# Gurara Reservoir Decision-Support Report

## Current Surface-Water Status

- Latest valid observation date: `2026-04-01`
- Latest surface-water area: `36.808 km2`
- Same-month climatological mean: `27.285 km2`
- Same-month anomaly: `9.522 km2` (`34.9%`)
- Data-quality flag passed: `True`
- Interpretation: **Above-normal surface-water extent**

## Long-Term Trend

- Analysis period: `2001-01-01` to `2026-04-01`
- Valid monthly observations: `196`
- Mann-Kendall tau: `0.431`
- Mann-Kendall p-value: `3.19e-19`
- Sen slope: `1.817 km2/year`

## Best Test-Period Models

|   horizon_months | model                |   rmse |   mae |    nse |   kge |   observation_count |
|-----------------:|:---------------------|-------:|------:|-------:|------:|--------------------:|
|                1 | sarima               |  8.014 | 5.393 |  0.075 | 0.516 |                  52 |
|                3 | sarima               |  9.648 | 7.011 | -0.341 | 0.317 |                  52 |
|                6 | seasonal_persistence |  9.836 | 5.029 | -0.292 | 0.088 |                  42 |
|               12 | persistence          |  9.836 | 5.029 | -0.292 | 0.088 |                  42 |

## Latest Backtest Forecasts

These are the most recent test-period backtest forecasts available from the saved prediction files. They are not operational future forecasts unless the model has been run beyond the latest observed month.

|   horizon_months | best_model           | forecast_origin   | target_date   |   forecast_water_area_km2 |   observed_water_area_km2 |   test_rmse |   test_kge |
|-----------------:|:---------------------|:------------------|:--------------|--------------------------:|--------------------------:|------------:|-----------:|
|                1 | sarima               | 2026-03-01        | 2026-04-01    |                    46.799 |                    36.808 |       8.014 |      0.516 |
|                3 | sarima               | 2026-01-01        | 2026-04-01    |                    40.299 |                    36.808 |       9.648 |      0.317 |
|                6 | seasonal_persistence | 2025-09-01        | 2026-03-01    |                    53.245 |                    52.711 |       9.836 |      0.088 |
|               12 | persistence          | 2025-03-01        | 2026-03-01    |                    53.245 |                    52.711 |       9.836 |      0.088 |

## Interpretation Rules

- High seasonal water-stress watch: latest area is within 5% of the historical same-month minimum.
- Moderate seasonal shrinkage watch: latest area is at least 20% below the same-month mean.
- Above-normal extent: latest area is at least 20% above the same-month mean.
- Near-normal extent: latest area is within the expected same-month range.

## Cautions

- Water extraction is constrained to the 55.84 km2 JRC-derived recurring-water footprint; it is a multi-year reservoir envelope rather than a surveyed shoreline for one date.
- Forecasts represent visible surface-water extent, not storage volume.
- Results must be validated against reference water observations before use in formal planning.
- Operational dam releases, abstraction, sedimentation, and field measurements are not yet included.