A SOIL WATER-BALANCE BUCKET MODEL FOR PALEOCLIMATIC PURPOSES .2. MODEL APPLICATION TO LATE HOLOCENE CLIMATE

The paper describes the application of the Soil Water-Balance Bucket M odel (SWBBM), version B, to outline potential Holocene climate conditi ons leading to water fluctuations at the Lagoni peat-bog (Mercurago, N orthern Italy). These are reconstructed from a series of radiocarbon-d ated peat cores taken along present-day shores. Attention focuses on a n event occurring during the late Sub-Boreal (4000-3000 years before p resent [BP]), during which peat recedes and subsequently expands, indi cating reduced and increased water availability, respectively. This pe riod is associated with a major change in human settlement patterns, b oth at local and regional scales, the appearance and disappearance of Bronze age lake-dwelling sites in Northern Italy; settlement patterns shift from the low plains of the Po valley to the upper plain and hill s of the pre-Alpine system. Palynological data indicate no shift in me sic regional vegetation while changes are documented at the local scal e, with an increase in hygrophilous vegetation as a response to raised lake levels. SWBBM/B, using a limited number of input climate paramet ers (temperature, precipitation and insolation), quantifies changes in soil hydrology parameters (evapotranspiration, soil water, percolatio n and runoff). Modern climate at the site is perturbed with insolation , temperature and precipitation altered to obtain variations in percol ation and runoff, without varying evapotranspiration. Results show tha t 10% seasonal differences in total precipitation, with only a minor t emperature change < 1 degrees C, lead to 30% changes in percolation an d runoff but with no change in evapotranspiration. It appears that for this minor climatic shift in the late Sub-Boreal, palynological evide nce does not seem to be a suitable proxy-climate indicator at regional scales. This results from sensitivity of lake levels and vegetation t o different components of the hydrological cycle.