The variation of discharge entering the Niger Delta system, 1951-2000, and estimates of change under global warming

摘要

A simple and effective statistical scheme for estimating river discharges on the River Niger has been derived using catchment rainfall data. Observed station annual average discharges at two locations were correlated with averaged annual rainfall data in recent years (1951-2000). A comparison of the estimated discharge and the observed discharge showed good agreement. The upstream station of Gaya on the border of Niger and Nigeria, with more extensive records, was used to validate the technique. A more limited discharge record at Lokoja, at the focal point of the Niger Delta, is used to reconstruct the discharge over 1951-2000. Despite the extensive dam construction on the Upper Niger during this period the main determinant of flow into the Delta has remained upstream rainfall. The relationship between the past rainfall data and river discharges at Lokoja are used to predict flows in the 2070s using rainfall values derived from various scenarios of a set of coupled climate model simulations. While there is uncertainty even over the sign of future change in west African rainfall, the river flow inferred from those models predicting increased rainfall over the coming century is at a level consistent with rapid change in channel position, as observed during the 1990s. This technique could be applied more widely to forecast future discharges from major river systems. Copyright (c) 2007 Royal Meteorological Society.