Study of morphometry and land coverage to help urban planning in Barbosa and Barbosinha Brooks watershed, Lins - SP

Urbanization in hydrographic basins promotes changes in the hydrological cycle through the impermealized areas. Not only surface runoff is increased, reducing infiltration, but also the susceptibility to extreme hydrological events. The objective of this study is to analyze the natural susceptibility of Córregos Barbosa e Barbosinha (Barbosa and Barbosinha Brooks) watershed to flooding. Morphometric parameters of land use and occupation were analyzed, in order to subsidize management and planning in an area of urban expansion. The analysis of land use and occupation was based on the supervised classification method of Landsat-5 Thematic Mapper (TM) sensor and Landsat-8 Operational Land Imager sensor (OLI) satellite images dated 1990, 2006 and 2020. Morphometric indices were calculated using the SPRING 5.4.3 software and a SRTM image with a spatial resolution of 30 meters. The results indicate that the natural susceptibility to flooding of the study area is medium to high, and can be intensified by the dynamics of land use and occupation and increasing impervious areas in the basin. Over the period of study, the growth of impervious areas was 133% relative to 1990.

Mechanisms and possibilities for the emergence of extreme floods in arid zones (Tiznit plain - Morocco): ميكانزمات واحتمالات نشأة الفيضانات المتطرفة بالمناطق الجافة (سهل تزنيت - المغرب)

In Morocco, the dynamics of change in rainfall patterns have been underway for decades. It is characterized by increasingly frequent and violent hydrological and climatic events (floods and droughts). This work aims to study the peculiarities and mechanisms of the appearance of floods in the watershed of the Oudodou wadi (Province of Tiznit - southwestern Morocco) and conduct a frequency analysis of the extreme hydrological events associated with floods to estimate their probabilities and their return periods. In addition to the diagnosis of natural factors in the area studied and their relationship to the emergence of floods, the methodological approach adopted is divided into two stages. The first, known as historical, is based on the study of 8 flooding cases (1942 - 2014) and the delimitation of threatened areas through the representations of residents. The second step focused on analyzing the frequencies of extreme hydrological events to determine their severity and return periods. Analysis of the results showed that flood thresholds are always associated with the strength and concentration of rainfall, giving them a sudden behavior like summer floods. To guide the interventions of actors in the field, the areas threatened by flooding have been identified according to their degrees of severity. The recurrence of the flows was modeled using the GAMMA law which makes it possible to estimate the probability of occurrence of extreme events (floods) and the instantaneous flows corresponding to the return periods of 2, 5, 10, 20, 50 and 100 years. Biannual and five-year hydrological events correspond to instantaneous flows of 120 and 331 m3/s, while exceptional or even very exceptional cases have a return period of more than 50 and 100 years and correspond to instantaneous flows of 912 and 1035 m3/s.

Recent Changes in Hydroclimatic Patterns over Medium Niger River Basins at the Origin of the 2020 Flood in Niamey (Niger)

Niamey, the capital of Niger, is particularly prone to floods, since it is on the banks of the Niger River, which in its middle basin has two flood peaks: one in summer (the red flood) and one in winter (the black flood). In 2020, the Niger River in Niamey reached its all-time highest levels following an abundant rainy season. On the other hand, the floods in Niamey have been particularly frequent in the last decade, a symptom of a change in hydroclimatic behaviour already observed since the end of the great droughts of the 1970s and 1980s and which is identified with the name of Sahelian Paradox. This study, starting from the analysis of the 2020 flood and from the update of the rating curve of the Niamey hydrometric station, analyses the rainfall–runoff relationship on the Sahelian basins of the Medium Niger River Basin (MNRB) that are at the origin of the local flood. The comparative analysis of runoffs, annual maximum flows (AMAX) and runoff coefficients with various rainfall indices calculated on gridded datasets allowed to hydroclimatically characterise the last decade as a different period from the wet one before the drought, the dry one and the post-drought one. Compared to the last one, the current period is characterised by a sustained increase in hydrological indicators (AMAX +27%) consistent with the increase in both the accumulation of precipitation (+11%) and the number (+51%) and magnitude (+54%) of extreme events in the MNRB. Furthermore, a greater concentration of rainfall and extremes (+78%) in August contributes to reinforcing the red flood’s positive anomalies (+2.23 st.dev in 2020). The study indicates that under these conditions the frequency of extreme hydrological events in Niamey will tend to increase further also because of the concurrence of drivers such as river-bed silting and levee effects. Consequently, the study concludes with the need for a comprehensive flood-risk assessment on the Niamey city that considers both recent hydroclimatic trends and urbanisation dynamics in flood zones hence defining the most appropriate risk-reduction strategies.

Simulation of flood hydrographs in urban channels: a tool for urban planning

Floods caused by extreme hydrological events and their consequences are one of the major challenges faced by local government authorities about urban planning. In this context, we studied the urban cross channel sections behaviour located in the Jatobá stream catchment, in the city of Belo Horizonte, Brazil. Different precipitation scenarios were used as input parameters for the hydraulic simulation. For this purpose, the accumulated rainfall was disaggregated and a frequency analysis was performed to compute different duration times (from 10 to 120 minutes) and return periods (from 2 to 100 years). Then, hydrological and hydraulic simulations were carried out using HEC-HMS and HEC-RAS models, respectively. The results showed that the average time until the channel overflows was 58 minutes and the average duration time for the overflow was 28 minutes. The channel overflowed in 77.14% of the simulated scenarios. The simulations were carried out for different rainfall return periods and time duration to characterize extreme events for this catchment, aiding the decision- making process and assisting in the development of strategies to improve the drainage system.

Projections of Local Knowledge-Based Adaptation Strategies of Mexican Coffee Farmers

Local knowledge can be a strategy for coping with extreme events and adapting to climate change. In Mexico, extreme events and climate change projections suggest the urgency of promoting local adaptation policies and strategies. This paper provides an assessment of adaptation actions based on the local knowledge of coffee farmers in southern Mexico. The strategies include collective and individual adaptation actions that farmers have established. To determine their viability and impacts, carbon stocks and fluxes in the system’s aboveground biomass were projected, along with water balance variables. Stored carbon contents are projected to increase by more than 90%, while maintaining agroforestry systems will also help serve to protect against extreme hydrological events. Finally, the integration of local knowledge into national climate change adaptation plans is discussed and suggested with a local focus. We conclude that local knowledge can be successful in conserving agroecological coffee production systems.

Study of groundwater salinity in the HAHA syncline by the Kohonen self-organized classification (Essaouira, Morocco)

The coastal aquifer of the Essaouira syncline (Morocco) was studied to identify the main processes at the origin of the salinization of groundwater. In fact, a multicriteria analysis approach on hydrochemical data and physicochemical parameters of the Plio-Quaternary aquifer was used to understand their spatio-temporal variation and their origins. Currently, integrated water resources management has become paramount to both local, regional, national and international. This management is favored by extreme hydrological events (droughts or floods) which can have direct influences on human, economic and political aspects. Appropriate management of a resource requires its evaluation. The statistical study by Kohonen's self-organized classification (SOM) of hydrochemical data for the years 1995 and 2009 is used to process 47 samples distributed over the entire study area; it showed an evolution of the values of the parameters. Physico-chemical as a function of time and space with an increase in the values of the parameters, from the center of the study area towards the southwest.

Effect of a Summer Flood on Benthic Macroinvertebrates in a Medium-Sized, Temperate, Lowland River

Floods are naturally occurring extreme hydrological events that affect stream habitats and biota at multiple extents. Benthic macroinvertebrates (BM) are widely used to assess ecological status in rivers, but their resistance and resilience to floods in medium-sized, temperate, lowland rivers in Europe have not been sufficiently studied. In this study, we quantified the effect of a moderate (5-year return period) yet long-lasting and unpredictable flood that occurred in summer 2020 on the BM community of the Jeziorka River in central Poland. To better understand the mechanisms by which the studied flood affected the BM community, we also evaluated the dynamics of hydrological, hydraulic, channel morphology, and water quality conditions across the studied 1300 m long reach. Continuous water level monitoring, stream depth surveying, and discharge measurements. As well, in-situ and lab-based water quality measurements were carried out between March and August 2020. BM communities were sampled three times at eight sites along the reach, once before and twice after the flood. High flow velocities during the flood resulted in stream bed instability leading to sand substrate movement that caused streambed aggradation by up to 0.2 m. Dissolved oxygen and ammonium-nitrogen were major drivers of BM community structure. Taxa richness, abundance, and the BMWP-PL index declined significantly, whereas Shannon evenness and Simpson diversity indices showed no significant change in the first post-flood sampling, as indicated by Kruskal–Wallis and Tukey tests. Non-metric multidimensional scaling (NMDS) analysis showed that community composition was also significantly affected by the flood. Seven weeks after the flood peak (August 2020 sampling), BM communities had fully recovered from the disturbance. The results can serve as a first approximation of the resistance and resilience of BM communities for relevant applications in other medium-sized, low-gradient, temperate rivers.