# Split Design For FireWx-FM Refinement

This document defines the split logic needed to make FireWx-FM harder to
criticize as a regional or autocorrelated supervised model.

## Required Split Families

### 1. Chronological CONUS Split

Purpose: test future-season performance across the Lower 48.

Recommended default:

- Train: 2021-2024 fire seasons.
- Validation: 2025 fire season.
- Test: 2026 fire season or latest available held-out year.

Config support:

- Use `split_years` in `stage1_cache_conus_multiyear_template.json`.

### 2. Region-Disjoint Split

Purpose: test whether the model transfers beyond the regions it saw during
training.

Recommended holdout regions:

- California / Pacific Coast.
- Pacific Northwest.
- Rockies / Intermountain West.
- Southeast including Florida.
- Great Plains / Central.

Implementation note:

- Masked evaluation can be done with trained full-CONUS checkpoints.
- Strict region-disjoint training requires region masks inside the training tile
  sampler so positive and negative crops from the held-out region are excluded.

### 3. Spatial Block Split

Purpose: reduce local grid-cell autocorrelation.

Recommended design:

- Divide the Lower 48 grid into large projected blocks.
- Hold out non-adjacent blocks for testing.
- Add buffer blocks between train and test when data volume permits.

### 4. Seasonal Robustness Split

Purpose: test whether the model only fits one seasonal window.

Recommended designs:

- Train early season and test late season.
- Train excluding October-like months and test October-like months.
- Report monthly positive rate and metric curves.

## Reporting Requirements

Every experiment should save:

- Config path and SHA-256.
- Cache manifest path and SHA-256.
- Split rule name.
- Number of samples per split.
- Number of positive cells per split.
- Total FIRMS fire points per split.
- Date range per split.
- Region mask used, if any.

## Claim Boundary

Do not claim broad foundation-model generalization unless both cross-year and
region-disjoint tests are reported. A chronological split alone is not enough.