Why have some stretches of the Rio Grande had little or no surface flow?

Stretches of the Rio Grande have experienced little or no surface flow primarily due to the intensive consumption of water for irrigation and human use.1

Because the river's water is a vital resource for agriculture and growing populations, it is heavily managed through various water treaties and compacts between the United States and Mexico, as well as among the states of Colorado, New Mexico, and Texas. Essentially all of the average annual water production in the upper Rio Grande subbasin is consumed within that region. Consequently, in many areas—ranging from the New Mexico-Colorado border to downstream of Brownsville—the river has at times been reduced to a bare trickle or has dried up completely.1