Yes, as others said, you need to take this insurance otherwise you could be liable for damage from natural disasters.

In short, in Canton Vaud, this insurance covers the liability for natural disasters, and is done at the Canton level. This means that in cases of some damages, there is a separate state insurer ECA. However, the private insurers are still necessary for other damages, ie. fire, theft etc. so you need this as well. It is just that the private insurer premium covers only these damages in VD, and in some other cantons it is one insurance covering all damage from all causes.