Why in the News
A study by Virginia Tech researchers (lead author Esther Oyedele, co-author Susanna Werth), published in Water Resources Research on 13 October 2026, found that during the severe drought of 2020 to 2022 the Upper Basin of the Colorado River lost far more groundwater than the Lower Basin - even though the Upper Basin has long been considered to have greater natural recharge. According to Virginia Tech News (13 October 2026), the Upper Basin lost about 4.6 trillion gallons of groundwater in this period - nearly twice the Lower Basin's estimated 2.5 trillion gallons; this volume is enough to fill about half of the Lake Powell reservoir (KUNR, 20 October 2026). The study used satellite and hydrological data from 2004 to 2023, including gravity measurements from the GRACE and GRACE Follow-On missions.
The Colorado River: Key Facts for the Prelims
- A major river of North America; the name comes from the Spanish language, meaning "reddish-brown" - the colour of the water because of heavy silt.
- Source: the Rocky Mountains of Colorado, United States.
- Course: flows about 2,330 kilometres to the west-southwest and empties into the Gulf of California in north-western Mexico.
- Flows through seven US states and two Mexican states; forms the international border between Arizona (US) and Mexico for about 29 kilometres.
- Called the "lifeline of the Southwest"; major reservoirs - Lake Mead and Lake Powell.
- Major tributaries: Green, Gunnison, San Juan, Dolores, Little Colorado, Gila and Virgin; the longest tributary is the Green River.
- The Grand Canyon was cut by this river - a UNESCO World Heritage Site; Canyonlands National Park and Horseshoe Bend are also linked to it.
- Major dams: Hoover Dam (arch-shaped; Lake Mead), Parker Dam (the deepest dam by depth), Glen Canyon Dam (Lake Powell).
From the Exam's Point of View
The study shows that under climate stress even a "higher-recharge" region does not remain groundwater-secure - the joint management of surface water and groundwater is essential.
Prelims Style: Practice Questions
Question 1. According to the recent study, during the 2020-22 drought, in which basin of the Colorado River was the groundwater loss greater?
(a) Lower Basin
(b) Upper Basin
(c) Equal in both
(d) Only the Green River basin
See answer and reason
Answer: (b) Upper Basin. According to the Water Resources Research study (13 October 2026), the Upper Basin lost about 4.6 trillion gallons of groundwater - nearly twice the Lower Basin's estimated 2.5 trillion gallons - even though the Upper Basin has long been considered to have greater natural recharge.
Question 2. Which is the longest tributary of the Colorado River?
(a) Gila
(b) Gunnison
(c) Green River
(d) San Juan
See answer and reason
Answer: (c) Green River. Among the Colorado's major tributaries - Green, Gunnison, San Juan, Dolores, Little Colorado, Gila and Virgin - the longest is the Green River.
Sources and Limitations
- Research paper (Water Resources Research), DOI 10.1029/2025WR041695, 13 October 2026 (opened; publication date verified): https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2025WR041695
- Virginia Tech News, 13 October 2026 (read; 4.6 trillion gallons Upper Basin / 2.5 trillion Lower Basin, author names, GRACE period): https://news.vt.edu/articles/2026/10/science-crb-groundwater-loss.html
- KUNR Public Radio, 20 October 2026 (read; volume "enough to fill half of Lake Powell"): https://www.kunr.org/local-stories/2026-10-20/colorado-river-basin-lost-trillions-gallons-groundwater-severe-drought
- Live Science, 22 October 2026 (read; the contrasting pattern of the Upper and Lower Basins): https://www.livescience.com/planet-earth/rivers-oceans/surprising-new-pattern-of-groundwater-loss-may-signal-a-turning-point-for-the-colorado-river-basin
- Limitations: The groundwater-volume figures are satellite-measurement (GRACE) based estimates, not direct underground measurements. The general facts about the river are from standard geography references.