COMMON MODULAR WIND AND WATER EROSION MODELING FOR CONSERVATION PLANNING
Location: National Soil Erosion Research Lab
Title: Impact of Precipitation Changes on Runoff and Soil Erosion in Korea using CLIGEN and WEPP
Submitted to: Journal of Soil and Water Conservation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 11, 2008
Publication Date: May 1, 2009
Citation: Kim, M., Flanagan, D.C., Frankenberger, J.R., Meyer, C. 2009. Impact of Precipitation Changes on Runoff and Soil Erosion in Korea using CLIGEN and WEPP. Journal of Soil and Water Conservation. 64(2):154-162.
Interpretive Summary: Soil erosion by water is caused by the erosive forces of raindrop impact and concentrated water flow. Changes in climate that are forecast in the near future may alter the rain storm events that occur, as well as the amount of rainfall. More frequent and larger rainfall may increase soil loss significantly, but various interacting factors may work to either modify or enhance the effects. For example, more rainfall in a particular location may improve plant growth, so that soil is not as vulnerable to the larger storm events. Alternately, the increased rainfall may increase soil moisture to the point that more frequent subsequent storms can have excessive soil loss. In order to evaluate these different possibilities, a modeling study was conducted with the Water Erosion Prediction Project (WEPP) model and utilizing the CLIGEN (CLImate Generator) weather generator. The model response at two locations in Korea having similar annual rainfall amounts but greatly different soils and topography were evaluated. Rainfall depth and frequency of occurrence were both decreased and increased by 10% and 20%, independently and concurrently. The climate change scenario in which both rainfall depth and occurrence increased by 20% had the greatest effect on the model simulations, resulting in a 54% increase in average annual runoff and a 52% increase in soil erosion at the steeper and sandier site. At the other location with much flatter slopes and a silt loam soil, the combined 20% increases in rainfall resulted in a 60% increase in runoff, but only a 27% increase in soil loss. Definitely the specific location and its characteristics will greatly affect the impacts of climate change. These results impact scientists, conservation agency personnel, extension agents, and others interested in assessing the impacts of changing climates on runoff and soil loss. This technique, when applied to a range of different regions in a country with various topography, soils, management and climate can provide results that can be used by policymakers to decide which areas may be most critically affected by projected climate changes in precipitation, and how to best respond to conserve the soil natural resource.
The quality of spatially and temporally distributed weather information is critical in soil erosion model results because of the primary influence of rainfall on runoff and soil movement. Detailed climate data for the Water Erosion Prediction Project (WEPP) model can be generated by a climate generator (CLIGEN) based on long-term statistical parameters for more than 4,000 locations in the United States. The objectives of this study were to apply CLIGEN and WEPP and examine the effects of changing storm frequency, storm depth, or a combination of the two on predicted rainfall, runoff, and soil loss. Two different sites, Chun-Cheon and Jeon-Ju, were studied and compared for the period 1966 to 2005. Chun-Cheon is located at a higher altitude and is surrounded with forest, while Jeon-Ju is located in the plains. CLIGEN was used to generate 100-year climate sequences with daily climate data e.g., temperature, precipitation, wind, and solar radiation for a representative climate station in the study sites to predict runoff and soil loss with WEPP. Three precipitation change scenarios were examined in this study: (1) adjusting the number of days with rainfall, (2) adjusting the mean amount of rainfall on a wet day, and (3) a combination of 1 and 2. Observed mean annual precipitation at Chun-Cheon (1,305 mm [50.9 in]) was similar to Jeon-Ju (1,291 mm [50.4 in]). CLIGEN simulated mean annual precipitation depths in Chun-Cheon and Jeon-Ju were very close to the observed data. The WEPP model predicted runoff in Jeon-Ju was 48.8% higher than that in Chun-Cheon and estimated soil loss in Chun-Cheon was 55.6% higher than that in Jeon-Ju. Precipitation change scenario 3 that combined changes in precipitation occurrence with changes in rainfall storm depths showed the largest impacts on predicted runoff and soil loss. A combined 20% increase in these precipitation parameters resulted in increases of 44%, 54%, and 52% in generated average annual precipitation, predicted runoff and predicted soil loss, respectively, at Chun-Cheon, while increases at Jeon-Ju were 44%, 60%, and 27%. Increases in rainfall due to future climate change may thus potentially result in substantial and nonlinear increases in runoff and soil loss in Korea.