Larger Future Intensification of Rainfall in the West African Sahel in a Convection‐Permitting Model

Berthou, Ségolène; Kendon, Elizabeth J.; Rowell, David P.; Roberts, Malcolm; Tucker, Simon; Stratton, Rachel

doi:10.1029/2019gl083544

Cited by 37 publications

(35 citation statements)

References 57 publications

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“…Hence, we suggest that over the Sahel, precipitation intensity may increase more than projected in our study, as result of the increasing meridional temperature gradient between the Sahel and the Sahara. For instance, Berthou et al (2019) have shown that over the West Sahel, future changes in extreme rainfall increase by a factor 5 to 10 at 4.5 km resolution (convection-permitting model allowing a good representation of MCSs), as compared to a factor 2 to 3 at 25 km resolution. Similarly, the impacts of atmospheric aerosols, particularly abundant over West Africa due to seasonal desert dusts (Konare et al, 2008;N'Datchoh Touré et al, 2018), are only partially accounted for in CORDEX-Africa due to the simplified parameterization schemes for aerosols in this dataset.…”

Section: Discussionmentioning

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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Section: Discussionmentioning

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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“…Soil moisture feedbacks on length scales approximately hundreds of kilometers may amplify that external forcing. Similar land feedbacks could amplify storms associated with a moister, future atmosphere, which is already more prone to explosive convection, and contribute to strong increases in intense rainfall and dry spells (34). Thus, soil moisture feedback may provide a mechanism that translates global warming into a more extreme Sahelian hydroclimate.…”

Section: Discussionmentioning

confidence: 99%

Dry soils can intensify mesoscale convective systems

Klein

Taylor

2020

Proc. Natl. Acad. Sci. U.S.A.

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Soil moisture can feed back on rainfall through the impact of surface fluxes on the environment in which convection develops. The vast majority of previous research has focused on the initiation of convection, but in many regions of the world, the majority of rain comes from remotely triggered mesoscale convective systems (MCSs). Here we conduct a systematic observational analysis of soil moisture feedbacks on propagating MCSs anywhere in the world and show a strong positive impact of drier soils on convection within mature MCSs. From thousands of storms captured in satellite imagery over the Sahel, we find that convective cores within MCSs are favored on the downstream side of dry patches ≥200 km across. The effect is particularly strong during the afternoon–evening transition when convection reaches its diurnal peak in intensity and frequency, with dry soils accounting for an additional one in five convective cores. Dry soil patterns intensify MCSs through a combination of convergence, increased instability, and wind shear, all factors that strengthen organized convection. These favorable conditions tend to occur in the vicinity of a surface-induced anomalous displacement of the Sahelian dry line/intertropical discontinuity, suggesting a strong link between dry line dynamics and soil moisture state. Our results have important implications for nowcasting of severe weather in the Sahel and potentially in other MCS hotspot regions of the world.

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“…The code used for the analyses presented in this manuscript is developed by Berthou et al (2019) 1971-2005 1971-2005 1971-2005 1971-2003 1971-2005 1971-2005 Table 3: Information about the observational datasets used in this study (refer to Fig S1 for the coverage). The time period concerns that considered in this study, not the available period of each observational datasets.…”

Section: Code Availabilitymentioning

confidence: 99%

“…We calculate the daily precipitation distribution in terms of the actual contribution from 100 different intensity bins to mean precipitation. In order to account for the high frequency of low intensity precipitation events and the low frequency of high intensity events, we use an exponential bin distribution, as described by Berthou et al, 2019 (see their Fig. S5).…”

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confidence: 99%

“…Computation of p-values. P-values are computed following Berthou et al (2019) and Kendon et al (2019). P-values are estimated for each bin as follows: 1) for each bin, the difference in precipitation contribution is calculated 1000 times using a bootstrap resampling (performed on the ensemble for the models, and the inter-annual variability for the observations); 2) the mean of the bootstrapped metric is computed, and subtracted from each 1000 bootstrap estimates; this creates 1000 zero-275 centred metrics and gives us an estimate of the probability distribution of the test statistic under the null hypothesis that the two ensembles are the same; 3) the original metric is then compared with this null distribution, and the p-value is estimated based on which quantile the original metric corresponds to relative to the null distribution.…”

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confidence: 99%

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Can high-resolution GCMs reach the level of information provided by 12–50 km CORDEX RCMs in terms of daily precipitation distribution?

Demory¹,

Berthou

Sørland³

et al. 2020

Preprint

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In this study, we perform an evaluation of PRIMAVERA high-resolution (25-50 km) Global Climate Models (GCMs) relative to CORDEX Regional Climate Models (RCMs) over Europe (12-50 km resolutions). It is the first time such assessment is performed for regional climate information using ensembles of GCMs and RCMs at similar horizontal resolutions. We perform this exercise for the distribution of daily precipitation contributions to rainfall bins over Europe 25 under current climate conditions. Both ensembles are evaluated against high quality national gridded observations in terms of resolution and station density. We show that PRIMAVERA GCMs simulate very similar distribution to CORDEX RCMs that CMIP5 cannot because of their coarse resolutions. PRIMAVERA and CORDEX ensembles generally show similar strengths and weaknesses. They are of good quality in summer and autumn in most European regions, but tend to overestimate precipitation in winter and spring. PRIMAVERA show improvements in the latter bias by reducing mid-rain 30 rate biases in Central and Eastern Europe. Moreover, CORDEX simulate less light rainfall than PRIMAVERA in most regions and seasons, which improves this common GCM bias. Finally, PRIMAVERA simulate less heavy precipitation than CORDEX in most regions and seasons, especially in summer. PRIMAVERA appear to be closer to observations. However, when we apply an averaged precipitation undercatch error of 20%, CORDEX become closer to these synthetic datasets.Considering 50 km resolution GCM or RCM datasets over Europe results in large benefits compared to CMIP5 models for 35 impact studies at the regional scale. The effect of increasing resolution from 50 km to 12 km in CORDEX simulations is, in comparison, small in most regions and seasons outside mountainous regions (due to the importance of orography) and coastal regions (mostly depending on the resolution of the land-sea contrast). Now that GCMs are able to reach the level of information provided by CORDEX RCMs run at similar resolutions, there is an opportunity to better coordinate GCM and RCM simulations for future model intercomparison projects. 1 IntroductionClimate models are essential tools to provide information on the evolution of climate quantities, their variability and interactions with various components of the Earth System. There have been two main streams of development in the climate modelling community: Global Climate Models (GCMs) and Regional Climate Models (RCMs). GCMs are complex models that account for interactions at the global scale between various components of the Earth System (e.g. atmosphere, ocean, sea 45 ice, vegetation). They are designed to balance model resolution, physics complexity and computational requirements, and are therefore commonly run at coarse spatial resolution. RCMs are complex models that dynamically downscale GCM results to obtain fine climate information at the regional scale. The main advantages of the dynamical downscaling approach are that: 1) RCMs are computationally cheaper and use a higher horizo...

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Larger Future Intensification of Rainfall in the West African Sahel in a Convection‐Permitting Model

Cited by 37 publications

References 57 publications

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

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

Dry soils can intensify mesoscale convective systems

Can high-resolution GCMs reach the level of information provided by 12–50 km CORDEX RCMs in terms of daily precipitation distribution?

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