Regional-Scale Rainy Season Onset Detection: A New Approach Based on Multivariate Analysis

Boyard-Micheau, Joseph; Camberlin, Pierre; Philippon, Nathalie; Moron, Vincent

doi:10.1175/jcli-d-12-00730.1

Cited by 42 publications

(37 citation statements)

References 23 publications

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“…Previous work has demonstrated the stability of the method described in section 2.2.2 for capturing onset and cessation dates [ Liebmann et al , ; Boyard‐Micheau et al , ]. This is further discussed in section 4.…”

Section: Physical Relevance Of the Seasonality Metricsupporting

confidence: 86%

The onset and cessation of seasonal rainfall over Africa

2016

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Variation in the seasonal cycle of African rainfall is of key importance for agriculture. Here an objective method of determining the timing of onset and cessation is, for the first time, extended to the whole of Africa. The method is applied to five observational data sets and the ERA‐Interim reanalysis. Compatibility with known physical drivers of African rainfall, consistency with indigenous methods, and generally strong agreement between satellite‐based rainfall data sets confirm that the method is capturing the correct seasonal progression of African rainfall. The biannual rainfall regime is correctly identified over the coastal region of Ghana and the Ivory Coast. However, the ERA‐Interim reanalysis exhibits timing biases over areas with two rainy seasons, and both ERA‐Interim and the ARCv2 observational data set exhibit some inconsistent deviations over West Africa. The method can be used to analyze both seasonal‐interannual variability and long‐term change. Over East Africa, we find that failure of the rains and subsequent humanitarian disaster is associated with shorter as well as weaker rainy seasons, e.g., on average the long rains were 11 days shorter in 2011. Cessation of the short rains over this region is 7 days later in El Niño and 5 days earlier in La Niña years with only a small change in onset date. The methodology described in this paper is applicable to multiple data sets and to large regions, including those that experience multiple rainy seasons. As such, it provides a means for investigating variability and change in the seasonal cycle over the whole of Africa.

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Section: Physical Relevance Of the Seasonality Metricsupporting

confidence: 86%

The onset and cessation of seasonal rainfall over Africa

2016

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“…This onset-cessation methodology identifies the period when the rainfall is persistent in occurrence, duration, and intensity relative to the mean climate (Diaconescu et al 2015) and has been used in a number of studies (Boyard-Micheau et al 2013;Diaconescu et al 2015;Monerie et al 2016;Liebmann et al 2017). The lack of dependence on a particular threshold facilitates the production of contemporaneous onset and cessation dates across datasets with contrasting rainfall biases (Liebmann et al 2012;Dunning et al 2016), enabling application to climate model simulations without the need for bias correction (Dunning et al 2017) as the cumulative rainfall anomaly is calculated separately for each model and grid point.…”

Section: B Methodology For Identifying Onset and Cessation Of Rainfamentioning

confidence: 99%

Later Wet Seasons with More Intense Rainfall over Africa under Future Climate Change

2018

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Later wet seasons with more intense rainfall over Africa under future climate change Article Published Version Dunning, C., Black, E. and Allan, R. (2018) Later wet seasons with more intense rainfall over Africa under future climate change. Journal of Climate, 31. pp. 97199738. ISSN 0894 8755ABSTRACT Changes in the seasonality of precipitation over Africa have high potential for detrimental socioeconomic impacts due to high societal dependence upon seasonal rainfall. Here, for the first time we conduct a continental-scale analysis of changes in wet season characteristics under the RCP4.5 and RCP8.5 climate projection scenarios across an ensemble of CMIP5 models using an objective methodology to determine the onset and cessation of the wet season. A delay in the wet season over West Africa and the Sahel of over 5-10 days on average, and later onset of the wet season over southern Africa, is identified and associated with increasing strength of the Saharan heat low in late boreal summer and a northward shift in the position of the tropical rain belt over August-December. Over the Horn of Africa rainfall during the ''short rains'' season is projected to increase by over 100 mm on average by the end of the twenty-first century under the RCP8.5 scenario. Average rainfall per rainy day is projected to increase, while the number of rainy days in the wet season declines in regions of stable or declining rainfall (western and southern Africa) and remains constant in central Africa, where rainfall is projected to increase. Adaptation strategies should account for shorter wet seasons, increasing rainfall intensity, and decreasing rainfall frequency, which will have implications for crop yields and surface water supplies.

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“…It is also necessary to synthesize observations made from individual stations. Objective approaches to this step have been taken by Riddle and Wilks [2013], using principal component analysis and cluster analysis, and by Boyard-Micheau et al [2013], using multivariate analysis.…”

Section: The Seasonal Progressionmentioning

confidence: 99%

Climate and climatic variability of rainfall over eastern Africa

Nicholson

2017

Reviews of Geophysics

547

425

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This review examines several aspects of the climate of eastern Africa. The climatic commonality throughout the region is the frequent occurrence of drought severe enough to incapacitate the population. Because of recent droughts and evidence of disastrous, long‐term climatic change, the region has become a major focus of meteorological research. This review covers six relevant topics: climatic regionalization, seasonal cycle, intraseasonal variability, interannual variability, recent trends, and seasonal forecasting. What emerges is a markedly different view of the factors modulating rainfall, the dynamics associated with the seasons, and the character of teleconnections within the region and the interrelationships between the various rainy seasons. Some of the most important points are the following. (1) The paradigm of two rainy seasons resulting from the biannual equatorial passage of the Intertropical Convergence Zone is inadequate. (2) The “long rains” should not be treated as a single season, as character, causal factors, and teleconnections are markedly different in each month. (3) The long rains have been declining continuously in recent decades. (4) The Madden‐Julian Oscillation has emerged as a factor in interannual and intraseasonal variability, but the relative strength of Pacific and Indian Ocean anomalies plays a major role in the downward trend. (5) Factors governing the short rains are nonstationary. (6) Droughts have become longer and more intense and tend to continue across rainy seasons, and their causes are not adequately understood. (7) Atmospheric variables provide more reliable seasonal forecasts than the factors traditionally considered in forecast models, such as sea surface temperatures and El Niño–Southern Oscillation.

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Regional-Scale Rainy Season Onset Detection: A New Approach Based on Multivariate Analysis

Cited by 42 publications

References 23 publications

The onset and cessation of seasonal rainfall over Africa

The onset and cessation of seasonal rainfall over Africa

Later Wet Seasons with More Intense Rainfall over Africa under Future Climate Change

Climate and climatic variability of rainfall over eastern Africa

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