July rains give Rio Grande a water boost, but the region isn’t out of the woods yet

Recent July rains have delivered a much-needed boost to the Rio Grande, but the two reservoirs that store much of the river’s water remain less than half full.

Amistad and Falcon reservoirs, which supply water to communities, farms, and businesses throughout the Rio Grande Valley and along the U.S.-Mexico border, gained more than 232,000 acre-feet of water over the past week. 

That’s enough water to fill about 115,000 Olympic-sized swimming pools.

Even with those gains, Amistad Reservoir is about 42% full and Falcon Reservoir is about 37% full, underscoring how much water the region still needs after years of drought.

The increase began after runoff from heavy rains over West Texas started flowing into Amistad Reservoir on July 14. Those flows reached Falcon Reservoir on July 18, causing water levels at both reservoirs to rise quickly.

Amistad recorded the larger increase.

Between July 13 and July 22, the reservoir rose 7.44 feet and gained nearly 149,000 acre-feet of water after accounting for releases downstream. The largest one-day increase came July 19, when nearly 48,000 acre-feet flowed into the reservoir.

As of July 22, Amistad held about 758,600 acre-feet of water.

Falcon Reservoir also benefited from the inflows.

Between July 18 and July 22, the reservoir rose 2.88 feet and gained more than 83,000 acre-feet of water after accounting for upstream releases. That figure does not include any water released from Falcon itself. The reservoir’s biggest one-day increase came July 21, when storage increased by nearly 50,000 acre-feet.

As of July 22, Falcon held about 580,400 acre-feet of water.

Under the 1944 Water Treaty, the International Boundary and Water Commission divides water stored in the reservoirs between the United States and Mexico based on where the rainfall originated. The United States receives all flows from seven measured Texas tributaries, one-third of the flows from six measured Mexican tributaries and half of the flows from unmeasured tributaries.

Editor’s note: The reservoir data was compiled by Sonny Hinojosa using the International Boundary and Water Commission’s Near Real-Time Streamflow Data system.