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Universität zu Köln (2009)

Statistisch-dynamische Regionalisierung von Niederschlag und Evapotranspiration für den Hohen Atlas in Marokko

Piecha, Kristina

Titre : Statistisch-dynamische Regionalisierung von Niederschlag und Evapotranspiration für den Hohen Atlas in Marokko

Auteur : Piecha, Kristina

Université de soutenance : Universität zu Köln

Grade : Doktorgrade 2009

Résumé
With the mesoscale meteorological model FOOT3DK and a classification method for so-called Circulation Weather Types (CWTs), a statistical-dynamical downscaling of precipitation and evapotranspiration is accomplished for the Drâa valley south of the High Atlas in Morocco. With this, information on the behaviour of precipitation and evapotranspiration in a future period can be obtained. To this end, FOOT3DK is first of all adjusted to the simulation area. Additionally, the number of possible land use classes is enlarged to 17, and an extended map of soil types is implemented into the cadastre of FOOT3DK. Subsequently, the sensitivity of evapotranspiration with respect to different parameters is determined, and the results are included in the ensuing simulations. For the statistical-dynamical downscaling an objective classification of the ground-level flow in CWTs is conducted. The mean sea level pressure data required for this are taken from reanalysis- and model data. The model data are based on two different SRES scenarios - A1B and B1. In the following, representatives (i.e. simulations of 24-hour episodes) for the different CWTs are determined ; representatives with and representatives without rain in the investigation area are modelled. A validation is conducted for the year 2002 since measured data of various climate stations in the simulation area, in addition to the forcing data for FOOT3DK, are available for this year. The recombination of precipitation and evapotranspiration takes into account the frequency distribution of the various CWTs, as well as their probability to occur with and without rain. The resulting precipitation pattern exhibits a realistic distribution which is in good agreement with the measured precipitation. The difference between the total measured precipitation and the total recombined precipitation of the station-related grid meshes is merely 1.1 mm for 2002. The High Atlas and the adjacent mountains can be identified as precipitation borders. The decrease in precipitation from north to south is reproduced by the recombination, too. Also, the spatial distribution of evapotranspiration delivers results which appear realistic enough, but they are only evaluated with difficulty ; hardly any evaporation measurements are performed in this region, although evaporation is an important part of the hydrological cycle. Subsequently, the method is applied to a future time period for the SRES scenarios A1B and B1. Comparison of the CWT distribution of the reanalyses to the control period of the combined CWTs from 1970 to 1999 shows a good agreement. Firstly, changes in the frequency of occurence of the CWTs based on REMO between control and forcing period are determined. The classification of CWTs provides first indications for the precipitation tendencies to be expected, because significant changes arise in the frequency of the various CWTs. Secondly, the statistical-dynamical downscaling of precipitation and evapotranspiration is accomplished. A significant increase of up to 20 mm per year results for the precipitation in the north-eastern region of the Drâa catchment. In contrast, a significant decrease of precipitation is apparent in the north of the High Atlas for the investigated period (up to 30 mm less per year). Evapotranspiration decreases significantly in virtually the entire area. The results of the statistical-dynamical downscaling based on the SRES scenarios A1B and B1 suggest that there will be no major changes in the inflow of water in the Mansour Eddahbi, due to a slight increase in precipitation in the north-eastern region of the Drâa catchment until the middle of the century. If merely precipitation was taken into account, water availability would remain at a similar scale as today. Considering further criteria, a decrease is more probable.

Mots clés  : Statistisch-dynamische Regionalisierung , Marokko , Hoher Atlas , Niederschlag , Evapotranspiration — Statistical-dynamical downscaling , Morocco , High Atlas , Precipitation , Evapotranspiration

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