This is the 3743rd most frequent German word.
regenfällen
"Regenfällen" means "rainfalls" in English.
'Regenfällen' in this sentence is the plural dative form indicating the heavy rainfalls responsible for the floods.
Die starken Regenfällen führten zu Überschwemmungen.
The heavy rainfalls led to floods.
Here, 'Regenfällen' uses the plural dative case to express the cause of the dull weather.
Wegen der anhaltenden Regenfällen bleibt das Wetter trüb.
Due to the persistent rainfalls, the weather remains dull.
In this context, 'Regenfällen' is the plural dative form indicating the time following the rainfalls which affected the ground.