Decadal and century-long changes in the reconstruction of erosive rainfall anomalies in a Mediterranean fluvial basin

摘要

Rain erosivity is difficult to reconstruct for past periods due to the few long detailed instrumental series. This paper deals with the potential of written historical documents to reconstruct yearly erosive rain anomalies (differences between erosivity values and long-term average). A detailed analysis was undertaken of the Calore River Basin (South Italy) erosive rainfall using data from 425-year-long series of both observations (1922-2004) and proxy-based reconstructions (1580-1921). Annual erosivity was computed for the observational time based on the Revised Universal Soil Loss Equation (RUSLE) scheme, whilst documentary descriptions described the course of rain events for the previous times. A method was proposed that uses a weather index to account for the abundance of weather anomalies (rainfall extremes) as registered in historical documents. A model was developed to provide annual rain-erosivity data comparable with the RUSLE scheme, using the weather index sum (June-October) and variance (January-December) and the annual precipitation amount as inputs. This model was applied to reconstruct annual rain-erosivity anomalies for the pre-modern instrumental time. A long continuous series of rain-erosivity anomalies was produced by combining (and homogenizing) model-reconstructed and RUSLE data, thus providing a range of natural variability in climate erosivity to detect the main changes from 1580 to 2004. The climate history of the Calore River Basin shows pronounced interdecadal variations, with multidecadal erosivity reflecting the mixed population of thermoconvective and cyclonic rainstorms with large anomalies. The so-called Little Ice Age (16th to mid-19th centuries) was identified as the stormiest period, with mixed rainstorm types and high frequency of floods and erosive rainfall. Important historical climate fluctuations were observed, but with a relevant smoothing in the last 150 years of the series. For the recent, warm period, investigations at higher time resolution are required to assess the seasonal changes of rain erosivity and their relationship to soil conservation. Copyright (c) 2008 John Wiley & Sons, Ltd.