Canadian doctor trapped in Gaza volunteers at hospital, urges entry of medical aid
(www.winnipegfreepress.com)
Did you read the links in your own source? These were a) not Israeli, but rather Qatari dollars and b) according to a source your article cites completely unavoidable. Here's a direct quote from an article linked in what you just sent -- "... this seems to be the right thing to do under the circumstances... the alternative is war".
As for how Israel warns civilians -- while the power Israel provided free of charge to Gaza is currently shut off, yours presumably isn't. Google is free, and reveals that Israel has literally showered Gaza in leaflets warning about this bombing. So long as the Gazans know how to read, your point is moot.