The Soil Moisture and Net Primary Production Affected by CO₂ and Climate Change Using a Coupled Model

Abstract

In this paper, a coupled model was used to estimate the responses of soil moisture and net primary production of vegetation (NPP) to increasing atmospheric CO₂ concentration and climate change. The analysis uses three experiments simulated by the second-generation Earth System Model (CanESM2) of the Canadian Centre for Climate Modelling and Analysis (CCCma), which are part of the phase 5 of the Coupled Model Intercomparison Project (CMIP5). The authors focus on the magnitude and evolution of responses in soil moisture and NPP using simulations modeled by CanESM, in which the individual effects of increasing CO₂ concentration and climate change and their combined effect are separately accounted for. When considering only the single effect of climate change, the soil moisture and NPP have a linear trend of 0.03 kg m^–2 yr^–1 and −0.14 gC m^–2 yr^–2, respectively. However, such a reduction in the global NPP results from the decrease of NPP at lower latitudes and in the Southern Hemisphere, although increased NPP has been shown in high northern latitudes. The largest negative trend is located in the Amazon basin at −1.79 gC m^–2 yr^–2. For the individual effect of increasing CO₂ concentration, both soil moisture and NPP show increases, with an elevated linear trend of 0.02 kg m–2 yr–1 and 0.84 gC m–2 yr–2, respectively. Most regions show an increasing NPP, except Alaska. For the combined effect of increasing atmospheric CO₂ and climate change, the increased soil moisture and NPP exhibit a linear trend of 0.04 kg m–2 yr–1 and 0.83 gC m–2 yr–2 at a global scale. In the Amazon basin, the higher reduction in soil moisture is illustrated by the model, with a linear trend of −0.39 kg m–2 yr–1, for the combined effect. Such a change in soil moisture is caused by a weakened Walker circulation simulated by this coupled model, compared with the single effect of increasing CO₂ concentration (experiment M2), and a consequence of the reduction in NPP is also shown in this area, with a linear trend of −0.16 gC m^–2 yr^–2.

Key Words:

• increasing atmospheric CO₂
• climate change
• soil moisture
• net primary production
• coupled model