Patterns of monthly rainfall shortage and excess in terms of the standardized precipitation index for Catalonia (NE Spain)

126

This paper analyses the spatial and temporal variability of winter droughts in a semi-arid geographic gradient in Northeast Spain, from the Pyrenees in the north to the Mediterranean coastland in the south. Droughts that occurred between 1952 and 1999 were analysed by means of the Standardised Precipitation Index (SPI). The influence of the weather-type frequency and of the general North Atlantic atmospheric circulation patterns was analysed. The results indicate that winter droughts show an important spatial variability in the study area, differentiating three well-defined patterns. These correspond to the Pyrenees, the centre of the Ebro Valley, and the Mediterranean coastland. General negative trends in winter SPI have been found, which are indicative of the increase in winter drought conditions in the study area. Nevertheless, important spatial differences have also been recorded. Dominant north-south gradients in the influence of weather types are shown. Moreover, the negative trends in winter-SPI values agree with the negative trend in the frequency of the weather types prone to cause precipitation, such as the C, SW and W weather types and the increase in the frequency of A weather types. Nevertheless, in the Mediterranean coastland, the positive trend in SPI values agrees with the increase in the frequency of weather types of the east (E, SE), which are prone to cause precipitation in this area. Interannual variations in the frequency of the different weather types have been highly determined by different general atmospheric circulation patterns, mainly the North Atlantic Oscillation (NAO). Nevertheless, the correlation between the time series of weather-type frequency and the winter SPI is higher than that found between the SPI and the NAO. Thus, although the interannual NAO variability explains a high percentage of the interannual differences in the frequency of different weather types, it is not sufficient to explain the spatial and temporal variability of droughts, which respond better to atmospheric variability at more detailed (synoptic) spatial scales.

Section: Drought Spatial and Temporal Patterns During The Winter Seasonmentioning

confidence: 89%

“…Components obtained were rotated (Varimax) to obtain more stable patterns, maintaining the orthogonal structure of components (Richman, 1986). Because the SPI is a standardised variable, the components obtained can be identified as the regional SPI of a representative region (Lana et al, 2001).…”

Section: Analysis Of Drought Spatial and Temporal Patternsmentioning

confidence: 99%

The influence of atmospheric circulation at different spatial scales on winter drought variability through a semi‐arid climatic gradient in Northeast Spain

Vicente‐Serrano

López‐Moreno

2006

126

“…According to several authors (e.g. Hayes et al, 1999;Lana et al, 2001;Lloyd-Hughes and Saunders, 2002), the SPI presents the following advantages: (a) different monthly pluviometric regimes can be compared with a common pluviometric index; (b) it can be easily computed at annual or seasonal scales; and (c) it ensures that the frequencies of extreme events at any location and on any time scale are consistent.…”

Section: Methodsmentioning

confidence: 99%

“…Brunetti et al, 2002), and the standardized precipitation index (e.g. Delitala et al, 2000;Lana et al, 2001;Bordi et al, 2001;Lloyd-Hughes and Saunders, 2002). It emerges that the Mediterranean region has been affected by severe and more or less prolonged periods of drought in the last 50 years.…”

Section: Introductionmentioning

confidence: 99%

Trend analysis of precipitation and drought in Basilicata from 1923 to 2000 within a southern Italy context

Piccarreta

Capolongo

Boenzi

2004

145

Series of annual, monthly and seasonal precipitation from 50 stations, distributed all over the Basilicata territory (southern Italy), were studied for the period 1923-2000. All the series were checked for homogeneity using MASH v. 1.0.1 software and the time series analysis was performed with the Mann-Kendall nonparametric test in order to detect possible trends. The results show that the annual total rainfall decreased by about 156 mm during the period investigated; the decrease becomes stronger in the last 30 years. There are considerably different trends for the different seasons. In particular, only the winter trend, which is downward, is statistically significant. In this season the total rainfall has decreased by about 133 mm. For this same period the standardized precipitation index (SPI) for multiple time scales of 12, 24 and 48 months has been computed. It appears that periods of drought have been quite frequent starting from 1975, with SPI ranging from about −1 to about −3.

“…The homogeneity of the pluviometric series was analysed by means of the Von Neumann ratio test (Mitchell et al, 1966), which is applied to the residuals of monthly amounts in the way described by Lana et al (2001) for a similar pluviometric network. Figure 3 shows four examples for gauges 6, 16, 23 and 49, whose location is shown in Figure 2, and which were selected to represent the whole set of rain gauges because of their increasing distance from the Mediterranean Sea.…”

Section: Databasementioning

confidence: 99%

Spatial and temporal variability of the daily rainfall regime in Catalonia (northeastern Spain), 1950–2000

Lana

Martínez

Serra

et al. 2004

Self Cite

Spatial and temporal patterns in the daily rainfall regime of Catalonia (northeastern Spain) recorded for the 1950-2000 period are analysed from several points of view, including the irregularity of the time series in terms of entropy, the Mann-Kendall test for time trends, a principal component analysis (PCA), an average linkage (AL) clustering algorithm and, finally, a power spectrum analysis, which includes a comparison of white-noise and Markovian red-noise hypotheses. The analyses are based on three monthly variables derived from the amounts recorded on a daily basis: the average daily rainfall and the standard deviation of the daily rainfall for each month, together with the corresponding coefficient of variation. The joint spatial-temporal variability is manifested by the irregularity index, which is characterized by relevant values in all cases and gradients from the north (Pyrenees and Pre-Pyrenees mountain ranges) to the south (Ebro Valley) and to the Mediterranean coast. The interpretation of the factor scores derived from the PCA and of the clusters obtained from the AL algorithm also describes the complex spatial distribution of the daily rainfall regime, given that the effects of atmospheric circulation patterns on rainfall regimes are conditioned by the complex orography of Catalonia and its proximity to the Mediterranean Sea. The factor loadings associated with the PCA also suggest a distinction between hot, cold and mild seasons. Finally, it is worth noting that monthly series are usually accompanied by white background noise and, in a few cases, signs of Markovian behaviour and some significant periodicities, which are generally of less than 10 months and which change from one cluster to another.