Frequency of extreme Sahelian storms tripled since 1982 in satellite observations

Taylor, Christopher M.; Belušić, Danijel; Guichard, Françoise; Parker, Douglas J.; Vischel, Théo; Bock, Olivier; Harris, Phil; Janicot, Serge; Klein, Cornelia; Panthou, Gérémy

doi:10.1038/nature22069

Cited by 301 publications

(315 citation statements)

References 44 publications

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“…A general increase in turbid water surface was diagnosed in the Gourma over 1975-2002 by Gardelle et al [4], but the SPM trend in these turbid lakes was not documented. The last two decades have seen the emergence of another factor that may also impact SPM, namely an intensification of the precipitation regime, suggested by Frappart et al [8], established by Panthou et al [9], and generalized by Taylor et al [10]. This last study showed a threefold increase in the frequency of extreme rainfall over the last 35 years, due to a constant increase in the most intense Mesoscale Convection Systems in the Sahel and in the associated daily rainfall extremes.…”

Section: Trends Over 2000-2016mentioning

confidence: 57%

“…The increase in concentrated runoff, the overall vegetation decay, and the soil erosion over shallow soils have been identified as the main factors responsible for the increase of surface water in this region [6,7]. In addition, a recent trend towards increasing daily precipitation extremes has also been detected in the Sahel [8][9][10]. The increase in runoff and erosion, as well as the precipitation intensification, points towards a possible increase in turbidity and suspended particulate matter (SPM) in Sahelian lakes and ponds.…”

Section: Introductionmentioning

confidence: 99%

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Analysis of Suspended Particulate Matter and Its Drivers in Sahelian Ponds and Lakes by Remote Sensing (Landsat and MODIS): Gourma Region, Mali

Robert

Kergoat

Soumaguel³

et al. 2017

Remote Sensing

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Abstract:The Sahelian region is characterized by significant variations in precipitation, impacting water quantity and quality. Suspended particulate matter (SPM) dynamics has a significant impact on inland water ecology and water resource management. In-situ data in this region are scarce and, consequently, the environmental factors triggering SPM variability are yet to be understood. This study addresses these issues using remote sensing optical data. Turbidity and SPM of the Agoufou Lake in Sahelian Mali were measured from October 2014 to present, providing a large range of 'values (SPM ranging from 106 to 4178 mg/L). These data are compared to satellite reflectance from Landsat (ETM+, OLI) and MODIS (MOD09GQ, MYD09GQ). For each of these sensors, a spectral band in the near infrared region is found to be well suited to retrieve turbidity and SPM, up to very high values (R 2 = 0.70) seldom addressed by remote sensing studies. The satellite estimates are then employed to assess the SPM dynamics in the main lakes and ponds of the Gourma region and its links to environmental and anthropogenic factors. The main SPM seasonal peak is observed in the rainy season (June to September) in relation to precipitation and sediment transport. A second important peak occurs during the dry season, highlighting the importance of resuspension mechanisms in maintaining high values of SPM. Three different periods are observed: first, a relatively low winds period in the early dry season, when SPM decreases rapidly due to deposition; then, a period of wind-driven resuspension in January-March; and lastly, an SPM deposition period in April-May, when the monsoon replaces the winter trade wind. Overall, a significant increase of 27% in SPM values is observed between 2000 and 2016 in the Agoufou Lake. The significant spatio-temporal variability in SPM revealed by this study highlights the importance of high resolution optical sensors for continuous monitoring of water quality in these poorly instrumented regions.

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Section: Trends Over 2000-2016mentioning

confidence: 57%

Section: Introductionmentioning

confidence: 99%

Analysis of Suspended Particulate Matter and Its Drivers in Sahelian Ponds and Lakes by Remote Sensing (Landsat and MODIS): Gourma Region, Mali

Robert

Kergoat

Soumaguel³

et al. 2017

Remote Sensing

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“…CWV between 1 and 3 h leading the MCSs is higher on average than that observed leading the isolated cells, but increases to a comparable magnitude of ∼ 59 mm within the hour. CWV increases by an average of 1.5 mm in the 2 h leading the passage of MCSs, which is slightly less than the increases reported in Taylor et al (2017) (∼ 4 mm) in the Sahel, though the Amazon is a more humid environment. Values of θ e leading the passage of MCSs (350.3 K) are 3.4 K lower than the θ e values leading the isolated cells (353.7 K), mostly due to lower surface temperatures (27.0 K for MCSs vs. 28.9 K for isolated cells).…”

Section: Surface Thermodynamicsmentioning

confidence: 65%

Tropical continental downdraft characteristics: mesoscale systems versus unorganized convection

Schiro

Neelin

2018

Atmos. Chem. Phys.

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Abstract. Downdrafts and cold pool characteristics for strong mesoscale convective systems (MCSs) and isolated, unorganized deep precipitating convection are analyzed using multi-instrument data from the DOE Atmospheric Radiation Measurement (ARM) GoAmazon2014/5 campaign. Increases in column water vapor (CWV) are observed leading convection, with higher CWV preceding MCSs than for isolated cells. For both MCSs and isolated cells, increases in wind speed, decreases in surface moisture and temperature, and increases in relative humidity occur coincidentally with system passages. Composites of vertical velocity data and radar reflectivity from a radar wind profiler show that the downdrafts associated with the sharpest decreases in surface equivalent potential temperature (θ e ) have a probability of occurrence that increases with decreasing height below the freezing level. Both MCSs and unorganized convection show similar mean downdraft magnitudes and probabilities with height. Mixing computations suggest that, on average, air originating at heights greater than 3 km must undergo substantial mixing, particularly in the case of isolated cells, to match the observed cold pool θ e , implying a low typical origin level. Precipitation conditionally averaged on decreases in surface equivalent potential temperature ( θ e ) exhibits a strong relationship because the most negative θ e values are associated with a high probability of precipitation. The more physically motivated conditional average of θ e on precipitation shows that decreases in θ e level off with increasing precipitation rate, bounded by the maximum difference between surface θ e and its minimum in the profile aloft. Robustness of these statistics observed across scales and regions suggests their potential use as model diagnostic tools for the improvement of downdraft parameterizations in climate models.

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“…During this Great Drought period, despite the lack of rainfall, an increase in Sahelian river discharge was observed [2][3][4][5]. This rise was later defined as the first "Sahelian hydrological paradox [6]".…”

Section: Introductionmentioning

confidence: 98%

“…In addition, the statistical analysis of rainfall over Central Sahel by Panthou et al [4] shows that the contribution of extreme events to the cumulative annual rainfall is higher now (since 2000) than during the wet period [1950][1951][1952][1953][1954][1955][1956][1957][1958][1959][1960][1961][1962][1963][1964][1965][1966][1967][1968][1969]. Taylor et al [5] identified, using satellite infrared temperature (IRT) data, a robust and strong positive trend in the frequency of intense Sahelian mesoscale convective systems (MCS) since 1982 (in which MCS-mean IRT was used as a measure of intensity). Similar conclusions emerge from Sanogo et al [106] and Zhang et al [107].…”

Section: Main Trends Described In Recent Workmentioning

confidence: 99%

Evolution of Surface Hydrology in the Sahelo-Sudanian Strip: An Updated Review

Descroix

Guichard

Grippa

et al. 2018

Water

Self Cite

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Abstract:In the West African Sahel, two paradoxical hydrological behaviors have occurred during the last five decades. The first paradox was observed during the 1968-1990s 'Great Drought' period, during which runoff significantly increased. The second paradox appeared during the subsequent period of rainfall recovery (i.e., since the 1990s), during which the runoff coefficient continued to increase despite the general re-greening of the Sahel. This paper reviews and synthesizes the literature on the drivers of these paradoxical behaviors, focusing on recent works in the West African Sahelo/Sudanian strip, and upscaling the hydrological processes through an analysis of recent data from two representative areas of this region. This paper helps better determine the respective roles played by Land Use/Land Cover Changes (LULCC), the evolution of rainfall intensity and the occurrence of extreme rainfall events in these hydrological paradoxes. Both the literature review and recent data converge in indicating that the first Sahelian hydrological paradox was mostly driven by LULCC, while the second paradox has been caused by both LULCC and climate evolution, mainly the recent increase in rainfall intensity.

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Frequency of extreme Sahelian storms tripled since 1982 in satellite observations

Abstract: International audienc

Cited by 301 publications

References 44 publications

Analysis of Suspended Particulate Matter and Its Drivers in Sahelian Ponds and Lakes by Remote Sensing (Landsat and MODIS): Gourma Region, Mali

Analysis of Suspended Particulate Matter and Its Drivers in Sahelian Ponds and Lakes by Remote Sensing (Landsat and MODIS): Gourma Region, Mali

Tropical continental downdraft characteristics: mesoscale systems versus unorganized convection

Evolution of Surface Hydrology in the Sahelo-Sudanian Strip: An Updated Review

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