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This repository provides weekly US Drought Monitor (USDM) data aggregated to US Census American Indian/Alaska Native/Native Hawaiian Area (AIANNH) boundaries. This dataset facilitates AIANNH-level analysis of drought conditions, supporting research, policy-making, and climate resilience planning.

📂 View the US Drought Monitor AIANNH archive listing here.

The goal of this repository is to aggregate AIANNH-level US Drought Monitor data in a consistent and reproducible way, using authoritative US Census AIANNH boundaries.

📈 About the US Drought Monitor (USDM)

The US Drought Monitor is a weekly map-based product that synthesizes multiple drought indicators into a single national assessment. It is produced by:

  • National Drought Mitigation Center (NDMC)
  • US Department of Agriculture (USDA)
  • National Oceanic and Atmospheric Administration (NOAA)

Each weekly map represents a combination of data analysis and expert interpretation.

The USDM weekly maps depicting drought conditions are categorized into six levels:

  • None: Normal or wet conditions
  • D0: Abnormally Dry
  • D1: Moderate Drought
  • D2: Severe Drought
  • D3: Extreme Drought
  • D4: Exceptional Drought

While USDM drought class boundaries are developed without regard to political boundaries, it is often aggregated by political boundaries to assist in decision-making and for regulatory purposes. This repository focuses on aggregating these data to the AIANNH level, enabling more localized analysis and decision-making.

Note: This archive is maintained by the Montana Climate Office, but all analytical authorship of the USDM drought maps belongs to the named USDM authors.

🗂 Directory Structure

  • usdm-aiannh.R: R script that processes and aggregates weekly USDM shapefiles to AIANNH boundaries.
  • data/: Directory containing processed AIANNH-level USDM data and US Census AIANNH boundary files.
  • README.Rmd: This README file, providing an overview and usage instructions.
  • usdm-aiannh.parquet: processed AIANNH-level USDM data.
  • census-aiannh-2024.parquet: processed AIANNH boundaries from the US CENSUS

Data Sources

  • USDM Polygons: Weekly .parquet files from sustainable-fsa/usdm
  • U.S. Census AIANNH Boundaries: Downloaded from the U.S. Census TIGER/Line archive for 2024.

All boundaries are reprojected to EPSG:4326, geospatially validated, and saved in .parquet format.

Processing Pipeline

The analysis pipeline is fully contained in usdm-aiannh.R and proceeds as follows:

  1. Install and load dependencies:
  • Uses pak::pak() to ensure fresh, source-built installs of critical geospatial packages.

  1. Download AIANNH boundary shapefiles for 2024 directly from US Census and store in data/census.

  2. Convert the shapefile to (Geo)Parquet:

  • Extract and clean up attributes
  • Encode using UTF-8, fix geometries, cast to MULTIPOLYGON, and calculate area
  • Output is saved to census-aiannh-2024.parquet
  1. Match USDM dates with appropriate AIANNH vintage:
  • Each USDM date is paired with the most recent AIANNH boundary file available for that year
  • The full list of USDM dates is generated starting from 2000-01-04, up to two days before the current date
  1. Download and intersect:
  • For each weekly USDM .parquet file:
  • Read AIANNH and drought geometries
  • Perform spatial intersection
  • Calculate the percent of each AIANNH area affected by each drought class
  • Tabular output is saved to data/usdm/USDM_{YYYY-MM-DD}.parquet
  1. Output Structure: Each output file is a non-spatial .parquet file with the following fields:
  • GNIS, Name, NameLSAD, LSAD, CountyLSAD
  • Date: Date of the USDM map (weekly, on Tuesdays)
  • USDM Class: One of D0, D1, D2, D3, D4
  • Total Area (m^2): Total area of the AIANNH
  • USDM Class Area (m^2): Area of the AIANNH in the USDM drought class
  • USDM Class Area (%): Percent of the AIANNH in this drought class (between 0 and 100)

🛠️ Dependencies

Key R packages used:

  • sf
  • terra
  • arrow
  • tidyverse
  • curl

The script installs all required packages using the pak package.

📍 Quick Start: Visualize a Weekly County USDM Map in R

This snippet shows how to load a weekly GeoParquet file from the archive and create a simple drought classification map using sf and ggplot2.

# Load required libraries
library(arrow)
library(sf)
library(ggplot2) # For plotting
library(tigris)  # For state boundaries
library(rmapshaper) # For innerlines function

## Get latest USDM data
latest <-
  jsonlite::fromJSON(
    "manifest.json"
  )$path |>
  stringr::str_subset("parquet") |>
  max()
# e.g., [1] "data/usdm-aiannh/USDM_2025-05-27.parquet"

date <-
  latest |>
  stringr::str_extract("\\d{4}-\\d{2}-\\d{2}") |>
  lubridate::as_date()

states <-
  tigris::states(cb = TRUE, 
                 resolution = "5m",
                 progress_bar = FALSE) |>
  dplyr::filter(!(STUSPS %in% c("MP", "VI", "AS", "GU"))) |>
  sf::st_cast("POLYGON", warn = FALSE, do_split = TRUE) |>
  tigris::shift_geometry()

# Get the highest (worst) drought class in each county
usdm <-
  latest |>
  arrow::read_parquet() |>
  dplyr::group_by(GNIS) |>
  dplyr::filter(`USDM Class` == max(`USDM Class`))

aiannh <- 
  tigris::native_areas(cb = TRUE, 
                       progress_bar = FALSE) |>
  sf::st_cast("POLYGON", warn = FALSE, do_split = TRUE) |>
  tigris::shift_geometry()

usdm_aiannh <-
  usdm |>
  dplyr::left_join(aiannh) |>
  sf::st_as_sf()

## Warning in dplyr::left_join(usdm, aiannh): Detected an unexpected many-to-many relationship between `x` and `y`.
## ℹ Row 1 of `x` matches multiple rows in `y`.
## ℹ Row 4 of `y` matches multiple rows in `x`.
## ℹ If a many-to-many relationship is expected, set `relationship =
##   "many-to-many"` to silence this warning.

# Plot the map
ggplot(states) +
  geom_sf(data = sf::st_union(states),
          fill = "grey80",
          color = NA) +
  geom_sf(data = usdm_aiannh,
          aes(fill = `USDM Class`), 
          color = "white",
          linewidth = 0.01) +
  geom_sf(data = states |>
            rmapshaper::ms_innerlines(),
          fill = NA,
          color = "white",
          linewidth = 0.2) +
  scale_fill_manual(
    values = c("#ffff00",
               "#fcd37f",
               "#ffaa00",
               "#e60000",
               "#730000"),
    drop = FALSE,
    name = "Drought\nClass") +
  labs(title = "US Drought Monitor",
       subtitle = format(date, " %B %d, %Y")) +
  theme_void()

📝 Citation & Attribution

Citation format (suggested):

Native Resilience Project. US Drought Monitor weekly maps aggregated to US Census American Indian/Alaska Native/Native Hawaiian Area (AIANNH) boundaries. Data curated and archived by R. Kyle Bocinsky, Montana Climate Office. Accessed via GitHub archive, YYYY. https://native-resilience.github.io/usdm-aiannh/

Acknowledgments:

  • Map content by USDM authors.
  • Data curation and archival structure by R. Kyle Bocinsky, Montana Climate Office, University of Montana.

📄 License

  • Raw USDM data (NDMC): Public Domain (17 USC § 105)
  • Processed data & scripts: © R. Kyle Bocinsky, released under CC0 and MIT License as applicable

⚠️ Disclaimer

This dataset is archived for research and educational use only. The National Drought Mitigation Center hosts the US Drought Monitor. Please visit https://droughtmonitor.unl.edu.

👏 Acknowledgment

This project is part of:

Native Resilience Project: Sustaining Water Resources and Agriculture in a Changing World
Supported by USDA NIFA and USDA Climate Hubs under grant number 2022-68015-36357 Prepared by the Montana Climate Office

📬 Contact

R. Kyle Bocinsky
Director of Climate Extension
Montana Climate Office
📧 kyle.bocinsky@umontana.edu
🌐 https://climate.umt.edu