WetSpass-M Modern
Spatially distributed monthly water balance model for QGIS. Estimates groundwater recharge, evapotranspiration, surface runoff, and interception using GeoTIFF inputs. Adds a dynamic soil-water bucket to the original Wetspass-M 2016 physics, with automatic spin-up convergence detection, focused recharge along ephemeral streams, a climate-zone-based recharge cap, and polygon-based output cropping.
WetSpass-M Modern is a modernized version of the original Wetspass-M 2016 model (Abdollahi, Bashir & Batelaan, Vrije Universiteit Brussel). It estimates diffuse and focused groundwater recharge, evapotranspiration, surface runoff, and interception at monthly, seasonal, and annual time steps.
The modernization preserves the original physics but adds:
- A dynamic soil-water bucket (soil moisture carried forward between months) replacing the original quasi-steady-state assumption. Essential for seasonally-concentrated rainfall regimes such as monsoonal, Mediterranean, and semi-arid climates.
- An ET cap at (P - runoff) instead of P, ensuring the catchment-scale mass balance closes exactly.
- Groundwater-fed ET reported separately as Cell_gw_discharge, outside the precipitation balance.
- Nodata-preserving aggregation so annual rasters share the same valid-cell mask.
- Automatic spin-up with convergence detection (mean |dS| compared to max(1 mm, 0.5% of mean annual P), with a 5% tolerance margin so residuals on the numerical noise floor are recognised as converged).
- Automatic checkpointing after every completed month, so a power loss or drive disconnection resumes where it stopped.
- A Skip to final cycle button on the Progress tab, so a run that has essentially converged can jump straight to the final output cycle without waiting for the spinner count.
- A dedicated Water Balance tab with explicit dS and an acceptability verdict.
- A Wetspass-M 2016 compatibility mode for validation against legacy results.
- A Focused Recharge module for streambed infiltration along ephemeral stream networks.
- A user-selectable combine method for diffusive + focused recharge: Addition (default), Replace-by-max (conservative), or Focused-over-diffusive.
- A physical cap on total recharge derived automatically from mean annual precipitation and the standard climate-zone reference table (Arid to Extreme cloud forest). Includes a Preview button that reports, without writing anything to disk, how many cells a given cap would clip.
- Rainfall-driven climate-regime auto-selection (P < 300 arid; 300-700 semi-arid; 700-1200 mixed; >= 1200 humid). The gwdepth-based classifier remains available as a secondary cross-check.
- A Crop outputs to boundary tool that replaces the failing QGIS gdal:rasterize workflow. Presents a file-selection dialog with filter and quick-select buttons, auto-reprojects the boundary vector to each raster's CRS, retains edge pixels with all_touched=True, and writes cropped copies to a cropped_to_boundary/ subfolder. Originals are never modified.
Inputs: 12 monthly climate rasters (rainfall, PET, temperature, wind, groundwater depth), a DEM, land use, soil, and optional slope. Outputs: monthly, seasonal, and annual GeoTIFFs of every flux, plus a per-month summary table.
Original authors (Wetspass-M 2016):
K. Abdollahi, I. Bashir, O. Batelaan - Vrije Universiteit Brussel
Modernization:
M. G. Gurmu
Email: [email protected]