Fernando Dornelles

Flood-risk assessments often lack globally consistent hazard layers because design-grade hydrodynamic models require local calibration, detailed boundary conditions, and substantial computation. We present a data-light framework that uses application programming interfaces to assemble the globally available elevation model, hydrography, and road network data needed to infer flood-hazard susceptibility. Height Above Nearest Drainage was computed using a drainage calibration constrained by OpenStreetMap data to improve channel alignment, and the Multiresolution Index of Valley-Bottom Flatness provides complementary planarity information. An interpretable monotonic gradient-boosted regressor was trained against return-period inundation inventories, and the continuous score was converted to a common five-class ordinal scale using prototype-aware threshold sets for planar and incised fluvial regimes. The model was applied to three independent reaches, and the five-class hazard maps consistently captured the 100-year flood footprint within the upper hazard tiers (Classes 4–5). The ordinal ranking remained physically coherent across all return periods: low-susceptibility terrain was essentially invariant to increasing flood severity, whereas higher classes exhibited progressively greater inundation likelihood, reproducing the expected behaviour of flood-frequency analysis. The model correctly distinguished flooded from non-flooded terrain in 78–83 % of pairwise comparisons and maintained reliable identification of the most flood-prone terrain under strict false-alarm constraints (partial AUC at false-positive rate ≤ 0.20 of 0.365–0.420), supporting its use for screening-level prioritisation. The framework provides rapid, auditable screening-grade hazard layers suitable for coupling with exposure and vulnerability in risk workflows, complementing rather than replacing site-specific hydraulic studies.

We present an overview of the unprecedent hydrological event that occurred in Rio Grande do Sul state in late April and early May 2024, causing floods and landslides in a scale that was not seen before in Brazil. The rainfall that caused the disaster is incomparable to any recent event in Brazil at large spatial and temporal scale. The intense and long-lasting precipitation led to record floods from small rivers with drainage areas below 1000 km² to the Patos Lagoon, which drains more than 180,000 km². The rainfall also led to landslides that rank first in Brazil in terms of spatial scale and number of occurrences. Mountain rivers experienced flash floods with extreme water levels, while in the lowlands the large rivers and the Patos Lagoon experienced long duration flooding, with stage remaining high for about 30 days. The flood event is probably ranked first in terms of displaced people and damage to property and infrastructure in Brazil. Almost 200 fatalities occurred due to the disaster and protection structure failures. The April-May hydrological event show a glimpse of what can be expected along the coming decades due to climate change in a region that covers South Brazil, and parts of the neighboring countries.

Resumo Este artigo evidencia a utilização das Soluções baseadas na Natureza como alternativa complementar adotada pela gestão pública brasileira para o manejo de águas pluviais urbanas. O aumento da impermeabilização do solo decorrente da urbanização, a mudança climática, a degradação ambiental e poluição hídrica, além dos desafios hidrológicos deste século, têm alavancado a busca por opções sustentáveis a fim de reduzir a sobrecarga dos sistemas tradicionais de drenagem que causa alagamentos e inundações, melhorar a qualidade da água, aumentar a resiliência urbana e a valorização do ambiente natural e seus benefícios. Nesse contexto, este trabalho tem por objetivo elucidar a utilização dessas técnicas nos Planos Diretores de Drenagem Urbana e respectivos Manuais de Drenagem Urbana, ferramentas indispensáveis de regulamentação, em um contexto nacional. Esta investigação define-se metodologicamente como uma pesquisa exploratória e documental, na qual foi salientado que, apesar da gestão pública, através de suas normas e regulamentações de manejo de águas pluviais, propor a utilização de várias dessas técnicas como parte da drenagem urbana, e das Soluções baseadas na Natureza serem uma opção valiosa, ainda é preciso uma abordagem integrada que contemple a diversidade das áreas urbanas, a participação de diversos agentes da sociedade e as particularidades de cada dispositivo.

The degradation of urban rivers is a phenomenon caused by virtually all cities intersected by rivers. Currently, there is a substantial number of revitalization projects in progress. Nonetheless, their execution demands significant investments, particularly for water quality enhancement. Moreover, apart from the cost factor, the scarcity of space along their banks constrains the implementation of improvement systems. This study introduces a simplified methodology aimed at evaluating the technical feasibility of revitalization interventions within urban river segments, with a focus on enhancing water quality and user experience. The method follows a structured framework encompassing four sequential phases: execution of hydraulic, hydrological, and sanitary analyses concerning the watershed; development of foundational principles and intervention strategies pertaining to the riverbed; appraisal of the congruence between proposed interventions and the intrinsic attributes of the river channel; comprehensive assessment of the overall viability of the revitalization initiative. The method's validation was conducted through a case study involving the Dilúvio Stream in Porto Alegre, RS, showcasing its coherent application and adaptability within the predetermined premises. Thus, the methodology emerges as a preliminary decision-making support tool for projects related to the urban river requalification domain, facilitating the identification of met prerequisites and provision of informed guidance.

In Brazil, little is known about climate change impacts on extreme events at local scale. Here, we explored ways of communicating it, in the form of intensity-duration-frequency (IDF) curves, using the nonstationary equidistant quantile matching (EQM_NS) method. EQM_NS was applied in two urbanized areas of Brazil: São Paulo and Porto Alegre. This research was conducted using recorded and modeled precipitation data, the latter using the Regional Climate Model Eta. Results indicated an increase in rainfall intensity for rare events, which were intensified under nonstationarity. The use of stationarity misrepresented the trends related to precipitation, being able to mask the direction of change in future conditions. Future IDFs with Eta’s 3-hourly resolution appeared to be intensified when compared with those from daily resolution. The increase in rainfall intensity was more significant for short durations than for daily ones, bringing concerns about associated hazards and their impacts on society and urban infrastructure.

Increasing urbanization coupled with climate change and poor urban drainage management can lead to several water-related problems, such as floodi |

The intensity-duration-frequency (IDF) equations establish the relationship between the intensity and the duration of an extreme precipitation associated to the probability of its occurrence. Some studies have fitted multiple IDF equations per rain gauge, valid for certain rain duration ranges. An example is the IDF equation for the 8^th District of Meteorology of Porto Alegre rain gauge, established and published by the CPRM in the Pluviometric Atlas Project. The main objective of the present study is to evaluate the implication of using this type of IDF equation, referred to as a “discontinuous IDF equation”, in the generation of runoff hydrographs, using the mentioned IDF as case study. The methodology consisted in comparing the peak flow and the runoff volume of hydrographs generated by the discontinuous IDF equation with the hydrographs obtained by using a single IDF equation. The runoff hydrographs were generated for hypothetical basins with the following characteristics: contribution areas of 5, 20 and 80 km²; CN of 70, 80 and 90; and time of concentration of 20, 40, 60, 100 and 200 minutes. A 24-hour rainfall event was considered with return period of 5, 10, 25, 50 and 100 years. As results, it was observed that, in the case studied, the multiple IDF equation present a better fit to the observed rainfall data than the single IDF equation. However, the discontinuity at the transition point between the equations, depending on its magnitude, may present some influence on the peak flow and on the runoff volume due to occurrence of secondary peaks on the runoff hydrographs. Therefore, it is recommended that a maximum limit of discontinuity must be observed between the multiple equations in order to avoid the occurrence of secondary peaks in the runoff hydrographs.

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