Mesure de la vulnérabilité des milieux urbains au Cameroun face au changement climatique

Les différentes catastrophes survenues en milieu urbain au Cameroun récemment, mettent en exergue les désormais dangers permanents qui pèsent sur les habitants. On note une augmentation des extrêmes : de hautes températures, des perturbations des régimes pluvieux et la récurrence des vents violents. Certains de ces effets sont amplifiés par la géographie contraignante de plusieurs villes et par l’influence anthropique sur l’environnement. En effet, d’une part les sites de plusieurs villes camerounaises ont soit des reliefs accidentés qui favorisent l’érosion des terrains, soit des configurations planes qui limitent l’évacuation gravitaire de l’eau de ruissellement. D’autre part, la croissance urbaine rapide et la prolifération des bidonvilles qui couvrent près de 65 à 70% de la superficie urbaine, usent plus rapidement les ouvrages et infrastructures d’assainissement urbaines lorsqu’ils existent dus à l’imperméabilisation accélérée et continue du sol urbain ainsi qu’à la mauvaise gestion des déchets. L’urgence de trouver des solutions durables à ce phénomène est désormais sans équivoque. Elle nécessite un encadrement normatif inclusif plus performant que celui actuellement en vigueur, qui amène le pays vers la résilience. The disasters that’ve occurred recently in urban areas in Cameroon, highlight the permanent dangers weighing on the inhabitants. There is an increase in extremes climate parameters: high temperatures, rainfall disturbances and the recurrence of gales. Some of these effects are amplified by both the constraining relief of several cities and human influence on the environment. In fact, on the one hand, the sites of several Cameroonian cities either have rugged reliefs that promote land erosion, or flat configurations that limit the gravity discharge of runoff water. On the other hand, the rapid urban growth and the proliferation of slums which cover nearly 65 to 70% of the urban area, wear out more quickly the works and urban sanitation infrastructures when they exist due to the accelerated and continuous waterproofing soil in addition to the poor waste management. The urgency to find lasting solutions to this phenomenon is now unequivocal. It requires an inclusive normative framework that is more effective than that currently in force, which brings the country towards resilience.

Adaptation Strategies for Flooding Risk from Rainfall Events in Southeast Spain: Case Studies from the Bajo Segura, Alicante

The management of runoff during torrential rainfall events is a significant problem in urban areas of southeast Spain. The increase in soil sealing and the occupation of areas prone to flooding have aggravated this problem. Due to this situation, municipal administrations, in collaboration with the concession holder for the supply of water and sewage services, Hidraqua Gestión Integral de Aguas de Levante SA, are committed a more efficient management of non-conventional water resources. An example of this can be found in the municipalities of Rojales, Daya Nueva, and San Fulgencio. These towns are located in the Bajo Segura region of the province of Alicante, where various initiatives have been implemented that break away from the traditional paradigm of rigid infrastructures. These initiatives include green spaces or areas, and sustainable urban drainage systems (SUDS) or nature-based solutions (NBS). This article presents various case studies. Firstly, in the town of Rojales, where several actions are being undertaken to improve the management of wastewater and rainwater and provide a solution to unauthorised dumping, as well as encouraging the use of reclaimed water with the creation of a recreational green area, El Recorral Park. Secondly, in the case of Daya Nueva, the Europa Park constitutes a recreational green area, Europa Park, facilitates runoff drainage by SUDS and NBS. Finally, the creation of a floodable pond in the municipality of San Fulgencio encourages the use of wastewater, thus avoiding the discharge of this non-conventional water resource into the sea. In addition, the pond facilitates the appropriate management of runoff water. The working method in this article has been twofold: firstly, bibliographical references have been consulted from other national and international areas; and secondly, the technical projects in the case studies have been analysed in detail. Several field trips have been made to the selected municipalities, accompanied by the technical personnel in charge of the execution of the projects, to examine the measures adopted. The results show that the implementation of these systems contributes to adapting to climate change and creates more resilient urban spaces.

Identifying potential sites for artificial groundwater recharge using GIS and AHP techniques: A case study of Erbil basin, Iraq

Excessive extraction, uncontrolled withdrawal of groundwater, and unregulated practices have caused severe depletion of groundwater resources in the Erbil basin, Iraq. This situation has had a number of negative consequences on human settlement, agricultural activities, clean water supply, and the environment. Runoff harvesting and artificial groundwater recharge play a significant role in the sustainable management of water resources, particularly in arid and semi-arid regions. This study aims to: (1) delineate groundwater recharge zones using multiple thematic layers that control the groundwater recharge process, and (2) identify prospective sites and structures to perform artificial groundwater recharge. In order to generate a potential map for groundwater recharge zones, seven thematic layers are considered in this study, namely, topographic position index, geomorphology, lithology, land cover, slope, drainage-length density, and lineament-length density. After that, the analytic hierarchy process was applied to weight, rank, and reclassify these seven thematic layers. All maps are then integrated within the ArcGIS environment for delineating groundwater recharge zones. Accordingly, the resulting map categorizes the study area into five zones: extremely high, high, moderate, low, and extremely low potential for groundwater recharge. As expected, areas along the Greater Zab river show the highest possibility for groundwater recharge. Likewise, rugged eastern hills demonstrate an encouraging capacity for artificial aquifer recharge, whereas the least effective area is represented by built-up land. Based on the generated map, two dams are proposed as promising artificial recharge structures for harvesting runoff water east of Erbil city. Lastly, the resulting map of the potential groundwater recharge zones is verified using static water level data, where the coefficient of determination (R2) achieved a satisfactory result (0.73). These findings provide crucial evidence for implementing a sustainable management plan of surface and groundwater resources. The applied method is eventually valid for regions where appropriate and adequate field data availability is a serious issue.

RAINWATER MANAGEMENT PROBLEMS IN CITIES IN DEVELOPING COUNTRIES: THE CASE OF THE MUNICIPALITY OF ZIGUINCHOR, SENEGAL

Senegalese cities are experiencing very rapid growth in terms of both spatial and demographic development, which has an impact on the management of runoff water, which is increasingly a major concern of authorities and urban populations. In these cities, public sanitation infrastructure is insufficient and unevenly distributed in urban space. The objective of this study is to characterize the problem of rainwater management in the city of Ziguinchor (southern Senegal). The methodology is based on an administration, a questionnaire submitted to 288 heads of households, and an interview guide with 13 actors who stand out in the environmental management component at the local level. The results obtained attest to a real problem of sanitation of rainwater managed in precarious conditions due to the lack of infrastructure and water management methods used by households. The infrastructural problem is a factor in the poor management of rainwater in Ziguinchor, while rainwater drainage practices do not protect the living environment of the populations. In the city of Ziguinchor, the main strategies adopted in the face of the sanitation network deficit are based on backfilling, the laying of sandbags and stones, evacuation through buckets.

Application of curvilinear base flow recession model for estimating storage losses in a red soil watershed

The curvilinear recessions relating to storage losses with runoff water collected at storage structure, G R Halli watershed, Chitradurga district, Karnataka fitted best with the observations. The method of estimation of the model parameter is presented in the paper. Relating storage to storage on preceding day gives more information about water balance of this catchment. It is observed from the data that more emphasis is to be given for in situ conservation measures.

GIS-Based Surface Runoff Modeling Using Empirical Technique For A River Basin In South India

Precipitation is the primary source of fresh water in the world. Surface runoff will happen when the amount of rainfall is greater than the soil’s infiltration capacity. In most water resource applications, runoff is the most important hydrological variable. Aside from these rainfall characteristics, there are a number of catchment-specific elements that have a direct impact on runoff amount and volume. This research focuses on estimating surface runoff over the lower Vellar basin, a river basin in the southern part of India, by integrating Soil Conservation Service-Curve Number (SCS-CN) method with GIS. This technique is one of the most common methods used by hydrologists for estimating surface runoff. Curve Number (CN) is an index established by the Natural Resource Conservation Service (NRCS) to denote the potential for stormwater runoff. The nature of the watershed is explored first by creating land use and land cover pattern followed by the preparation of slope, drainage, and location maps. The area taken for this study is the lower Vellar basin situated in the Cuddalore District of Tamil Nadu, India. The curve number is analyzed using the rainfall data of 15 years (2001-2015) and the runoff is being calculated. The watershed pattern of the study area is also explored being analyzed and executed. Preservation of the runoff water is also discussed.

Runoff optimization and control for basin water allocation

The water distribution plan for the three major irrigation districts (Changma, Shuangta, and Huahai) in the Shule River Basin in the planned year was analyzed in this study in an effort to resolve the insufficient natural endowment of water resources and contradiction between supply and demand throughout the basin. Based on this plan, and under the condition of satisfying the scheduling constraints of cascade reservoirs, the minimum total water supply shortage in the watershed was taken as the main goal coupled with the cascade reservoir runoff optimization control coefficient. An optimized dispatch model of the reservoir group was established accordingly. The large system coordination decomposition algorithm was called to solve the model and obtain the water scheduling scheme of each reservoir. After the optimal regulation of runoff, the water demand of the three major irrigation areas of Changma, Shuangta, and Huahai in the planned year is greater than the available water resources of the Shule River and the Petroleum River. The total surface runoff water shortage is 66.01 million m3, which cannot be satisfied. Among the reservoirs, Shuangta has the highest water shortage quota of 43.503 million m3, followed by Chijinxia with a water deficit quota of 22.18 million m3, and finally by Changma with a minimum water shortage quota of 0.3277 million m3. The results of this work may provide technical support for water resource allocation and regulations, as well as for the efficient usage of the Shule River Basin.

Predicting the Hydrological Impacts of Future Climate Change in a Humid-Subtropical Watershed

Future climate change is expected to impact the natural systems. This study used future climate data of general circulation models (GCMs) to investigate the impacts of climate change during the future period (2062–2095) relative to the historical period (1981–2014) on the hydrological system of the Minjiang river watershed, China. A previously calibrated soil and water assessment tool (SWAT) was employed to simulate the future hydrology under the impacts of changes in temperature, precipitation, and atmospheric CO2 concentration for four shared socioeconomic pathways (SSP 1, 2, 3, and 5) of the CMIP6. The study revealed that the impacts of increase in future temperature, i.e., increase in ET, and decrease in surface runoff, water, and sediment yield will be countered by increased atmospheric [CO2], and changes in the hydrological parameters in the future will be mostly associated to changes in precipitation. Data of the GCMs for all the SSPs predicts increase in precipitation of the watershed, which will cause increase in surface runoff, water yield, and sediment yield. Surface runoff will increase more in SSP 5 (47%), while sediment and water yield will increase more in SSP 1, by 33% and 23%, respectively. At the seasonal scale, water yield and surface runoff will increase more in autumn and winter in SSP 1, while in other scenarios, these parameters will increase more in the spring and summer seasons. Sediment yield will increase more in autumn in all scenarios. Similarly, the future climate change is predicted to impact the important parameters related to the flow regime of the Minjiang river, i.e., the frequency and peak of large floods (flows > 14,000 m3/s) will increase along the gradient of scenarios, i.e., more in SSP 5 followed by 3, 2, and 1, while duration will increase in SSP 5 and decrease in the other SSPs. The frequency and duration of extreme low flows will increase in SSP 5 while decrease in SSP 1. Moreover, peak of extreme low flows will decrease in all scenarios except SSP 1, in which it will increase. The study will improve the general understanding about the possible impacts of future climate change in the region and provide support for improving the management and protection of the watershed’s water and soil resources.

Phosphorus Export From Two Contrasting Rural Watersheds in the (Sub) Humid Ethiopian Highlands

Establishing worldwide sustainable and phosphorus efficient cropping systems is urgently needed because the supply of suitable phosphate rock is limited, and excess phosphorus in streams causes eutrophication. One of the impediments in the developing world for sustainable P practices is the lack of studies on P transport and its eventual disposition in the environment. One of these regions with few studies is the Ethiopian Highlands, with permeable volcanic soils. The objective was to establish baseline data on P watershed export in the (sub)humid highlands. Two contrasting watersheds were selected near Lake Tana. For 2 years, stream discharge and sediment, total P, dissolved P, and bioavailable particulate P concentrations were determined at the watershed outlet. The first watershed is the 57 km2 Dangishta, with lava intrusion dikes, forcing subsurface flow through faults to the surface and preventing gully formation. Subsurface flow was half of the 1745 mm annual precipitation, and surface runoff and erosion were minimal. The second watershed is the 9 km2 Robit Bata with 1,420 mm precipitation. The banks of several river banks were slumping. The upper part of the watershed generates saturation excess runoff. A hillslope aquifer in the lower part provided interflow. The average sediment concentrations of 10.5 g L−1 in the stream in Robit Bata (11 times that in Dangishta) reflected the sediments from banks slipping in the stream. The hydrology and the soil loss directly affected the phosphorus export. In Dangishta, the total P concentration averaged 0.5 mg L−1 at the outlet. In Robit Bata, the average total P concentration was 2 mg L−1. The bioavailable particulate P concentration was only twice the concentration in the runoff water. The low phosphorus content of the subsoil slipping in Robit Bata moderated biologically available particulate P at the outlet. Average dissolved P concentrations for both watersheds were around 0.1 mg L−1 in the low range found in temperate climates. It reflects the difference in length of time that phosphorus fertilizers have been applied. Our research concludes that commonly implemented practices such as strengthening river banks and stabilizing gully might not lead to improved water quality in Lake Tana.

PERSPECTIVES ON MALAYSIA'S LACK OF IMPLEMENTATION OF GREEN BACK LANES

Malaysia has been utilising green back lanes since the ‘90s. In spite of the several benefits of these lanes, such as the formation of active spaces, decrease in runoff water, and visitor attractions, green back lanes are yet to be deployed in the residential regions of Malaysia, prompting the question as to why these lanes have not yet been installed extensively. The objectives of this research work were: to determine what experts opined regarding the installation of green back lanes in the country, study the scenarios which caused the absence of implementation, produce a report showing the outcomes and analysis, and offer suggestions. The researcher deployed the interview strategy for ascertaining the views and standpoints of architects, town planners, maintenance staffs, project managers, and marketers on the dearth of green back lane installation. The research emphasises on the aspects of cost, maintenance, and safety.