Preprint Article Version 2 This version is not peer-reviewed

Uncertainties in the Annual Cycle of Rainfall Characteristics over West Africa in CMIP5 Models

Version 1 : Received: 28 June 2019 / Approved: 1 July 2019 / Online: 1 July 2019 (11:24:35 CEST)
Version 2 : Received: 1 July 2019 / Approved: 3 July 2019 / Online: 3 July 2019 (09:44:32 CEST)

How to cite: Sow, M.; Diakhaté, M.; Guichard, F.; Dieng, D.; Gaye, A.T. Uncertainties in the Annual Cycle of Rainfall Characteristics over West Africa in CMIP5 Models. Preprints 2019, 2019070007 (doi: 10.20944/preprints201907.0007.v2). Sow, M.; Diakhaté, M.; Guichard, F.; Dieng, D.; Gaye, A.T. Uncertainties in the Annual Cycle of Rainfall Characteristics over West Africa in CMIP5 Models. Preprints 2019, 2019070007 (doi: 10.20944/preprints201907.0007.v2).

Abstract

This study analyses uncertainties associated with the annual cycle of West African rainfall characteristics in 15 simulations of the Coupled Model Intercomparison Project phase 5 (CMIP5) over the Sahel and Guinean regions. Indices based on daily rainfall such as the frequency and the ntensity of wet days, the consecutive dry days (CDD) and wet days (CWD), the 95th percentile of daily rainfall (R95) and its contribution to the umulative monsoon rainfall (R95PTOT) have been assessed. Over both regions, TRMM, GPCP and CHIRPS observational datasets provide very consistent results on the annual cycle of precipitation but less so on the frequency of wet days. Conversely, higher uncertainties are noted on the intensity of wet days over both study areas, particularly over the Guinean region. Overall, CMIP5 simulations present much higher uncertainties in the representation of the mean precipitation climatology, often provide too early (late) onset dates over the Sahel (the Guinean region) and overestimate rainfall during the early and late monsoon phases. These errors do not compensate at the annual scale nor when considering West Africa as a hole. Results also reveal that over the Guinean region, the difficulty of models to represent the annual structure of the mean precipitation strongly involves biases in the representation of the annual cycle of the frequency of wet days. We found strong uncertainties in the simulation of the CWD and he CDD over both areas. Conversely for R95 and R95PTOT, the ncertainties in CMIP5 models appear somewhat weaker, but the magnitude of R95 is largely underestimated in most models.

Subject Areas

West Africa; rainfall; annual cycle; CMIP5 models; onset; cessation; extremes; uncertainties

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