Watershed Assessment Data Types
Watershed assessment data in a NetMap Level 1 Assessment include lines and grids (or rasters). In particular, it is important to note that the attributes of slope stability, wildfire risk and climate change are represented by both rasters and lines (e.g., stream channel lines).
In NetMap, grid data, such as shallow landslide potential, fire risk and climate change, are also represented at the scale of individual channel segments and drainage wings (drainage wings refer to local contributing areas located on either side of individual stream segments in NetMap, typically on the order of tenths of a square kilometer in area) (Figures 1 and 2).
NetMap’s aggregation tool reports GEP to individual stream segments (GEP units/km2) and also routes that information downstream. In NetMap, each channel segment’s local contributing drainage area is defined on both sides of the channel (called drainage wings, Figure 1) and information contained on those hillsides is reported to the channel segment (Figure 2). That information is then routed downstream.
Figure 1. NetMap applies a universal data structure to its watershed assessments. This involves organizing river networks into stream segments (with Ids), confluence nodes, and local contributing drainage areas. Hillslope and channel information is routing downstream revealing patterns across multiple scales.
Figure 2. NetMap drainage wings are located on either side of individual channel segments (#1 segment length ranges from approximately 50 to 200 m). Watershed attributes located in the wings (#2) such shallow landslide potential, fire risk and climate change forecasts are summarized at that scale (approximately a few tenths of a square kilometer) and reported to stream segments, providing a fish eye view of terrestrial conditions. In addition, channel segment data are aggregated or accumulated downstream (routed) revealing spatial patterns of those terrestrial attributes at any spatial scale defined by the channel network. See examples below.
Example: Wildfire
Fire probability and fire severity (flame length) are accessed from federal wildfire predictions (WWETAC).
Wildfire probability and severity forecasts as spatial grid (rater) data (30 m pixel) is shown in Figure 3.
Figure 3. The predicted fire probability (lower) and fire severity in terms of flame length (upper) are mapped across the US portion of the Flathead River watershed. See Figure 4 for a channel or fish eye view of fire severity.
Using the channel segment scale drainage wings in NetMap (Figures 1 and 2), predicted fire severity is reported to stream segments, offering a channel- or fish-eye view of fire severity (Figure 4). In addition, the channel segment values are aggregated (summed and area weighted) downstream in NetMap, providing a means to examine predicted fire severity at any spatial scale defined by the channel network (Figure 5). Such raster converted to line data allows analysts using Level 1 Watershed Assessments to use the Watershed Risk Identifier Tool to quickly identify locations where the highest fire probability overlaps with the highest fire severity, and where that pair of stressors intersect with cutthroat trout habitat (Figure 6).
Figure 4. Predicted fire severity in terms of flame length is mapped onto individual channel segments using NetMap’s reach scale local contributing area, providing a fish eye view of fire severity.
Figure 5. Predicted fire severity (flame length) is aggregated downstream revealing tributary scale patterns of fire severity across the US portion of the watershed. The smaller tributaries with the highest fire severity are shown in red indicating general geographic areas with higher fire severity potential.
Figure 6. Using NetMap's Watershed Risk Identifier Tool in the Level 1 Assessment, the intersections between the highest 10% of fire probability and the highest 10% of fire severity is highlighted. These areas as represented at the channel segment scale (4% of all segments) are mapped (color coded) according to the predicted Westslope Cutthroat Trout habitat intrinsic potential score (habitat quality). Certain areas of the Flathead River watershed are highlighted (no data in the Canadian portion). This information, among other NetMap analyses, could be used in pre wildfire planning activities (e.g., fuels reduction, prescribed fire etc.).
