Preprints
https://doi.org/10.5194/esd-2021-31
https://doi.org/10.5194/esd-2021-31

  06 May 2021

06 May 2021

Review status: this preprint is currently under review for the journal ESD.

Exploring how groundwater buffers the influence of heatwaves on vegetation function during multi-year droughts

Mengyuan Mu1, Martin G. De Kauwe1, Anna M. Ukkola1, Andy J. Pitman1, Weidong Guo2, Sanaa Hobeichi1, and Peter R. Briggs3 Mengyuan Mu et al.
  • 1ARC Centre of Excellence for Climate Extremes and Climate Change Research Centre, University of New South Wales, Sydney 2052, Australia
  • 2School of Atmospheric Sciences and Joint International Research Laboratory of Atmospheric and Earth System Sciences, Nanjing University, Nanjing 210023, China
  • 3Climate Science Centre, CSIRO Oceans and Atmosphere, Canberra 2601, ACT, Australia

Abstract. The co-occurrence of droughts and heatwaves can have significant impacts on many socioeconomic and environmental systems. Groundwater has the potential to moderate the impact of droughts and heatwaves by moistening the soil and enabling vegetation to maintain higher evaporation, thereby cooling the canopy. We use the Community Atmosphere Biosphere Land Exchange (CABLE) land surface model, coupled to a groundwater scheme, to examine how groundwater influences ecosystems under conditions of co-occurring droughts and heatwaves. We focus specifically on South East Australia for the period 2000–2019 when two significant droughts and multiple extreme heatwave events occurred. We found groundwater plays an important role in helping vegetation maintain transpiration, particularly in the first 1–2 years of a multi-year drought. Groundwater impedes gravity-driven drainage and moistens the root zone via capillary rise. These mechanisms reduced forest canopy temperatures by up to 5 °C during individual heatwaves, particularly where the water table depth is shallow. The role of groundwater diminishes as the drought lengthens beyond 2 years and soil water reserves are depleted. Further, the lack of deep roots or stomatal closure caused by high vapour pressure deficit or high temperatures can reduce the additional transpiration induced by groundwater. The capacity of groundwater to moderate both water and heat stress on ecosystems during simultaneous droughts and heatwaves is not represented in most global climate models, suggesting model projections may overestimate the risk of these events in the future.

Mengyuan Mu et al.

Status: open (until 11 Jul 2021)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on esd-2021-31', Anonymous Referee #1, 03 Jun 2021 reply
  • RC2: 'Comment on esd-2021-31', Anonymous Referee #2, 07 Jun 2021 reply

Mengyuan Mu et al.

Mengyuan Mu et al.

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Short summary
Groundwater can buffer the impacts of drought and heatwave on ecosystems, which is often neglected in model studies. Using a land surface model with groundwater, we explained how groundwater sustains transpiration and eases heat pressure on plants in heatwaves during multi-year droughts. Our results showed the groundwater’s influences diminish as drought extends and are regulated by plant physiology. We suggest neglecting groundwater in models may overstate projected future heatwave intensity.
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