diff --git a/CHANGELOG.md b/CHANGELOG.md
index d2c238a094..3820756fd3 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -31,6 +31,9 @@ Code freeze date: YYYY-MM-DD
 - `Hazard.from_raster_xarray` now returns a sparse matrix instead of a sparse array [#1261](https://github.com/CLIMADA-project/climada_python/pull/1261).
 - `ImpactCalc.impact` now raises a clear `ValueError` when the supplied `Hazard` contains no events, instead of failing later inside `np.array_split` with an obscure message [#814](https://github.com/CLIMADA-project/climada_python/issues/814).
 - Fix TCTracks.from_FAST duplicate loading from year loop [#1269](github.com/CLIMADA-project/climada_python/pull/1269)
+- `TropCyclone.apply_climate_scenario_knu` now raises its `ValueError` for negative frequencies (the check `any(x) < 0` never triggered) [#1338](https://github.com/CLIMADA-project/climada_python/pull/1338).
+- Fix missing spaces and `f` prefixes in warning and error messages [#1338](https://github.com/CLIMADA-project/climada_python/pull/1338).
+- Remove debug `print` calls [#1338](https://github.com/CLIMADA-project/climada_python/pull/1338).
 
 ### Deprecated
 - `Impact.calc_freq_curve()` should not be given the parameter `return_per`. Use the parameter `return_periods` in `Impact.calc_freq_curve().interpolate()` instead.
diff --git a/climada/engine/calibration_opt.py b/climada/engine/calibration_opt.py
index a443f00a09..d9fc8976a6 100644
--- a/climada/engine/calibration_opt.py
+++ b/climada/engine/calibration_opt.py
@@ -221,7 +221,7 @@ def change_impf(impf_instance, param_dict):
             )
         else:
             raise AttributeError(
-                "keys in param_dict not recognized. Use only:"
+                "keys in param_dict not recognized. Use only: "
                 "paa_shift, paa_scale, mdd_shift, mdd_scale"
             )
 
@@ -394,7 +394,6 @@ def calib_all(
         for x in itertools.product(*param_full_dict.values())
     )
     for param_dict in params_generator:
-        print(param_dict)
         df_out = copy.deepcopy(df_impact_data)
         impact_func_final, df_out = init_impf(impf_name_or_instance, param_dict, df_out)
         df_out = calib_instance(
@@ -475,7 +474,6 @@ def calib_optimize(
     # definie specific function to
     def specific_calib(values):
         param_dict_temp = dict(zip(param_dict.keys(), values))
-        print(param_dict_temp)
         return calib_instance(
             hazard,
             exposure,
@@ -519,7 +517,7 @@ def specific_calib(values):
     else:
         LOGGER.info(
             "Opimization did not finish successfully. Check you input"
-            " or consult the detailed returns (with argument"
+            " or consult the detailed returns (with argument "
             "show_details=True) for further information."
         )
 
diff --git a/climada/engine/impact.py b/climada/engine/impact.py
index a4755c42e7..e029d137e1 100644
--- a/climada/engine/impact.py
+++ b/climada/engine/impact.py
@@ -283,7 +283,7 @@ def tot_value(self):
            instead.
         """
         LOGGER.warning(
-            "The Impact.tot_value attribute is deprecated."
+            "The Impact.tot_value attribute is deprecated. "
             "Use Exposures.affected_total_value to calculate the affected "
             "total exposure value based on a specific hazard intensity "
             "threshold"
@@ -294,7 +294,7 @@ def tot_value(self):
     def tot_value(self, value):
         """Set the total exposure value close to a hazard"""
         LOGGER.warning(
-            "The Impact.tot_value attribute is deprecated."
+            "The Impact.tot_value attribute is deprecated. "
             "Use Exposures.affected_total_value to calculate the affected "
             "total exposure value based on a specific hazard intensity "
             "threshold"
@@ -485,7 +485,7 @@ def impact_at_reg(self, agg_regions=None):
     def calc_impact_year_set(self, all_years=True, year_range=None):
         """This function is deprecated, use Impact.impact_per_year instead."""
         LOGGER.warning(
-            "The use of Impact.calc_impact_year_set is deprecated."
+            "The use of Impact.calc_impact_year_set is deprecated. "
             "Use Impact.impact_per_year instead."
         )
         return self.impact_per_year(all_years=all_years, year_range=year_range)
@@ -566,7 +566,7 @@ def local_exceedance_impact(
         )
         if self.imp_mat.size == 0:
             raise ValueError(
-                "Attribute imp_mat is empty. Recalculate Impact"
+                "Attribute imp_mat is empty. Recalculate Impact "
                 "instance with parameter save_mat=True"
             )
 
@@ -713,7 +713,7 @@ def local_return_period(
         LOGGER.info("Computing return period map for impacts: %s", threshold_impact)
         if self.imp_mat.size == 0:
             raise ValueError(
-                "Attribute imp_mat is empty. Recalculate Impact"
+                "Attribute imp_mat is empty. Recalculate Impact "
                 "instance with parameter save_mat=True"
             )
 
@@ -1077,7 +1077,7 @@ def plot_hexbin_impact_exposure(
         """
         if self.imp_mat.size == 0:
             raise ValueError(
-                "Attribute imp_mat is empty. Recalculate Impact"
+                "Attribute imp_mat is empty. Recalculate Impact "
                 "instance with parameter save_mat=True"
             )
         if "cmap" not in kwargs:
@@ -1145,7 +1145,7 @@ def plot_basemap_impact_exposure(
         """
         if self.imp_mat.size == 0:
             raise ValueError(
-                "Attribute imp_mat is empty. Recalculate Impact"
+                "Attribute imp_mat is empty. Recalculate Impact "
                 "instance with parameter save_mat=True"
             )
 
diff --git a/climada/engine/impact_calc.py b/climada/engine/impact_calc.py
index 1e274ce445..41e7c01580 100644
--- a/climada/engine/impact_calc.py
+++ b/climada/engine/impact_calc.py
@@ -252,7 +252,7 @@ def _return_impact(self, imp_mat_gen, save_mat):
         else:
             if isinstance(self.hazard, HazardForecast):
                 raise ValueError(
-                    "Saving impact matrix is required when using HazardForecast."
+                    "Saving impact matrix is required when using HazardForecast. "
                     "Please set save_mat=True."
                 )
             imp_mat = None
diff --git a/climada/engine/impact_data.py b/climada/engine/impact_data.py
index 56f16a84ad..3f03033f9c 100644
--- a/climada/engine/impact_data.py
+++ b/climada/engine/impact_data.py
@@ -898,7 +898,6 @@ def scale_impact2refyear(impact_values, year_values, iso3a_values, reference_yea
             # get GDP value for each country and year:
             gdp_years[country] = dict()
             years_country = np.unique(year_values[iso3a_values == country])
-            print(years_country)
             for year in years_country:
                 gdp_years[country][year] = gdp(country, year)[1]
         # loop through each value and apply scaling:
diff --git a/climada/engine/unsequa/calc_base.py b/climada/engine/unsequa/calc_base.py
index 70151d8485..16dcdbcb7f 100644
--- a/climada/engine/unsequa/calc_base.py
+++ b/climada/engine/unsequa/calc_base.py
@@ -173,7 +173,7 @@ def est_comp_time(self, n_samples, time_one_run, processes=None):
         if time_one_run > 5:
             LOGGER.warning(
                 "Computation time for one set of parameters is "
-                "%.2fs. This is rather long."
+                "%.2fs. This is rather long. "
                 "Potential reasons: InputVars are loading data, centroids have "
                 "been assigned to exp before defining input_var, ..."
                 "\n If computation cannot be reduced, consider using"
@@ -249,7 +249,7 @@ def make_sample(self, N, sampling_method="saltelli", sampling_kwargs=None):
         if sampling_method == "ff":
             LOGGER.warning(
                 "You are using the 'ff' sampler which does not require "
-                "a value for N. The entered N value will be ignored"
+                "a value for N. The entered N value will be ignored "
                 "in the sampling process."
             )
         uniform_base_sample = self._make_uniform_base_sample(
diff --git a/climada/engine/unsequa/calc_delta_climate.py b/climada/engine/unsequa/calc_delta_climate.py
index 97d45e8258..8e0053b345 100644
--- a/climada/engine/unsequa/calc_delta_climate.py
+++ b/climada/engine/unsequa/calc_delta_climate.py
@@ -235,7 +235,7 @@ def uncertainty(
 
         if unc_sample.samples_df.empty:
             raise ValueError(
-                "No sample was found. Please create one first"
+                "No sample was found. Please create one first "
                 "using UncImpact.make_sample(N)"
             )
 
diff --git a/climada/engine/unsequa/calc_impact.py b/climada/engine/unsequa/calc_impact.py
index 93d3fc6584..5b96c17254 100644
--- a/climada/engine/unsequa/calc_impact.py
+++ b/climada/engine/unsequa/calc_impact.py
@@ -197,7 +197,7 @@ def uncertainty(
 
         if unc_sample.samples_df.empty:
             raise ValueError(
-                "No sample was found. Please create one first"
+                "No sample was found. Please create one first "
                 "using UncImpact.make_sample(N)"
             )
 
diff --git a/climada/entity/_legacy_measures/measure_set.py b/climada/entity/_legacy_measures/measure_set.py
index 228788ba15..dbdaf386fa 100755
--- a/climada/entity/_legacy_measures/measure_set.py
+++ b/climada/entity/_legacy_measures/measure_set.py
@@ -451,7 +451,7 @@ def read_att_mat(measures, data, file_name, var_names):
     def read_mat(self, *args, **kwargs):
         """This function is deprecated, use MeasureSet.from_mat instead."""
         LOGGER.warning(
-            "The use of MeasureSet.read_mat is deprecated."
+            "The use of MeasureSet.read_mat is deprecated. "
             "Use MeasureSet.from_mat instead."
         )
         self.__dict__ = MeasureSet.from_mat(*args, **kwargs).__dict__
@@ -557,7 +557,7 @@ def read_att_excel(measures, dfr, var_names):
     def read_excel(self, *args, **kwargs):
         """This function is deprecated, use MeasureSet.from_excel instead."""
         LOGGER.warning(
-            "The use ofMeasureSet.read_excel is deprecated."
+            "The use of MeasureSet.read_excel is deprecated. "
             "Use MeasureSet.from_excel instead."
         )
         self.__dict__ = MeasureSet.from_excel(*args, **kwargs).__dict__
diff --git a/climada/entity/disc_rates/base.py b/climada/entity/disc_rates/base.py
index e18daaf919..09513e7d36 100755
--- a/climada/entity/disc_rates/base.py
+++ b/climada/entity/disc_rates/base.py
@@ -259,7 +259,7 @@ def from_mat(cls, file_name, var_names=None):
     def read_mat(self, *args, **kwargs):
         """This function is deprecated, use ``DiscRates.from_mat`` instead."""
         LOGGER.warning(
-            "The use of DiscRates.read_mat is deprecated."
+            "The use of DiscRates.read_mat is deprecated. "
             "Use DiscRates.from_mat instead."
         )
         self.__dict__ = DiscRates.from_mat(*args, **kwargs).__dict__
@@ -305,7 +305,7 @@ def from_excel(cls, file_name, var_names=None):
     def read_excel(self, *args, **kwargs):
         """This function is deprecated, use DiscRates.from_excel instead."""
         LOGGER.warning(
-            "The use of DiscRates.read_excel is deprecated."
+            "The use of DiscRates.read_excel is deprecated. "
             "Use DiscRates.from_excel instead."
         )
         self.__dict__ = DiscRates.from_excel(*args, **kwargs).__dict__
diff --git a/climada/entity/entity_def.py b/climada/entity/entity_def.py
index c1bc3b2550..634adb1038 100755
--- a/climada/entity/entity_def.py
+++ b/climada/entity/entity_def.py
@@ -105,7 +105,7 @@ def from_mat(cls, file_name):
     def read_mat(self, *args, **kwargs):
         """This function is deprecated, use Entity.from_mat instead."""
         LOGGER.warning(
-            "The use of Entity.read_mat is deprecated." "Use Entity.from_mat instead."
+            "The use of Entity.read_mat is deprecated. Use Entity.from_mat instead."
         )
         self.__dict__ = Entity.from_mat(*args, **kwargs).__dict__
 
diff --git a/climada/entity/exposures/base.py b/climada/entity/exposures/base.py
index 1989e0fd80..04a4c276e7 100644
--- a/climada/entity/exposures/base.py
+++ b/climada/entity/exposures/base.py
@@ -1180,7 +1180,7 @@ def write_hdf5(self, file_name):
     def read_hdf5(self, *args, **kwargs):
         """This function is deprecated, use Exposures.from_hdf5 instead."""
         LOGGER.warning(
-            "The use of Exposures.read_hdf5 is deprecated."
+            "The use of Exposures.read_hdf5 is deprecated. "
             "Use Exposures.from_hdf5 instead."
         )
         self.__dict__ = Exposures.from_hdf5(*args, **kwargs).__dict__
@@ -1233,7 +1233,7 @@ def from_hdf5(cls, file_name):
     def read_mat(self, *args, **kwargs):
         """This function is deprecated, use Exposures.from_mat instead."""
         LOGGER.warning(
-            "The use of Exposures.read_mat is deprecated."
+            "The use of Exposures.read_mat is deprecated. "
             "Use Exposures.from_mat instead."
         )
         self.__dict__ = Exposures.from_mat(*args, **kwargs).__dict__
diff --git a/climada/entity/exposures/litpop/litpop.py b/climada/entity/exposures/litpop/litpop.py
index ef28b3ba5d..9d1d5ad5b7 100644
--- a/climada/entity/exposures/litpop/litpop.py
+++ b/climada/entity/exposures/litpop/litpop.py
@@ -94,7 +94,7 @@ def __init__(
     def set_countries(self, *args, **kwargs):
         """This function is deprecated, use LitPop.from_countries instead."""
         LOGGER.warning(
-            "The use of LitPop.set_countries is deprecated."
+            "The use of LitPop.set_countries is deprecated. "
             "Use LitPop.from_countries instead."
         )
         self.__dict__ = LitPop.from_countries(*args, **kwargs).__dict__
@@ -307,7 +307,7 @@ def from_countries(
     def set_nightlight_intensity(self, *args, **kwargs):
         """This function is deprecated, use LitPop.from_nightlight_intensity instead."""
         LOGGER.warning(
-            "The use of LitPop.set_nightlight_intensity is deprecated."
+            "The use of LitPop.set_nightlight_intensity is deprecated. "
             "Use LitPop.from_nightlight_intensity instead."
         )
         self.__dict__ = LitPop.from_nightlight_intensity(*args, **kwargs).__dict__
@@ -409,7 +409,7 @@ def from_nightlight_intensity(
     def set_population(self, *args, **kwargs):
         """This function is deprecated, use LitPop.from_population instead."""
         LOGGER.warning(
-            "The use of LitPop.set_population is deprecated."
+            "The use of LitPop.set_population is deprecated. "
             "Use LitPop.from_population instead."
         )
         self.__dict__ = LitPop.from_population(*args, **kwargs).__dict__
@@ -510,7 +510,7 @@ def from_population(
     def set_custom_shape_from_countries(self, *args, **kwargs):
         """This function is deprecated, use LitPop.from_shape_and_countries instead."""
         LOGGER.warning(
-            "The use of LitPop.set_custom_shape_from_countries is deprecated."
+            "The use of LitPop.set_custom_shape_from_countries is deprecated. "
             "Use LitPop.from_shape_and_countries instead."
         )
         self.__dict__ = LitPop.from_shape_and_countries(*args, **kwargs).__dict__
@@ -646,7 +646,7 @@ def from_shape_and_countries(
             gdf = exp.gdf.loc[idx]
         else:
             raise NotImplementedError(
-                "Not implemented for `shape` of type {type(shape)}"
+                f"Not implemented for `shape` of type {type(shape)}"
             )
 
         exp.description = (
@@ -681,7 +681,7 @@ def from_shape_and_countries(
     def set_custom_shape(self, *args, **kwargs):
         """This function is deprecated, use LitPop.from_shape instead."""
         LOGGER.warning(
-            "The use of LitPop.set_custom_shape is deprecated."
+            "The use of LitPop.set_custom_shape is deprecated. "
             "Use LitPop.from_shape instead."
         )
         self.__dict__ = LitPop.from_shape(*args, **kwargs).__dict__
diff --git a/climada/entity/impact_funcs/base.py b/climada/entity/impact_funcs/base.py
index 3642eed7a8..ff7a7c2482 100644
--- a/climada/entity/impact_funcs/base.py
+++ b/climada/entity/impact_funcs/base.py
@@ -306,7 +306,7 @@ def from_sigmoid_impf(
     def set_sigmoid_impf(self, *args, **kwargs):
         """This function is deprecated, use LitPop.from_countries instead."""
         LOGGER.warning(
-            "The use of ImpactFunc.set_sigmoid_impf is deprecated."
+            "The use of ImpactFunc.set_sigmoid_impf is deprecated. "
             "Use ImpactFunc.from_sigmoid_impf instead."
         )
         self.__dict__ = ImpactFunc.from_sigmoid_impf(*args, **kwargs).__dict__
diff --git a/climada/entity/impact_funcs/impact_func_set.py b/climada/entity/impact_funcs/impact_func_set.py
index b6f4cf73d7..6c6ccd13e6 100755
--- a/climada/entity/impact_funcs/impact_func_set.py
+++ b/climada/entity/impact_funcs/impact_func_set.py
@@ -535,7 +535,7 @@ def _get_hdf5_str(imp, idxs, file_name, var_name):
     def read_mat(self, *args, **kwargs):
         """This function is deprecated, use ImpactFuncSet.from_mat instead."""
         LOGGER.warning(
-            "The use of ImpactFuncSet.read_mat  is deprecated."
+            "The use of ImpactFuncSet.read_mat  is deprecated. "
             "Use ImpactFuncSet.from_mat  instead."
         )
         self.__dict__ = ImpactFuncSet.from_mat(*args, **kwargs).__dict__
diff --git a/climada/entity/impact_funcs/storm_europe.py b/climada/entity/impact_funcs/storm_europe.py
index 76973c3df2..9f4a0588f5 100644
--- a/climada/entity/impact_funcs/storm_europe.py
+++ b/climada/entity/impact_funcs/storm_europe.py
@@ -118,7 +118,7 @@ def set_schwierz(self, impf_id=1):
         instead.
         """
         LOGGER.warning(
-            "The use of ImpfStormEurope.set_schwierz is deprecated."
+            "The use of ImpfStormEurope.set_schwierz is deprecated. "
             "Use ImpfStormEurope.from_schwierz instead."
         )
         self.__dict__ = ImpfStormEurope.from_schwierz(impf_id=impf_id).__dict__
@@ -129,7 +129,7 @@ def set_welker(self, impf_id=1):
         instead.
         """
         LOGGER.warning(
-            "The use of ImpfStormEurope.set_welker is deprecated."
+            "The use of ImpfStormEurope.set_welker is deprecated. "
             "Use ImpfStormEurope.from_welker instead."
         )
         self.__dict__ = ImpfStormEurope.from_welker(impf_id=impf_id).__dict__
diff --git a/climada/entity/impact_funcs/trop_cyclone.py b/climada/entity/impact_funcs/trop_cyclone.py
index ac578fde1e..45fdd3447e 100644
--- a/climada/entity/impact_funcs/trop_cyclone.py
+++ b/climada/entity/impact_funcs/trop_cyclone.py
@@ -135,7 +135,7 @@ def __init__(self):
     def set_emanuel_usa(self, *args, **kwargs):
         """This function is deprecated, use from_emanuel_usa() instead."""
         LOGGER.warning(
-            "The use of ImpfTropCyclone.set_emanuel_usa is deprecated."
+            "The use of ImpfTropCyclone.set_emanuel_usa is deprecated. "
             "Use ImpfTropCyclone.from_emanuel_usa instead."
         )
         self.__dict__ = ImpfTropCyclone.from_emanuel_usa(*args, **kwargs).__dict__
@@ -210,7 +210,7 @@ def __init__(self):
     def set_calibrated_regional_ImpfSet(self, *args, **kwargs):
         """This function is deprecated, use from_calibrated_regional_ImpfSet() instead."""
         LOGGER.warning(
-            "ImpfSetTropCyclone.set_calibrated_regional_ImpfSet is deprecated."
+            "ImpfSetTropCyclone.set_calibrated_regional_ImpfSet is deprecated. "
             "Use ImpfSetTropCyclone.from_calibrated_regional_ImpfSet instead."
         )
         self.__dict__ = ImpfSetTropCyclone.from_calibrated_regional_ImpfSet(
diff --git a/climada/hazard/base.py b/climada/hazard/base.py
index b06c22e989..8aa875fd39 100644
--- a/climada/hazard/base.py
+++ b/climada/hazard/base.py
@@ -855,7 +855,7 @@ def set_frequency(self, yearrange=None):
         """
         if self.frequency_unit not in ["1/year", "annual", "1/y", "1/a"]:
             LOGGER.warning(
-                "setting the frequency on a hazard object who's frequency unit"
+                "setting the frequency on a hazard object who's frequency unit "
                 "is %s and not %s will most likely lead to unexpected results",
                 self.frequency_unit,
                 u_const.DEF_FREQ_UNIT,
@@ -1208,8 +1208,8 @@ def get_mdr(self, cent_idx, impf):
             mdr.data = impf.calc_mdr(mdr.data)
         else:
             LOGGER.warning(
-                "Impact function id=%d has mdr(0) != 0."
-                "The mean damage ratio must thus be computed for all values of"
+                "Impact function id=%d has mdr(0) != 0. "
+                "The mean damage ratio must thus be computed for all values of "
                 "hazard intensity including 0 which can be very time consuming.",
                 impf.id,
             )
diff --git a/climada/hazard/centroids/centr.py b/climada/hazard/centroids/centr.py
index 7fcc769b52..a2e08b26c4 100644
--- a/climada/hazard/centroids/centr.py
+++ b/climada/hazard/centroids/centr.py
@@ -1091,7 +1091,7 @@ def _ne_crs_geom(self):
 
     @classmethod
     @deprecated(
-        details="Reading Centroids data from matlab files is not supported anymore."
+        details="Reading Centroids data from matlab files is not supported anymore. "
         "This method has been removed with climada 5.0"
     )
     def from_mat(cls, file_name, var_names=None):
diff --git a/climada/hazard/io.py b/climada/hazard/io.py
index 03e608d050..dc99057694 100644
--- a/climada/hazard/io.py
+++ b/climada/hazard/io.py
@@ -98,7 +98,7 @@ class HazardIO:
     def set_raster(self, *args, **kwargs):
         """This function is deprecated, use Hazard.from_raster."""
         LOGGER.warning(
-            "The use of Hazard.set_raster is deprecated."
+            "The use of Hazard.set_raster is deprecated. "
             "Use Hazard.from_raster instead."
         )
         self.__dict__ = self.__class__.from_raster(*args, **kwargs).__dict__
@@ -783,7 +783,7 @@ def _attrs_to_kwargs(attrs: Dict[str, Any], num_events: int) -> Dict[str, Any]:
     def read_excel(self, *args, **kwargs):
         """This function is deprecated, use Hazard.from_excel."""
         LOGGER.warning(
-            "The use of Hazard.read_excel is deprecated."
+            "The use of Hazard.read_excel is deprecated. "
             "Use Hazard.from_excel instead."
         )
         self.__dict__ = self.__class__.from_excel(*args, **kwargs).__dict__
@@ -961,7 +961,8 @@ def write_hdf5(self, file_name, todense=False):
     def read_hdf5(self, *args, **kwargs):
         """This function is deprecated, use Hazard.from_hdf5."""
         LOGGER.warning(
-            "The use of Hazard.read_hdf5 is deprecated." "Use Hazard.from_hdf5 instead."
+            "The use of Hazard.read_hdf5 is deprecated. "
+            "Use Hazard.from_hdf5 instead."
         )
         self.__dict__ = self.__class__.from_hdf5(*args, **kwargs).__dict__
 
diff --git a/climada/hazard/storm_europe.py b/climada/hazard/storm_europe.py
index 2fe7c6c861..23a50fc946 100644
--- a/climada/hazard/storm_europe.py
+++ b/climada/hazard/storm_europe.py
@@ -130,7 +130,7 @@ def __init__(
     def read_footprints(self, *args, **kwargs):
         """This function is deprecated, use StormEurope.from_footprints instead."""
         LOGGER.warning(
-            "The use of StormEurope.read_footprints is deprecated."
+            "The use of StormEurope.read_footprints is deprecated. "
             "Use StormEurope.from_footprints instead."
         )
         self.__dict__ = StormEurope.from_footprints(*args, **kwargs).__dict__
@@ -288,7 +288,7 @@ def _read_one_nc(cls, file_name, centroids, intensity_thres):
     def read_cosmoe_file(self, *args, **kwargs):
         """This function is deprecated, use StormEurope.from_cosmoe_file instead."""
         LOGGER.warning(
-            "The use of StormEurope.read_cosmoe_file is deprecated."
+            "The use of StormEurope.read_cosmoe_file is deprecated. "
             "Use StormEurope.from_cosmoe_file instead."
         )
         self.__dict__ = StormEurope.from_cosmoe_file(*args, **kwargs).__dict__
@@ -357,7 +357,7 @@ def from_cosmoe_file(
                         "Extraction of date and coordinates failed. This is most likely "
                         "because the selected event_date "
                         f'{event_date.strftime("%Y-%m-%d")} is not contained in the '
-                        "weather forecast selected by fp_file {fp_file}. Please adjust "
+                        f"weather forecast selected by fp_file {fp_file}. Please adjust "
                         f"event_date or fp_file."
                     ) from ker
                 considered_dates = np.datetime64(event_date)
@@ -419,7 +419,7 @@ def from_cosmoe_file(
     def read_icon_grib(self, *args, **kwargs):
         """This function is deprecated, use StormEurope.from_icon_grib instead."""
         LOGGER.warning(
-            "The use of StormEurope.read_icon_grib is deprecated."
+            "The use of StormEurope.read_icon_grib is deprecated. "
             "Use StormEurope.from_icon_grib instead."
         )
         self.__dict__ = StormEurope.from_icon_grib(*args, **kwargs).__dict__
diff --git a/climada/hazard/tc_clim_change.py b/climada/hazard/tc_clim_change.py
index 1745c43f3e..2848431251 100644
--- a/climada/hazard/tc_clim_change.py
+++ b/climada/hazard/tc_clim_change.py
@@ -135,7 +135,7 @@ def get_knutson_scaling_factor(
     ):
 
         raise ValueError(
-            "The selected historical baseline falls outside"
+            "The selected historical baseline falls outside "
             f"the GMST data period {gmst_info['gmst_start_year']}"
             f"-{gmst_info['gmst_end_year']}"
         )
@@ -160,7 +160,7 @@ def get_knutson_scaling_factor(
 
     except KeyError:
         LOGGER.warning(
-            f"No scaling factors are defined for basin {basin} therefore"
+            f"No scaling factors are defined for basin {basin} therefore "
             "no change will be projected for tracks in this basin"
         )
         return pd.DataFrame(
diff --git a/climada/hazard/tc_tracks.py b/climada/hazard/tc_tracks.py
index 71b9c69558..c0b75d9816 100644
--- a/climada/hazard/tc_tracks.py
+++ b/climada/hazard/tc_tracks.py
@@ -1677,7 +1677,7 @@ def equal_timestep(self, time_step_h=1, land_params=False, pool=None):
     def calc_random_walk(self, **kwargs):
         """Deprecated. Use `TCTracks.calc_perturbed_trajectories` instead."""
         LOGGER.warning(
-            "The use of TCTracks.calc_random_walk is deprecated."
+            "The use of TCTracks.calc_random_walk is deprecated. "
             "Use TCTracks.calc_perturbed_trajectories instead."
         )
         if kwargs.get("ens_size"):
diff --git a/climada/hazard/test/test_trop_cyclone.py b/climada/hazard/test/test_trop_cyclone.py
index b04ae3420c..c4a3f9cd0c 100644
--- a/climada/hazard/test/test_trop_cyclone.py
+++ b/climada/hazard/test/test_trop_cyclone.py
@@ -475,6 +475,16 @@ def test_apply_climate_scenario_knu_calculations(self):
                 future_tc.frequency[cat45_sel & basin_sel],
             )
 
+    def test_knu_negative_frequency(self):
+        """A scenario that makes a frequency negative must raise."""
+        self.create_tc()
+        # Mostly intense storms: the weak storms would need to lose more than 100% of their frequency.
+        self.tc.category = np.array([4, 4, 0, 1])
+        with self.assertRaises(ValueError):
+            self.tc.apply_climate_scenario_knu(
+                percentile="90/95", scenario="8.5", target_year=2100
+            )
+
     def test_apply_climate_scenario_knu_target_year_out_of_range(self):
         self.create_tc()
         with self.assertRaises(KeyError):
diff --git a/climada/hazard/trop_cyclone/trop_cyclone.py b/climada/hazard/trop_cyclone/trop_cyclone.py
index a42c226e28..3455485d26 100644
--- a/climada/hazard/trop_cyclone/trop_cyclone.py
+++ b/climada/hazard/trop_cyclone/trop_cyclone.py
@@ -435,8 +435,8 @@ def apply_climate_scenario_knu(
 
         if self.category.size == 0:
             LOGGER.warning(
-                "Tropical cyclone categories are missing and"
-                "no effect of climate change can be modelled."
+                "Tropical cyclone categories are missing and "
+                "no effect of climate change can be modelled. "
                 "The original event set is returned"
             )
             return self
@@ -478,7 +478,7 @@ def apply_climate_scenario_knu(
             tc_cc.frequency[sel_cat03 & bas_sel] *= 1 + scale_year_rcp_03 / 100
             tc_cc.frequency[sel_cat45 & bas_sel] *= 1 + scale_year_rcp_45 / 100
 
-            if any(tc_cc.frequency) < 0:
+            if np.any(tc_cc.frequency < 0):
                 raise ValueError(
                     " The application of the climate scenario leads to "
                     " negative frequencies. One solution - if appropriate -"
@@ -490,7 +490,7 @@ def apply_climate_scenario_knu(
     def set_climate_scenario_knu(self, *args, **kwargs):
         """This function is deprecated, use TropCyclone.apply_climate_scenario_knu instead."""
         LOGGER.warning(
-            "The use of TropCyclone.set_climate_scenario_knu is deprecated."
+            "The use of TropCyclone.set_climate_scenario_knu is deprecated. "
             "Use TropCyclone.apply_climate_scenario_knu instead."
         )
         return self.apply_climate_scenario_knu(*args, **kwargs)
@@ -785,7 +785,7 @@ def _apply_knutson_criterion(self, chg_int_freq: List, scaling_rcp_year: float):
 
         if (tc_cc.frequency < 0).any():
             raise ValueError(
-                "The application of the given climate scenario"
+                "The application of the given climate scenario "
                 "resulted in at least one negative frequency."
             )
 
diff --git a/climada/hazard/trop_cyclone/trop_cyclone_windfields.py b/climada/hazard/trop_cyclone/trop_cyclone_windfields.py
index a33ac6bf25..db46319c25 100644
--- a/climada/hazard/trop_cyclone/trop_cyclone_windfields.py
+++ b/climada/hazard/trop_cyclone/trop_cyclone_windfields.py
@@ -131,7 +131,7 @@ def compute_angular_windspeeds(
 
     if cyclostrophic is not None:
         warnings.warn(
-            "The 'cyclostrophic' argument is deprecated and will be removed in a future"
+            "The 'cyclostrophic' argument is deprecated and will be removed in a future "
             "release. Include it in 'model_kwargs' instead.",
             DeprecationWarning,
         )
diff --git a/climada/util/coordinates.py b/climada/util/coordinates.py
index 2c6320383c..ff50b3b3a7 100644
--- a/climada/util/coordinates.py
+++ b/climada/util/coordinates.py
@@ -1128,7 +1128,7 @@ def estimate_matching_threshold(coords_to_assign):
     """
     if len(coords_to_assign) < 2:
         raise ValueError(
-            "The coordinate assignement threshold cannot be"
+            "The coordinate assignement threshold cannot be "
             "estimated for a single coordinate. Please set the threshold explicitly"
         )
     return 2 * max(abs(r) for r in get_resolution(coords_to_assign.T))
diff --git a/climada/util/interpolation.py b/climada/util/interpolation.py
index bf64f37cd7..87b9fc0a3b 100644
--- a/climada/util/interpolation.py
+++ b/climada/util/interpolation.py
@@ -392,7 +392,7 @@ def _group_frequency(frequency, value, bin_decimals):
     if value_unique.size != frequency.size:
         if not all(sorted(start_indices) == start_indices):
             LOGGER.warning(
-                "After grouping values using to their decimals, the value array is not sorted."
+                "After grouping values using to their decimals, the value array is not sorted. "
                 "The values are not binned. This might be due to floating point error while "
                 "binning. Please choose a larger value of bin_decimals=%s.",
                 bin_decimals,
diff --git a/climada/util/lines_polys_handler.py b/climada/util/lines_polys_handler.py
index 8bcfd7899f..49c2e90696 100755
--- a/climada/util/lines_polys_handler.py
+++ b/climada/util/lines_polys_handler.py
@@ -604,7 +604,7 @@ def gdf_to_grid(gdf, grid):
 
     if line_mask.any() or pnt_mask.any():
         raise AttributeError(
-            "The dataframe contains lines and/or polygons."
+            "The dataframe contains lines and/or polygons. "
             "Currently only polygon dataframes can be "
             "disaggregated onto a fixed grid."
         )
diff --git a/climada/util/test/test_coordinates.py b/climada/util/test/test_coordinates.py
index b0703c568a..b9a24a4760 100644
--- a/climada/util/test/test_coordinates.py
+++ b/climada/util/test/test_coordinates.py
@@ -446,7 +446,7 @@ def test_estimate_matching_threshold(self):
         with self.assertRaises(ValueError) as cm:
             u_coord.estimate_matching_threshold(coords_fail)
         self.assertIn(
-            "The coordinate assignement threshold cannot be"
+            "The coordinate assignement threshold cannot be "
             "estimated for a single coordinate. Please set the threshold explicitly",
             str(cm.exception),
         )