Abstract
Abstract. A general consensus on the concept of rainfall intermittency has not yet been reached, and intermittency is often attributed to different aspects of rainfall variability, including the fragmentation of the rainfall support (i.e., the alternation of wet and dry intervals) and the strength of intensity fluctuations and bursts. To explore these different aspects, a systematic analysis of rainfall intermittency properties in the time domain is presented using high-resolution (1-min) data recorded by a network of 201 tipping-bucket gauges covering the entire island of Sardinia (Italy). Four techniques, including spectral and scale invariance analysis, and computation of clustering and intermittency exponents, are applied to quantify the contribution of the alternation of dry and wet intervals (i.e., the rainfall support fragmentation), and the fluctuations of intensity amplitudes, to the overall intermittency of the rainfall process. The presence of three ranges of scaling regimes between 1 min to ~ 45 days is first demonstrated. In accordance with past studies, these regimes can be associated with a range dominated by single storms, a regime typical of frontal systems, and a transition zone. The positions of the breaking points separating these regimes change with the applied technique, suggesting that different tools explain different aspects of rainfall variability. Results indicate that the intermittency properties of rainfall support are fairly similar across the island, while metrics related to rainfall intensity fluctuations are characterized by significant spatial variability, implying that the local climate has a significant effect on the amplitude of rainfall fluctuations and minimal influence on the process of rainfall occurrence. In addition, for each analysis tool, evidence is shown of spatial patterns of the scaling exponents computed in the range of frontal systems. These patterns resemble the main pluviometric regimes observed on the island and, thus, can be associated with the corresponding synoptic circulation patterns. Last but not least, we demonstrate how the methodology adopted to sample the rainfall signal from the records of the tipping instants can significantly affect the intermittency analysis, especially at smaller scales. The multifractal scale invariance analysis is the only tool that is insensitive to the sampling approach. Results of this work may be useful to improve the calibration of stochastic algorithms used to downscale coarse rainfall predictions of climate and weather forecasting models, as well as the parameterization of intensity-duration-frequency curves, adopted for land planning and design of civil infrastructures.
Highlights
Results are presented for the series built with the CC method: in Sect. 5.1, we show evidence of scaling regimes as emerged by applying each of the four metrics; in Sect. 5.2, we analyze and compare the intermittency properties of rainfall intensity and support, while in Sect. 5.3 we discuss the existence of spatial patterns for the metrics on the island and of linkages with topography and weather patterns
We conducted a systematic study aimed at characterizing different aspects related to the nature of rainfall intermittency through the analysis of high-resolution (1-min) data recorded by a network of 201 tipping-bucket gauges covering the entire island of Sardinia (Italy)
Periods and (ii) the fluctuations of rainfall intensity amplitudes. Each of these tools involves the investigation of a scaling law and the computation of a scaling exponent, which was used as a metric to quantify the different aspects of rainfall intermittency
Summary
The investigation of rainfall statistical variability is of paramount importance given the central role of this geophysical variable in a wide range of disciplines, including hydrology (Georgakakos and Kavvas, 1987; Dingman, 2008), meteorology (Huffman et al, 1997; Trenberth et al, 2003), hydrometeorology (Seo et al, 2000; Langousis and Veneziano, 2009a,b; Cuo et al, 2011), ecology (Eagleson, 2002), and agronomy (Moonen et al, 2002). The increasing availability of large records of highresolution (up to few tens of seconds) point measurements provided by automatic rain gauges and, in some recent experiments, by disdrometers has allowed the study of intermittency properties in the time domain within a wide range of scales For this purpose, techniques originally adopted to examine scalar turbulence have been used, including spectral analysis (Rebora et al, 2006), investigation of scale invariance and multifractality (Veneziano et al, 2006, and references therein), and wavelet-based methods (Venugopal et al, 2006). These authors used data observed by five rain gauges located in different climates and found that the scaling and intermittency properties have distinct features across gauges (i.e., climatic conditions), whereas the support variability has similar characteristics
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