Simulated Local and Remote Biophysical Effects of Afforestation over the Southeast United States in Boreal Summer*

Abstract

Afforestation has been proposed as a climate change mitigation strategy by sequestrating atmospheric carbon dioxide. With the goal of increasing carbon sequestration, a Congressional project has been planned to afforest about 18 million acres by 2020 in the Southeast United States (SEUS), the Great Lake states, and the Corn Belt states. However, biophysical feedbacks of afforestation have the potential to counter the beneficial climatic consequences of carbon sequestration. To assess the potential biophysical effects of afforestation over the SEUS, the authors designed a set of initial value ensemble experiments and long-term quasi-equilibrium experiments in a fully coupled Community Climate System Model, version 3.5 (CCSM3.5). Model results show that afforestation over the SEUS not only has a local cooling effect in boreal summer [June-August (JJA)] at short and long time scales but also induces remote warming over adjacent regions of the SEUS at long time scales. Precipitation, in response to afforestation, increases over the SEUS (local effect) and decreases over adjacent regions (remote effect) in JJA. The local surface cooling and increase in precipitation over SEUS in JJA are hydrologically driven by the changes in evapotranspiration and latent heat flux. The remote surface warming and decrease in precipitation over adjacent regions are adiabatically induced by anomalous subsidence. Our results suggest that the planned afforestation efforts should be developed carefully by taking account of short-term (local) and long-term (remote) biophysical effects of afforestation.

Community Earth System Model Simulations Reveal the Relative Importance of Afforestation and Forest Management to Surface Temperature in Eastern North America

“…Simulations were run on a 1.9 • × 2.5 • horizontal resolution for 30 years to allow the system to reach a dynamic equilibrium. While the simulations predicted climate over the entire globe, we focused our analysis on the grid-cells highlighted in Figure 1 and on the final 20 years of each simulation, discarding the first 10 years of simulation data as the model spin-up necessary to ensure that the climate has stabilized with the modified land surface (as commonly done in simulations focused on equilibrium differences in climate; [17,18]). We analyzed the responses of the 2-m air temperature variable simulated by the CESM because it is commonly reported in other modeling studies (e.g., [18]) and from meteorological stations in differing land-cover types [21].…”

“…Simulation studies also allow for the assessment of temperature changes that include the final outcome of the interactions and feedback between the surface and atmosphere. Earth System Model modeling is a key tool for the development of a more refined understanding of the drivers governing the role of afforestation in the climate system [17,18].…”

Land use/land cover changes and regional climate over the Loess Plateau during 2001–2009. Part II: interrelationship from observations

“…As a result, it is expected that LULCC would modify the existing nature of land-surfaceatmosphere interactions and, consequently, weather and climate. Many local-, regional-, and globalscale studies have demonstrated this assertion (e.g., Chase et al 2000;Chen et al 2012).…”

Short-term climatic impacts of afforestation in the East Asian monsoon region

“…In recent years, more and more scientists are focusing on the impacts of changes in vegetation cover on global and regional climate [1][2][3][4][5][6]. Vegetation affects climate mostly through albedo, evapotranspiration and surface roughness [7][8][9][10]. Charney [7] speculated overgrazing in the Sahel of Africa could lead to a loss of vegetation, which raises the surface albedo and cools the ground, so subsidence airflow continues and droughts increase in intensity.…”

“…Also, a reduction in evapotranspiration leads to decreased precipitation and a slowing of the hydrological cycle. Cheng et al [9] found an increase in the density of forest cover increase the surface roughness and induces convergence, so the anomalous ascent increases cloud cover and precipitation. Also, the ways in which vegetation affects climate may vary by latitudes [10][11][12].…”