Rain cycles for strategic water planning and management

摘要

A serendipitous finding, possibly important for strategic water planning, is supported by Mayan beliefs that earthly events such as rainfall occur in 13-year patterns, with a new regime beginning every 52 years. A Sri Lankan rainfall record of 100+ years exhibits a 13-year cycle. Grouping four such cycles reveals a 52-year period of significantly higher rainfall than preceding and following periods. Additional longer records representing about 2/3 of the island's area confirm this finding, and suggest that the entire cycle is completed in 104 years. Elsewhere in the world, still longer records confirm such cycles, but with amplitudes, impacts and phasing differing with location. It is concluded that 13-year, 52-year and 104-year cycles are present in rainfall behaviour, setting up varying degrees of predictability in different places. Possible applications in Sri Lanka include policy making in the fields of hydropower, tea production, and village tank rehabilitation for irrigation to extend crop-growing seasons in foreshortened rainfall seasons.