Timing and prediction of climate change and hydrological impacts: periodicity in natural variations

Hydrological impacts from climate change are of principal interest to water resource policy-makers and practicing engineers. Predictive climatic models have been extensively investigated to quantify the impacts. Palaeoclmatic investigations, on the other hand, show unequivocal and strong periodicity of climate variations in proxy evidence. Yet how to use the periodicity in future hydroclimatic timing and forecasting has received less attention. This paper examines the periodicity in Pleistocene–Holocene glacial–interglacial events and in modern precipitation records, and discusses a way in which the periodicity is used for hydroclimatic predictions. The analysis, based on published CO₂, ΔT (δ²H) and δ¹⁸O proxy data of polar ice cores and deep oceanic benthic fossils, shows a periodicity in a ~100, ~40 or 25 kyear duration consistent with Milankovitch orbital regulations during the glacial–interglacial periods. On a fine time scale, millennium and multi-decadal periodicity is observed in high-resolution proxy variations of Greenland ice cores and in instrumental precipitation records of the contiguous USA. A basic periodicity of decadal and multi-decadal changes in ~20 and ~10–15 year duration is apparent in wavelet frequency analysis of both ice core proxy and precipitation data. While the kyear-scale periodicity is found of global prevalence, the millennium and decadal variations vary in space and are region-specific. Based on these findings, a generalized time-downscaling hierarchy of periodicity is proposed as a potential approach for timing and forecasting future hydroclimatic conditions at a resolution relevant to the water resources engineering and management.