Climate change effects on extreme precipitation in Morocco

1. Climate change effects on extreme precipitation in Morocco Yves Tramblay, Luc Neppel, Eric Servat HydroSciences Montpellier, UMR 5569 (CNRS-IRD-UM1-UM2), France Salah El Adlouni Institut National de Statistique Appliquée, Rabat, Maroc Département de Mathématique et Statistique, Université de Moncton, Canada Wafae Badi, Fatima Driouech Direction de la Météorologie Nationale, Centre National de Recherche Météorologique, Casablanca, Maroc

2. Objectives Morocco is often hot by intense rainfall events, causing human losses and economic damages (ex. Ourika, 1995, Rabat, Casablanca, Tanger, 2009) Goals of the study: 1- Evaluate the past trends in the observed extreme precipitation records and the dependences with circulation indexes (NAO, MO) 2- Evaluate the possible future trends with outputs of different Regional Climate Models (RCM) from the ENSEMBLE project (www.ensembles-eu.org)

3. 1- Datasets and methods

4. Meteorological stations Daily precipitation between 1960 and 2007

5. Global and Regional Climate Models • Higher spatial resolution = better description of orography • Responds in a physically consistent way to different forcings • Better reproduce extreme events than GCMs (Frei, 2006, Fowler, 2007) • Dependent on the boundary conditions imposed by the parent GCM • Requires advanced computing resources

6. Extreme value models Extreme Value Distribution (GEV) with 3 parameters (µ,α,κ): κ≠0 κ=0 Generalized Maximum Likelihood (GML) estimation method [Martins & Stedinger 2000], with a prior distribution for κ:

7. 2- Past trends

8. Winter (Sep-April) extreme precipitation No trends in the observed extreme precipitation (Mann-Kendall test at the 5% level)

9. Non-stationary GEV The GML approach has been adapted for the non-stationary context by [El Adlouni et al. 2009], with linear or quadratic dependences of the scale and location parameters The Deviance test, based on the likelihood, allows to compare a stationary model (m0) with a non-stationary model (m1): (D~ Chi² with ʋ degrees of freedom)

10. Stationary vs. Non-stationary models Dependance with winter NAO and MO for some stations

11. Non-stationary quantiles dependant on winter NAO

12. 3- Evaluation of RCM outputs

13. ENSEMBLE Regional climate models Daily precipitation between 1950 and 2100

14. Monthly distribution of precipitation 1961-2007 Wrong representation of seasonality for RCM driven by HadCM

15. Extreme precipitation distribution The distribution of observed extremes is compared with the distribution simulated by the different RCMs Similar distributions, but RCMs underestimate extreme precipitation

16. Cramér-von Mises test = Quadratic distance between two distributions (specified or not) The statistical significance of the differences can be computed by bootstrap

17. Cramér-von Mises (CM) statistic The CM statistic is computed between observed and RCM distributions Can provide weights to combine the different model outputs

18. 5- Future trends

19. Methodology 1961-2007 2020-2050 2070-2099 GEV fit GEV fit GEV fit Quantile Qo Quantile Qp1 Quantile Qp2 Scaling factor for 2020-2050 = Qp1 / Qo Scaling factor for 2070-2099 = Qp2 / Qo

20. Scaling factors on extreme quantiles

21. Multi-model averaged climate change signal Multi model ensemble: 1) Arithmetic mean of the scaling factors obtained with the different RCMs 2) Weighted mean of the scaling factors obtained with the different RCMs, weights = the inverse of the CM statistic

22. Conclusions No trend identified during the observation period. Dependences between precipitation extremes with NAO and MO indexes, in particular for the Atlantic stations Great variability in the RCM performances to reproduce the annual cycles and the extreme precipitation distributions. Some models have good skills, with simulated and observed extreme distributions not statistically different The climate change signal in the RCM simulations indicate a decrease in extreme precipitation in particular for the projection period 2070-2099, and a great variability and lower convergence between the models for the projection period 2020-2050 Good model convergence towards a decrease for the Atlantic stations. For the Mediterranean stations, the projected changes are difficult to assess due to the great variability. The two weighting schemes tested for model outputs provide similar results

23. Thanks for your attention Contact: ytramblay@gmail.com Reference : Tramblay, Y., Badi, W., Driouech, F., El Adlouni, S., Neppel, L., Servat, E., Global and Planetary Change, 2011, submitted