The global footprint of persistent extra-tropical drought in the instrumental era

Publication Type  Journal Article
Year of Publication  2008
Authors  Herweijer, C.; Seager, R.
Journal Title  International Journal of Climatology
Volume  28
Issue  13
Pages  1761-1774
Journal Date  Nov 15
ISBN Number  0899-8418
Accession Number  ISI:000261003400006
Key Words  sea-surface temperature; nino-southern-oscillation; north-atlantic oscillation; el-nino; climate-change; united-states; precipitation variability; missionary correspondence; american droughts; severity index

The major North American droughts as per instrumental records are shown to be part of a larger, global pattern of low-frequency drought variability. Drought in western North America during the 1850s-1860s, 1870s, 1890s, 1930s and 1950s, is shown to coincide with the occurrence of prolonged dry spells in parts of Europe, southern South America and western Australia. Tropical land regions are mostly wet during these periods, with the exception of central east Africa, southern India and Sri Lanka, which are dry. The recent 1998-2003 period of drought in western North America reveals a similar global hydroclimatic 'footprint' with the exception of a wet southern South America and continued dry conditions in the Sahel. Common to each of the six droughts is the persistence of anomalously cool east central tropical Pacific sea surface temperatures (SSTs). For the 1998-2003 case, the warming of SSTs everywhere outside of the east central tropical Pacific may be influencing precipitation and masking the influence of persistent precipitation anomalies driven from the tropical Pacific alone. In general, examination of these major historical extra-tropical droughts reveals a hemispherically and, in the extra-tropics, a zonally symmetric pattern consistent with forcing from the Tropics.Ensembles of model simulations forced by observed SSTs globally (Global Ocean Global Atmosphere, GOGA) and only within the tropical Pacific (Pacific Ocean Global Atmosphere-Mixed Layer, POGA-ML) are both able to capture the global pattern of the persistent extra-tropical drought regimes since the mid-nineteenth century. This implies that the recently demonstrated link between SST forcing and drought in North America is in fact only one part of a global hydroclimatic response to the persistence of cool SST anomalies in the tropical Pacific. Indian Ocean SST forcing is required to capture the droughts in central east Africa. Over Europe, the modelled, low-frequency precipitation signal is unrealistically ENSO dominated, as the model does not faithfully reproduce the observed history of low-frequency NAO variability. Overall, our results Suggest that the global pattern of persistent drought appears to be a low-frequency version of interannual ENSO-forced variability. Copyright (c) 2008 Royal Meteorological Society


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URL  <Go to ISI>://000261003400006
DOI  Doi 10.1002/Joc.1590