Updated climate database and impacts on WEPP model predictions

Authors: SRIVASTAVA, ANURAG - Purdue University; Flanagan, Dennis; Frankenberger, James - Jim; ENGEL, BERNARD - Purdue University

Submitted to: Journal of Soil and Water Conservation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/15/2018
Publication Date: 7/3/2019
Citation: Srivastava, A., Flanagan, D.C., Frankenberger, J.R., Engel, B. 2019. Updated climate database and impacts on WEPP model predictions. Journal of Soil and Water Conservation. 74(4):334-349. https://doi.org/10.2489/jswc.74.4.334.
DOI: https://doi.org/10.2489/jswc.74.4.334

Interpretive Summary: Soil erosion is a serious problem in the U.S. and throughout the world. In order to reduce and control soil loss, computer simulation models are usually applied that estimate the amount of soil loss at a specific location for a particular slope, soil type, and land management. Alternative crops and management practices are also examined, to determine ones that minimize runoff and soil erosion. The driving factor for runoff and soil erosion by water is precipitation, and in general daily weather. Erosion models require inputs of daily weather (rainfall, temperatures, etc.), in order to determine processes such as infiltration, runoff, soil detachment, and sediment transport and delivery. Observed or generated climate inputs can be used, but typically generated daily climate inputs are used because they do not have problems associated with observations (missing data, insufficient periods of record). In this study, we looked at the effects of updating the database for a climate generator (CLIGEN) that creates daily climate inputs for the Water Erosion Prediction Project (WEPP) erosion model. The updated database contains statistical information from observed weather at 2765 stations in the United States, from 1974-2018. We found that in general annual precipitation and minimum temperatures increased across most of the U.S., while maximum temperatures increased in the western half of the country and in the Northeast. The updates in the climate database also resulted in greater WEPP runoff and erosion predictions in much of the U.S. These results impact conservation agency staff, farmers, scientists, and others involved in erosion prediction and soil conservation planning activities.

Technical Abstract: CLIGEN (v5.3), a stochastic weather generator, is widely used in conjunction with the Water Erosion Prediction Project (WEPP) model for runoff and soil loss predictions. CLIGEN generates daily estimates of weather based on long-term observed weather station data statistics. For the U.S., the original CLIGEN database released with WEPP in 1995 was derived using inconsistent periods of climate records through 1992 that could lead to significant variations in runoff and soil loss predictions on spatial and temporal scales. To achieve more reliable estimates of runoff and soil loss, an updated climate database was derived from a consistent 40 years of recent climate records of 1974–2013 in the U.S. The objectives of this study were to: 1) examine the spatial patterns in trends of differences in precipitation, and maximum and minimum temperatures between the two databases, and 2) evaluate the impacts on WEPP-predicted mean annual runoff and soil loss, from the original to the updated databases. For runoff and soil loss estimates, WEPP simulations were conducted under a tilled fallow condition for 1,600 CLIGEN locations in the contiguous U.S. for a slope profile of 22.1 m length, 9% slope gradient, and silt loam soil. Comparison of precipitation, and maximum and minimum temperatures between the original and update databases showed variations in spatial patterns both annually and seasonally. Annual precipitation and minimum temperature generally increased across most of the country while maximum temperature increased in the western half of the U.S. and parts of the Northeast. Seasonally, increases in precipitation are evident in the Midwest in spring, fall, and winter, the Northwest in spring, and the Southeast in fall. Maximum daily temperature has increased in the western half of U.S. and parts of the Northeast in the winter, fall, and spring, whereas minimum daily temperature has increased in all seasons across the U.S. Changes in WEPP-simulated mean annual runoff and soil loss, from the use of the original to the updated CLIGEN database showed increases in runoff and soil loss in most of the U.S. However, some stations showed either increases or decreases in runoff and/or soil loss with the updated database primarily because of differences in monthly precipitation and intensity values in the two databases. Understanding the impacts of the use of the updated database on runoff and soil loss from this study will help in making informed decisions for conservation planning and management when utilizing the WEPP erosion model.