Abstract
The relationships between atmospheric circulation patterns and daily Iberian rainfall are here explored at high spatial resolution (0.2°) using the Jenkinson and Collison automated classification scheme with 26 Weather Types (WTs). The WTs were computed by means of the daily EMULATE Mean Sea Level Pressure dataset (EMSLP) while the high resolution precipitation database corresponds to the recent Iberia02 daily gridded precipitation dataset over the 1950-2003 period. Six monthly indexes relating the WTs and precipitation were analyzed: their Frequency, the Mean Precipitation, the Percentage Contribution, the Area of Influence, the Precipitation Intensity and Efficiency. Except for the Frequency of the WTs, all other indexes were evaluated studying their spatial distribution over the Iberian Peninsula, focusing on a WT and a month at time. A small number of WTs (7) was found to capture a high percentage (~70%) of monthly Iberian precipitation. The Westerly WT is the most influent one, followed by the Cyclonic, the Northwesterly and the Southwesterly WTs. Westerly flows, however, do not affect the Mediterranean fringe or the Cantabrian coast, which are dominated by the Easterly and Northerly WTs, respectively. Rainfall along the Mediterranean coastline and the Ebro basin depends on a variety of WTs, but their effects are confined to narrow areas and short temporal intervals, suggesting that local factors such as convective processes, orography and the proximity to a warm water body could play a major role in precipitation processes. We show that the use of daily gridded precipitation dataset holds the advantage of measuring the daily rainfall amount due to each WT directly instead to relying on the predicted values of the regression model as done in previous works.
Highlights
Rainfall variability is a well know characteristic of Mediterranean climate, and it has been well studied around Mediterranean Basin at the monthly and seasonal scales (Corte-Real et al, 1995; Kutiel et al, 1996; Xoplaki et al, 2004; Paredes et al, 2006)
Highest effects are noticed to the northwestern areas where more than 30% of January, February and March precipitation depends on this Weather Types (WTs), even if its influence spreads even along the western part of the Pyrenees (Figure 1)
In a recent paper focused on WTs at general scale of the Iberian Peninsula (IP), Cortesi et al (2013a) stated that the number of WTs that contribute to monthly precipitation decreases from western areas to eastern Mediterranean fringe
Summary
Rainfall variability is a well know characteristic of Mediterranean climate, and it has been well studied around Mediterranean Basin at the monthly and seasonal scales (Corte-Real et al, 1995; Kutiel et al, 1996; Xoplaki et al, 2004; Paredes et al, 2006). This is due to the very high summer NE frequencies, that distributes the small NE rainfall amount in a large number of COMBINED ANALYSIS OF PRECIPITATION INDICES we perform a combined analysis of the three most innovative precipitation indices (Precipitation Intensity, Precipitation Efficiency, and Area of Influence) In this way, we can identify visually in appropriate scatter-plots the nature of these relationships (e.g., linear vs non-linear, level of dispersion, etc.) and how such links vary with WTs. In this way, we can identify visually in appropriate scatter-plots the nature of these relationships (e.g., linear vs non-linear, level of dispersion, etc.) and how such links vary with WTs In these representations (Figures 8–10) each point represents a single WT during a specific month, there is a total of 312 values (26 × 12 = 312 points).
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