diff --git a/CHANGELOG.md b/CHANGELOG.md
index 2060e68e2..173230606 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -15,11 +15,13 @@ Code freeze date: YYYY-MM-DD
 ### Changed
 
 - Adaptations to refactoring of the `climada.hazard.Centroids` class, to be compatible with `climada>=5.0` [#122](https://github.com/CLIMADA-project/climada_petals/pull/122)
+- Always assign `csr_matrix` to `Hazard.intensity` [#129](https://github.com/CLIMADA-project/climada_petals/pull/129)
 
 ### Fixed
 
 - Fix `climada.hazard.tc_rainfield` for TC tracks crossing the antimeridian [#105](https://github.com/CLIMADA-project/climada_petals/pull/105)
 - Update the table of content for the tutorials [#125](https://github.com/CLIMADA-project/climada_petals/pull/125)
+- Store all-zero fraction matrices in `LowFlow` and `WildFire` hazards [#129](https://github.com/CLIMADA-project/climada_petals/pull/129)
 
 ### Deprecated
 
diff --git a/climada_petals/hazard/low_flow.py b/climada_petals/hazard/low_flow.py
index a017ee5f1..f110f50eb 100644
--- a/climada_petals/hazard/low_flow.py
+++ b/climada_petals/hazard/low_flow.py
@@ -394,12 +394,11 @@ def events_from_clusters(self, centroids):
         self.orig = np.ones(uniq_ev.size)
         self.set_frequency()
 
-        self.intensity = self._intensity_loop(uniq_ev, centroids.coord, res_centr, num_centr)
+        intensity = self._intensity_loop(uniq_ev, centroids.coord, res_centr, num_centr)
 
         # Following values are defined for each event and centroid
-        self.intensity = self.intensity.tocsr()
-        self.fraction = self.intensity.copy()
-        self.fraction.data.fill(1.0)
+        self.intensity = intensity.tocsr()
+        self.fraction = sparse.csr_matrix(self.intensity.shape)
 
     def identify_clusters(self, clus_thresh_xy=None, clus_thresh_t=None, min_samples=None):
         """call clustering functions to identify the clusters inside the dataframe
diff --git a/climada_petals/hazard/test/test_wildfire.py b/climada_petals/hazard/test/test_wildfire.py
index 1ad875d3e..aa159769f 100644
--- a/climada_petals/hazard/test/test_wildfire.py
+++ b/climada_petals/hazard/test/test_wildfire.py
@@ -236,7 +236,7 @@ def test_calc_bright_pass(self):
         self.assertTrue(isinstance(wf.fraction, sparse.csr_matrix))
         self.assertEqual(wf.intensity.shape, (7, 19454))
         self.assertEqual(wf.fraction.shape, (7, 19454))
-        self.assertEqual(wf.fraction.max(), 1.0)
+        self.assertEqual(wf.fraction.nnz, 0)  # Zero everywhere means 1 everywhere
         self.assertAlmostEqual(wf.intensity[0, 16618], firms.loc[100].brightness)
         self.assertAlmostEqual(wf.intensity[1, 123], max(firms.loc[6721].brightness, firms.loc[6722].brightness))
         self.assertAlmostEqual(wf.intensity[2, :].max(), firms.loc[8105].brightness)
diff --git a/climada_petals/hazard/wildfire.py b/climada_petals/hazard/wildfire.py
index a74720119..a10609985 100644
--- a/climada_petals/hazard/wildfire.py
+++ b/climada_petals/hazard/wildfire.py
@@ -899,12 +899,11 @@ def _calc_brightness(self, df_firms, centroids, res_centr):
         self._set_frequency()
 
         # Following values are defined for each fire and centroid
-        self.intensity = sparse.lil_matrix(np.zeros((num_ev, num_centr)))
+        intensity = sparse.lil_matrix(np.zeros((num_ev, num_centr)))
         for idx, ev_bright in enumerate(bright_list):
-            self.intensity[idx] = ev_bright
-        self.intensity = self.intensity.tocsr()
-        self.fraction = self.intensity.copy()
-        self.fraction.data.fill(1.0)
+            intensity[idx] = ev_bright
+        self.intensity = intensity.tocsr()
+        self.fraction = sparse.csr_matrix(self.intensity.shape)
 
     @staticmethod
     def _brightness_one_fire(df_firms, tree_centr, ev_id, res_centr, num_centr):