earlier error message if subbasin is too small #236

hydromt_wflow/wflow.py

@@ -417,6 +417,13 @@ def setup_rivers(
         """
         self.logger.info("Preparing river maps.")
 
+        # Check that river_upa threshold is bigger than the maximum uparea in the grid
+        if river_upa < self.grid[self._MAPS["uparea"]].max():
+            raise ValueError(
+                f"river_upa threshold {river_upa} should be larger than the maximum \
+uparea in the grid {self.grid[self._MAPS['uparea']].max()}"
+            )
+
         rivdph_methods = ["gvf", "manning", "powlaw"]
         if rivdph_method not in rivdph_methods:
             raise ValueError(f'"{rivdph_method}" unknown. Select from {rivdph_methods}')

hydromt_wflow/workflows/basemaps.py

@@ -99,9 +99,27 @@ def hydrography(
         # NOTE: this mask is passed on from get_basin_geometry method
         logger.debug("Mask in dataset assumed to represent subbasins.")
     ncells = np.sum(ds["mask"].values)
-    logger.debug(f"(Sub)basin at original resolution has {ncells} cells.")
-
     scale_ratio = int(np.round(res / ds.raster.res[0]))
+
+    if ncells < 4:
+        raise ValueError(
+            "(Sub)basin at original resolution should at least consist of two cells on "
+            f"each axis and the total number of cells is {ncells}. "
+            "Consider using a larger domain or higher spatial resolution. "
+            "For subbasin models, consider a (higher) threshold on for example "
+            "upstream area or stream order to snap the outlet."
+        )
+    elif ncells < 100 and scale_ratio > 1:
+        logger.warning(
+            f"(Sub)basin at original resolution is small and has {ncells} cells. "
+            "This may results in errors later when upscaling flow directions. "
+            "If so, consider using a larger domain or higher spatial resolution. "
+            "For subbasin models, consider a (higher) threshold on for example "
+            "upstream area or stream order to snap the outlet."
+        )
+    else:
+        logger.debug(f"(Sub)basin at original resolution has {ncells} cells.")
+
     if scale_ratio > 1:  # upscale flwdir
         if flwdir is None:
             # NOTE initialize with mask is FALSE
@@ -251,7 +269,7 @@ def hydrography(
     logger.debug(f"Outlet coordinates ({len(xy_pit[0])}/{npits}): {xy_pit_str}.")
     if np.any(np.asarray(ds_out.raster.shape) == 1):
         raise ValueError(
-            "The output extent should at consist of two cells on each axis. "
+            "The output extent should at least consist of two cells on each axis. "
             "Consider using a larger domain or higher spatial resolution. "
             "For subbasin models, consider a (higher) threshold to snap the outlet."
         )