What is the most likely reason why modern cities in the Fertile Crescent may have a decreased water supply?

A hotter climate increases evaporation and can reduce rainfall and river flows, leaving less water available to cities. The most likely reason is therefore that the climate has become several degrees hotter. The other choices do not explain a broad decrease in water supply as well: dams are still built, and flood-control problems alone do not account for less water overall.

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