HR: 13:40h
AN: GC52A-01 INVITED     [PDF]
TI: The North American Drought Atlas
AU: * Cook, E R
EM: drdendro@ldeo.columbia.edu
AU: Krusic, P J
EM: pjk@ldeo.columbia.edu
AB: A large part of the western US has been experiencing unusually severe and persistent drought over the past 5 years. This drought highlights both the vulnerability of this semi-arid region to shortfalls in rainfall and the need to better understand long-term drought variability and its causes in North America. To this end, centuries long, annually-resolved tree-ring records have been used to reconstruct annual changes in both drought and wetness over large portions of North America. The drought metric used for this purpose is the summer-season Palmer Drought Severity Index (PDSI). The PDSI reconstructions have been produced on a 297-point 2.5x2.5$\deg$ regular grid that covers most of North America. This new generation of North American drought reconstructions was made possible through support from the NOAA Office of Global Programs. These drought reconstructions, some of which extend back almost 2,000 years into the past, have been used to create a North American Drought Atlas that provides a detailed spatial and temporal history of drought and wetness. This effort has been supported by the NSF Paleoclimatology Program. The North American Drought Atlas, which will be available on a CD-ROM and can be accessed inter-actively using standard web browsers, has been created to make the drought reconstructions easily accessible. Each of the 297-point summer PDSI reconstructions, with their estimated uncertainties, can be displayed in PDF format. There are also 1,992 annual PDSI maps also in PDF format that can be selected and displayed by year. The annual maps have also been linked together into an animation to provide a dynamic look at patterns of drought and wetness as they develop across parts of North America where tree-ring estimates exist back in time. The numerical values of the PDSI reconstructions will also be available on the CD-ROM for independent analyses. Some properties of past reconstructed drought over North America will also be described in context with that which is currently afflicting the western US. In particular, an examination of the area affected by drought conditions of at least incipient severity (i.e., PDSI$<-1$ or worse) reveals the occurrence of a prolonged period of elevated aridity over the western US during the AD 850-1300 interval. This dry epoch, which is arguably a hydrologic expression of the Medieval Warm Period, is unprecedented over the past 1,200 years. If this is an indication of how warmer conditions in the past have affected the incidence of drought in the western US, it cannot be viewed as good news as we enter into a warmer world increasingly forced by greenhouse gases.
DE: 1600 GLOBAL CHANGE (New category)
DE: 1812 Drought
DE: 1833 Hydroclimatology
DE: 3344 Paleoclimatology
DE: 4215 Climate and interannual variability (3309)
SC: Global Climate Change [GC]
MN: 2003 Fall Meeting