Polski
Science, In this issue, Issue 14/2025
Dams shift Earth’s poles
Sep
The results of a study led by a team of Harvard University scientists provide new insights into the impact of human activity on the physics of our planet. Although the construction of artificial reservoirs is mainly associated with water management and energy production, the authors show that millions of cubic meters of water retained by dams can… shift the Earth’s poles. The phenomenon is called True Polar Wander (TPW), or real polar wander, and results from a change in the distribution of mass on the globe’s surface.
Source data and time scope of the analysis
The research team, led by Natascha Valencic, analyzed data from the GRanD (Global Reservoir and Dam) database, which includes 6862 artificial reservoirs with a capacity of more than 0.1 km³, from 1835-2011. According to their calculations, which take into account corrections for filtration and filling below maximum capacity (according to the parameters of Chao et al., 2008), the total amount of water stored in them corresponds to a lowering of the mean sea level (GMSL) by 21.8 mm.
Importantly, as much as 88 percent of this volume – or 19mm – was not collected until after 1950, which clearly affected the pace and direction of TPW in the second half of the 20th century.
The research team used advanced numerical algorithms and the seismic model of the Earth, PREM (Dziewonski & Anderson, 1981), assuming that changes in mass distribution occur fast enough that deformation of the Earth is purely elastic. The influence of planetary rotation and the interaction between water retention (impoudment) and redistribution of masses in the oceans were also taken into account.
TPW was calculated separately for impoundment alone and for the combined effect of impoundment and corresponding changes in the oceans. In both cases, the results are presented with high precision.
Pole movement: reversal of direction after 1954.
According to a study by American scientists, between 1835 and 1954 the pole moved 20.5 cm toward 103.4°E, of which only 0.7 cm took place in the 19th century. After 1954, the direction of movement reversed – the pole moved 57.1 cm toward -117.5°E.
In the period 1835-2011, the TPW path length was 113.4 cm, of which as much as 103.8 cm was in the 20th century.
The average rate of pole movement in the 20th century was calculated as (-0.30; -0.23) cm/year, where the values correspond to the 0°E (Greenwich meridian) and 90°E directions. For comparison, it is worth adding that the team of Adhikari et al. (2018), based on earlier estimates by Chao et al. (2008), calculated a much smaller change of only (-0.14; -0.78) cm/year.
The change in the direction of TPW after 1954 is related to the geographic evolution of the location of the largest artificial reservoirs. Until the middle of the 20th century, investments in North America dominated – the mass of water concentrated on that continent caused the rotation axis to shift away from that location. After 1954, dam construction intensified in Asia and East Africa, resulting in a pole shift in the opposite direction – toward the west.
The aforementioned changes follow the principle of conservation of angular momentum: the pole moves in the opposite direction of where the extra mass is concentrated.
Impact of omitted reservoirs – does 28 percent make a difference?
According to data from the GRanD database, the volume of water retained is 28 percent lower than the estimates of the International Commission on Large Dams (WRD) indicate. The authors checked whether the missing data – most likely involving thousands of small reservoirs under 0.1 km³ – significantly affects the final result.
The analysis showed that after accounting for about 6,000 of the largest of the small reservoirs omitted earlier, the pole position virtually stabilized. It follows that small reservoirs had a negligible impact on TPW.
Water retention versus oceans – which has more impact?
Although in the first half of the twentieth century the TPW effect was caused by the reservoirs themselves, in the second half mass changes in the oceans as a consequence of water retention proved equally important. The TPW shift of about 44 cm between 1835 and 2011 was influenced to a similar degree by both of these factors. This means that both should be taken into account when analyzing the impact of human activity on Earth’s rotation.
The study by Valencic and co-authors shows that in less than two centuries, the retention of water in artificial reservoirs has shifted the Earth’s pole by more than a meter. This took place in a non-monotonic motion, and its direction changed after 1954 in response to changes in the location of large reservoirs. The average rate of movement in the second half of the 20th century was three times that of the first.
This is one of the first studies whose results show in such detail how human engineering – the construction of dams – can affect the fundamental physical parameters of the planet, including the position of its axis of rotation.
MAIN PHOTO: Gabor Koszegi/Unsplash
Sources:
Valencic, N., Speiser, E., Doi, E., Lee, E. T., Ford, B., Hatzius, A., et al. (2025). True polar wander driven by artificial water impoundment: 1835-2011. Geophysical Research Letters, 52, e2025GL115468. https://doi.org/10.1029/2025GL115468
Chao, B. F., Wu, Y. H., & Li, Y. S. (2008). Impact of artificial reservoir water impoundment on global sea level. Science, 320(5873), 212-214. https://doi.org/10.1126/science.1154580
Dziewonski, A. M., & Anderson, D. L. (1981). Preliminary reference Earth model. Physics of the Earth and Planetary Interiors, 25(4), 297-356. https://doi.org/10.1016/0031-9201(81)90046-7
