Introduction

Projected changes in the amount and distribution of global precipitation over the next century will almost certainly have greater impacts on the quality of human life and natural ecosystem functioning than temperature change (IPCC 2007). Most paleoclimate research to date, however, has concentrated on global and regional histories of temperature change. This is partly because most high-quality continental climate-proxy archives are located in regions with positive water balance and above-average temperature sensitivity. More fundamentally, reconstructing past precipitation variation independent of coincident temperature changes is a difficult task. Although temperature and precipitation co-vary on large spatial and long time-scales (Trenberth and Shea 2005), breakdown of this co-variation at smaller spatial and shorter time-scales is often a key to understanding the climate mechanisms involved. Improving our understanding of regional climate and hydrologic variability at decade to century time-scales thus represents a significant challenge for both the paleoclimate data and paleoclimate modeling communities. External climate forcing at this time-scale (solar variability, volcanic eruptions) is relatively modest and expressed through both direct and cumulative effects, therefore delays in the response of individual climate-system components and their associated climate archives to this forcing become more important than they are over longer time-scales. Consequently, uncertainty exists over the extent to which observed decadal to century-scale changes truly reflect abrupt events or result from the cumulative effect of interannual variation. A satisfactory answer to this question is critical to evaluate the exact relationship between climate variability and water-resource availability at the landscape scale that has often determined the success or failure of societies in the past (Weiss and Bradley 2001), and will do so in the future (IPCC 2007). A first step in providing this answer can be made through syntheses of paleohydrologic data at the continental scale, in an attempt to reconstruct large-scale spatial patterns of variability at decadal to centennial time-scales. In this contribution we aim to (i) review initial attempts to integrate proxy records of Holocene continental paleohydrology across regions; and (ii) juxtapose high-and low-latitude patterns of hydrologic change through time. Geographically, we focus on the PAGES-PANASH Europe-Africa transect (Bradley et al. 1995), which includes continental regions of Europe, adjacent Eurasia, and Africa bounded on the west by the Atlantic Ocean and extending east into monsoonal Asia (Figure 8.1).

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