New Role for Paleoclimatology: Routine Drought Monitoring

The instrumental record of drought exists for 100 years or less for most of North America. This record is inadequate for assessing the rarity of major drought events of the 20th century, and may not represent long-term natural climate variability. Paleoclimatic records are critical for evaluating extreme drought events and drought variability in the 20th century in a broader temporal context. In the last decade, a number of studies have reconstructed drought from paleoclimatic records, primarily tree rings and lake sediments. One of these was the first gridded Palmer Drought Severity Index (PDSI) reconstruction from tree rings for the conterminous United States from AD 1700-1978 (Cook et al., 1999). It provided the first nationwide patterns of pre-instrumental drought and a dataset for all parts of the conterminous U.S. Further work has extended these reconstructions back in time and to most of North America. In 2002, NOAA Paleoclimatology became part of NOAA's National Climatic Data Center and collaborative efforts between the Climate Monitoring Branch and the NOAA Paleoclimatology began to incorporate pre-instrumental perspectives on drought into the monthly and annual State of the Climate (SoC) Reports. Each month authors of the SoC Report select regions to be highlighted in the United States Drought section. While previously limited to instrumental data, the report now often features paleoclimatic records, using either reconstructions from research targeting the area of impact, or using data from the gridded tree-ring reconstructed PDSI dataset. These paleoclimatic data provide a multi-century record from which users can better assess the severity of ongoing droughts relative to droughts of previous centuries. Additionally, SoC Report authors have included spatial reconstructions and indices of paleodrought at regional to national levels. The extensive U.S. droughts in 2002 made the addition of paleoclimatic data to the State of the Climate Reports especially valuable. However, paleoclimatic reconstructions are computed differently than their instrumental counterparts and almost never extend to the current year. Planned reconstructed drought records that better integrate with the instrumental record, and blended and "living" integrations of paleoclimatic and instrumental data will improve the way that these data products can be used together in the new North American Drought Monitor. References: Cook, E.R., Meko, D.M., Stahle, D.W., and Cleaveland, M.K. 1999. Drought reconstructions for the continental United States. Journal of Climate 12:1145-1162