Short answers, pulled from the story.
The earliest known use of irrigation technology dates to the 6th millennium BCE in Khuzistan in the south-west of Iran. The site of Choga Mami, located in present-day Iraq on the border with Iran, is believed to be the earliest to show first canal irrigation in operation at about 6000 BCE.
Surface irrigation, also known as gravity irrigation, moves water across agricultural lands by following gravity or the slope of the land. This method involves significantly lower capital cost and energy requirements than pressurized irrigation systems, making it a common choice for developing nations and large fields.
India with 76 million hectares and China with 75 million hectares have the largest equipped area for irrigation worldwide. These two nations far exceed the United States of America, which has 27 million hectares of irrigated land.
Over-irrigation can lead to permanent loss of aquifer capacity, decreased water quality, ground subsidence, and salinization of crops. Projects that pump too much from underground aquifers create subsidence and allow salt to seep into drinking water while damaging agricultural output.
Congress passed the National Reclamation Act in 1902 to channel money from the sale of western public lands into irrigation projects on public or private land in the arid West. This legislation facilitated the development of infrastructure to support agriculture in regions like Arizona, Colorado, and Nevada.