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Impact of rainfall trends on flood in Agnéby watershed

Konin N’Da Jean Claude, N’go Yao Alexis, Soro Gneneyougo Emile, Goula Bi Tié Albert

Journal of Water and Land Development

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2022

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no. 52

9--20

EN

The aim of this study is to analyse the spatio-temporal evolution of hydro-rainfall variables in the Agnéby watershed in a disturbed climatic context. Rainfall data from the stations of Arrah, Bongouanou, M’Batto, Akoupé, Céchi, Agboville, Adzopé, Sikensi, Abidjan Airport and Dabou as well as hydrometric data from the stations of Agboville, Offoliguié, M’Bessé and Guessiguié were used. The methodological approach is based on the application of independence and trend tests and spatio-temporal analysis of daily rainfall maxima, duration of consecutive rainfall events, number of rainfall events above a threshold and daily flow maxima. The hypothesis of independence justified the relevance of the choice of variables. The trend test showed the dynamic upward evolution of extreme rainfall and the decrease in the duration of consecutive rainy episodes, in the number of rainy episodes and in the flows feeding the main watercourse. Moreover, spatial analysis of daily maximum rainfall amounts above 120 mm, consecutive maximum rainfall amounts above 160 mm and Gumbel rainfall amounts above 190 mm indicated heavy rainfall in the southern part of the watershed. However, a decrease in rainfall is recorded in the areas covered by the stations of Arrah, Bongouanou, M’Batto, Ce chi and Akoupé. An increase in the flood flow calculated from the Generalized Extreme Value (GEV) between 76.60 m3∙s-1 and 225.70 m3∙s-1 is presented in the main river. The spatio-temporal variation in annual rainfall heights showed a high rainfall in the southern part of the watershed with a decrease in rainfall over the decades (1976-1985 and 1996-2005) followed by an increase over the decades (1986-1995 and 2006-2015). Despite the general decrease in rainfall, extreme rainfall has become frequent, causing flooding in the watershed.

2

Temporal and spatial trend analysis of rainfall on Bhogavo River watersheds in Sabarmati lower basin of Gujarat, India

Patel Pratik S., Rana Shilpesh C., Joshi Geeta S.

Acta Geophysica

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2021

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Vol. 69, no. 1

353--364

EN

Global warming is a biggest issue around the world. In this research paper, the temporal and spatial trend analysis of seasonal and annual rainfall on Bhogavo River watersheds in Sabarmati lower basin of Gujarat state of India has been analysed using the data of 11 rain gauge stations installed in Bhogavo watershed. Linear regression, Mann–Kendall Test, Sen’s slope test and innovative trend analysis methods are used to carry out monthly and annual rainfall trend analysis. In addition to the rainfall analysis, a number of rainy days change in magnitude as a percentage of mean rainfall have also been analysed using linear regression and Sen’s slope method, respectively. The IDW method is used to develop a spatial distribution of annual and seasonal rainfall trend over the study area. From the results, it is concluded that annual rainfall shown increasing (positive) trend at nine stations out of 11 stations. The highest value of change in magnitude of trend as a percentage of mean monthly rainfall has been obtained in the month of July, attributing increasing trend at Sayla station and lowest value magnitude of trend as a percentage of mean rainfall in the monthly rainfall has been obtained in the month of August, attributing decreasing trend at Bavla station.

3

Statistical assessment of rainfall variability and trends in northeastern Algeria

Merniz Noureddine, Tahar Ali, Benmehaia Amine M.

Journal of Water and Land Development

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2019

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no. 40

87--96

EN

In the present study, time series for annual, monthly rainfall and number of rainy days per year were analysed to quantify spatial variability and temporal trends for 22 rainfall stations distributed in northeastern Algeria for the period 1978– 2010. The Mann–Kendall test and the Sen’s slope estimator were applied to assess the significance and magnitude of the trend. The results showed that precipitation decreases spatially from North to South and from East to West. The application of the Mann–Kendall test (for 0.05% threshold) to the time series data showed that for annual precipitation, no station showed statistically significant trends, unlike the number of rainy days, where there was a significant negative trend in four stations (Jijel, Constantine, Oum El Bouaghi and Tébessa). For the monthly time series, significant positive trends were observed during the months of September in the coastal stations and July for the plateaus and southern Saharan Atlas stations, while significant negative trends were recorded during the months of February and March for the stations of the extreme East in the study area. These results revealed that for the period analysed, there was no significant climate change in northeastern Algeria but there is a seasonal delay having important agroecological implications.

PL

W przedstawionych badaniach analizowano serie rocznych i miesięcznych opadów oraz liczbę dni z deszczem w ciągu roku celem ustalenia przestrzennej zmienności i czasowych trendów w latach 1978–2010 dla 22 stacji pomiarowych rozmieszczonych w północnowschodniej Algierii. Wykorzystano test Manna–Kendalla i estymator Sena do oceny istotności i rozmiaru trendu. Wyniki dowodzą, że opady malały z północy na południe i ze wschodu na zachód. Zastosowanie testu Manna–Kendalla (p < 0,05) do serii danych pomiarowych nie wykazały w żadnej stacji statystycznie istotnych trendów dla rocznych opadów w przeciwieństwie do liczby dni z opadem, które cechował istotny negatywny trend w czterech stacjach pomiarowych (Jijel, Constantine, Oum El Bouaghi i Tébessa). Analiza serii miesięcznych opadów dowiodła występowania dodatniego trendu w odniesieniu do sierpnia w stacjach na wybrzeżu i w odniesieniu do lipca w stacjach na płaskowyżach i w południowym Atlasie Saharyjskim. Istotny trend ujemny uzyskano w przypadku lutego i marca w stacjach na wschodzie badanego obszaru. Wyniki dowodzą, że w analizowanym okresie nie stwierdzono istotnych zmian klimatu w północnowschodniej Algierii, z wyjątkiem sezonowych opóźnień, które wywołują ważne skutki agro-ekologiczne.