Effects of Climate and Antecedent Soil Moisture on the Areal Average Abstraction Losses

The influence of climate on the flood generation process is nowadays a topic of striking impact and particular remark due to the necessity of improving the available techniques and procedures for risk assessments and land protection. In particular great efforts of the recent research are provided to support the flood frequency analysis exploiting the amount of information available by the observation of the frequency of precipitation, vegetation coverage, soil permeability, etc in order to improve the performances of models for flood prediction. The aim of this paper is to focus on links and significant relationships between infiltration models, valid at small scale, and average processes observed at the medium (hillslope) and large (basin) scales, by the light of climate and permeability of soil. A significant interpretation to the observed relationships observed between total water losses F-A, climate and basin area A is provided. By means of results obtained on basins in Southern Italy, it is possible to conclude that in dry regions rain losses are mainly due to the initial abstraction phenomenon and the estimated values of F-A are quite constant and invariant with basin area, Such findings are consistently matched to what one could expect from Hortonian behavior of soils. Conversely, in humid basins, the values F-A, show a strong relationship with climate represented by a climatic index. In this case, the basin's behavior is consistent with Dunne's model of runoff generation. Those results are supported by the theoretical framework provided by the classical analysis of infiltration in unsaturated porous media.