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Adaptive mesh precipitation mapping from ERA5 Zarr v3 on Google Cloud Storage.

Prerequisites

• Rust >= 1.91 (rustup update if needed)
• Internet connection (reads from public GCS bucket, no credentials required)

Build

cargo build --release

Usage

Fetch ERA5 total precipitation for a bounding box at a specific UTC datetime:

cargo run --release -- \
  --bbox "lat_min,lat_max,lon_min,lon_max" \
  --datetime "YYYY-MM-DDTHH:MM:SS" \
  -o output.png

Examples

Central US:

cargo run --release -- --bbox "35.0,45.0,-90.0,-75.0" --datetime "2023-06-15T12:00:00" -o precip.png

Western Europe:

cargo run --release -- --bbox "42.0,52.0,-5.0,10.0" --datetime "2023-01-10T06:00:00" -o europe.png

Southeast Asia:

cargo run --release -- --bbox "-10.0,20.0,95.0,120.0" --datetime "2023-08-01T00:00:00" -o asia.png

Arguments

Argument	Description
--bbox	Bounding box as lat_min,lat_max,lon_min,lon_max. Latitude: [-90, 90]. Longitude: [-180, 360].
--datetime	UTC datetime in ISO 8601 format. Data available from 1940 to ~2023.
-o, --output	Output PNG path (default: precip.png).

Verbose logging

RUST_LOG=debug cargo run --release -- --bbox "35.0,45.0,-90.0,-75.0" --datetime "2023-06-15T12:00:00"

Testing

Run offline tests (domain validation + plot rendering):

cargo test

Run integration test (fetches real data from GCS):

cargo test -- --ignored

Run all tests:

cargo test -- --include-ignored

Data Source

Reads from the ARCO ERA5 Zarr v3 store on Google Cloud Storage:

• Bucket: gs://gcp-public-data-arco-era5
• Variable: total_precipitation (meters of water, hourly)
• Resolution: 0.25 degrees (~25 km), hourly
• Coverage: Global, 1940-2023
• Access: Anonymous (no credentials needed)

Output values are displayed in millimeters (mm).