Author: Mitchell Manware
Date: 2026-01-26

# Climatology Lab gridMET

#### Mitchell Manware

#### 2026-01-26

This vignette demonstrates how to download, process, and calculate covariates from the Climatology Lab’s gridMET dataset using `amadeus` functions. Details are provided for each function’s parameters and outputs. The examples utilize daily specific humidity data. See https://www.climatologylab.org/wget-gridmet.html for full variable names and acronyms. The messages returned by `amadeus` functions have been omitted for brevity.

### Download

Start by downloading the netCDF data files with `download_data`.

- `dataset_name = "gridmet"`: gridMET dataset name.
- `variable = "Near-Surface Specific Humidity"`: specific humidity variable name.
- `year = c(2019, 2020)`: years of interest.
- `directory_to_save = dir`: directory to save the downloaded files.
- `acknowledgement = TRUE`: acknowledge that the raw data files are large and may consume lots of local storage.
- `download = TRUE`: download the data files.
- `remove_command = TRUE`: remove the temporary command file used to download the data.
- `hash = TRUE`: generate unique SHA-1 hash for the downloaded files.

    dir <- tempdir()
    amadeus::download_data(
      dataset_name = "gridmet",
      variable = "Near-Surface Specific Humidity",
      year = c(2019, 2020),
      directory_to_save = dir,
      acknowledgement = TRUE,
      download = TRUE,
      remove_command = TRUE,
      hash = TRUE
    )

    [1] "aa5116525468299d1fc483b108b3e841fc40d7e5"

Check the downloaded netCDF files.

    list.files(dir, recursive = TRUE, pattern = "sph")

    [1] "sph/sph_2019.nc" "sph/sph_2020.nc"

### Process

Import and process the downloaded netCDF files with `process_covariates`.

- `covariate = "gridmet"`: gridMET dataset name.
- `variable = "Near-Surface Specific Humidity"`: specific humidity variable name.
- `date = c("2019-12-13", "2022-01-10")`: date range of interest.
- `path = paste0(dir, "/sph")`: directory containing the downloaded files.

    sph_process <- amadeus::process_covariates(
      covariate = "gridmet",
      variable = "Near-Surface Specific Humidity",
      date = c("2019-12-18", "2020-01-10"),
      path = file.path(dir, "/sph")
    )

Check the processed `SpatRaster` object.

    sph_process

    class       : SpatRaster
    dimensions  : 585, 1386, 24  (nrow, ncol, nlyr)
    resolution  : 0.04166667, 0.04166667  (x, y)
    extent      : -124.7875, -67.0375, 25.04583, 49.42083  (xmin, xmax, ymin, ymax)
    coord. ref. : lon/lat WGS 84 (EPSG:4326)
    sources     : sph_2019.nc  (14 layers)
                  sph_2020.nc  (10 layers)
    varnames    : sph (near-surface specific humidity)
                  sph (near-surface specific humidity)
    names       : sph_20191218, sph_20191219, sph_20191220, sph_20191221, sph_20191222, sph_20191223, ...
    unit        :        kg/kg,        kg/kg,        kg/kg,        kg/kg,        kg/kg,        kg/kg, ...
    time (days) : 2019-12-18 to 2020-01-10

    terra::plot(sph_process[[1]])

### Calculate covariates

Calculate covariates for California county boundaries with `calculate_covariates`. County boundaries are accessed with the `tigris::counties` function.

- `covariate = "gridmet"`: gridMET dataset name.
- `from = sph_process`: processed `SpatRaster` object.
- `locs = tigris::counties("CA", year = 2019)`: California county boundaries.
- `locs_id = "NAME"`: county name identifier.
- `radius = 0`: size of buffer radius around each county.
- `geom = "sf"`: return covariates as an `sf` object.

    library(tigris)
    sph_covar <- amadeus::calculate_covariates(
      covariate = "gridmet",
      from = sph_process,
      locs = tigris::counties("CA", year = 2019),
      locs_id = "NAME",
      radius = 0,
      geom = "terra"
    )

Check the calculated covariates `sf` object.

    sph_covar

    class       : SpatVector
    geometry    : polygons
    dimensions  : 1392, 3  (geometries, attributes)
    extent      : -124.482, -114.1312, 32.52883, 42.0095  (xmin, xmax, ymin, ymax)
    coord. ref. : lon/lat WGS 84 (EPSG:4326)
    names       :          NAME       time    sph_0
    type        :         <chr>   <POSIXt>    <num>
    values      :        Sierra 2019-12-18 0.003101
                     Sacramento 2019-12-18 0.005791
                  Santa Barbara 2019-12-18 0.004594