Downscaling of current and future rainfall climatologies for southern Morocco. Part I: Downscaling method and current climatology

Abstract

Abstract:The use of a statistical-dynamical downscaling approach to obtain a high-resolution rainfall climatology for a subtropical region in southern Morocco is analysed. The statistical part of the downscaling uses Circulation Weather Types (CWTs) as a measure for near-surface wind fields calculated from sea-level pressure (SLP) data. The daily CWTs are correlated with daily rainfall data at three different climate stations in the region for the period 1978-1997 and systematic differences are discussed. Results are viewed for one extreme dry year (1984) and one extreme wet year (1989) to show the limits of purely statistical downscaling.Dynamical downscaling is realized for representative days to enable statistical-dynamical downscaling. Comparison of statistically-dynamically downscaled rainfall with measured rainfall for the year 2002 and climatological results show that the method is capable of capturing the relevant mechanisms triggering rainfall in the area. For extreme dry (wet) years, rainfall is overestimated (underestimated) by the method and errors might occur even for normal years. However, application to a climatology calculated for the period 1958-1997 via analysing daily SLP fields from NCEP Reanalyses gives satisfactory results. For sufficiently long periods, the method is well capable of producing a reliable high-resolution rainfall climatology. We will therefore apply the method to climate change simulations in part II of this paper.

Climate change impacts on extreme precipitation in Morocco

“…Several authors have shown the impact of the NAO index on precipitation in particular for the Atlantic part of Morocco (El Hamly and Sebbari, 1998;Knippertz et al, 2003, Huebener andKerschgens, 2007a). However Knippertz et al (2003) indicate a lower correlation with the NAO index in the Mediterranean region, more influenced by local mechanisms and by the Mediterranean cyclonic activity.…”

“…However, they observed a bad representation of the influence of mountainous areas in the GCM. Together with Huebener and Kerschgens (2007a), they recommended the use of downscaling approaches to better reproduce the climate of the center and southern parts of Morroco, highly influenced by orography. Driouech et al (2009) have shown the ability of the variable resolution ARPEGE climate model at a 50 km resolution to reproduce heavy rainfall and long dry periods in the center of Morocco.…”

Assessment and Comparison of TMPA Satellite Precipitation Products in Varying Climatic and Topographic Regimes in Morocco

“…The spatial and temporal precipitation distributions are affected by the Atlantic Ocean, the Mediterranean Sea, and the Sahara and Atlas Mountains [65]. Several studies demonstrated strong correlations between inter-annual precipitation variability and the North Atlantic Oscillation (NAO), the Atlantic Multi-Decadal Oscillation (AMO), and the El Niño-Southern Oscillation (ENSO) indices [65][66][67][68]. Therefore, both local and large-scale factors impact the precipitation that is characterized by a strong irregularity in time and space.…”

Climate Change Characterization in the Semi-Arid Abda Plain in Western Central Morocco.

“…Morocco by its geographical position dominated by the semi-arid bioclimatic zones (more than 85 % of cultivated areas) has shown signs of climate variability during the last decades (Huebener and Kerschgens, 2007). The extension of dry periods became a reality in this part of the globe.…”