The local climate adaptation potential of reforestation, and how it changes during heat waves

Managed alterations to ecosystems designed to increase carbon sequestration or reduce greenhouse gas emissions – so-called “natural” or “nature-based” climate solutions like reforestation and cover cropping - have growing public and private support. Despite this enthusiasm, the realizable benefits of these strategies, and unintended consequences to be avoided, are not well understood. In particular, land cover and management changes designed to affect carbon cycles will also impact water and energy cycles in ways that may or may not be climatically beneficial, but we lack systematic frameworks for assessing and valuing these “biophysical impacts.” Moreover, most of the existing observation-driven work on the topic has been limited to impacts on surface temperature; we still know relatively little about when and where modifications to surface temperature extend to the near-surface air temperature, which is arguably the more relevant target for climate adaptation. In this talk, I will describe a new approach for leveraging flux tower observations to understand the duality of surface and air temperature responses to land cover change. Then, using Eastern US reforestation as a case study, I will apply the approach together with analysis of remote sensing and meteorological data to demonstrate that over annual time scales, reforestation substantially lowers both surface and air temperature, due to canopy structural effects that enhance both sensible heat flux and latent heat flux. However, during heat waves when cooling benefits are most needed, divergent responses of sensible and latent heat fluxes between forested and non-forested ecosystems may reduce the local climate adaptation potential of reforestation.