The Yellow River, the world's fifth longest river, watered some of the oldest farms on earth.How does it happen? Its source(源头)on Qinghai-Tibet Plateau is drying up. In most of the past 35 years, it didn't reach the sea.
The Nile in Egypt, running 6, 650 km, is the longest river in the world. Dams provide fields with water and make power.Now it is down to 2 billion m³ or so. Australia's Murray River reaches the sea only every other year. One fifth of America's Rio Grande has no water, either.