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| Titel |
Universal Multifractal description of a daily rainfall time series from Ebro River Watershed |
| VerfasserIn |
J. L. Valencia, A. M. Tarquis, J. M. Gascó, A. Saa |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250029196
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| Zusammenfassung |
| The Ebro River is very important in Spanish water policy. There are different water transfer
projects to other regions. It’s important to know the characteristics of rainfall in the watershed
before developing models river flows. This help us to understand the relationships
between rainfall and runoff and predict the results that produce the plans over the
basin.
The objective of the present work is to validate the daily rainfall data generated by a
regional climate model by using multifractal analysis. This will allow us to determine what
extent there are singular variations in a region rainfall and so contribute to a better
understanding of the variability of precipitation in the Ebro River watershed.
An important aspect of this study consists in the unusual fact of considering a complete
river watershed, so that we examine 265 rain gauges in an area that contains around 85000
km2. Daily rainfall was recorded over a period of almost 23 years (1980-2002). The west of
the region the climate is oceanic. As we advance towards the east the climate becomes
progressively Mediterranean.
We calculate the Lovejoy multifractal parameters:α, C1 and H by DDT analysis technique
based on multiscaling properties of the intermittent fluxes of daily rainfall. The mean values
for the parameters are:
α = 0.72 (0.10) C1 = 0.23 (0.05) H = - 0.14 (0.05)
where the value in brackets is the standard deviation
We study the evolution about the Lovejoy Universal Parameters in this region, and we
conclude that the multifractality increases as the climate is turning more Mediterranean.
Nevertheless the Universal parameters values can be modified by the altitude and conditions
of water retention in endorheic regions.
We can establish a power law between multifractality parameter C1 and mean rainfall for
this region and we compare this result with another ones obtained by Labat, Tessier and
Garcia-Marin.
We study the “fingerprint” a, b for time-series suggest by Kantelhardt and Koscienly.
They are extracted from the extended multiplicative cascade model and must verify the
relationship with the generalized Hurst exponent:
q q
h(q) = 1 - ln(a-+-b) + ln(a+-b)-
q qln(2) ln(2)
Clasical spectral analysis S(f) = f-βof the all time series were calculated. In nearly all
station there are two principal peaks: one at 6 months and one year. Only the rain gauges with
high multifractality don’t follow this pattern of behaviour. They have most peaks and they
don’ present a big peak at one year.
In resume for lower frequencies, β -0 is found. The break detected in the periodograms
for approximately f - 0.40. It corresponds with a period of 16 days like other studies (Labat
et al. 2002, Tessier et al. 1996). They are essentially the “synoptic maximum” found
when performing the analysis of the exponential function of the empirical moments
scaling.
Finally we obtain a clustering for the rain gauges with the universal parameters and for
extension we divided the Ebro River watershed in degree of multifractality, intermittency and
persistency of multifractal model. |
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