Water availability and cycles of drought and plenty

Abstract

Water availability in terms of rainfall and/or river flow tends to be analysed and predicted in probabilistic terms. That is to say historic records are analysed to produce such things as mean years and 95% wet or 95% dry years. However, there is increasing evidence to show that, on occasions, sustained periodicities appear in such records. Where this happens they can be used to supplement probabilities by better targeting which years are likely to be wet and which years are likely to be dry. The benefits in terms of planning crop yields, hydropower output, water supply and even targeting needs for famine relief are obvious. The author explores this with some examples from his own experience and that based on a talk he delivered in London on 20 February 2015 to a joint meeting of the Irrigation and Water Forum and the British Dam Society.