Comparison of nitrate leaching to groundwater: CV-GNLM vs CV-SWAT

CV-GNLM (Groundwater Nitrate Loading Modeling) and CV-SWAT (Soil & Water Assessment Tool) are two different approaches to estimate nitrate loading leaching rates to groundwater.

CV-GNLM  ("GNLM") is a field-based N mass balance approach considering average practices and harvest by crop, with dairy- and waste processing-plant specific land applications being specific to each location based on facility size and land availability. CV-SWAT  ("SWAT") is a physically based soil-water-crop model. CV-GNLM considers historic conditions from 1945 onward, in 15-year intervals and takes into account land use changes and historic changes in practices and yields (by crop). CV-SWAT considers year-to-year climate variability, daily precipitation and ET, soils information, varying crop management conditions among the same crop, but is using 2014 land use throughout the simulation period.

The following interactive application compares the nitrate loading distributions between the two modeling approaches.

Nitrate Comparison by Crop Type

The application has five dropdown menus 

  1. The first dropdown menu selects one of the three basins
    Sacramento Valley (SAC), San Joaquin Valley (SJV) or Tulare Lake Basin (TLB)
  2. Selects the GNLM type of groundwater loading.
  3. Selects a GNLM crop category
  4. Selects a SWAT loading scenario (baseline: efficient irrigation and efficient fertilization;  high fertilization:  high fertilization amount and efficient irrigation;  high irrigation:  efficient fertilization and high irrigation amount; high fertilization and high irrigation: worst case scenario.) 
  5. Selects a SWAT crop category

The plot shows the 5, 25, 50, 75 and 95 percentile of the distribution nitrate loading for the selected crop.


GNLM-SWAT comparison image

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