Precipitation over Northern Italy: A Description by Means of Principal component Analysis

148

Abstract:One of the key features of global climate change will be perturbations to the hydrological regime across Europe. To date, assessments of the impacts of future change have generally used results from only one climate model, thus underestimating the range of possible change projected by different climate models. Here, the skill of six regional climate models (RCMs) in reproducing the mean precipitation for the 1961-1990 period for six catchments across Europe is compared and their projections of changes in future precipitation are assessed. A simple drought index based on monthly precipitation anomalies is also described and used to assess the models. Considerable variation in model skill in reproducing monthly mean precipitation and drought statistics is observed, with model errors in the reproduction of drought events independent of those for the mean, suggesting that the models have difficulties in reproducing the observed persistence of low monthly rainfall totals. In broad terms, the models indicate decreases in summer and increases in winter precipitation across Europe. On the regional scales required for impacts analysis, considerable model uncertainty is demonstrated for future projections, particularly for drought frequency. Although increases in the frequency of long-duration droughts are identified for catchments in southern Europe, the magnitude of this change is not certain. In contrast, for a catchment in northern England, such events are likely to become less frequent. For shorter-duration droughts, future changes encompass the direction of change. For stakeholders in each of the regions, these changes and uncertainties pose different challenges for the management of water resources. For the scientific community, the challenge raised is how to incorporate this uncertainty in climate change projections in a way that allows those groups to make informed decisions based on model projections. It is suggested that probabilistic scenarios for specific hydrological impacts offer considerable potential to achieve this.

Section: Reproducing Observed Meansmentioning

confidence: 99%

Changes in European drought characteristics projected by the PRUDENCE regional climate models

Blenkinsop

Fowler

2007

148

“…With regard to the Mediterranean region, eigenvector studies were often applied to categorise the area into homogeneous fields in terms of a specific climatic variable (Goossens, 1985;Maheras, 1985;Serra et al, 1999). In other cases, they enabled the investigators to specify temperature and/or rainfall patterns (Cacciamani et al, 1994;Fernandez Mills, 1995;Romero et al, 1999), to analyse the Mediterranean rainfall distribution (Molteni et al, 1983), or to examine the large scale circulation over the Mediterranean and study their linkages to some climatic factor such as winter time precipitation (Quadrelli et al, 2001).…”

Section: Introductionmentioning

confidence: 97%

Comprehensive analysis of the climate variability in the eastern Mediterranean. Part I: map‐pattern classification

Κωστοπούλου

Jones

2007

Abstract:This paper provides an extended study of the dominant daily circulation patterns governing the climate variability in the eastern Mediterranean. The methodology adopted to determine the circulation patterns is based on combined analysis of the spatial and temporal variation of rotated principal components of sea-level pressure. A catalogue of characteristic seasonal composites is presented and discussed. It is found that, during winter and spring, large scale features situated in northern Europe affect the atmospheric circulation over the domain of study, whereas the Atlantic (Azores) anticyclone and the Asian Thermal Low define most of the observed circulation types in summer. In autumn, the area exhibits a rapid transition from the warm to cold season showing climatic features from both extreme seasons. Similarities between winter and spring/autumn patterns are detected and correlation analyses are employed between their spatial patterns to reveal that similar circulation patterns occur amongst the three seasons, which usually appear more pronounced during winter. Frequencies and trends of the proposed circulation types are examined for each season. A linear trend analysis for the overall period exhibits a significant increase in the anticyclonic types particularly in winter. With respect to the cyclonic types, statistically significant negative trends have been found in all seasons especially for types associated with depressional activity in central the Mediterranean.

“…Each principal component has a score for each place and represents an orthogonal pattern in the spatial domain (Molteni et al, 1983). Molteni et al (1983), Pandzic (1988), and Mallants and Feyen (1990) are examples of the large body of precipitation spatial analyses that use principal components methodology. In those studies, though the power of this method as a data reductor is evident, its difficulty and its deficiencies as an interpretational tool can be detected.…”

Section: Classification Of the Spatial Distribution Of Torrential Raimentioning

confidence: 95%

“…Alternatively, in a T-mode analysis (temporal), a series of temporal elements is correlated, each element being characterized by a group of observed values; frequently, as in our study, these values are spatially referenced. Each principal component has a score for each place and represents an orthogonal pattern in the spatial domain (Molteni et al, 1983). Molteni et al (1983), Pandzic (1988), and Mallants and Feyen (1990) are examples of the large body of precipitation spatial analyses that use principal components methodology.…”

Section: Classification Of the Spatial Distribution Of Torrential Raimentioning

confidence: 99%

Classification of daily rainfall patterns in a Mediterranean area with extreme intensity levels: the Valencia region

Peñarrocha

Estrela

Millán

2002

The objective of this paper is to identify the spatial distribution patterns of heavy rainfall in the Valencia region, Spain. Rainfall in this area reaches one of the highest intensity levels in the Mediterranean, with daily precipitation values above 800 mm. Although high intensities characterize the region's precipitation, there is a zone situated in the south of the Gulf of Valencia that registers exceptionally high daily precipitation intensities.Our spatial analysis is based on two different perspectives and methods. In the first, we studied the most important torrential rain events in the period 1971-95 and obtained a classification based on the geographical distribution of the daily precipitation maxima. In the second, we applied statistical techniques to classify the distribution patterns of torrential rain by using principal components analysis and cluster analysis. This analysis was conducted for the 1981-90 period. The results of both methodologies are similar and reflect the main characteristics and sub-types of the spatial distribution of the daily precipitation patterns. These spatial patterns are directly linked to the action of topographic factors in atmospheric situations of humid easterly flows.