Sensitivity of the US corn belt to climate change and elevated CO 2: II. Soil erosion and organic carbon

Abstract

Climate models indicate that increasing atmospheric concentrations of carbon dioxide and other greenhouse gases could alter climate globally. The EPIC (Erosion/Productivity Impact Calculator) model was used to examine the sensitivity of soil erosion (wind, water) and soil organic carbon (SOC) (15 cm and 1 m depth) across the US corn belt to changes in temperature (+ 2°C), precipitation (±10%, ±20%), wind speed (±10%, ±20%), and atmospheric CO 2 concentration (350, 625 ppmv). One-hundred-year simulations were run for each of 100 sites under 36 climate/CO 2 regimes. The 100-year regionally aggregated mean water erosion rates increased linearly with precipitation, whereas the wind erosion rates decreased and total erosion rates increased non-linearly. Increasing temperature by 2°C (with CO 2 and mean wind speed held constant) decreased water erosion by 3–5%, whereas wind erosion increased by 15–18%. Total erosion increased with increased temperature. Increasing CO 2 from 350 to 625 ppmv (with temperature increased by 2°C and mean wind speed held constant) had no effect on water erosion, despite increases in annual total and peak runoff; this was attributed to increased vegetation cover. Wind erosion decreased by 4–11% under increased CO 2. Wind erosion was very sensitive to mean wind speed, increasing four-fold and decreasing 10-fold for a 20% increase or decrease in mean wind speed, respectively. This was attributed to a threshold effect. SOC to 1 m decreased 4·8 Mg-C ha −1 from an initial value of 18·1 Mg-C ha −1 during the 100-year baseline simulation. About 50% of this loss (2·3 Mg-C ha −1) was due to transport off-site by soil erosion. SOC in the top 15 cm decreased 0·8 Mg-C ha −1 from an initial value of 4·9 Mg-C ha −1. Increased temperature and precipitation accelerated these losses of SOC, whereas increased CO 2 slowed the losses.