4 - Assessment of the impacts of climate variability and change on the hydrology of North America

Summary

INTRODUCTION

Historical evidence of the effects of climate variability on the hydrology of North America is found in paleorecords interpreted from a variety of sources, including ice cores, lake sediment cores, tree rings, and pack rat middens. These records help identify the occurrence, duration, and effects of climate extremes that have ranged from cold and wet periods of major glaciations, to warmer and drier periods that were ice-free. Recorded climatological and hydrological data from the past few hundred years provide more detailed measures of the effects of climate variability, including extreme events such as the drought of the 1930s and significant floods such as the recent Upper Mississippi River floods of 1993.

The effects of climate variability and change on the hydrology and water resources of different regions of North America have been investigated by a variety of researchers for several decades. The most recent concerns regarding the effects of increasing greenhouse gases on climate variability and change have expanded these research efforts (1) to better define ‘natural’ climate variability; (2) to look for the effects of greenhouse gas increases on the climate and hydrological systems; and (3) to develop methodologies to estimate the effects of future climate variability and change on hydrological systems.

A variety of empirical, conceptual and physically based models have been employed using historical data and the estimates of future climate scenarios. Early investigations of climate change used hypothetical climate scenarios based on historical records and investigators' ‘best estimates’ of possible changes in temperature and precipitation.