What can we know about future precipitation in Africa? Robustness, significance and added value of projections from a large ensemble of regional climate models

Dosio, Alessandro; Jones, Richard G.; Jack, Christopher; Lennard, Christopher; Nikulin, Grigory; Hewitson, Bruce

doi:10.1007/s00382-019-04900-3

Cited by 171 publications

(162 citation statements)

References 89 publications

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“…The analysis also showed how these rainfall types project geographically on southern West Africa, enabling a better knowledge of the mechanisms attached to intense rainfall events in the various parts of the region. While projections for West Africa found contrasted future trends in AEWs frequency [58,59] and an increase of rainfall intensity [40,60], more focused high-resolution studies need to be carried out for the coastal area in view of its specificity in terms of rainfall intensity.…”

Section: Summary and Discussionmentioning

confidence: 99%

Classification of Intense Rainfall Days in Southern West Africa and Associated Atmospheric Circulation

2020

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Daily rainfall in southern West Africa (4-8 • N, 7 • W-3 • E) is analyzed with the aim of documenting the intense rainfall events which occur in coastal Ivory Coast, Ghana, Togo, and Benin. The daily 99th percentile (P99) shows that the coastline experiences higher intensity rainfall than inland areas. Using Tropical Rainfall Measuring Mission (TRMM) rainfall data for 1998-2014, a novel way of classifying the intense events is proposed. We consider their space-time structure over a window of 8 • latitude-longitude and five days centered on the event. A total 39,680 events (62 at each location) are classified into three major types, mainly found over the oceanic regions south of 5 • N, the Bight of Benin, and the inland regions respectively. These types display quite distinct rainfall patterns, propagation features, and seasonal occurrence. Three inland subtypes are also defined. The atmospheric circulation anomalies associated with each type are examined from ERA-interim reanalysis data. Intense rainfall events over the continent are mainly a result of westward propagating disturbances. Over the Gulf of Guinea, many intense events occur as a combination of atmospheric disturbances propagating westward (mid-tropospheric easterly waves or cyclonic vortices) and eastward (lower tropospheric zonal wind and moisture anomalies hypothesized to reflect Kelvin waves). Along the coast, there is a mixture of different types of rainfall events, often associated with interacting eastward-and westward-moving disturbances, which complicates the monitoring of heavy precipitation.

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Section: Summary and Discussionmentioning

confidence: 99%

Classification of Intense Rainfall Days in Southern West Africa and Associated Atmospheric Circulation

2020

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“…We focus on annual values over the period 2006-2099. Following previous studies (Froidurot and Diedhiou, 2017;Bichet and Diedhiou, 2018a, b), we define a wet (dry) day using the threshold of 1 mm d −1 . We define a dry spell as a sequence of 2 or more consecutive dry days that are preceded and followed by a wet day.…”

Section: Methodsmentioning

confidence: 99%

Intensification of the hydrological cycle expected in West Africa over the 21st century

Todzo¹,

Bichet

Diedhiou

2020

Earth Syst. Dynam.

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Abstract. This study uses the high-resolution outputs of the recent CORDEX-Africa climate projections to investigate the future changes in different aspects of the hydrological cycle over West Africa. Over the twenty-first century, temperatures in West Africa are expected to increase at a faster rate (+0.5 ∘C per decade) than the global average (+0.3 ∘C per decade), and mean precipitation is expected to increase over the Guinea Coast (+0.03 mm d−1 per decade) but decrease over the Sahel (−0.005 mm d−1 per decade). In addition, precipitation is expected to become more intense (+0.2 mm d−1 per decade) and less frequent (−1.5 d per decade) over all of West Africa as a result of increasing regional temperature (precipitation intensity increases on average by +0.35 mm d−1 ∘C−1 and precipitation frequency decreases on average by −2.2 d ∘C−1). Over the Sahel, the average length of dry spells is also expected to increase with temperature (+4 % d ∘C−1), which increases the likelihood for droughts with warming in this subregion. Hence, the hydrological cycle is expected to increase throughout the twenty-first century over all of West Africa, on average by +11 % ∘C−1 over the Sahel as a result of increasing precipitation intensity and lengthening of dry spells, and on average by +3 % ∘C−1 over the Guinea Coast as a result of increasing precipitation intensity only.

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“…So far, CORDEX activities have resulted in many improvements to simulate the present day climate with high resolution climate models set up for many regions of the world (e.g. Adloff et al 2017;Akhtar et al 2017;Choudhary and Dimri 2017;Ho-Hagemann et al 2017;Poan et al 2017;Dosio et al 2019;Primo et al 2019). More recent CORDEX activities likewise addressed the problem of future climate change by downscaling available global climate simulations from the Coupled Model Intercomparison Project (CMIP).…”

Section: Introductionmentioning

confidence: 99%

Is interactive air sea coupling relevant for simulating the future climate of Europe?

2020

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The majority of regional climate change assessments for the Euro-CORDEX region is based on high resolution atmosphere models. These models use prescribed lower boundary conditions, such as sea surface temperatures (SST) from global ocean General Circulation Models (GCMs), that do not respond to changes simulated by the regional atmosphere model, thus lacking an important feedback to the atmosphere. However, research during the past decade indicated that the use of coupled atmosphere–ocean models can lead to significantly altered model solutions compared to standalone atmosphere models for the present day climate imposing some uncertainty on the widely used uncoupled future scenarios. We here present the first multi-model and multi scenario (RCP2.6, RCP4.5, RCP8.5) ensemble of future climate change scenarios downscaled with a coupled atmosphere—ocean model in which sea surface temperature and sea ice fields are explicitly simulated by a coupled state-of-the-art high resolution ocean model and communicated to the atmosphere at 3-hourly time steps. Our ensemble generally confirms results of previous uncoupled ensembles over land areas implying that the coupling effect is restricted mainly to the coupled area and the adjacent coastal zone. By contrast, over the North Sea and Baltic Sea small scale processes point to important coupling effects that mediate the response to climate change and that can not be simulated by uncoupled models. Our results therefore impose general uncertainty on the usage of regional climate change data from uncoupled ensembles over marine areas such as for purposes of offshore wind or mussel farming, the planing of marine protected areas, and marine recreation along the coastal zone. It further sets in question the usage of uncoupled scenario data (such as Euro-CORDEX) to force high resolution ocean models. Comparing coupled and uncoupled hindcast simulations reveals that the coupling effect over land is most pronounced during the warm season when prescribed and modelled sea surface temperatures (SST) differ strongest. In addition, a generally weaker wind regime in summer damps the heat dispersion in the atmosphere so that air temperature anomalies can extent further over land compared to winter. Future projections are discussed under consideration of land-sea warming characteristics for selected climate indices as well as mean seasonal climate change. At the end of the century a clear land-sea pattern is seen in all scenarios with stronger warming over land than over open sea areas. On average land areas warm at a rate 1.5 times faster than areas over the open ocean. Over the coupled area, i.e. the North Sea and Baltic Sea tropical nights are impacted strongest and the Baltic Sea turns out to be a hot spot in future climate. This has been unrecognized in previous studies using high resolution atmosphere models with prescribed SSTs from global models which do not represent small scale ocean processes in the Baltic Sea adequately.

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What can we know about future precipitation in Africa? Robustness, significance and added value of projections from a large ensemble of regional climate models

Cited by 171 publications

References 89 publications

Classification of Intense Rainfall Days in Southern West Africa and Associated Atmospheric Circulation

Classification of Intense Rainfall Days in Southern West Africa and Associated Atmospheric Circulation

Intensification of the hydrological cycle expected in West Africa over the 21st century

Is interactive air sea coupling relevant for simulating the future climate of Europe?

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