Impacts of annual precipitation extremes on soil and nutrient losses in vineyards of NE Spain

The objective of this research was to characterise annual precipitation extremes in a Mediterranean vineyard region. The number of exceptional events (P > 95th percentile) and annual extreme events (P > 99th percentile), as well as their strength, erosive character and return period were analysed for 2000-2004. The erosive character was evaluated according to the R-factor (kinetic energy x maximum intensity in 30-min periods). Soil and nutrient losses caused by these events were evaluated by combining field sampling and a hydrological model to estimate total runoff in a vineyard plot. The results show a clear increase in the number of very wet days and extreme events (P > 95th percentile). which represented up to 88% of annual rainfall. The severity of the extreme events (TS = precipitation event P > 99th percentile) reached values higher than 50 mm almost every year. These values were far exceeded in 2000. when one extraordinary event recorded 50% of the annual rainfall, with TS of 189 mm. about 80% of total rainfall being lost as runoff. Annual erosivity was driven not only by extreme events, but also by short events of less depth but high intensity. During some of the years analysed. rainfall erosivity was two or three times the average in the area. Most soil and nutrient losses occurred in a small number of events: one or two events every year were responsible for more than 75% of the annual soil and nutrient losses on average. Antecedent soil moisture conditions, runoff rates. and events with a return period higher than two years were responsible for the higher erosion rates. Apart from an exceptional event recorded in 2000. which produced more than 200 Mg ha(-1) soil losses, annual soil losses up to 25 Mg ha(-1) were recorded, which are much higher than the soil loss tolerance. Copyright (c) 2008 John Wiley & Sons, Ltd.