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

• Published in: Hydrology and Earth System Sciences
• Main Authors: Machado, María José, Botero, B. A., López, J., Francés, F., Díez Herrero, Andrés, Benito, Gerardo
• Format: Article in Journal/Newspaper
• Language: English
• Published: European Geosciences Union 2015
• Subjects: North Atlantic; North Atlantic oscillation
• Online Access: http://hdl.handle.net/10261/118196; https://doi.org/10.5194/hess-19-2561-2015

Received: 14 December 2014 – Published in Hydrol. Earth Syst. Sci. Discuss.: 14 January 2015 - Revised: 14 April 2015 – Accepted: 11 May 2015 – Published: 2 June 2015 Historical records are an important source of information about extreme and rare floods with a great value to establish a reliable flood return frequency. The use of long historic 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 year flood record from the Tagus River in Aranjuez (Central Spain) was analysed under stationary and non-stationary flood frequency approaches, to assess their implications on 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 on 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 index (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; (b) a time–varying model based on "generalized additive models for location, scale and shape" (GAMLSS) modelling, that incorporates external covariates related to ...