Picture: Remnant native vegetation at Avoca. Credit: Greenfleet Australia.

Groundwater buffers negative impacts of droughts and heatwaves on ecosystems. However, most climate models do not represent groundwater dynamics and neglect its moderation effects, which undermines our confidence in the predicted impacts of future climate extremes.

CLEX researchers and colleagues used a land-surface model that considered groundwater dynamics to explain how groundwater sustains transpiration and eases plant heat pressure during the heatwaves that occurred during the Millennium Drought and the 2017-2019 severe drought over southeast Australia.

The results show groundwater plays an essential role in helping vegetation maintain transpiration and reduces forest temperatures by up to 5°C during individual heatwaves, particularly where the water table depth is shallow. Nevertheless, the role of groundwater diminishes as the drought lengthens beyond two years and soil water reserves are depleted. The lack of deep roots or the closure of stomata (tiny pores on leaves used for gas exchange) caused by dry air or high temperatures can also reduce the extra transpiration sustained by groundwater.

Our study suggests neglecting groundwater in models may overestimate the risk of droughts and heatwaves.

  • Paper: Mu, M., De Kauwe, M. G., Ukkola, A. M., Pitman, A. J., Guo, W., Hobeichi, S., and Briggs, P. R.: Exploring how groundwater buffers the influence of heatwaves on vegetation function during multi-year droughts, Earth Syst. Dynam., 12, 919–938, https://doi.org/10.5194/esd-12-919-2021, 2021.