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Climate and Soils Databases and Sub-Models

WEPS:  Weather Sub-model and Databases

WEPS requires wind speed and direction to simulate the wind erosion process.  These and other weather variables such as precipitation, air temperature, and solar radiation are the primary drivers of changes in soil surface physical processes, are also needed to drive temporal changes in hydrology, soil erodibility, crop growth, and residue decomposition in WEPS.  The WEPS weather generators simulate the needed weather data through two separate weather models. The CLIGEN model is a stochastic generator of climate (weather) data, simulating daily estimates of precipitation (amount, duration, peak intensity), temperature (maximum, minimum, dewpoint), wind (direction and speed), and solar radiation. It generates these for a single geographic point, using monthly statistical parameters (means, standard deviations, skewness, etc.) derived from historic measurements. The wind parameters in CLIGEN are not sufficient for WEPS, so the WINDGEN model was created to provide the needed wind parameters.  Similar to CLIGEN, WINDGEN is a stochastic wind generator that uses the frequency distributions of historic sub-daily (i.e., hourly) wind speeds by direction for each month to generate wind parameters, providing the unique requirements of hourly wind speeds and daily wind direction for each day of simulation.

Since WINDGEN bases its generations on historical statistics of wind data gathered from climate stations, it reflects past wind history data at a given location. Station parameter files (summary statistics) to run both generators are available for several thousand U.S. climate station locations. CLIGEN and WINDGEN data were often not collected at the same location, making the data sets and location for each generator distinct. The hydrology sub-model of WEPS simulates soil energy dynamic changes, including soil temperature and water content at the surface, including snow, and in soil layers, including the effects on the growing plants and standing and flat surface residue decomposition. This sub-model maintains a continuous, daily, soil water balance and flow accounting for water in the soil profile, daily precipitation and irrigation, snow depth and melt, runoff, evapotranspiration, and deep percolation. Evapotranspiration is partitioned into evaporation at the soil and/or snow atmospheric interface and crop transpiration, accounting for standing and flat crop residue evaporation suppression effects.

All climate and wind data for US locations is provided as a part of the WEPS 1.5.52 installation.  Windgen data is interpolated from nearby stations to the county’s centroid latitude/longitude location east of the Rocky Mountains.  Climate data from the nearest Cligen station is used in most locations east of the Rocky Mountains.  Climate data from both Cligen and Windgen stations are assigned to polygon regions west of the Rocky Mountains. 

WEPS:  Soil Sub-model and Databases

Soil properties that control soil wind erodibility vary with time during a crop rotation or annually. The objective of the SOIL sub-model is to simulate these temporal soil properties daily in response to various driving processes. On days when wind erosion or management activities occur, the EROSION and MANAGEMENT sub-models may also update some of the same temporal variables. The driving processes that change soil temporal properties are mostly weather related and the sequence of occurrence of individual processes that drive wind erosion is highly variable.  The SOIL sub-model can update the soil variables, since the processes that drive wind erosion are arbitrary and based on the soil conditions from the prior day.

Soil data that is accessed and used by WEPS is from current NRCS SSURGO soil survey data.  When downloading the current WEPS model, NRCS soil data mart with all pertinent soil parameters can be accessed directly within the model.  NRCS SSURGO soil survey data is updated at least once per year.  If current data is not available, contact your NRCS State Soil Scientist to request the most current SSURGO soils data.