Exploring the Relationship between Polar Motion and Runoff

The evidence of the relationship between polar motion and runoff is reviewed. The relationship between the runoff of Yarlung Zangbo, a primitive river in Tibet, China and polar motion with data records from about 1846 to present is explored. First, the action path framework was structured based on geophysical principles. In order to make time series stationary, the initial time series of polar motionXcomponent, Ycomponent and runoff were transformed into their corresponding fi rst order difference time series ΔX, ΔY, and ΔQ. The Granger causality test between ΔX, ΔYand ΔQwas conducted on monthly, seasonal and annual time scales. It is found that on a monthly scale ΔXinfluences ΔQat the lag being from the 1^stto the 21^stmonth, with the 9^thmonth being an exception. ΔYinfluences ΔQat the lag from the 1^stto the 9^thmonth and from the 17^thto the 24^thmonth. On a seasonal scale, the influence of ΔXon ΔQcan be seen in the 2^ndseason (i.e. from the 4^thto the 6^thmonth). The influence of ΔYon ΔQcan be seen on a seasonal scale from the 4^thto the 6^thseason (i.e. from the 10^thto 18^thmonth). We cannot see evident Granger causality from ΔX, ΔYto ΔQ, on annual scales. For the Granger influence of ΔQto ΔX, ΔY, it is found that on a monthly scale the influences are prominent at the lag being from the 3^rdto the 25^thmonths for the ΔX, for the ΔYit is the 1^stand the 3^rdto the 25^thmonths. On a seasonal scale these influences can be seen at the lag from the 2^ndto the 8^thseason (corresponding to the 4^thto the 24^thmonth) for ΔXand at the lag from the 1^stto the 8^thseason (corresponding to from the 1^stto the 24^thmonth) for ΔY. Again, on a annual scale no evident granger causality can be found from runoff to polar motion. The different behaviours on monthly, seasonal and annual scales suggest that using the monthly data of polar motion to obtain the monthly runoff data is more practicable than borrowing the data from polar motion for river runoff on seasonal and annual scales.