Index: wflow-py/wflow/wflow_sbm.py
===================================================================
diff -u -rd2b5037dd62b44e62015464f65c2fab14cd8fd86 -r363f5dc521b4d3026d37824098e697324fabcfb9
--- wflow-py/wflow/wflow_sbm.py	(.../wflow_sbm.py)	(revision d2b5037dd62b44e62015464f65c2fab14cd8fd86)
+++ wflow-py/wflow/wflow_sbm.py	(.../wflow_sbm.py)	(revision 363f5dc521b4d3026d37824098e697324fabcfb9)
@@ -77,12 +77,10 @@
         -u [1 , 4 ,13]
         The above example uses column 1, 4 and 13
         
-    -P: set parameter multiply dictionary (e.g: -P {'self.SatWaterDepth' : 1.2}
-        to increase self.SatWaterDepth by 20%, multiply with 1.2)
+    -P: set parameter change string (e.g: -P 'self.FC = self.FC * 1.6') for non-dynamic variables
 
-    -p: set input parameter (dynamic, e.g. precip) multiply dictionary
-        (e.g: -p {'self.Precipitation' : 1.2} to increase Precipitation
-        by 20%, multiply with 1.2)
+    -p: set parameter change string (e.g: -P 'self.Precipitation = self.Precipitation * 1.11') for
+        dynamic variables
 
     -l: loglevel (most be one of DEBUG, WARNING, ERROR)
 
@@ -924,6 +922,7 @@
         # Read forcing data and dynamic parameters
 
         self.wf_updateparameters()
+        self.Precipitation = max(0,0,self.Precipitation)
 
 
         if hasattr(self,"LAI"):