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Trends in Hydrological and Climate Extremes in Africa

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A special issue of Atmosphere (ISSN 2073-4433). This special issue belongs to the section "Climatology".

Deadline for manuscript submissions: closed (30 June 2020) | Viewed by 62589

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Dr. Arona Diedhiou

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Institute of Environmental Geosciences (IGE), Université Grenoble Alpes/National Research Institute for Sustainable Development (IRD), 38000 Grenoble, France
Interests: African climate system; hydroclimatic extremes and drivers; hydrometeorology, West African monsoon dynamics and teleconnections; atmospheric dynamic and climate change in the tropics
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Special Issue Information

Dear Colleagues,

Several programs such as START, CCAA, ClimDev-Africa and recent past/ongoing projects such as “Future Climate for Africa” in Southern, Eastern, and Western Africa, ACASIS, WASCAL, and SASSCAL in Western and Southern Africa, MedCLIVAR, HyMEX in Northern Africa, based on in situ and remote sensing data as well as on outputs from CORDEX and CMIP5 with regional and global climate models have contributed to the understanding of climate change and impacts in the Africa continent. These regional and continental intiatives have provided significant inputs to the last UNFCCC assessments and reports on climate change in Africa, but efforts need to be pursued to deliver climate information at regional and local scales to support impact studies as well as adaptation and mitigation policies leading to a climate-resilient development to face increase of extreme events which are likely to be more frequent and more intense in several parts of the continent.

This Special Issue focuses on original contributions related to regional and local trends of hydrological and climate extremes, (i) in documenting changes of observed extreme events in the past and present period, (ii) in adressing how they are linked to changing global/regional/local climate and land use, and (iii) how they may evoluate in the future. Papers contributing to these following objectives are welcome:

to understand of the impacts of global warming and/or land use on trends in hydrological and climate extremes in all the regions of Africa at different time scales;
to identify the atmospheric and large scale drivers of hydrological and climate extremes at regional and local levels and to describe how they may change at different time horizons;
to use different sources of climate information (from in situ and remote sensing) to reduce the uncertainty of the prediction of extreme events in regional and global climate models.

Manuscript on physical processes underpinning past, present and future trends in hydrological and climatic extremes and impacts, both from an observational and modelling perspective are welcome, as well as case studies in different regions of Africa quantifying the potential impacts of changes in hydrological and climate extremes on African cities or on key sectors such as agriculture, water resource or renewable energy at regional and local scales.

Dr. Arona Diedhiou
Guest Editor

Manuscript Submission Information

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Keywords

Africa
CMIP
CORDEX-AFRICA
Hydrological extremes
Climate extremes
Global warming
Land use and land cover
Drought
Floods
Landslides
Heat waves
Tipping point
Slow onset

Published Papers (10 papers)

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Research

21 pages, 8357 KiB

Open AccessArticle

Intensification of Summer Rainfall Extremes over Nigeria during Recent Decades

by Victor Nnamdi Dike, Zhao-Hui Lin and Chikwem Coleman Ibe

Atmosphere 2020, 11(10), 1084; https://doi.org/10.3390/atmos11101084 - 12 Oct 2020

Cited by 27 | Viewed by 6907

Abstract

Rainfall extremes can cause a significant loss of lives and economic losses in Nigeria. This study aims to investigate the trends of summer rainfall extremes over Nigeria with daily station datasets from 1975 to 2013. Using the rainfall extreme indices recommended by the Expert Team on Climate Change Detection Monitoring Indices (ETCCDMI), it is found that regionally averaged summer total wet-day rainfall amount (PRCPTOT), maximum consecutive 5-day rainfall amount (RX5day), and wet-day rainfall intensity (SDII) have increased in the three climatic regions of Nigeria namely Guinea coast, Sub-Sahel, and the Sahel regions. Meanwhile, heavy rainfall days (R20mm) increased significantly over the Guinea coast and sub-Sahel regions, while the wet-day frequency (RR1) only increased slightly. The increase in PRCPTOT over the two regions is mainly resulting from the increasing intensity and frequency of rainfall extremes. However, the Nigerian Sahel is characterized by a decreasing wet-day frequency, which demonstrates that a large proportion of the increasing PRCPTOT in the region is more associated with intense rainfall than its frequency. These characteristic increasing trends of rainfall extremes may explain the frequent flood events over Nigeria and as such this study may give guidance to stakeholders on how best to cope with it in the future. Full article

(This article belongs to the Special Issue Trends in Hydrological and Climate Extremes in Africa)

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23 pages, 6247 KiB

Open AccessArticle

Spatial Variation and Trend of Extreme Precipitation in West Africa and Teleconnections with Remote Indices

by Samo Diatta, Cheikh Waly Diedhiou, Didier Maria Dione and Soussou Sambou

Atmosphere 2020, 11(9), 999; https://doi.org/10.3390/atmos11090999 - 18 Sep 2020

Cited by 24 | Viewed by 3411

Abstract

Extreme precipitation is a great concern for West Africa country, as it has serious consequence on key socio-economic activities. We use high resolution data from the Climate Hazards Group InfraRed Precipitation Stations (CHIRPS) to determine the spatial variability, trend of 8 extreme precipitation indices in West Africa and their relationship to remote indices. Spatial variability of extreme is characterized by maximum precipitation over the orographic regions, and in southern Sahel. The trend analysis shows a decrease of dry condition in Sahel and Sahara, and an increase tendency of wet indices over western Sahel and southern Sahel. The correlation analysis reveals that extreme precipitation in Sahel is strongly teleconnected to the Eastern Mediterranean Sea (EMS), whereas western and western-north Sahel is associated with both Atlantic Meridional Mode (AMM), Maiden Julian Oscillation phase 8 (MJO8), El Niño 3.4 index (NINO.3.4), and Trans-Atlantic-Pacific Ocean Dipole Index (TAPODI) but with different characteristics or directions. Guinean coast extreme precipitation is highly associated with Atlantic zone 3 SST anomaly (ATL3), Northern Cold Tongue Index (NCTI), TAPODI but also with an opposite sign with NINO.3.4 and in somewhat with the MJO8. Full article

(This article belongs to the Special Issue Trends in Hydrological and Climate Extremes in Africa)

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20 pages, 10195 KiB

Open AccessArticle

Assessment of Meteorological Drought and Wet Conditions Using Two Drought Indices Across KwaZulu-Natal Province, South Africa

by Minenhle Siphesihle Ndlovu and Molla Demlie

Atmosphere 2020, 11(6), 623; https://doi.org/10.3390/atmos11060623 - 12 Jun 2020

Cited by 39 | Viewed by 22085

Abstract

South Africa has been experiencing a series of droughts for the last few years, limiting the availability of water supply in reservoirs and impacting many sectors of the economy. These droughts have affected even the wetter eastern provinces including KwaZulu-Natal. This paper presents the results of analyses and assessment of meteorological drought across KwaZulu-Natal (KZN) Province of South Africa using two drought indices. The main objective of the study is to understand the changes in rainfall patterns for a period of 48 years (i.e., 1970 to 2017) and identify wet and dry years. The percent of normal precipitation index (PNPI) and rainfall anomaly index (RAI) were used to explore and categorize the wet and dry periods at 18 selected rainfall gauging stations across the province. Mann–Kendall statistics and Sen’s slope were employed on the indices to further understand the trend of drought conditions. The results revealed that 1992 and 2014/15 were the most extremely dry years with 2015 being the driest year over the studied period induced by El Niño. The extremely wet periods were 1987, 1996, and 2000 which have been associated with cyclonic events. Droughts have become more frequent and intense, while wet conditions are less frequent. The drought condition was observed not to be peculiar to one region and to vary from year-to-year. These variations have been associated with global climate drivers including El Niño-southern oscillation (ENSO) and sea surface temperature (SST) conditions. The northern region around Magudu, Hlobane, Vryheid and Dundee were relatively the most affected during periods of extreme drought conditions. Comparative analysis showed that RAI is more robust than PNPI in understanding drought conditions. Thus, it can be applied effectively in Southern Africa in analyzing dry and wet conditions. Full article

(This article belongs to the Special Issue Trends in Hydrological and Climate Extremes in Africa)

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20 pages, 10590 KiB

Open AccessArticle

Late 21st Century Projected Changes in the Relationship between Precipitation, African Easterly Jet, and African Easterly Waves

by Ibourahima Kebe, Ismaila Diallo, Mouhamadou Bamba Sylla, Fernando De Sales and Arona Diedhiou

Atmosphere 2020, 11(4), 353; https://doi.org/10.3390/atmos11040353 - 04 Apr 2020

Cited by 11 | Viewed by 3782

Abstract

The present study utilizes three high-resolution simulations from the Regional Climate Model version 4 (RegCM4) to examine the late 21st century changes (2080–2099) in the West African Monsoon (WAM) features. A set of three Earth System Models are utilized to provide initial and lateral boundary conditions to the RegCM4 experiments. Our analysis focuses on seasonal mean changes in WAM large-scale dynamical features, along with their connections with the summer monsoon precipitation. In the historical period, the simulation ensemble means mimic reasonably well the intensity and spatial distribution of the WAM rainfall as well as the WAM circulation patterns at different scales. The future projection of the WAM climate exhibits warming over the whole West Africa leading to precipitation reduction over the Sahel region, and a slight increase over some areas of the Guinea Coast. The position of the African Easterly Jet (AEJ) is shifted southward and the African Easterly Waves (AEWs) activities are reduced, which affect in turn the WAM rainbelt characteristics in terms of position and strength. Overall the changes in simulated AEJ and AEWs contribute substantially to reduce the seasonal summer mean precipitation in West Africa by the late 21st century, with prevailing negative changes in the Savanna-Sahel region. To further explore the robustness of the relationships revealed in this paper, future studies using different high-resolution regional climate models with large ensemble are recommended. Full article

(This article belongs to the Special Issue Trends in Hydrological and Climate Extremes in Africa)

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24 pages, 4138 KiB

Open AccessArticle

Analyzing Trend and Variability of Rainfall in The Tafna Basin (Northwestern Algeria)

by Hanane Bougara, Kamila Baba Hamed, Christian Borgemeister, Bernhard Tischbein and Navneet Kumar

Atmosphere 2020, 11(4), 347; https://doi.org/10.3390/atmos11040347 - 31 Mar 2020

Cited by 29 | Viewed by 4593

Abstract

Northwest Algeria has experienced fluctuations in rainfall between the two decades 1940s and 1990s from positive to negative anomalies, which reflected a significant decline in rainfall during the mid-1970s. Therefore, further analyzing rainfall in this region is required for improving the strategies on water resource management. In this study, we complement previous studies by dealing with sub basins that were not previously addressed in Tafna basin (our study area located in Northwest Algeria), and by including additional statistical methods (Kruskal–Wallis test, Jonckheere-Terpstra test, and the Friedman test) that were not earlier reported on the large scale (Northwest Algeria). In order to analyse the homogeneity, trends, and stationarity in rainfall time series for nine rainfall stations over the period 1979–2011, we have used several statistical tests. The results showed an increasing trend for annual rainfall after the break detected in 2007 for Djbel Chouachi, Ouled Mimoun, Sidi Benkhala stations using Hubert, Pettitt, and Buishand tests. The Lee and Heghinian test has detected a break at the same year in 2007 for all stations except Sebdou, Beni Bahdel, and Hennaya stations, which have a break date in 1980. We have confirmed this increasing trend for rainfall with other trend detection methods such as Mann Kendall and Sen’s method that highlighted an upward trend for all the stations in the autumn season, which is mainly due to an increase in rainfall in September and October. On a monthly scale, the date of rupture is different from one station to another because the time series are not homogeneous. In addition, we have applied three tests enabling further results: (i) the Jonckheere-Terpstra test has detected an upward trend for two stations (Khemis and Hennaya), (ii) Friedman test has indicated the difference between the mean rank again with Khemis and Hennaya stations and the Merbeh station, (iii) according to the Kruskal-Wallis test, there have been no variance detected between all the rainfall stations. The increasing trend in rainfall may lead to a rise in stream flow and enhance potential floods risks in low-lying regions of the study area. Full article

(This article belongs to the Special Issue Trends in Hydrological and Climate Extremes in Africa)

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16 pages, 4622 KiB

Open AccessArticle

Understanding the Variability of West African Summer Monsoon Rainfall: Contrasting Tropospheric Features and Monsoon Index

by Akintomide Afolayan Akinsanola and Wen Zhou

Atmosphere 2020, 11(3), 309; https://doi.org/10.3390/atmos11030309 - 22 Mar 2020

Cited by 16 | Viewed by 5317

Abstract

West African Summer Monsoon (WASM) rainfall exhibits large variability at interannual and decadal timescales, causing droughts and floods in many years. Therefore it is important to investigate the major tropospheric features controlling the WASM rainfall and explore its potential to develop an objective monsoon index. In this study, monthly mean reanalysis data from the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) and monthly rainfall data from three gridded observations during the 65-year period of 1950–2014 were employed. Dry and wet rainfall years were identified using a standardized precipitation index. In a composite analysis of wet and dry years, the dynamical features controlling the WASM exhibit an obvious contrast between these years, and a weaker (stronger) African Easterly Jet (Tropical Easterly Jet) is observed during the wet years. Also, a well-developed and deep low-level westerly flow at about 850 hPa is evident in wet years while an obvious reversal is observed in dry years. Considering this, the main regions of the two easterly jet streams and low-level westerly wind are proposed for objectively defining an effective WASM index (WASMI). The results indicate that the WASMI defined herein can reflect variations in June–September rainfall over West Africa. The index exhibits most of the variabilities observed in the rainfall series, with high (low) index values occurring in the 1950–1960s (1970–1980s), suggesting that the WASMI is skilled in capturing the respective wet and dry rainfall episodes over the region. Also, the WASMI is significantly correlated (r = 0.8) with summer monsoon rainfall, which further affirms that it can indicate not only variability but also the intensity of WASM rainfall. Full article

(This article belongs to the Special Issue Trends in Hydrological and Climate Extremes in Africa)

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30 pages, 4542 KiB

Open AccessArticle

A Boundary Forcing Sensitivity Analysis of the West African Monsoon Simulated by the Modèle Atmosphérique Régional

by Guillaume Chagnaud, Hubert Gallée, Thierry Lebel, Gérémy Panthou and Théo Vischel

Atmosphere 2020, 11(2), 191; https://doi.org/10.3390/atmos11020191 - 11 Feb 2020

Cited by 2 | Viewed by 2543

Abstract

The rainfall regime of West Africa is highly variable over a large range of space and time scales. With rainfall agriculture being predominent in the region, the local population is extremely vulnerable to intraseasonal dry spells and multi-year droughts as well as to intense rainfall over small time steps. Were this variability to increase, it might render the area close from becoming unhabitable. Anticipating any change is thus crucial from both a societal and a scientific perspective. Despite continuous efforts in Global Climate Model (GCM) development, there is still no agreement on the sign of the future rainfall regime change in the region. Regional Climate Models (RCMs) are used for more accurate projections of future changes as well as end-user-oriented impact studies. In this study, the sensitivity of the Modèle Atmosphérique Régional (MAR) to homogeneous perturbations in boundary forcing air temperature and/or SST is assessed with the aim to better understand (i) the thermodynamical imprint of the recent rainfall regime changes and (ii) the impact of errors in driving data on the West African rainfall regime simulated by an RCM. After an evaluation step where the model is proved to satisfactorily simulate the West African Monsoon (WAM), sensitivity experiments display contrasted, sizable and robust responses of the simulated rainfall regime. The rainfall responses to the boundary forcing perturbations compare in magnitude with the intrinsic model bias, giving support for such an analysis. A physical interpretation of the rainfall anomalies provides confidence in the model response consistency and shows the potential of such an experimental protocol for future climate change downscalling over this region. Full article

(This article belongs to the Special Issue Trends in Hydrological and Climate Extremes in Africa)

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26 pages, 12672 KiB

Open AccessArticle

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

by Pierre Camberlin, Marc Kpanou and Pascal Roucou

Atmosphere 2020, 11(2), 188; https://doi.org/10.3390/atmos11020188 - 11 Feb 2020

Cited by 5 | Viewed by 3919

Abstract

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. Full article

(This article belongs to the Special Issue Trends in Hydrological and Climate Extremes in Africa)

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15 pages, 3955 KiB

Open AccessArticle

Recent Trends in the Daily Rainfall Regime in Southern West Africa

by Francis Nkrumah, Théo Vischel, Geremy Panthou, Nana Ama Browne Klutse, David C. Adukpo and Arona Diedhiou

Atmosphere 2019, 10(12), 741; https://doi.org/10.3390/atmos10120741 - 26 Nov 2019

Cited by 28 | Viewed by 4970

Abstract

Extreme climate events, either being linked to dry spells or extreme precipitation, are of major concern in Africa, a region in which the economy and population are highly vulnerable to climate hazards. However, recent trends in climate events are not often documented in this poorly surveyed continent. This study makes use of a large set of daily rain gauge data covering Southern West Africa (extending from 10° W to 10° E and from 4° N to 12° N) from 1950 to 2014. The evolution of the number and the intensity of daily rainfall events, especially the most extremes, were analyzed at the annual and seasonal scales. During the first rainy season (April–July), mean annual rainfall is observed to have a minor trend due to less frequent but more intense rainfall mainly along the coast of Southern West Africa (SWA) over the last two decades. The north–south seasonal changes exhibit an increase in mean annual rainfall over the last decade during the second rainy season (September–November) linked by both an increase in the frequency of occurrence of rainy days as well as an increase in the mean intensity and extreme events over the last decade. The study also provides evidence of a disparity that exists between the west and east of SWA, with the east recording a stronger increase in the mean intensity of wet days and extreme rainfall during the second rainy season (September–November). Full article

(This article belongs to the Special Issue Trends in Hydrological and Climate Extremes in Africa)

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16 pages, 2117 KiB

Open AccessArticle

Impacts of 1.5 and 2.0 °C Global Warming on Water Balance Components over Senegal in West Africa

by Mamadou Lamine Mbaye, Mouhamadou Bamba Sylla and Moustapha Tall

Atmosphere 2019, 10(11), 712; https://doi.org/10.3390/atmos10110712 - 15 Nov 2019

Cited by 10 | Viewed by 3986

Abstract

This study assesses the changes in precipitation (P) and in evapotranspiration (ET) under 1.5 °C and 2.0 °C global warming levels (GWLs) over Senegal in West Africa. A set of twenty Regional Climate Model (RCM) simulations within the Coordinated Regional Downscaling Experiment (CORDEX) following the Representative Concentration Pathways (RCP) 4.5 emission scenario is used. Annual and seasonal changes are computed between climate simulations under 1.5 °C and 2.0 °C warming, with respect to 0.5 °C warming, compared to pre-industrial levels. The results show that annual precipitation is likely to decrease under both magnitudes of warming; this decrease is also found during the main rainy season (July, August, September) only and is more pronounced under 2 °C warming. All reference evapotranspiration calculations, from Penman, Hamon, and Hargreaves formulations, show an increase in the future under the two GWLs, except annual Penman evapotranspiration under the 1.5 °C warming scenario. Furthermore, seasonal and annual water balances (P-ET) generally exhibit a water deficit. This water deficit (up to 180 mm) is more substantial with Penman and Hamon under 2 °C. In addition, analyses of changes in extreme precipitation reveal an increase in dry spells and a decrease in the number of wet days. However, Senegal may face a slight increase in very wet days (95th percentile), extremely wet days (99th), and rainfall intensity in the coming decades. Therefore, in the future, Senegal may experience a decline in precipitation, an increase of evapotranspiration, and a slight increase in heavy rainfall. Such changes could have serious consequences (e.g., drought, flood, etc.) for socioeconomic activities. Thus, strong governmental politics are needed to restrict the global mean temperature to avoid irreversible negative climate change impacts over the country. The findings of this study have contributed to a better understanding of local patterns of the Senegal hydroclimate under the two considered global warming scenarios. Full article

(This article belongs to the Special Issue Trends in Hydrological and Climate Extremes in Africa)

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