Length-of-Day Changes Driven by Artificial Water Impoundment Post-1835

Summary We compute changes in the Earth’s rotation period caused by water impoundment in artificial reservoirs from 1835 to 2011. The change is the sum of two effects that nearly cancel: increased water in reservoirs, which increases the rotation period, and ocean mass loss, which decreases it. Our computation, which includes the spatially varying effects on sea level of Earth loading and mass change, shows a decrease in the rotation period of ~0.01 ms per day over the 176-year timespan. Our computed time series of the change in the rotation period is comparable to a previously published estimate, though during the time of greatest change (1935–1980) our computed rate is ~50 per cent greater than the earlier estimate. The total volume of our database of reservoirs is 72 per cent of an independent global estimate; we demonstrate that the missing 28 per cent of the total global storage impacts our estimate of angular velocity change by less than ~10 per cent.