Northwestern Alps 1000 Year Warm Season Precipitation and Flood Reconstructions Amann, B.; Szidat, S.; Grosjean, M. Amann, B. Szidat, S. Grosjean, M. Precipitation Reconstruction earth science/paleoclimate/climate reconstructions|paleolimnology (precipitation,varve thickness,null,millimeter,May-Aug,climate reconstructions|paleolimnology,null,null,N,null) earth science/paleoclimate/paleolimnology (depth,null,null,centimeter,null,paleolimnology,null,null,N,null) earth science/paleoclimate/climate reconstructions|paleolimnology (age,null,null,calendar year before present,null,climate reconstructions|paleolimnology,null,null,N,null) earth science/paleoclimate/paleolimnology (event layer,null,null,millimeter,null,paleolimnology,null,null,N,flood layer) earth science/paleoclimate/paleolimnology (event layer,null,null,count,null,paleolimnology,filtered,null,N,flood frequency of layers >5 mm; 31yr filtered) earth science/paleoclimate/paleolimnology (event layer,null,null,count,null,paleolimnology,filtered,null,N,flood frequency layers >5 mm; 51yr filtered) earth science/paleoclimate/climate reconstructions|paleolimnology (depth,null,null,centimeter,null,climate reconstructions|paleolimnology,null,null,N,null) earth science/paleoclimate/climate reconstructions|paleolimnology (precipitation,varve thickness,null,millimeter,May-Jun,climate reconstructions|paleolimnology,null,null,N,null) earth science/paleoclimate/paleolimnology (varve thickness,null,null,millimeter,null,paleolimnology,null,null,N,null) earth science/paleoclimate/paleolimnology (age,null,null,calendar year before present,null,paleolimnology,null,null,N,null) earth science/paleoclimate/reconstructions (Lake Oeschinen>LATITUDE 46.4983>LONGITUDE 7.7269) The recent warming of the global climate is well recognized. However, does a warmer climate also mean a moister climate? Does dry get drier and wet get wetter? There are important questions as they relate to changes in the water cycle and impacts the water resources as well as the frequency and intensity of storms and floods in the near future. In Europe, regional climate models do not show consistent and robust results for future hydroclimatic changes and how extreme events will evolve in response to future climate change. Paleo-hydroclimatic data from natural archives are one of the few means to assess such changes in the longer context. Here, we present an annually-resolved record of warm season (MJJA) precipitation and summer flood frequency from the varved (annually laminated) sediments of proglacial Lake Oeschinen (46 30 N-7 44 E, 1580 m, NW Swiss Alps) back to AD 884. These data sets are inferred from the thickness of annual sediment deposits and the occurrence of flood event layers in the sediments. The chronology of the sediment record is based on multiple varve counts and validated with historical floods chronicled in written documents (back to the 14th century) and 14C AMS dates. The precipitation record shows pronounced interannual to centennial variability with humid warm season phases between AD 920-950, AD 1100-1180, AD 1300-1400, AD 1590-1650, AD 1700-1790, AD 1820-1880, and AD 1960-2008. Driest conditions are reconstructed for AD 960-1080, AD 1250-1300 and for AD 1880-1900. Our precipitation record is consistent with the few multi-centennial warm-season precipitation records available for Europe. We did not find a persistent relationship between warm-season precipitation and temperature. In contrast, results show that the relation between precipitation and temperature has oscillated between positive correlations (warmer gets wetter, cooler gets drier) and negative correlations (warmer gets drier, cooler gets wetter) with a highly significant (X2 = 99%) multidecadal (60-70 yrs) periodicity over the last millennium. Possible explanations for this phenomenon are changes in the weather type statistics or the within-weather-type variability, which influence the combinations between precipitation and temperature over continental central Europe and operate at multidecadal scales. Such multidecadal effects might also be important for precipitation scenarios in the Alpine area under future warming. Our record of flood frequency suggests more frequent floods under cool and humid climate during the warm seasons. This picture is consistent with other studies from small and medium size catchments at mid- and high elevations in the Alpine area. However, the 13th century reveals a period with high flood frequency during warm and moderately dry (average precipitation) conditions. This anomalous situation is currently not understood; nonetheless, this is also one out of several possible scenarios for the future. From the different combinations found in our record, we conclude that the relation between floods, precipitation and temperature and, in consequence, future projections remain poorly constrained. STUDY NOTES: 1,000-year warm season precipitation and flood frequency reconstructions for the northern European Alps, based on sediment accumulation (varve thickness) of Lake Oeschinen (Swiss Alps). The sediment record is based on a highly accurate, precise and reproducible varve chronology. NCDC-Paleoclimatology https://www.ncdc.noaa.gov/data-access/paleoclimatology-data - Bauer Bruce Investigator : Amann, B. Investigator : Szidat, S. Investigator : Grosjean, M. 2015-08-06 ONLINE Files online, ASCII https://www.ncdc.noaa.gov/paleo/study/19102 https://www1.ncdc.noaa.gov/pub/data/paleo/paleolimnology/europe/switzerland/oeschinen2015flood.txt https://www1.ncdc.noaa.gov/pub/data/paleo/paleolimnology/europe/switzerland/oeschinen2015precip.txt https://www1.ncdc.noaa.gov/pub/data/paleo/paleolimnology/europe/switzerland/oeschinen2015flood.txt https://www1.ncdc.noaa.gov/pub/data/paleo/paleolimnology/europe/switzerland/oeschinen2015precip.txt English https://www.ncdc.noaa.gov/paleo/study/19102 https://www1.ncdc.noaa.gov/pub/data/paleo/paleolimnology/europe/switzerland/oeschinen2015flood.txt https://www1.ncdc.noaa.gov/pub/data/paleo/paleolimnology/europe/switzerland/oeschinen2015precip.txt Amann, Benjamin; Szidat, Sönke; Grosjean, Martin2015A millennial-long record of warm season precipitation and flood frequency for the North-western Alps inferred from varved lake sediments: implications for the futureQuaternary Science Reviews11589-10010.1016/j.quascirev.2015.03.002http://dx.doi.org/10.1016/j.quascirev.2015.03.002 START YEAR: 884 AD * END YEAR: 2008 AD 7.7269 46.4983 7.7269 46.4983