2.3 Regional- to global-scale hydrologic variability

An objective of CLIVAR-GOALS is to document the range of climate and hydrological variability over the continents, and to exploit any predictability associated with this variability. As discussed in Section 2.1, the paleoclimate community is already developing the long-term perspective necessary to understand tropical ocean (e.g., ENSO) and monsoon variability in a manner that is directly applicable to understanding the effect these systems have on climate variability within and outside the tropics. In parallel to this work, others in the paleoclimate community are also focused on reconstructing and understanding regional- to continental- scale climate and hydrologic variability. Given the significant dependence of societies around the world on this latter variability, a high priority has been placed on using the paleoclimate perspective to improve skill in predicting this hydrologic variability, particularly in the way it is influenced by the oceans. Regional- to subcontinental-scale, seasonally-to-annually-resolved reconstructions have already been generated using data from trees and historical documents. These include 250-300-year reconstructions of spring/summer temperature for western North America and western Europe (Briffa et al., 1988, 1992a), winter half-year precipitation and annual temperature in western North America (Fritts, 1991), drought in the coterminous United States (Fig. 7; Meko et al., 1993; Cook et al., 1996), El Niņo strength in Peru (Quinn, 1992), and a wide range of variables for Europe, China, and Japan (Frenzel et al., 1994; Zhang, 1988; Mikami, 1992). A number of smaller regional or local reconstructions exist for similar or longer periods, for example, in Morocco (Till and Guiot, 1990; Chbouki, 1992), the southeastern U.S. (Stahle and Cleaveland, 1992), high-latitude North America (Jacoby and D'Arrigo, 1989), California (Graumlich, 1993; Hughes and Brown, 1992), Scandinavia (Briffa et al., 1992b), the Mediterranean region (Serre-Bachet, 1994), Siberia (Graybill and Shiyatov, 1992), southern South America (Lara and Villalba, 1993; Boninsegna, 1992; Villalba, 1990), the Himalaya (Hughes, 1992), China (Hughes et al., 1994), Tasmania (Cook, 1992), and New Zealand (Norton and Palmer, 1992). Ice-core and laminated sediment records have provided key reconstructions as well (Fig. 8; Dansgaard et al., 1993; Mosley-Thompson et al., 1993; Thompson et al., 1992; Baumgartner et al., 1989; Lange and Schimmelman, 1994; Fisher and Koerner, 1994; Meese et al., 1994; O'Brien et al., 1995; Thompson, 1996)

Although networks of annually dated paleohydrologic records spanning the last several centuries will be critical to understanding climate and hydrological variability over the continents, it is also recognized that an understanding of the full range of hydrologic variability requires an even-longer perspective. Holocene-length (10,000 years) records indicate that major decade-to- century-scale shifts in moisture balance, dwarfing those of the last ...