Preprints
https://doi.org/10.5194/egusphere-2024-710
https://doi.org/10.5194/egusphere-2024-710
21 Mar 2024
 | 21 Mar 2024
Status: this preprint is open for discussion.

Global and Regional Hydrological Impacts of Global Forest Expansion

James A. King, James Weber, Peter Lawrence, Stephanie Roe, Abigail L. S. Swann, and Maria Val Martin

Abstract. Large-scale reforestation, afforestation, and forest restoration schemes have gained global support as climate change mitigation strategies due to their significant carbon dioxide removal (CDR) potential. However, there has been limited research into the unintended consequences of forestation from a biophysical perspective. In the Community Earth System Model version 2 (CESM2), we apply a global forestation scenario, within a Paris Agreement-compatible warming scenario to investigate the land surface and hydroclimate response. Compared to a control scenario where land use is fixed to present-day levels, the forestation scenario is up to 2 °C cooler at low latitudes by 2100, driven by a 10 % increase in evaporative cooling in forested areas. However, afforested areas where grassland or shrubland are replaced lead to a doubling of plant water demand in some tropical regions, causing significant decreases in soil moisture (~5 % globally, 5–10 % regionally) and water availability (~10 % globally, 10–15 % regionally) in regions with increased forest cover. While there are some increases in low cloud and seasonal precipitation over the expanded tropical forests, with enhanced negative cloud radiative forcing, the impacts on large-scale precipitation and atmospheric circulation are limited. This contrasts with the precipitation response to simulated large-scale deforestation found in previous studies. The forestation scenario demonstrates local cooling benefits without major disruption to global hydrodynamics beyond those already projected to result from climate change, in addition to the cooling associated with CDR. However, the water demands of extensive forestation, especially afforestation, have implications for its viability given uncertainty in future precipitation changes.

James A. King, James Weber, Peter Lawrence, Stephanie Roe, Abigail L. S. Swann, and Maria Val Martin

Status: open (until 02 May 2024)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
James A. King, James Weber, Peter Lawrence, Stephanie Roe, Abigail L. S. Swann, and Maria Val Martin

Data sets

CESM2 land use data for study on hydrological impacts of large-scale forest expansion James A. King https://doi.org/10.5281/zenodo.10782834

CESM2 land output data for study on hydrological impacts of large-scale forest expansion James A. King https://doi.org/10.5281/zenodo.10797041

CESM2 atmosphere output data for study on hydrological impacts of large-scale forest expansion James A. King https://doi.org/10.5281/zenodo.10797083

CESM2 atmosphere output data for study on hydrological impacts of large-scale forest expansion James A. King https://doi.org/10.5281/zenodo.10797087

CESM2 atmosphere output data for study on hydrological impacts of large-scale forest expansion James A. King https://doi.org/10.5281/zenodo.10797092

James A. King, James Weber, Peter Lawrence, Stephanie Roe, Abigail L. S. Swann, and Maria Val Martin

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Latest update: 13 Apr 2024
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Short summary
Tackling climate change by adding, restoring, or enhancing forests is gaining global support. However, it’s important to investigate the broader implications of this. We used a computer model of the Earth to investigate a future where tree cover expanded as much as possible. We found that some tropical areas were cooler because of trees pumping water into the atmosphere, but this also led to soil and rivers drying. This is important because it might be harder to maintain the forests as a result.