SIMULATING THE LATE PLEISTOCENE/HOLOCENE RECORD OF RIVER DISCHARGE IN EUROPE

We simulate the Late Pleistocene/Holocene record of river discharge for the major rivers of Europe using a macrophysical runoff model. The macrophysical approach differs from the more common microphysical modeling, which involves modeling the individual weather processes and substrate characteristics every place in a watershed, or representative places, and then integrating the effect of these processes in time and space to estimate the mean discharge from the watershed. The macrophysical model treats the net runoff/discharge from the entire watershed as a product of the simulated climatic conditions that are responsible for producing precipitation, evaporation rates, and the like. We apply this model to eleven major rivers in Western, Central, and Eastern Europe for the last 14000 years. After calibrating and validating the macrophysical model with modern mean monthly river discharge data, the river discharge is simulated at 200-year intervals for each river basin from 14 ka BP to the present. The simulated discharge in Western Europe (Po, Rhone, Garonne, Seine, and Elbe Rivers) show a similar pattern of steadily decreasing discharge from 14 ka BP to present (about 10-20% greater than present in the Late Pleistocene and < 10% greater in the middle Holocene). This is in qualitative agreement with observational evidence for the late Pleistocene which indicates conditions wetter than present in the Mediterranean and perhaps northwestern Europe. Pollen evidence indicates wetter than present conditions in the middle Holocene in the Mediterranean region consistent with our simulations but dryer than present in northwestern Europe, which our simulations do not show. The simulated discharge of the rivers originating in the Alps, Central, and Eastern Europe (Danube, Volga, Dniester, Odra, Dniepr, and Rhine) are, in general, decreased (about 10%-30%) compared to present in the Late Pleistocene and slightly increased (< 10%) compared to present during the middle Holocene. This is in qualitative agreement with pollen and lake level data indicating dryer than present conditions in Central and SE Europe in the Late Pleistocene and wetter conditions in the Balkans and Eastern Europe to northern Russia during the middle Holocene.