CDL Crop Type 176 (Grassland/Pasture)

[cgmorton]

Crop class 176 grassland/pasture is a mix of western desert grasslands and irrigated grass hay lands. The two classes loosely follow the NLCD classes 71 and 81 (hence the 176 code in the CDL numbering where the standard NLCD values are increased by 100).

Combining these two vegetation types into a single class is causing issues in EEMETRIC, since that model applies separate momentum roughness calculations for grassland and agriculture crops/classes. To account for this, the EEMETRIC team is proposing that we unpack or revert the 176 pixels back to separate grassland (71) and agriculture (81) like values using the nearest NLCD image in time. This should be relatively simple, except that crop type assets have the dominant crop type within a field applied to the entire field ("burned in"). This burn in process means that there can be 176 pixels across an entire field, even if the field was a mix of different NLCD classes.

As an initial fix, we will skip all fields with a 176 crop type when burning the fields into the images, and let the underlying CDL values remain. This should make it easy for the EEMETRIC model to adjust any 176 pixels using whatever approach they choose.

For future versions of the crop type assets, we may consider remapping some of the CDL 176 pixels to other classes while building the crop type image assets. For example, CDL 176 & NLCD 81/82 could be remapped to CDL 37 (Other Hay/Non Alfalfa), since EEMETRIC will remap this internally to NLCD 81/82. Note, this change will impact the SIMS model results, so we will need to check with that team first before making this change.

Finally, we may also want to consider either not burning in other non-Ag CDL codes or only burning in fields with specific crop types.