Flood frequency analysis of historical flood data under stationary and non-stationary modelling

Abstract

Historical records are an important source of information
 on extreme and rare floods and fundamental to establish
 a reliable flood return frequency. The use of long historical
 records for flood frequency analysis brings in the question
 of flood stationarity, since climatic and land-use conditions
 can affect the relevance of past flooding as a predictor
 of future flooding. In this paper, a detailed 400 yr flood
 record from the Tagus River in Aranjuez (central Spain)
 was analysed under stationary and non-stationary flood frequency
 approaches, to assess their contribution within hazard
 studies. Historical flood records in Aranjuez were obtained
 from documents (Proceedings of the City Council, diaries,
 chronicles, memoirs, etc.), epigraphic marks, and indirect
 historical sources and reports. The water levels associated
 with different floods (derived from descriptions or
 epigraphic marks) were computed into discharge values using
 a one-dimensional hydraulic model. Secular variations
 in flood magnitude and frequency, found to respond to climate
 and environmental drivers, showed a good correlation
 between high values of historical flood discharges and a negative
 mode of the North Atlantic Oscillation (NAO) index.
 Over the systematic gauge record (1913–2008), an abrupt
 change on flood magnitude was produced in 1957 due to
 constructions of three major reservoirs in the Tagus headwaters
 (Bolarque, Entrepeñas and Buendia) controlling 80%
 of the watershed surface draining to Aranjuez. Two different
 models were used for the flood frequency analysis: (a)
 a stationary model estimating statistical distributions incorporating
 imprecise and categorical data based on maximum
 likelihood estimators, and (b) a time-varying model based on
 “generalized additive models for location, scale and shape”
 (GAMLSS) modelling, which incorporates external covariates
 related to climate variability (NAO index) and catchment
 hydrology factors (in this paper a reservoir index; RI). Flood
 frequency analysis using documentary data (plus gauged
 records) improved the estimates of the probabilities of rare
 floods (return intervals of 100 yr and higher). Under nonstationary
 modelling flood occurrence associated with an exceedance
 probability of 0.01 (i.e. return period of 100 yr)
 has changed over the last 500 yr due to decadal and multidecadal
 variability of the NAO. Yet, frequency analysis under
 stationary models was successful in providing an average
 discharge around which value flood quantiles

Spanish Ministry of Economy and Competitiveness research projects FLOODMED (CGL2008-06474-C02/BTE), SCARCECONSOLIDER (CSD2009-00065), CLARIES (CGL2011-29176) and PALEOMED (CGL2014-58127-C3-1-R)

CSIC PIE intramural project (201430E003).

Machado, M.; Botero, B.; López, J.; Francés, F.; Díez-Herrero, A.; Benito, G. (2015). Flood frequency analysis of historical flood data under stationary and non-stationary modelling. Hydrology and Earth System Sciences. 19(6):2561-2576. doi:10.5194/hess-19-2561-2015.

Senia

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