bVOCs) with potential implications for air quality, climate and human health. While the effects of changing temperature and photosynthetically active radiation (PAR) on the synthesis and emission of isoprene, the most abundant of these bVOCs, are well known, the role of other environmental factors such as soil moisture stress are not fully understood and are therefore poorly represented in land surface models. As part of the Wytham Isoprene iDirac Oak Tree Measurements campaign, continuous measurements of isoprene mixing ratio were made throughout the summer of 2018 in Wytham Woods, a mixed deciduous woodland in southern England. During this time, the United Kingdom experienced a prolonged heatwave and drought, and isoprene mixing ratios were observed to increase by more than 400% at Wytham Woods under these conditions. We applied the state-of-the-art FORest Canopy-Atmosphere Transfer canopy exchange model to investigate the processes leading to these elevated concentrations. We found that although current isoprene emissions algorithms reproduced observed mixing ratios in the canopy before and after the heatwave, the model underestimated observations by similar to 40% during the heatwave-drought period implying that models may substantially underestimate the release of isoprene to the atmosphere in future cases of mild or moderate drought. Stress-induced emissions of isoprene based on leaf temperature and soil water content (SWC) were incorporated into current emissions algorithms leading to significant improvements in model output. A combination of SWC, leaf temperature and rewetting emission bursts provided the best model-measurement fit with a 50% improvement compared to the baseline model. Our results highlight the need for more long-term ecosystem-scale observations to enable improved model representation of atmosphere-biosphere interactions in a changing global climate.

AB - Projected future climatic extremes such as heatwaves and droughts are expected to have major impacts on emissions and concentrations of biogenic volatile organic compounds (bVOCs) with potential implications for air quality, climate and human health. While the effects of changing temperature and photosynthetically active radiation (PAR) on the synthesis and emission of isoprene, the most abundant of these bVOCs, are well known, the role of other environmental factors such as soil moisture stress are not fully understood and are therefore poorly represented in land surface models. As part of the Wytham Isoprene iDirac Oak Tree Measurements campaign, continuous measurements of isoprene mixing ratio were made throughout the summer of 2018 in Wytham Woods, a mixed deciduous woodland in southern England. During this time, the United Kingdom experienced a prolonged heatwave and drought, and isoprene mixing ratios were observed to increase by more than 400% at Wytham Woods under these conditions. We applied the state-of-the-art FORest Canopy-Atmosphere Transfer canopy exchange model to investigate the processes leading to these elevated concentrations. We found that although current isoprene emissions algorithms reproduced observed mixing ratios in the canopy before and after the heatwave, the model underestimated observations by similar to 40% during the heatwave-drought period implying that models may substantially underestimate the release of isoprene to the atmosphere in future cases of mild or moderate drought. Stress-induced emissions of isoprene based on leaf temperature and soil water content (SWC) were incorporated into current emissions algorithms leading to significant improvements in model output. A combination of SWC, leaf temperature and rewetting emission bursts provided the best model-measurement fit with a 50% improvement compared to the baseline model. Our results highlight the need for more long-term ecosystem-scale observations to enable improved model representation of atmosphere-biosphere interactions in a changing global climate.

KW - Isoprene emissions

KW - Isoprene mixing ratios

KW - Heatwave-drought

KW - Soil Water 59 Content

KW - Rewetting

KW - Canopy exchange modelling

KW - Climate change

U2 - 10.1111/GCB.14963

DO - 10.1111/GCB.14963

M3 - Journal article

VL - 26

SP - 2320

EP - 2335

JO - Global Change Biology

JF - Global Change Biology

SN - 1354-1013

IS - 4

ER -