Effects c / Medieval Vvarm reriod and Little e:, I ige on the hydrology of Mediterranean region European Geosciences Union A s s e m ~ ~ y Vienna, Austria, 22-27 April 2012 YmMarkonis, PmKossieris, A m Lykou and D m Koutsoyiannis, Department of Water Resources and Environmental Engineering, National Technical University of Athens Session 7.4: Climate, Hydrology and Water Infrastructure - references abstract - Medieval Warm Period (950 1250) and Little Ice Age (1450 1850) are the most recent periods that reflect the magnitude of natural climate variability. As their names suggest, the first one was characterized by higher temperatures and a generally moister climate, while the opposite happened during the second period. Although their existence is well documented for Northern Europe and North America, recent findings suggest strong evidence in lower latitudes as well. Here we analyze qualitatively the influence o f these climatic fluctuations on the hydrological cycle all over the Mediterranean basin, highlighting t h e spatial characteristics o f precipitation and runoff. We use both qualitative estimates from literature review in the field of paleoclimatology and statistical analysis o f proxy data series. proxy data The literature reviewed included many different methods for r a~anrorlo, ~ m u and Schilman (Marine aL, 2001 1995 kd) II@ (MnalcalJ t h e reconstruction o f the past hydro-climatic conditions. These reconstructions were based on: Historical documents Tree-Rings Marine / Lake sediments Lake levels Speleotherms (caves) Glaciers River alluvation Pollen data map legend I timeline legend Temperature Precipitation remperature general findings High Temperatures I Extremely Dry conditions 1 Low During the Medieval Warm Period (MWP, 950 - 1250 AD) the Hot Summers Precipitation temperature was generally higher than today at the western Low Temperatures 1 Severe Humid condiions IHigh ) High Temperatures Mediterranean basin especially in the summer. However, there was a Winters Pwcipitation - Low Temperatures certain interval (1080 - 1140 AD), when temperature had fallen Drop in Temperature during Humid condiions IHigh Sewre Winters sharply causing a temporary glacier expansion. Interestingly, 1080 - 1140 AD Precipitation according to the (scarce) available historical information, during MWP Enhancedvariability (out of the eastern Mediterranean experienced rather cold conditions with season rainlsnow, etc.) severe, extended winters. The hydro-meteorological conditions that prevailed during this period show distinct regional variability. Arid conditions dominated in Spain and S. France, and gradually became more humid towards eastern longitudes. Between these two opposing regimes (western dry/eastern wet) climate exhibited enhanced variability and instability in the northern central part of Mediterranean, where years of droughts and extreme floods succeeded each other; also, there were consecutive years with out-of-season rain or even snow. The low temperatures that characterized the Little Ice Age (1450 - 1850) all over the northern latitudes were evident in the Mediterranean basin as well. The decline in temperature was homogenous, although locally some periods with exceptionally hot summers can be observed for few decades. At the western Mediterranean this was a period of consecutive heavy rainfall, severe floods and high humidity. This has been confirmed by a new proxy series of paleo-storm events along the French Mediterranean coast (Sabbatier et al., 2012 -see graph below). At the same time, in the eastern part the opposite conditions prevailed: droughts were more frequent, river flow was generally low, as well as lake levels. Similarly to Medieval Warm Period, the region of northern central Mediterranean exhibited enhanced climatic variability. The overall precipitation regime of inverse correlation between western and eastern Mediterranean, is in agreement with the 'See- saw' pattern hypothesis, also known as Mediterranean Oscillation (Conte et al., 1989; Martin-Puertas et al., 2010; Roberts et al., 2011), both in Medieval Warm Period and Little Ice Age. requency of Paleo-stormevents in Gulf of Lions in S. France. ,he y-axis is reversed as low values of smectite/(illite+chlorite) correspond to periodsof high storm activity (Sabbatier et al., 2012).