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Comparing households’ perception of flood hazard with historical climate and hydrological data in the Lower Mono River catchment (West Africa), Benin and Togo [1]

['Nadège I. P. Dossoumou', 'West African Science Service Centre On Climate Change', 'Adapted Land Use', 'Wascal', 'Program In Climate Change', 'Disaster Risk Management', 'University Of Lomé', 'Lomé', 'Masamaéya D. T. Gnazou', 'Department Of Geology']

Date: 2023-04

Abstract The comparison of local perception of flood hazards, with hydrological and climate parameters, can give more insight and understanding on the causes of flood, its impacts and the strategies to effectively address the problem. This study examines whether households’ perception of rainfall and flood occurrence are consistent with observed variation in climate parameter (rainfall) and hydrological (discharge) data in the Lower Mono River catchment (Togo-Benin, West Africa). Perceptions of the 744 households from the catchment were collected and compared to historical climatic and hydrological data using correlation analysis. The Standardized Precipitation Index was utilized to identify the extreme years in terms of precipitation. Chi-test and binary regression analyses were performed to identify the most affected communes within the catchment, and the factors that influence household perceptions on rainfall change, respectively. Findings reveal that 85% of the respondents perceived an excess in rainfall during the last 20 years and identify two particular years as the most affected by flood, which correspond to the climate data analysis. Households’ perceptions on flooded months are correlated with the monthly precipitation and discharge at the upper part of the catchment while the ones at down part are not correlated. Furthermore, the chi-test analysis shows that in the perception of households, the communes at the down part are more affected by flood than those at the upper part of the catchment. It is then important for decision maker to consider local communities’ perception for having insight regarding climate parameters, the causes of flood and in the decision making for implementing measures to cope with this phenomenon.

Citation: Dossoumou NIP, Gnazou MDT, Villamor GB, Agbossou EK, Thiam S, Wagner S, et al. (2023) Comparing households’ perception of flood hazard with historical climate and hydrological data in the Lower Mono River catchment (West Africa), Benin and Togo. PLOS Clim 2(4): e0000123. https://doi.org/10.1371/journal.pclm.0000123 Editor: Bharath Haridas Aithal, Indian Institute of Technology Kharagpur, INDIA Received: September 3, 2022; Accepted: March 20, 2023; Published: April 24, 2023 Copyright: © 2023 Dossoumou et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Data Availability: The data is available on the repository DRYAD. The citation is as follows: NADEGE, DOSSOUMOU (2022), Comparing households’ perception of flood hazard with historical climate and hydrological data in the Lower Mono River catchment (West Africa), Benin and Togo, Dryad, Dataset, https://doi.org/10.5061/dryad.6m905qg2v. Funding: This research was funded by the German Federal Ministry of Education and Research (BMBF) via the WASCAL program and CLIMAFRI project (grant number: 01LZ1710C). Competing interests: The authors declare no competing interests.

1. Introduction Climate related hazard and disasters have increased worldwide with huge damages on populations. Specifically, floods, storms, droughts and heat waves have become more intense and are on the rise globally [1]. It was reported by Emergency Event Database [2] that in 2020 there were “26% more storms than the annual average of 102 events, 23% more floods than the annual average of 163 events, and 18% more flood deaths than the annual average of 5,233 deaths” (page 1). The global growth in occurrence of these phenomena is linked to climate change [3]. In fact, climate change caused by the increasing of greenhouse concentration gases, contributes to making these events worse with the increasing of temperature, variability and more extreme rainfall pattern [4, 5]. These consequences of climate change lead to the increasing of extreme weather events and disaster frequency and magnitude [6] including flood [7, 8] generating intersecting disasters [9]. Floods particularly represent the disaster which occurs more (60% of the total number of major disasters events in 2020) worldwide and deadliest (41% of total disaster’ deaths in 2020) type after drought [2, 10]. Recent study on satellite imaging reveals that the proportion of population exposed to flood has increased from 20 to 24% previously due to the increase of flood and migration [11]. It was shown that climate and demographic change would add 25 new countries to list of 32 that are already experiencing increasing flood globally. Furthermore, the majority of population in Asia and Africa were flooded between 2000 and 2015, and the projection give a gloomy picture with a large number of people exposed for 2030. In West Africa, flood is the top most frequent natural hazard from 1900 to 2022 among other disasters (https://public.emdat.be/mapping). In Benin and Togo, the communities in the Lower Mono River (LMR) catchment have for a several times experienced flood event. As a result of flood impacts in 2010, it causes enormous damages to the populations in Benin and Togo [12, 13]. In 2019, the communities in the LMR catchment experienced one of the most severe floods affecting thousands of people living close to the river. Indeed, in the catchment, the level of water in the river jumped a meter in four days and lead to flood which affected around 50 000 residents of Benin and Togo [14]. With the rise of extreme events, this situation is likely to worsen in the future [15]. Indeed, a study on climate and extreme rainfall events conducted in the Mono River catchment revealed that the intensity of extreme rainfall events and daily precipitation will significantly increase by 2050 [16], which could trigger future flood events in the region. Given the current context of climate change and rapid population growth, without effective adaptation strategies, the future flood damages on local communities in Lower Mono River catchment will persist and become more alarming. Therefore, proper adaptive strategies are required to deal with future flood risk, which may be numerous due to global warming and urbanization [17]. Previous studies suggest that comparing local population‘s perception of flood risk with historical climate data could contribute to identify efficient adaptation and improve flood management [18, 19]. Understanding how people perceive, experience and interpret climate change related hazards event is crucial for designing and implementing efficient policies and responses to this phenomena [20–22]. The way local communities perceived climate change influenced how they adapt to climate change [23, 24] compared farmers ‘observations Kalapara subdistrict in Bangladesh on climate change and variability to meteorological data in order to assess the way farmers’ perceptions confirm or contradict the climatic trends and analyses their adaptive strategies with a conclusion of good fit of households’ perception to climate trend. Similarly, many other studies were conducted in hazard-prone areas such as various agroecological zones in Kenya, communities of the Upper East Region of Ghana, Agroecological Zones in Southern Ethiopia, hazard ‑ prone districts of northwest Bangladesh, Kalapara subdistrict in Bangladesh, in northern Ghana and Ensaro District in Ethiopia by comparing farmers’ perceptions of climate change or variability with meteorological trends and examined adaptive strategies [23, 25–30]. [31] reviewed the West African’s climate trend to local perception in Burkina Faso to dig deeper insight in their decision making in response to climate change, which allowed for a better understanding of extreme events related to climate change and better guidance on adaptation strategies to be implemented in Burkina Faso. Moreover, [32] have shown the importance of local knowledge in understanding climate chnages implications in agriculture. [29] advocated for the importance of mixing approaches that integrate local perceptions with scientific evidence in order to develop effective and sustainable adaptation strategies. Most of these studies compared specific climate parameters to household perceptions in general for determining adaptive strategies, but less attention was given to flooding. In addition, despite many studies were conducted in the Lower Mono River (LMR) catchment for analyzing the climatic and hydrological causes of flood and getting more insight in its causes in the study area [33–37], the information on local communities and stakeholders perceptions on this matter remain limited. [38] noted that local community perception is an important predictor for flood mitigation in the catchment. Therefore, this paper aims at filling this knowledge gap by comparing local perception on flood with hydrological and climate parameters. Specifically, we looked at 1) the trends of climatic and hydrological data as well as the households’ perceptions on flood trend, 2) their relationship and climate and hydrological causes of flood in the Lower Mono River catchment, and 3) factors which influence household perception on rainfall change. Establishing this information can provide insights into flood risks and inform better adaptation strategies in the region.

4. Discussion This study compares household perception of flood to climate (rainfall) with hydrological data in the Mono river catchment. The annual rainfall analysis for the 8 localities purposely selected for this study revealed that the years 2010 and 2019 had recorded high rainfall values and were classified as severe and extreme flooded years. These same years were characterized by households as the most flooded years, which shows that households’ rainfall perception is in good tracked with climate data. Similar finding was reported by [57] in Bangladesh. Also, it appears that rainfall is the principal cause of flooding in the region, shown both by the empirical data and the household perceptions. This result corroborates with many studies and reports conducted in the study area, which have also shown how hydro metrological event, especially floods, have caused huge damage to local population [58–61]. The dynamic of monthly rainfall and discharge at the upper and down part of the basin revealed that both maximal monthly rainfall and discharge are obtained in the same month (October). In the same line with that, the study conducted by [62] on the hydrometeorological analysis of floods in the Mono watershed in West Africa with a conceptual rainfall-runoff model shows that the discharge at the entrance as well as at the exit of the dam has a seasonal regime between the months of June and October. Similarly, the rainfall-runoff model, HBV-light (Hydrologiska Byråns Vat- tenbalansavdelning) was used in the study conducted by [63] whereby the satellite rainfall data were used to assess the utility of the satellite data in runoff modelling, flood forecasting and climate change impact assessment. This study reveals that there is concordance between the discharge simulated (except of the Climate Hazards Group Infrared Precipitation with Station data version v2.0) with the observed value of discharge within the basin. Furthermore, the monthly precipitation is correlated with the household perception of flooded months reported by the respondents from the upper part of the basin, and opposite from the respondent from the lower part (with no correlation). Then, it raises the question of whether household perceptions vary according to their location within the catchment, or whether households are more interested in dealing with other flood causes than rainfall because of religious beliefs (e.g., some believe that rainfall and floods are God’ will and that have no control over them, see Fig 12). In the view of household, at the upper part, rainfall is link to flood while in the down part flooding are less associated to rainfall and other factors such as dam management contributes to flooding. On other hand, the most flood-affected communes including Athiémé, Grand Popo, Lacs and Yoto, which are situated in the lower part of the basin [64, 65]. The communes of Bas-Mono and Moyen Mono were considered averagely flood affected whereas the communes of Ogou and Lokossa were less affected. However, it can be noticed that the communes of Lokossa and Bas Mono, which are in the down part of the basin are considered as averagely and less affected based on perception of households. This observation is due to the location of protective dam in Bas-Mono. Also, Lokossa is located after the commune of Athiémé and therefore far from the main line of the river. This could be the results of the extreme rainfall that lead to increased discharge, causing the river to overflow and affecting the surrounding households [66]. In addition to extreme rainfall, other major causes of flooding such as the Nangbeto dam management was also reported by respondents. Indeed, the communes in the lower part of the basin receive the accumulation of water due to the opening the Nangbeto dam releases combined with the short rainy season, which increases their vulnerability to this phenomenon. This statement was also confirmed by stakeholders during our workshop organized on March 2022 on drivers to flood risk (forthcoming publication) (Fig 12). They classified climate change through extreme rainfall and Nangbeto water release as the first principal cause of flood. According to Red Cross during the CLIMAFRI workshop in 2022, the fact that households in the down part of the basin are more affected by the flood is due to the fact that they received the accumulation of water and runoff through the river coming from the upper part of the basin. It was also reported that, in 2021, some communes were affected by flood without experiencing extreme rainfall event (2019). This was also mentioned by, official press agency of the government of Benin (Agence Bénin Presse (ABP)) that “the flooding was exacerbated by dam releases at Nangbéto and Anié in the Plateaux Region of Togo. Several small tributaries of the Mono have also flooded” [67]. PPT PowerPoint slide

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TIFF original image Download: Fig 12. Perception of stakeholders on flood drivers (source: stakeholders’ workshop, CLIMAFRI 2022). https://doi.org/10.1371/journal.pclm.0000123.g012 Similarly, [68] reported that communities at higher elevation are less at risk than the ones at the low altitude and concluded the causes of flood risk in the lower part of the catchment do not only come from the extreme rainfall but also the result of the bad regulation of Nangbeto dam. Our study corroborates with the study of [38], that the population at the lower part of the catchment ranked the “release of water by the Nangbeto dam” as the main cause of flooding in the target study communities. Furthermore, [69] showed that stakeholders perceived the flood duration, depth, velocity and spatial extent in the LMR catchment are associated with the discharge at Nangbeto. This has been observed in in a Transboundary River Basin in Korean Peninsula showed that the released of water from the dam constructed on the river represents the principal cause of flood in the downstream part [70]. Regarding the factors affecting household’s perception on rainfall change, our findings corroborate with other studies. For example, [71] showed that the increasing size of the household lead to an increase in the level on climate change perception of farmer. Others studies have the same conclusion such as of [72, 73]. Households with agricultural experience between 11 to 20 years represent the ones who identify change rainfall pattern compared to the other categories. This can be explain by the fact that, majority of the respondents (88%) are in their middle age (25–50). [56] found that increases in farming experience permit the increasing of awareness in rainfall change. This result is also confirmed by others studies [71, 74]. Also, household income may constitute a factor which make household vulnerable to the impact of extreme or less rainfall as more households’ incomes is small, more household are aware of change in rainfall pattern. In addition, the soil type (Dystric Nitosols) of household agricultural plot and the households ‘house altitude represents variables which permit to household to identify a change in rainfall pattern. Dystric Nitosols can be find at the lower altitude [75]. Finally, households with homes located at higher elevations are more likely to notice a change in rainfall.

5. Conclusion Flood is one of the disasters which occurs more in the transboundary basin shared between Benin and Togo. Despite the plan set up by the governments of each country to cope with that phenomenon, the risk is still high, and the projections are worst. Adaptation strategies are therefore necessary to reduce the risk of flooding and improve the living conditions of communities. In order to identify an efficient and sustainable strategy, it is important to know the perception of the households for understanding the flood’ causes. It is within this context that this study has been conducted. This study reveals that respondents perceive the year 2010 and 2019 as the year they were most affected by flood, these years are perceived as the excess rainfall years in term of rainfall. Households’ perception on flooded month is correlated with the monthly precipitation and discharge in some commune. This show that rainfall induces the increase of discharge and subsequently in some communes. Adaptive strategies need to pay more attention on combining structural and non-structural measure to reduce the impact due to flood in the Lower Mono River catchment. From the findings, the perception of the local communities is important for having more insight in the real causes of the flood. The local perception can also guide decision makers in taking the best measures to tackle flood risk in the Mono river catchment. Climate and hydrologic data show that all the communes or prefectures at the down part of the catchment are more vulnerable because of the fact that they received the accumulation run off water. But in the perception of households, some communes are not because there are some hydraulic infrastructures. This denotes the importance of considering local communities need to be considered for choosing the efficient measures in order to cope with flood risk. Therefore, proposition of efficient adaptive strategies needs to pay more attention on local communities’ participation to reduce the impact of flood in the Lower Mono River catchment. Future work could concentrate on the utility or efficiency of installing hydraulic infrastructures in the most vulnerable prefectures. This article represents the result of my thesis work.

Acknowledgments This work would not have been possible without the financial support and capacity building of West African Science Service Centre on Climate Change and Adapted Land Use (WASCAL) and Implementation of Climate-sensitive Adaptation Strategies to Reduce the Flood Risk in the Catchment Area of the Cross-border Lower Mono River (CLIMAFRI) project. A big thank to the Center for Development Research (ZEF) support.

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[1] Url: https://journals.plos.org/climate/article?id=10.1371/journal.pclm.0000123

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