Characterization of Monsoonal Rainfall in the Sudano-Sahelian Zone of Northwestern Nigeria (original) (raw)
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Assessment of Long-Term Spatio-Temporal Rainfall Variability over Ghana using Wavelet Analysis
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Rainfall variability has strong impact on food security, livelihood and socioeconomic activities as farming in West Africa is mainly rain-fed. The annual, seasonal and decadal rainfall variability over Ghana has been studied and their periodicities analysed using wavelet analysis. A rainfall time series from 1901-2010 from the Global Precipitation Climatology Center (GPCC) was used in this analysis. It was observed that high mean annual rainfall totals ranging from 900-1900 mm are recorded over the entire country. In addition, very high totals between 1500-1900 mm are recorded at the SouthWestern part of the country whereas low totals (900-1200 mm) are recorded in the Savannah and East coast of the country. In general, a decreasing trend was observed for the annual rainfall over all the agro-ecological zones except for the coastal zone, where a slight increasing trend of 0.1600 mm per year was seen. The seasonal trend analysis revealed a significant decreasing trend at 0.01 significance level in all the agro-ecological zones except for the Savannah during the DJF season indicating an intensification of the Harmattan. The Coastal zone recorded the lowest mean rainfall values for all seasons with the highest of about 150 mm in MAM. The Forest zone on the other hand recorded very high rainfall values for all seasons with the maximum of about 200 mm in JJA. The Transition zone, however, recorded almost quite stable rainfall amount for all seasons except for DJF. On the decadal time scale, below normal rainfall values were observed between the 1901-1920 and 1980-2010 periods for almost all the agro-ecological zones except for the Savannah which showed above normal rainfall values within the 1901-1940 period. Indicating that, the decreasing trend observed in recent years is not solely due to antropogenic factors but have a strong contribution from a natural climate variability. The wavelet analysis also revealed a strong annual periodicity over all the agro-ecological zones except for the Coastal and Forest zones where the annual periodicity was accompanied by 4-8 months signal. The results of both the 5 year moving average and the decadal anomaly confirm a significant decrease in rainfall amount. This will have negative consequences on agricultural practices, water resource management and food security.
Variability changes of some climatology parameters of Nigeria using wavelet analysis
Scientific African, 2018
Monthly total rainfall and monthly average temperature data of Nigeria were downloaded from World Bank Data Group site for year 1901 to 2015. Annual total rainfall and annual average temperature were calculated from the data. The decadal average and thirty-yearaverage of total rainfall and average temperature were also calculated. In order to describe the time-frequency of rainfall and temperature variability, wavelet analysis was employed on time series of the monthly total rainfall, monthly average temperature, annual total rainfall, and annual average temperature using MATLAB software. The constitution of the monthly rainfall and temperature frequency was studied by the global wavelet spectrum. In order to obtain more information, separate bands were modulated. Take for instance, on examining the 8-16-month band by mean of the scales within the range of 8 and 16 months, the periods with low or high variance of the mean monthly and annual temperature were discovered. Variability of the considered climatological parameters was more vivid on thirty-yearaverage basis than that of annual and decadal basis.
International Journal of Atmospheric Sciences, 2014
The interannual and decadal to multidecadal variability of precipitation in western Sahel region was examined using wavelet transform and coherency analysis. The aim was to identify the major climate index that has a robust relationship with Sahel precipitation (drought). The results show that ENSO, North Atlantic Oscillation (NAO), Atlantic Multidecadal Oscillation (AMO), and Indian Ocean Dipole (IOD) all have some relationship with precipitation at different time scales which is in agreement with recent studies. There is an antiphase relationship between Sahel precipitation and ENSO at the 3-4-year band localized around 1982/83 El Niño episode. This indicates a cause and effect relationship between the droughts of 1983 and 1982/83 El Niño. In addition, wavelet transform coherence analysis also revealed a relatively antiphase relationship between AMO and precipitation signifying cause and effect. The wavelet analyses indicate that IOD control on rainfall variability in Sahel is limited to the east (15 ∘ E-35 ∘ E). Advancing this understanding of variability in rainfall and climate forcing could improve the accuracy of rainfall forecast.
Water
This work is dedicated to the study of the spatio-temporal variability of climate in Morocco by the analysis of rainfall (gridded and gauged data) and runoff. The wavelet analysis method has been used in this study to compare the rainfall and runoff series and to show the major discontinuities identified in 1970, 1980, and 2000. Several modes of variability have been detected; this approach has been applied to show annual (1 year) and inter-annual modes (2–4 years, 4–8 years, 8–12/8–16 years, and 16–30 years), and some modes are specific to some stations. This analysis will be complemented by the gridded data covering the period from 1940 to 1999, which will allow for a better understanding of the spatial variability of the highlighted signals set, which identified frequencies at 1 year and 8–16 years, distinguished different time periods at each basin and identified three main discontinuities in 1970, 1980, and 2000. The contribution of climatic indices is important as it is betwee...
Investigating rainfall trend over India using the wavelet technique
Journal of Water and Climate Change, 2015
In this paper, using the wavelet technique we analysed rainfall behaviour in the country across different agro-climatic zones over a century. Findings indicate that at the national level there is no significant trend in rainfall in the long run, but there are pockets of change in the rainfall pattern. There was a significant increase in the rainfall in the arid zone, whereas in the humid, semi-arid tropics and semi-arid temperate zones the trend was downward but insignificant. The behaviour of rainfall was different during this period. Except in the arid zone, we find a similar trend in other zones increasing initially, tapering off in the middle and then declining but with some difference in time intervals. In the arid zone, the behaviour of rainfall had been erratic. In the short run, the direction of change in trend remains the same as in the long run but the change is statistically significant.
Rainfall data analysis using wavelet transform
An application of wavelet analysis is done with a long time series of the total monthly rainfall from several places from different regions of the world (i.e. Iberian Peninsula, Japan and north-eastern Brazil). Such an analysis was performed in order to fully characterize the distinct time-frequency rainfall variability observed in each of these areas. Besides the rainfall variability analysis, the main frequency components in the time series are studied by the global wavelet spectrum, revealing how the monthly rainfall frequency of each place is composed. This analysis is considered to be more accurate than the standard Fourier analysis. The modulation in separated bands was done in order to extract additional information; e.g. the 8-16-month band was examined by an average of all scales between 8 and 16 months, giving a measure of the average monthly variance versus time, where the periods with low or high variance could be identified.
Rainfall analysis in Klang River basin using continuous wavelet transform
The rainfall characteristics within Klang River basin is analyzed by the continuous wavelet transform using monthly rainfall data (1997–2009) from a raingauge and also using daily rainfall data (1998–2013) from the Tropical Rainfall Measuring Mission (TRMM). The wavelet power spectrum showed that some frequency components were presented within the rainfall time series, but the observed time series is short to provide accurate information, thus the daily TRMM rainfall data were used. In such analysis, two main frequency components, i.e., 6 and 12 months, showed to be present during the entire period of 16 years. Such semiannual and annual frequencies were confirmed by the global wavelet power spectra. Finally, the modulation in the 8–16-month and 256– 512-day bands were examined by an average of all scales between 8 and 16 months, and 256 and 512 days, respectively, giving a measure of the average monthly/daily variance versus time, where the periods with low or high variance could be identified.
International Journal of Climatology, 2019
Space-time variability of rainfall at local scale is affected by several regional factors such as aerosol concentration, GHGs, land cover changes, etc., along with large scale atmospheric circulations. Predictive ability of regional circulation models can be significantly improved and efficient management of water resources can be assured by identifying dominant variables controlling spatiotemporal variations in rainfall among aforementioned factors. The present study aims to investigate dominant climate systems controlling trends in rainfall over Chhattisgarh state (a semi-arid region) in India over the period of 115 years (1901-2015). Discrete wavelet transform (DWT) in conjunction with Mann-Kendall (MK) test are applied to the rainfall data series at different time scales (monthly, seasonal, annual, pre-monsoon, monsoon, post-monsoon and winter) in order to identify the long term trends and dominant periodic components influencing the trend. In the results, negative trends are found to exist in all rainfall time series at majority of districts (except for annual and monsoon rainfall at Bijapur and Sukma district). In addition, analysis of trend in actual evapotranspiration and soil moisture in the region does not exhibits the effect of anthropogenic variables such as land cover change, irrigation projects, etc. as significant negative trend are also observed in soil moisture for majority of districts. Overall, 2-year and 4-year periodic components have been detected to be dominating the trends in most of the rainfall time series (annual, monsoon, post-monsoon and winter). On comparing the identified dominating components with the existing climate systems (AMO, IOD, MJO, ITCZ. etc.), El-Nino Southern Oscillations (ENSO) has been recognized as predominant climate circulation influencing the rainfall trends over the study region. The study outcomes are expected to improve the regional Accepted Article This article is protected by copyright. All rights reserved. This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. Please cite this article as
Journal of Geological Resource and Engineering, 2015
This research exploited seventy years of daily precipitation data from Bukoba, Tanzania to understand precipitation variability and change important for water resource management. Morlet Wavelet Transform was applied to discriminate the distinct time-frequency rainfall variability in the 92 days long MAM ((March and May)) and OND (October to December) primary rainfall seasons for intraseasonal characteristics over the periods 1931-1960, 1961-1990 and 1971-2000. The time-frequency analysis yielded wavelets outlining the intraseasonal nature of sporadic wet and dry spells in each epoch. The characters of the spells designate changing distribution, intensity and frequency of occurrence across the three epochs. The profile of the erratic wet and dry spells speculates shift change and fading of high frequency, quasi biweekly and low frequency oscillations. The oscillations which act together across atmosphere, oceans and land surfaces through convective processes are likely to influence seasonal precipitation anomalies at intraseasonal scale. The variability of the observed daily precipitation is thus hypothesized to be linked to the fading oscillations in the later two epochs particularly during the main MAM season and thus the declining precipitation in the study domain. Global increased atmospheric carbon dioxide concentration could catalyze this process.
International journal of innovation and scientific research, 2016
Wavelet analysis was applied to the standardized rainfall time series in the south-eastern in the Democratic Republic of the Congo in order to determine periods of rainfall fluctuations in this region at interannual and decennial timescales and to assess the influence of regional or remote climate phenomena on the rainfall of that sector between 1940 and 1997. The local, the global and the scale-averaged wavelet power spectrum of the rainfall time series of that sector indicate an important fluctuation between practically 1960 and 1970. Wavelet coherence spectral analysis shows that the southern oscillation El Nino phenomenon, the Western Hemisphere Warm Pool, the Atlantic Ocean climate variability and the Indian Ocean dipole have a very weak influence on rainfall on this territory. Scale-averaged wavelet coherence in 2-16 years band is lower than 0.5 whatever the climate index considered. Other factors must also be considered in the study of rainfall variability in this study area.