The Ogallala aquifer is the largest in the United States, covering 450,000 km2 across eight states, from South Dakota to Texas. This aquifer provides 82% of the drinking water for the people who live in this region, although most (> 75%) of the water that is pumped from it is for irrigation. Irrigation withdrawals are approximately 18 billion gallons per day.
(a) The Ogallala aquifer might run dry, according to some estimates, in 25 years. How many cubic kilometers of water would be withdrawn in a 25-year period?
(b) Explain the processes that would recharge the aquifer.