Add fire module: burn severity, fire behavior, and KBDI (#922)

Seven per-cell raster functions with numpy/cupy/dask/dask+cupy backends:

Burn severity: dnbr, rdnbr, burn_severity_class (USGS 7-class)
Fire behavior: fireline_intensity (Byram), flame_length, rate_of_spread
  (simplified Rothermel with Anderson 13 fuel model lookup)
Fire danger: kbdi (single time-step Keetch-Byram Drought Index)

Includes 54 tests covering known values, NaN propagation, edge cases,
input validation, cross-backend parity, Dataset support, and accessor
smoke tests. Adds .xrs accessor methods for both DataArray and Dataset.

Author: brendancol

CHANGELOG.md

@@ -10,6 +10,7 @@ connected-component labelling; and broad dask+cupy backend coverage across the
 library.
 
 #### New Features
+- Add fire module: dNBR, RdNBR, burn severity class, fireline intensity, flame length, rate of spread (Rothermel), and KBDI (#922)
 - Add 3D multi-band support to focal functions (#924)
 - Add foundational hydrology tools (#921)
 - Add terrain metrics module: TRI, TPI, and Roughness (#920)

xrspatial/__init__.py

@@ -15,6 +15,13 @@
 from xrspatial.curvature import curvature  # noqa
 from xrspatial.emerging_hotspots import emerging_hotspots  # noqa
 from xrspatial.fill import fill  # noqa
+from xrspatial.fire import burn_severity_class  # noqa
+from xrspatial.fire import dnbr  # noqa
+from xrspatial.fire import fireline_intensity  # noqa
+from xrspatial.fire import flame_length  # noqa
+from xrspatial.fire import kbdi  # noqa
+from xrspatial.fire import rate_of_spread  # noqa
+from xrspatial.fire import rdnbr  # noqa
 from xrspatial.flood import curve_number_runoff  # noqa
 from xrspatial.flood import flood_depth  # noqa
 from xrspatial.flood import inundation  # noqa

xrspatial/accessor.py

@@ -257,6 +257,36 @@ def polygonize(self, **kwargs):
         from .polygonize import polygonize
         return polygonize(self._obj, **kwargs)
 
+    # ---- Fire ----
+
+    def dnbr(self, post_nbr_agg, **kwargs):
+        from .fire import dnbr
+        return dnbr(self._obj, post_nbr_agg, **kwargs)
+
+    def rdnbr(self, pre_nbr_agg, **kwargs):
+        from .fire import rdnbr
+        return rdnbr(self._obj, pre_nbr_agg, **kwargs)
+
+    def burn_severity_class(self, **kwargs):
+        from .fire import burn_severity_class
+        return burn_severity_class(self._obj, **kwargs)
+
+    def fireline_intensity(self, spread_rate_agg, **kwargs):
+        from .fire import fireline_intensity
+        return fireline_intensity(self._obj, spread_rate_agg, **kwargs)
+
+    def flame_length(self, **kwargs):
+        from .fire import flame_length
+        return flame_length(self._obj, **kwargs)
+
+    def rate_of_spread(self, wind_speed_agg, fuel_moisture_agg, **kwargs):
+        from .fire import rate_of_spread
+        return rate_of_spread(self._obj, wind_speed_agg, fuel_moisture_agg, **kwargs)
+
+    def kbdi(self, max_temp_agg, precip_agg, annual_precip, **kwargs):
+        from .fire import kbdi
+        return kbdi(self._obj, max_temp_agg, precip_agg, annual_precip, **kwargs)
+
     # ---- Multispectral (self = NIR band) ----
 
     def ndvi(self, red_agg, **kwargs):
@@ -471,6 +501,16 @@ def surface_direction(self, elevation, **kwargs):
         from .surface_distance import surface_direction
         return surface_direction(self._obj, elevation, **kwargs)
 
+    # ---- Fire ----
+
+    def burn_severity_class(self, **kwargs):
+        from .fire import burn_severity_class
+        return burn_severity_class(self._obj, **kwargs)
+
+    def flame_length(self, **kwargs):
+        from .fire import flame_length
+        return flame_length(self._obj, **kwargs)
+
     # ---- Multispectral (band mapping via kwargs) ----
 
     def ndvi(self, nir, red, **kwargs):