Decadal Variability of Rainfall in Senegal : beyond total seasonal amounts

2021 ◽  
Author(s):  
Aissatou Badji ◽  
Moussa Diakhaté ◽  
Amadou Tierno Gaye ◽  
Juliette Mignot ◽  
Elsa Mohino
Keyword(s):  
Rainy Season ◽  
Decadal Variability ◽  
Function Analysis ◽  
Monsoon Season ◽  
Daily Rainfall ◽  
Average Intensity ◽  
Main Mode ◽  
Clear Trend ◽  
Dry Spells ◽  
Rainy Days

<p>The intraseasonal characteristics of rainfall have important implications for agriculture in the Sahel. For example, the development and yield of millet, sorghum and maize depend not only on the rainfall seasonal total amounts, but also on the onset of the rainy season and the seasonal distribution of rainy days as well as the occurrence of dry spells. However, the decadal variability of intraseasonal rainfall characteristics in the Sahel and in particular in Senegal has received little attention in the literature so far. In this study, we analyze the decadal modulations of the intraseasonal characteristics of the monsoon season in Senegal over the period 1918-2000. From daily rainfall data measured at different stations in Senegal, we have defined indices characterizing, among others, the number of rainy days, the average intensity of rainy days, the starting day and ending day of the rainy season. The spatial patterns of the mean indices generally show a north/south gradient and their temporal modulations show a clear decadal signal. Application of EOF (Empirical Orthogonal Function) analysis provides a main mode of variability showing same-signed loads throughout the territory. The associated PCs show strong decadal variability for most indices with a strong link to the Atlantic Multidecadal Variability. The exception are the indices related to the duration of the monsoon season, which show a weaker decadal variability with a clear trend.</p>

scholarly journals Characteristics of the Northern Australian Rainy Season

2008 ◽  
Vol 21 (17) ◽  
pp. 4298-4311 ◽  
Author(s):  
I. N. Smith ◽  
L. Wilson ◽  
R. Suppiah
Keyword(s):  
Rainy Season ◽  
Climate Model ◽  
Southern Oscillation ◽  
Monsoon Season ◽  
Daily Rainfall ◽  
Summer Rainfall ◽  
Average Intensity ◽  
Australian Monsoon ◽  
Enso Events ◽  
Independent Features

Abstract A trend of increasing rainfall over much of north and northwest Australia over recent decades has contrasted with decreases over much of the rest of the continent. The increases have occurred during the summer months when the rainy season is dominated by the Australian monsoon but is also affected by other events such as tropical cyclones, Madden–Julian oscillations, and sporadic thunderstorms. The problem of diagnosing these trends is considered in terms of changes in the timing of the rainy season. While numerous definitions for rainy/monsoon season onset exist, most are designed to be useful in a predictive sense and can be limited in their application to diagnostic studies, particularly when they involve predetermined threshold amounts. Here the authors define indices, based on daily rainfall observations, that provide relatively simple, robust descriptions of each rainy season at any location. These are calculated using gridded daily rainfall data throughout the northern Australian tropics and also for selected stations. The results indicate that the trends in summer rainfall totals over the period from 1950 to 2005 appear to be mainly the result of similar trends in average intensity. Furthermore, the links between the September–October average Southern Oscillation index indicate that ENSO events affect season duration rather than average intensity. Because duration and average intensity are derived as independent features of each season, it is argued that the trends in rainfall totals are largely unrelated to trends in ENSO and most likely reflect the influence of other factors. Finally, diagnosing these features of the rainy season provides a basis for assessing the confidence one can attach to different climate model projections of changes to rainfall.

scholarly journals A study on effective monsoon and dry spells of short return periods The Indian mountain ranges during monsoon months in two north Bengal districts

MAUSAM ◽  
2021 ◽  
Vol 47 (2) ◽  
pp. 145-148
Author(s):  
A. D. DAS ◽  
S. K. MUKHOPADHYAY
Keyword(s):  
Monsoon Season ◽  
Daily Rainfall ◽  
Return Periods ◽  
Mountain Ranges ◽  
Dry Spells ◽  
Rainfed Farming ◽  
Dry Spell ◽  
Expected Length ◽  
The Mean ◽  
North Bengal

This article uses daily rainfall data (April-October) of Cooch Behar (1971-90) and Jalpaiguri (1972-90), the two predominantly rainfed farming districts of Terai zone of West Bengal, to study the, nature of different rainfall parameters of this area. It was observed that the mean date of Onset of Effective Monsoon (OEM) of this region is about one month in advance from the normal occurrence of monsoon over Kerala. However, the monsoon rains, here, retreat at about the same time with those of  Kerala. Distribution of the duration of dry spell has been studied to have some idea of the nature of critical dry spells during the monsoon season. The article also examines how prolonged, on the average, are the monsoon breaks for different return periods. Expected length of dry spell (in days) for 2, 5, 10 and 20 years return periods have been estimated with the help of suitably fitted curves for each location.

scholarly journals The Wet and Dry Spells across India during 1951–2007

2010 ◽  
Vol 11 (1) ◽  
pp. 26-45 ◽  
Author(s):  
Nityanand Singh ◽  
Ashwini Ranade
Keyword(s):  
Climate Change ◽  
Rainfall Intensity ◽  
Total Duration ◽  
Daily Rainfall ◽  
Annual Rainfall ◽  
Change Scenario ◽  
Monsoon Period ◽  
Northwestern India ◽  
Area Of Interest ◽  
Dry Spells

Abstract Characteristics of wet spells (WSs) and intervening dry spells (DSs) are extremely useful for water-related sectors. The information takes on greater significance in the wake of global climate change and climate-change scenario projections. The features of 40 parameters of the rainfall time distribution as well as their extremes have been studied for two wet and dry spells for 19 subregions across India using gridded daily rainfall available on 1° latitude × 1° longitude spatial resolution for the period 1951–2007. In a low-frequency-mode, intra-annual rainfall variation, WS (DS) is identified as a “continuous period with daily rainfall equal to or greater than (less than) daily mean rainfall (DMR) of climatological monsoon period over the area of interest.” The DMR shows significant spatial variation from 2.6 mm day−1 over the extreme southeast peninsula (ESEP) to 20.2 mm day−1 over the southern-central west coast (SCWC). Climatologically, the number of WSs (DSs) decreases from 11 (10) over the extreme south peninsula to 4 (3) over northwestern India as a result of a decrease in tropical and oceanic influences. The total duration of WSs (DSs) decreases from 101 (173) to 45 (29) days, and the duration of individual WS (DS) from 12 (18) to 7 (11) days following similar spatial patterns. Broadly, the total rainfall of wet and dry spells, and rainfall amount and rainfall intensity of actual and extreme wet and dry spells, are high over orographic regions and low over the peninsula, Indo-Gangetic plains, and northwest dry province. The rainfall due to WSs (DSs) contributes ∼68% (∼17%) to the respective annual total. The start of the first wet spell is earlier (19 March) over ESEP and later (22 June) over northwestern India, and the end of the last wet spell occurs in reverse, that is, earlier (12 September) from northwestern India and later (16 December) from ESEP. In recent years/decades, actual and extreme WSs are slightly shorter and their rainfall intensity higher over a majority of the subregions, whereas actual and extreme DSs are slightly (not significantly) longer and their rainfall intensity weaker. There is a tendency for the first WS to start approximately six days earlier across the country and the last WS to end approximately two days earlier, giving rise to longer duration of rainfall activities by approximately four days. However, a spatially coherent, robust, long-term trend (1951–2007) is not seen in any of the 40 WS/DS parameters examined in the present study.

scholarly journals Spatial structures and directionalities in Monsoonal precipitation over South Asia

2010 ◽  
Vol 17 (5) ◽  
pp. 371-381 ◽  
Author(s):  
N. Malik ◽  
N. Marwan ◽  
J. Kurths
Keyword(s):  
Indian Subcontinent ◽  
Monsoon Season ◽  
Daily Rainfall ◽  
Heavy Rain ◽  
Data Sets ◽  
Spatial Structures ◽  
Break Phase ◽  
Rainfall Events ◽  
Monsoonal Precipitation ◽  
Rain Events

Abstract. Precipitation during the monsoon season over the Indian subcontinent occurs in form of enormously complex spatiotemporal patterns due to the underlying dynamics of atmospheric circulation and varying topography. Employing methods from nonlinear time series analysis, we study spatial structures of the rainfall field during the summer monsoon and identify principle regions where the dynamics of monsoonal rainfall is more coherent or homogenous. Moreover, we estimate the time delay patterns of rain events. Here we present an analysis of two separate high resolution gridded data sets of daily rainfall covering the Indian subcontinent. Using the method of event synchronization (ES), we estimate regions where heavy rain events during monsoon happen in some lag synchronised form. Further using the delay behaviour of rainfall events, we estimate the directionalities related to the progress of such type of rainfall events. The Active (break) phase of a monsoon is characterised by an increase(decrease) of rainfall over certain regions of the Indian subcontinent. We show that our method is able to identify regions of such coherent rainfall activity.

scholarly journals A synthetic view of rainfall intensification in the West African Sahel

2022 ◽  
Author(s):  
Guillaume Chagnaud ◽  
Geremy Panthou ◽  
Theo Vischel ◽  
Thierry Lebel
Keyword(s):  
Decadal Variability ◽  
Regional Scale ◽  
Daily Rainfall ◽  
Extreme Value Distribution ◽  
Extreme Rainfall ◽  
West African ◽  
Rainfall Regime ◽  
The West ◽  
West African Sahel ◽  
African Sahel

Abstract The West African Sahel has been facing for more than 30 years an increase in extreme rainfalls with strong socio-economic impacts. This situation challenges decision-makers to define adaptation strategies in a rapidly changing climate. The present study proposes (i) a quantitative characterization of the trends in extreme rainfalls at the regional scale, (ii) the translation of the trends into metrics that can be used by hydrological risk managers, (iii) elements for understanding the link between the climatology of extreme and mean rainfall. Based on a regional non-stationary statistical model applied to in-situ daily rainfall data over the period 1983-2015, we show that the region-wide increasing trend in extreme rainfalls is highly significant. The change in extreme value distribution reflects an increase in both the mean and variability, producing a 5%/decade increase in extreme rainfall intensity whatever the return period. The statistical framework provides operational elements for revising the design methods of hydraulic structures which most often assume a stationary climate. Finally, the study shows that the increase in extreme rainfall is more attributable to an increase in the intensity of storms (80%) than to their occurrence (20%), reflecting a major disruption from the decadal variability of the rainfall regime documented in the region since 1950.

scholarly journals STUDY OF GPM-IMERG RAINFALL DATA PRODUCT FOR GANGOTRI GLACIER

2018 ◽  
Vol XLII-5 ◽  
pp. 383-388
Author(s):  
P. Verma ◽  
S. K. Ghosh
Keyword(s):  
Field Data ◽  
Monsoon Season ◽  
Meteorological Data ◽  
Data Product ◽  
Precipitation Measurement ◽  
Post Monsoon Season ◽  
Gangotri Glacier ◽  
New Generation ◽  
Global Precipitation ◽  
Rainy Days

<p><strong>Abstract.</strong> This study presents a comparison of new generation weather observatory satellites Global Precipitation Measurement (GPM) Integrated Multi-satellite Retrievals for GPM (IMERG) rainfall products with field data collected for Gangotri glacier in India. The meteorological analysis of rainfall estimates has been performed on GPM IMERG Final, Late and Early precipitation products available at daily scale with a spatial resolution of 0.1&amp;deg;<span class="thinspace"></span>&amp;times;<span class="thinspace"></span>0.1&amp;deg; for melting season from May to September for the year 2014 and 2015 respectively. The comparison of satellite products with field data was done using correlation coefficient and standard anomaly. The Late run curve showed a high degree of similarity with final run curve while early run showed variation from them. The satellite meteorological data correctly identified non-rainy days with an average of &amp;sim;86.7%, &amp;sim;67.5% and &amp;sim;95% for pre-monsoon, monsoon and post-monsoon season respectively. The rmse for final run data product for 2014 and 2015 are 4.5, 1.23, 1.55, 1.24, 0.8 and 1.14, 7.1, 1.82, 1.15, 1.52 from May to September respectively. Overall, it has been observed that for medium to heavy rainfall final run estimates are close to field data and for light to medium rainfall late run estimates are close. Similar results have been obtained from both datasets for non-rainy days in the study area.</p>

scholarly journals Modelling of monsoon rainfall for a mesoscale catchment in North-West India I: assessment of objective circulation patterns

2006 ◽  
Vol 10 (6) ◽  
pp. 797-806 ◽  
Author(s):  
E. Zehe ◽  
A. K. Singh ◽  
A. Bárdossy
Keyword(s):  
Monsoon Rainfall ◽  
Monsoon Season ◽  
Companion Paper ◽  
North West ◽  
Monthly Scale ◽  
Monsoon Variability ◽  
Circulation Patterns ◽  
Rainfall Model ◽  
Spatio Temporal ◽  
Rainy Days

Abstract. Within the present study we shed light on the question whether objective circulation patterns (CP) classified from either the 500 HPa or the 700 HPa level may serve as predictors to explain the spatio-temporal variability of monsoon rainfall in the Anas catchment in North West India. To this end we employ a fuzzy ruled based classification approach in combination with a novel objective function as originally proposed by (Stehlik and BᲤossy, 2002). After the optimisation we compare the obtained circulation classification schemes for the two pressure levels with respect to their conditional rainfall probabilities and amounts. The classification scheme for the 500 HPa level turns out to be much more suitable to separate dry from wet meteorological conditions during the monsoon season. As is shown during a bootstrap test, the CP conditional rainfall probabilities for the wet and the dry CPs for both pressure levels are highly significant at levels ranging from 95 to 99%. Furthermore, the monthly CP frequencies of the wettest CPs show a significant positive correlation with the variation of the total number of rainy days at the monthly scale. Consistently, the monthly frequencies of the dry CPs exhibit a negative correlation with the number of rainy days at the monthly scale. The present results give clear evidence that the circulation patterns from the 500 HPa level are suitable predictors for explaining spatio- temporal Monsoon variability. A companion paper shows that the CP time series obtained within this study are suitable input into a stochastical rainfall model.

scholarly journals Interdecadal Variability of the South American Precipitation in the Monsoon Season

2015 ◽  
Vol 28 (2) ◽  
pp. 755-775 ◽  
Author(s):  
Alice M. Grimm ◽  
João P. J. Saboia
Keyword(s):  
Function Analysis ◽  
Monsoon Season ◽  
Regional Scale ◽  
The Other ◽  
Interdecadal Variability ◽  
Monthly Precipitation ◽  
Monsoon Precipitation ◽  
Climatic Indices ◽  
Continental Scale ◽  
Sst Anomalies

Abstract Interdecadal variability modes of monsoon precipitation over South America (SA) are provided by a continental-scale rotated empirical orthogonal function analysis, and their connections to well-known climatic indices and SST anomalies are examined. The analysis, carried out for austral spring and summer, uses a comprehensive set of station data assembled and verified for the period 1950–2000. The presented modes are robust, consistent with previous regional-scale studies and with modes obtained from longer time series over smaller domains. Opposite phases of the main modes show differences around 50% in monthly precipitation. There are significant relationships between the interdecadal variability in spring and summer, indicating local and remote influences. The first modes for both seasons are dipole-like, displaying opposite anomalies in central-east and southeast SA. They tend to reverse polarity from spring to summer. Yet the summer second mode and its related spring fourth mode, which affect the core monsoon region in central Brazil and central-northwestern Argentina, show similar factor loadings, indicating persistence of anomalies from one season to the other, contrary to the first modes. The other presented modes describe the variability in different regions with great monsoon precipitation. Significant connections with different combinations of climatic indices and SST anomalies provide physical basis for the presented modes: three show the strongest connections with SST-based indices, and two have the strongest connections with atmospheric indices. However, the main modes show connections with more than one climatic index and more than one oceanic region, stressing the importance of combined influence.

scholarly journals A water risk index for portfolio exposure to climatic extremes: conceptualization and an application to the mining industry

2017 ◽  
Vol 21 (4) ◽  
pp. 2075-2106 ◽  
Author(s):  
Luc Bonnafous ◽  
Upmanu Lall ◽  
Jason Siegel
Keyword(s):  
Extreme Events ◽  
Decadal Variability ◽  
Risk Index ◽  
Mining Industry ◽  
Daily Rainfall ◽  
Extreme Rainfall ◽  
Time Correlation ◽  
Climatic Extremes ◽  
Mining Companies ◽  
Non Governmental Organizations

Abstract. Corporations, industries and non-governmental organizations have become increasingly concerned with growing water risks in many parts of the world. Most of the focus has been on water scarcity and competition for the resource between agriculture, urban users, ecology and industry. However, water risks are multi-dimensional. Water-related hazards include flooding due to extreme rainfall, persistent drought and pollution, either due to industrial operations themselves, or to the failure of infrastructure. Most companies have risk management plans at each operational location to address these risks to a certain design level. The residual risk may or may not be managed, and is typically not quantified at a portfolio scale, i.e. across many sites. Given that climate is the driver of many of these extreme events, and there is evidence of quasi-periodic climate regimes at inter-annual and decadal timescales, it is possible that a portfolio is subject to persistent, multi-year exceedances of the design level. In other words, for a multi-national corporation, it is possible that there is correlation in the climate-induced portfolio water risk across its operational sites as multiple sites may experience a hazard beyond the design level in a given year. Therefore, from an investor's perspective, a need exists for a water risk index that allows for an exploration of the possible space and/or time clustering in exposure across many sites contained in a portfolio. This paper represents a first attempt to develop an index for financial exposure of a geographically diversified, global portfolio to the time-varying risk of climatic extremes using long daily global rainfall datasets derived from climate re-analysis models. Focusing on extreme daily rainfall amounts and using examples from major mining companies, we illustrate how the index can be developed. We discuss how companies can use it to explore their corporate exposure, and what they may need to disclose to investors and regulators to promote transparency as to risk exposure and mitigation efforts. For the examples of mining companies provided, we note that the actual exposure is substantially higher than would be expected in the absence of space and time correlation of risk as is usually tacitly assumed. We also find evidence for the increasing exposure to climate-induced risk, and for decadal variability in exposure. The relative vulnerability of different portfolios to multiple extreme events in a given year is also demonstrated.

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