It is thought that Noah was a native of the lower Tigris-Euphrates valley. I have not found information on this region easy to come by. W.B.Fisher's book on 'The Middle East' although published in 1958 does contain some relevant details. The area is very prone to floods that rise spectacularly rapidly for the following reasons:
(1) The lower reaches of the Tigris and Euphrates have a very gentle gradient to the sea.
(2) The lower Tigris-Euphrates valley is very flat in cross-section.
(3) Tributaries to the Tigris from the Zagros Mountains have very steep long profiles.
(4) Mediterranean low pressure systems do occasionally move into the Zagros Mountains and intensify. Warm, moist air from the Arabian Sea is sucked into the system that gives very heavy rain. The rain is almost monsoonal in character. Run off is rapid and water reaches the Tigris from its tributaries very quickly.

Floods up to a depth of 8 to 9 metres have been recorded in the region in modern times.

I would welcome more information on:
(a) The weather systems associated with flooding in the Tigris-Euphrates valley. (b) The detailed topography of the Middle and Lower Tigris-Euphrates valley