Climate simulation over CORDEX Africa domain using

Authors: Leticia HernándezDíaz René Laprise Laxmi Sushama Andrey Martynov Katja Winger Bernard Dugas

Publish Date: 2012/05/27

Volume: 40, Issue: 5-6, Pages: 1415-1433

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Abstract

The new fifthgeneration Regional Climate Model CRCM5 was driven by ERA reanalyses for the period 1984–2008 over the African continent following the CORDEX experimental protocol Overall the model succeeds in reproducing the main features of the geographical distribution and seasonal cycle of temperature and precipitation the diurnal cycle of precipitation and the West African Monsoon WAM Biases in surface temperature and precipitation are discussed in relation with some circulation defects noted in the simulation In the African regions near the equator the model successfully reproduces the double peak of rainfall due to the double passage of the tropical rainbelt although it better simulates the magnitude and timing of the second peak of precipitation CRCM5 captures the timing of the monsoon onset for the Sahel region but underestimates the magnitude of precipitation The simulated diurnal cycle is quite well simulated for all of the regions but is always somewhat in advance for the timing of rainfall peak In boreal summer the CRCM5 simulation exhibits a weak cold bias over the Sahara and the maximum temperature is located too far south resulting in a southward bias in the position of the Saharan Heat Low The region of maximum ascent in the deep meridional circulation of the Hadley cell is well located in the CRCM5 simulation but it is somewhat too narrow The core of the African Easterly Jet is of the right strength and almost at the right height but it is displayed slightly southward as a consequence of the southward bias in the position of the Saharan Heat Low and the thermal wind relationship These biases appear to be germane to the WAM rainfall band being narrower and not moving far enough northward resulting in a dry bias in the SahelIn recent years there has been a surge of international interest in the study of the Africa’s climate and in particular the mechanisms explaining the geographic distribution and time variability of rainfall This is understandable as Africa is not only an exceptionally vulnerable region to climate change “because of the range of predicted impacts and low adaptive capacity” IPCC AR4 2007 but also to current levels of weather variability In particular semiarid regions such as the Sahel are heavily dependent on seasonal rainfall Severe droughts in this region have led to famine and deaths in the 1970s and 1980s Druyan 2010 More recently a severe drought led to a humanitarian crisis affecting 13 million people in the Horn of Africa region wwwredcrossca Last but not the least it has became clear from the IPCC AR4 2007 that climate models have difficulties in simulating key elements of present day climate for this continent and hence there is a need to further the understanding of the multiple interactions between the components of the African climate in order to improve climate simulations and projections for this region of the worldOne major element of the African climate is the West African Monsoon WAM for which substantial data collection and modelling efforts have been deployed since the African Multidisciplinary Monsoon Analysis AMMA project Redelsperger et al 2006 to name but a few the AMMA Model Intercomparison Project AMMAMIP Hourdin et al 2010 the AMMA landsurface Model Intercomparison Project ALMIP Boone et al 2009 the AMMA “Couplage de l’Atmosphère Tropicale et du Cycle Hydrologique” AMMACATCH project Lebel et al 2009 the West African Monsoon Modelling and Evaluation WAMME project Xue et al 2010 Druyan et al 2010 and the Ensemblesbased Predictions of Climate Change and their Impacts ENSEMBLES African project Paeth et al 2011It is thus not surprisingly that only in the last 2 years six Journals have dedicated Special Issues to different aspects of the WAM system Climate Dynamics 2010—West African Climate Journal of Hydrology 2009—Surface processes and water cycle in West Africa studied from the AMMAobserving system International Journal of Climatology 2009—African Climate and Applications Quarterly Journal of the Royal Meteorological Society 2010—Advances in understanding atmospheric processes over West Africa through the AMMA field campaign Weather and Forecasting 2010—West African weather prediction and predictability Journal of the Atmospheric Sciences 2010—Tropical Cloud Systems and Processes TCSP NASA African Monsoon Multidisciplinary Analyses NAMMA campaignAfrica is also the first target region of the COordinated Regional Climate Downscaling EXperiment CORDEX Giorgi et al 2009 http//cordexdmidk/joomla/ an initiative of the World Climate Research Programme WCRP http//wwwwcrpclimateorg/ aiming at regional climate modelling evaluation and improvement CORDEX also provides an opportunity to test the model outside its native region as strongly recommended by the GEWEX Transferability Working Group TWG http//rcmlabagroniastateedu/twg/regionalhtml and InterContinental Scale Experiments CSE transferability Study ICTS http//wwwclmcommunityeu/indexphpmenuid=1reporeid=25 Takle et al 2007The diversity of climate regimes over Africa covering tropical and midlatitudes in both hemispheres represents a considerable challenge for climate models IPCC AR4 2007 A recent analysis of simulated precipitation climatology from the first set of CORDEXAfrica ensemble simulations can be found in a recent paper by Nikulin et al 2012It is in this context that the new fifthgeneration Canadian Regional Climate Model CRCM5 has been applied to CORDEXAfrica which appears a good opportunity to study the model performance in simulating the key elements of the African climate including the WAM The aim of this paper is to describe CRCM5 and to show its skill in simulating present climate over a domain outside its “native” region as recommended by the WCRP the CORDEXAfrica domain The main features of CRCM5 are described in Sect 2 Section 3 follows with a description of the configuration of the model simulations and the data used as reference and Sect 4 with the presentation and discussion of results including the annual and diurnal cycle of precipitation over the continent and the simulated WAM climatology Conclusions are given in Sect 5

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