West African Summer Monsoon Precipitation Variability as Represented by Reanalysis Datasets

Abstract

Focusing on West Africa, a region riddled with in situ data scarcity, we evaluate the summer monsoon monthly rainfall characteristics of five global reanalysis datasets: ERA5, ERA-Interim, JRA-55, MERRA2, and NCEP-R2. Their performance in reproducing the West African monsoon (WAM) climatology, interannual variability, and long-term trends for the main monsoon months are compared to gauge-only and satellite products. We further examine their ability to reproduce teleconnections between sea surface temperatures and monsoon rainfall. All reanalyses are able to represent the average rainfall patterns and seasonal cycle; however, regional biases can be marked. ERA5, ERA-Interim, and NCEP-R2 underestimate rainfall over areas of peak rainfall, with ERA5 showing the strongest underestimation, particularly over the Guinea Highlands. The meridional northward extent of the monsoon rainband is well captured by JRA-55 and MERRA2 but is too narrow in ERA-Interim, for which rainfall stays close to the Guinea Coast. Differences in rainband displacement become particularly evident when comparing strong El Niño Southern Oscillation (ENSO) years, where all reanalyses except ERA-Interim reproduce wetter Sahelian conditions for La Niña, while overestimating dry conditions at the coast except for NCEP-R2. Precipitation trends are not coherent across reanalyses and magnitudes are generally overestimated compared to observations, with only JRA-55 and NCEP-R2 displaying the expected positive trend in the Sahel. ERA5 generally outperforms ERA-Interim, highlighting clear improvements over its predecessor. Ultimately, we find the strengths of reanalyses to strongly vary across the region.

Performance evaluation of reanalysis precipitation products in Egypt using fuzzy entropy time series similarity analysis

“…No study has been conducted so far to evaluate the performance of reanalysis GPDs in Egypt. A few studies have been undertaken to assess reanalysis GPDs in West Africa and nearby regions (Nkiaka et al ., 2017; Sahlu et al ., 2017; Dembélé et al ., 2020; Quagraine et al ., 2020). Dembélé et al .…”

“…Quagraine et al . (2020) evaluated five reanalyses GPDs, ERA5, ERA‐Interim, JRA‐55, MERRA2, and NCEP‐R2 in replicating the West African monsoon. They also reported different performance of different GPDs in reproducing different monsoon characteristics.…”

Evaluation of Areal Monthly Average Precipitation Estimates from MERRA2 and ERA5 Reanalysis in a Colombian Caribbean Basin

“…MERRA2 uses the Goddard Earth Observing System Version 5 (GOES-5). Similarly to its predecessor (MERRA), the reanalysis model focuses on conducting a historic climate analysis, providing estimations based on numerous satellite observa-tions, general circulation models, and ground measurements from hydrometeorological stations across the globe to parameterize initial conditions [35,41]. Other improvements compared to MERRA include the assimilation of aerosol observations-a more accurate representation of the stratosphere, water cycle, and cryospheric processes-and minimizing biases and the occurrence of falsely detected trends [55].…”

“…ERA5 estimations are based on the Integrated Forecasting System (IFS) Cycle 41r2, and this reanalysis incorporates new input variables, such as sea surface temperature, sea ice, and aerosols, aiming at making it appropriate for climate simulation. The ERA5 data is freely available on the ECMWF website [33], with precipitation estimates from 1979 onwards, although for some meteorological variables the dataset provides information for the period since 1950 [35,56]. ERA5 has a maximum temporal resolution of one hour and a 0.25 • × 0.25 • spatial resolution [16].…”

“…The choice of the dataset was based on this paper's corresponding authors' research interests and previous publications [19,21,[30][31][32], including the ERA5 reanalysis from the European Center for Medium-Range Weather Forecasts (ECMWF) [33], and the Modern-Era Retrospective Analysis for Research and Applications, Version (MERRA2), with the latter being produced by NASA's Global Modeling and Assimilation Office (GMAO) [34]. Other authors have also simultaneously included MERRA2 and ERA5 in performance evaluations of indirect rainfall estimations in similar studies across the world [35][36][37][38].…”