Riverflow reconstructions for 15 catchments over England and Wales and an assessment of hydrologic drought since 1865

Recent years have seen increased risks of water supply problems because of reduced rainfall in some seasons. Over England and Wales most riverflow records beign during the 1950s and 1960s. The short record length, therefore, makes assessment of the rarity of some flow flow sequences difficult. A means of extending riverflow records is to reconstruct them using a simple catchment model and the plentiful monthly rainfall totals available for England and Wales. Riverflow data on a monthly basis have been reconstructed for 15 catchments for the period since the 1860s. The reconstructions are produced with a regression-based catchment model that related lagged values of rainfall to runoff. The statistical nature of the model required that any reconstructions be assessed over an independent data period. All perform almost as well as during the calibaration periods. Using the reconstructions, recent hydrologic droughts are put into a longer term context. On one of the catchments is the most extreme 6 months (April-September) average riverflow found to occur during the 1986-1995 period. On a number of catchments, the extreme year is 1976 or 1984. Flows were low during 1989-1992 and 1995, with the former four year period being unusual, because the years occurred in succession. On all 15 catchments, however, an earlier sequence occurring between 1865 and 1980 is more severe.