Andes Temperate-Mediterranean Transition 657 Year PDSI Reconstruction Christie, D.A.; Boninsegna, J.A.; Cleaveland, M.K.; Lara, A.; Le Quesne, C.; Morales, M.; Mudelsee, M.; Stahle, D.W.; Villalba, R. Christie, D.A. Boninsegna, J.A. Cleaveland, M.K. Lara, A. Le Quesne, C. Morales, M. Mudelsee, M. Stahle, D.W. Villalba, R. Antarctic Oscillation (AAO) ENSO PAGES 2k Network PAGES LOTRED SA2k Palmer Drought Index Reconstruction earth science/paleoclimate/climate reconstructions|tree ring (age,null,null,year Common Era,null,climate reconstructions|tree ring,null,null,N,null) earth science/paleoclimate/climate reconstructions|tree ring (Palmer Drought Severity Index,ring width,null,dimensionless,Dec,climate reconstructions|tree ring,null,principal component analysis|regression analysis,N,calibration data set: Dai et al. 2004; calibration period: 1960-2000 A.D.; principal components regression) earth science/paleoclimate/reconstructions (Andes Temperate-Mediterranean Transition zone>LATITUDE >LONGITUDE ) The Andes Cordillera acts as regional "Water Towers" for several countries and encompasses a wide range of ecosystems and climates. Several hydroclimatic changes have been described for portions of the Andes during recent years, including glacier retreat, negative precipitation trends, an elevation rise in the 0° isotherm, and changes in regional streamflow regimes. The Temperate-Mediterranean transition (TMT) zone of the Andes (35.5°-39.5°S) is particularly at risk to climate change because it is a biodiversity hotspot with heavy human population pressure on water resources. In this paper we utilize a new tree-ring network of Austrocedrus chilensis to reconstruct past variations in regional moisture in the TMT of the Andes by means of the Palmer Drought Severity Index (PDSI). The reconstruction covers the past 657 years and captures interannual to decadal scales of variability in late spring-early summer PDSI. These changes are related to the north-south oscillations in moisture conditions between the Mediterranean and Temperate climates of the Andes as a consequence of the latitudinal position of the storm tracks forced by large-scale circulation modes. Kernel estimation of occurrence rates reveals an unprecedented increment of severe and extreme drought events during the last century in the context of the previous six centuries. Moisture conditions in our study region are linked to tropical and high-latitude ocean-atmospheric forcing, with PDSI positively related to Nino-3.4 SST during spring and strongly negatively correlated with the Antarctic Oscillation (AAO) during summer. Geopotential anomaly maps at 500-hPa show that extreme dry years are tightly associated with negative height anomalies in the Ross-Amundsen Seas, in concordance with the strong negative relationship between PDSI and AAO. The twentieth century increase in extreme drought events in the TMT may not be related to ENSO but to the positive AAO trend during late-spring and summer resulting from a gradual poleward shift of the mid-latitude storm tracks. This first PDSI reconstruction for South America demonstrates the highly significant hindcast skill of A. chilensis as an aridity proxy. STUDY NOTES: Reconstruction of Palmer Drought Severity Index (PDSI) for the southern Andes Temperate-Mediterranean Transition zone (~35.5°-39.5°S) for the past 657 years. The reconstruction is based on a six site network of Austrocedrus chilensis tree-ring widths. NCDC-Paleoclimatology https://www.ncdc.noaa.gov/data-access/paleoclimatology-data - Bauer Bruce Investigator : Christie, D.A. Investigator : Boninsegna, J.A. Investigator : Cleaveland, M.K. Investigator : Lara, A. Investigator : Le Quesne, C. Investigator : Morales, M. Investigator : Mudelsee, M. Investigator : Stahle, D.W. Investigator : Villalba, R. 2012-05-03 ONLINE Files online, ASCII https://www.ncdc.noaa.gov/paleo/study/12908 https://www1.ncdc.noaa.gov/pub/data/paleo/treering/reconstructions/southamerica/andes2011pdsi.txt https://www1.ncdc.noaa.gov/pub/data/paleo/treering/reconstructions/southamerica/andes2011pdsi.xls https://www1.ncdc.noaa.gov/pub/data/paleo/treering/reconstructions/southamerica/andes2011pdsi.txt https://www1.ncdc.noaa.gov/pub/data/paleo/treering/reconstructions/southamerica/andes2011pdsi.xls English https://www.ncdc.noaa.gov/paleo/study/12908 https://www1.ncdc.noaa.gov/pub/data/paleo/treering/reconstructions/southamerica/andes2011pdsi.txt https://www1.ncdc.noaa.gov/pub/data/paleo/treering/reconstructions/southamerica/andes2011pdsi.xls Christie, D.A., J.A. Boninsegna, M.K. Cleaveland, A. Lara, C. Le Quesne, M.S. Morales, M. Mudelsee, D.W. Stahle, and R. Villalba. 2011. Aridity changes in the Temperate-Mediterranean transition of the Andes since ad 1346 reconstructed from tree-rings. Climate Dynamics, Vol. 36, Numbers 7-8, pp. 1505-1521, DOI: 10.1007/s00382-009-0723-4 START YEAR: 1346 AD * END YEAR: 2002 AD -72 -39.5 -68 -35.5