Irrigation Runoff's Surprising Impact on Earth's Rotation: A Shift in the North Pole

Astonishingly, the runoff from irrigation may have moved enough water from land to sea to cause a perceptible shift in Earth's rotation. Recent computer simulations suggest that between 1993 and 2010, irrigation alone moved the North Pole by nearly 78 centimeters, as detailed in the Geophysical Research Letters published on June 28. This makes irrigation the second largest contributor to polar drift, only surpassed by the ongoing rebound of Earth’s surface following the glacial retreat since the last ice age.

The movement of the North Pole across the Arctic landscape in a circle of a few meters diameter is a well-established fact among researchers. This cyclical drift is partially caused by seasonal weather patterns and driven by long-term changes in ocean water temperature and salinity, resulting in a 14-month oscillation known as the Chandler wobble.

However, Clark Wilson, a Geophysicist at the University of Texas, Austin, explains that these oscillations aren't the only factors influencing the pole's movement. There's also a more subtle, non-cyclical polar drift caused by the transfer of terrestrial water to the ocean. This is due to the melting of glaciers globally and ice sheets in Greenland and Antarctica.

In addition to these, the runoff from irrigation surprisingly plays a significant role in this phenomenon.

New research reveals that irrigation practices significantly influence Earth's rotational dynamics, with the North Pole shifting about 78 centimeters towards eastern Greenland between 1993 and 2010 due to irrigation-induced water redistribution. This movement, caused by approximately 2 trillion metric tons of water being transferred from terrestrial aquifers to oceans, is second only to the impact of glacial retreat on polar drift. 

The researchers found that the North Pole's shift, while seemingly minute, averaged over four centimeters each year during the study period. When considering all water movement sources, including glacial melt, the North Pole moved about 1.6 meters towards eastern Greenland. Notably, the impact of irrigation is permanent and likely increasing each year, highlighting the long-term implications of human activities on Earth's physical processes.

These findings also underscore how large-scale irrigation can influence local and regional climates. For instance, irrigation has been shown to cool temperatures, increase humidity in California's Central Valley, and enhance rainfall patterns in the Four Corners area of the American Southwest. It also impacts flow volumes in the Colorado River, demonstrating the broad reach of irrigation's effects on Earth's rotational dynamics and climate patterns.