SCIMAP for QGIS 1.10: what’s new since 1.7

Version 1.10 of the SCIMAP plugin for QGIS is now on the QGIS plugin repository. It is the first release since 1.7. The biggest change is under the hood: SCIMAP’s hydrology now runs on Whitebox Workflows instead of the WhiteboxTools program, which is no longer developed.

Most users can upgrade straight away. Read Before you upgrade first if you use an Intel Mac or ARM Linux, or if you compare new runs with results from 1.7.

Change	What it means for you	Do you need to act?
Hydrology runs on Whitebox Workflows	No separate WhiteboxTools download or path to set	Accept the install offer when the plugin first loads
Intel Macs and ARM Linux dropped	Whitebox Workflows has no builds for them	Stay on 1.7 on those computers
New default depression removal	Results from default settings differ from 1.7	Re-run any baseline you compare against
Critical source areas as a map layer	The ten priority areas come straight out of SCIMAP Sediment and SCIMAP FIO	None
Choice of depression removal method	Match your own DEM preparation, or the SCIMAP web app	Optional
About a quarter of the memory	Larger catchments run on the same computer	None
One-click install of numba	Connectivity and flood runs many times faster	Optional; restart QGIS after
Web dashboard upgrades	Where to act first, every layer in 3D, AR export, terrain clipped to the catchment	None
Land cover classification choice	ESA WorldCover built in alongside UKCEH LCM	Check the classification each tool asks for
Routing fix for GDAL 3.13	Risk concentration and stream risk values were wrong on GDAL 3.13	Re-run results made on GDAL 3.13

Before you upgrade

Version 1.10 needs Whitebox Workflows, which runs on fewer computers than WhiteboxTools did, and its default settings route flow differently from 1.7.

Which computers it runs on. Whitebox Workflows has builds for Windows (x64), macOS on Apple silicon and Linux (x86-64) only. On an Intel Mac or an ARM Linux computer, keep using 1.7. The plugin works in QGIS 3.28 and later, including QGIS 4.

Installing Whitebox Workflows. You no longer download WhiteboxTools or tell the plugin where it is. When the plugin first loads, it offers to install Whitebox Workflows into your QGIS profile. You can also install it later from the SCIMAP panel: open the Settings tab (the spanner), then Python packages, then Install…. The WhiteboxTools executable setting and Processing parameter are gone, so remove that parameter from any Processing model or Python script that sets it.

Why your results will change. Version 1.7 removed the DEM’s depressions with WhiteboxTools’ BreachDepressions, which Whitebox Workflows does not have. The default now breaches each depression along its least-cost route and fills whatever it cannot breach. On 5 m LiDAR, the flow directions this gives match 1.7’s on 87 to 95% of cells. Everything else matches WhiteboxTools to within single-precision rounding.

If you compare new runs with older ones, for example before and after a change in land management, re-run the older scenario in 1.10. Both runs then route flow the same way, and the difference you see comes from the land management change itself.

Critical source areas as a map layer

SCIMAP Sediment and SCIMAP FIO now save the critical source areas as a polygon layer, so you no longer need to build a web dashboard to get them. Critical source areas are the patches of land most likely to deliver sediment or faecal indicator organisms to the river. They are the joined-up patches of the catchment’s top 5% of land by risk times connectivity, and the layer holds the ten largest.

Each area records:

• its rank, from 1 to 10
• what puts it there: high erosion risk, high connectivity, or both
• its area in hectares
• its share of the whole catchment’s risk times connectivity
• its mean risk and connectivity scores

On the map, each area is outlined in the colour of what puts it there and numbered by rank. The areas are the same as the web dashboard’s Where to act first list, and use your DEM’s coordinate system. The layer is made by default. You can switch it off in the Processing dialog, and the SCIMAP panel adds it to the map after each run.

What this means for you: you can take the priority areas straight into a farm plan, a field visit or a report, or overlay them on field boundaries in QGIS.

Choose how the DEM’s depressions are removed

You can now choose how SCIMAP removes depressions from the DEM before it routes flow over it. Depressions are hollows in the DEM, real or caused by errors, where water would collect instead of flowing on. How they are removed decides where flow goes, so it changes the connectivity and risk maps.

Option in the plugin	What it does
Breach, then fill what remains (SCIMAP default)	Cuts a least-cost channel out of each depression, searching up to 1000 cells, then fills any it could not breach. Removes every depression while changing the DEM least.
Fill depressions	Fills every depression to its spill point (priority flood), with a slight slope across the filled flats so they drain
Fill depressions (Wang and Liu)	Fills every depression with Wang and Liu’s method
Fill depressions (Planchon and Darboux)	Fills every depression with Planchon and Darboux’s method
Breach depressions only (least cost)	Breaching without the fill. Flow ends in any depression it cannot breach.
Breach single-cell pits only	Carves a channel out of each one-cell pit. Larger depressions stay.
Fill single-cell pits only	Raises each one-cell pit to drain into its lowest neighbour. Larger depressions stay.
SCIMAP web application sequence	Matches the SCIMAP web application, so results can be compared with it
None: use the DEM as supplied	For a DEM you have conditioned yourself, for example with streams burnt in

The choice is a new DEM pre-processing parameter on every tool that routes flow over a DEM: SCIMAP Sediment, SCIMAP FIO, Network Index, Delineate Catchment, Overland Flow Distance to Point, and SCIMAP Fitted 1 and 3.

In the SCIMAP panel, the choice is on the new Settings tab and applies to every run from the panel. It replaces the Breach depressions tick box on the Catchment tab. A catchment and the risk maps run on it now always route flow the same way.

Bigger catchments, faster runs

The SCIMAP tools now use about a quarter of the memory they did, so larger catchments run on the same computer. Each tool works through its rasters a block of rows at a time instead of holding them all in memory.

Tool, on a 4000 × 4000 cell DEM	Peak memory before	Peak memory now
SCIMAP Sediment	2.1 GB	0.6 GB
SCIMAP Flood	2.4 GB	0.6 GB
SCIMAP Fitted catchment statistics	2.6 GB	0.7 GB

Results are the same to within single-precision rounding, and run times are unchanged. If a run fails part of the way through, it now deletes the outputs it had already written.

Optional speed-up. The plugin can now install its optional Python packages for you. numba makes the connectivity and flood calculations many times faster on large rasters, and matplotlib draws the SCIMAP Fitted plots. The plugin offers numba when it is missing, or you can use Install… under Python packages on the Settings tab. The packages go into a folder in your QGIS profile, so QGIS’s own Python is left as it is. Restart QGIS after installing numba to start using it.

Web dashboard

The web dashboard now opens on where to act first, and its 3D view shows everything the 2D map does.

• Where to act first. The Analysis tab now opens with the critical source areas. The ten largest are listed with what puts each one there, outlined on the map and the 3D terrain, and offered as a GeoJSON download.
• Every layer in 3D. The layer tick boxes and opacity sliders now control the 3D terrain as well as the 2D map. This replaces the old 3D button, which draped one layer at a time. The 3D view also draws the catchment boundary, pour point and stream risk points.
• Consistent layer order. Where layers overlap, the one higher in the list is drawn on top, in both views and in saved map images.
• Augmented reality. The 3D model can be saved as USDZ, which opens in AR Quick Look on an iPhone or iPad at its printed size. All exported 3D models are also smaller.
• Terrain clipped to the catchment. Before, the 3D terrain and exported 3D models covered the whole DEM. Given a catchment boundary, Create Web Dashboard now clips the DEM to it. This spends the dashboard’s detail on the catchment, and puts the clipped DEM in the download bundle. A new option turns clipping off.
• Catchment passed on from the panel. The SCIMAP panel now gives the dashboard the catchment the run was clipped to. Before, it did so only when that catchment had been delineated in the same QGIS session.

Land cover and input data

SCIMAP now reads more land cover maps and more DEM files without any preparation on your part.

Land cover classification. SCIMAP Sediment and Apply Land Cover Risk Weights now ask which classification your land cover map uses, as the SCIMAP Fitted tools already did. The choices are:

• CEH LCM 2015 and later
• CEH LCM 2007 (the default, as before)
• ESA WorldCover
• land cover already in SCIMAP classes
• a custom remap table

This replaces the “Land cover already uses SCIMAP classes” tick box. If your map is UKCEH LCM 2015 or later, choose CEH LCM 2015+: UKCEH changed its class list in 2015, and the 2007 table reads Urban and Suburban in later maps as Other. ESA WorldCover is built in, so you can use SCIMAP outside the UK without writing a remap table. It adds two SCIMAP classes, 8 Snow and 9 Water, each with a default risk weight of 0.5, the same as Other.

Compressed and virtual DEMs. Many downloaded DEMs, such as LINZ’s LiDAR cloud-optimised GeoTIFFs, use compression the hydrology engine cannot read: ZSTD, LZMA, LERC or a TIFF predictor. GDAL virtual rasters (VRT) are the same. SCIMAP now hands the engine a readable temporary copy of such a DEM and deletes it after the run. A DEM stored south-up is refused, with a message saying how to fix it.

Coordinate systems recorded by name only. Some GeoTIFFs, including some NZTM (EPSG:2193) files, record their coordinate system by name alone. Aligning a rainfall map in another coordinate system to them used to fail with “Cannot find coordinate operations”. SCIMAP now looks the name up in the EPSG database. If it does not recognise the name, it asks you to assign the layer’s coordinate system.

SCIMAP Fitted. SCIMAP Fitted 3 can now route on the breached DEM that SCIMAP Fitted 1 writes. Before, WhiteboxTools could not read that file.

The SCIMAP panel

The panel is wider, shorter and has a new Settings tab.

• Settings tab. A new tab, shown as a spanner, holds the depression removal choice and the Python packages. The packages used to sit at the bottom of the Results tab.
• Width. The panel opens a quarter wider and can be dragged to any width, which it remembers. It used to be fixed at 340 pixels, which cut off the longer labels.
• Flood tab. The rainfall pattern and overland flow distance rasters are now picked from drop-down tick lists that follow the layers in your project. The Refresh raster lists button is gone, and the panel’s tallest tab is about 170 pixels shorter.

Changes that affect your results

Four changes since 1.7 can give different numbers from the same inputs. Re-run any result you still rely on if one of them applies to it.

Change	It affects your results if	What to do
New default depression removal	You used the default settings (almost everyone)	Re-run baselines you compare against; on 5 m LiDAR, 87 to 95% of flow directions are unchanged
Routing fix for GDAL 3.13	Your QGIS runs GDAL 3.13 (see Help › About in QGIS)	Re-run: risk concentration, stream network risk values, stream risk points and SCIMAP Fitted’s dilution factor and ensemble maps were wrong
Land cover resampling	Your DEM cells are larger than your land cover cells	Re-run for the better resampling: each DEM cell now takes the most common land cover class rather than the nearest one, and continuous rasters are averaged rather than interpolated
Land cover classification	You used a UKCEH LCM 2015 or later map with SCIMAP Sediment	Re-run with CEH LCM 2015+ chosen, so Urban and Suburban are read correctly

The models in the plugin now come from pySCIMAP, a Python package shared with the SCIMAP web application. The plugin and the web application therefore run the same code, and give the same answers from the same data and settings.

Upgrading, step by step

1. Check your computer is a Windows (x64) PC, an Apple silicon Mac or a Linux (x86-64) machine. If not, stay on 1.7.
2. In QGIS, open Plugins › Manage and Install Plugins…, select SCIMAP and click Upgrade Plugin.
3. When the plugin offers to install Whitebox Workflows, accept. If you missed the offer, open the SCIMAP panel’s Settings tab and use Install… under Python packages.
4. Optionally, install numba from the same place for faster runs, then restart QGIS.
5. On the Settings tab, check the depression removal method, then re-run any baselines you compare against.