The flow series for the River Thames near its tidal limit is one of the most studied in the world. Its length and completeness, and the richness of the historical information which augments the formal flow record, ensures that the series is of immense value. However, the variability in flood magnitude and frequency that it captures needs to be interpreted with caution. The homogeneity of the time series is influenced by a wide range of factors, including changes in the hydrometric capability of the gauging station and the impact of differing water, river and land management practices on the flow regime. Nevertheless, both the daily flow series and the record of lock levels provide some reassuring signals regarding the resilience of the Thames to fluvial flood risk in a warming world. Since routine flow measurement began in 1883, the Thames basin has seen a substantial rise in air temperature and a tendency for both winter rainfall and annual runoff to increase. There is no trend in fluvial flood magnitude however, partly reflecting a decline in snowmelt contributions to major floods and annual maximum lock levels show a significant decline, reflecting a highly sustained programme of river management.

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