Infrequent Floods Research Articles

Modeling the Dynamics of Social Preparedness with Regional Interactions to Explore Efficient Flood Early Warning Systems

Abstract Flood early warning systems (FEWS) are essential in mitigating flood damage. To optimize their effectiveness, it is important to understand how people respond to warnings and prepare for flooding events. The key factors influencing social preparedness include 1) direct and 2) indirect experiences of floods and 3) trust in warnings. However, existing sociohydrological models do not incorporate all these elements. To include these elements for social preparedness, we propose an idealized model that allows multiple regions to influence one another (i.e., regional interactions). We investigate the dynamics of social preparedness in a society composed of regions with varying infrastructure levels (e.g., levee heights) and explore strategies for developing a socially efficient FEWS. Numerical analyses reveal that in a society that has a region characterized by a low infrastructure level (i.e., a region with frequent floods), regional interactions lead to a pronounced cry wolf effect due to false alarms from other regions, diminishing social preparedness in the low-infrastructure region. These interactions also prevent a warning strategy that optimizes the natural-science-based index (i.e., threat score) from maximizing social efficiency. Conversely, in a society that has a region characterized by a high infrastructure level (i.e., a region with infrequent floods), regional interactions enhance the efficiency of FEWS by improving social preparedness through indirect experiences with floods. These findings suggest that as regional heterogeneity increases, it becomes increasingly vital for forecasters to consider social aspects (e.g., people’s experiences, trust, and interactions) when establishing a socially efficient FEWS. The refined model will be valuable to forecasters in designing effective FEWS in real-world situations.

Improving streamflow forecasting in semi-arid basins by combining data segmentation and attention-based deep learning

The increasing threats of flash floods and water scarcity in semi-arid regions necessitate high-quality streamflow forecasting with process-based or data-driven models. However, temporal heterogeneity of hydrological patterns and infrequent flood events present challenges for accurate streamflow forecasting. To address this issue, we purpose an effective modeling approach that combines a novel data segmentation method, BPX, with an attention-based deep learning (DL) model. BPX integrates Bai-Perron analysis and XGBoost to accurately identify dry and wet periods from hydro-meteorological variables both in the past and future times. The DL model introduces an attention mechanism to temporal convolutional network (TCN) to enhance its ability in handling heterogeneous time-series data. We demonstrate the effectiveness of our approach using nearly 20 years of hydro-meteorological data from the Wei River basin in China. Various modeling methods are compared, including two process-based models (Xinanjiang and GR4J) and four DL models (classical RNN, GRU, LSTM and TCN) with or without the attention module. After systematic benchmarking, it is found that both the BPX segmentation and the attention mechanism can improve streamflow forecasting with DL. Among the various modeling approaches, BPX-TCN exhibits the best overall performance throughout the prediction period, achieving the highest Kling-Gupta efficiency of 0.91 (compared to 0.45–0.88 for the other models), while BPX-TCN-attention provides more accurate predictions of floods and multi-step predictions. In similar applications in semi-arid regions, our approach may serve as a valuable reference where temporal heterogeneity is significant and poses challenges to traditional modeling methods.

Large wood fluctuation and longitudinal connectivity conditions along a segment of the Blanco River (Chilean Patagonia)

Data collected between 2015 and 2022 was utilised to assess longitudinal connectivity and explain the temporal and spatial fluctuation of large wood (LW) along the Blanco River, which was severely affected by the 2008 eruption of the Chaitén Volcano in southern Chile. The study was performed along a ~ 10.6-km long segment, which was divided into two sub-segments (upper and lower). LW source areas were identified using information from previous research, complemented by the analysis of satellite images to cover the study period. LW fluctuation was studied for the period 2017–2022, using field data and images from an unmanned aerial vehicle along seven 80 m-long reaches located within the lower sub-segment of the river. Using the generated georeferenced orthomosaics and digital elevation models, LW and wood jams (WJs) locations, abundance, dimensions, volumes, and WJs stability were assessed, as well as wood deposition patterns. Streambank erosions and landslides were found to be the main LW sources. Considering wood sourcing, and the variations in the number of LW and WJs, in the dimensions of individual LW and WJs volume and deposition patterns as indicators, it was possible to infer the longitudinal connectivity conditions for the studied segment through time. The results showed that the upper and lower subsegments were poorly connected. However, changes in LW abundance over time, its dimensions and volumes, and the very low stability of WJs, and LW deposition patterns indicative of fluvial transport confirmed that the lower subsegment was longitudinally connected. The results also verified that the presence of LW did not affect water or sediment longitudinal connectivity along the fluvial system. The volume of individual LW and WJs showed a decreasing trend with time in all study reaches. As the bank erosions able to source LW to the channel are also reducing with time, pieces of wood deposited in the active channel may become the only way to sustain LW availability for the next few years. Things could change with the occurrence of an extreme and infrequent flood able to connect the upper and lower sub-segments and force the river to initiate a new phase of planform adjustments.

Characteristics and Management of Drainage Infrastructure in Medan Sunggal District, Medan City

Climate change, characterized by high-intensity rainfall, coupled with inadequate drainage systems, small and shallow river dimensions, and a lack of community awareness, has caused flooding and inundation in Medan Sunggal District. This study aims to understand the characteristics and management of drainage infrastructure in Medan Sunggal Subdistrict, Medan City, to identify its characteristics and implement suitable management efforts. The research adopts a positivism paradigm with a positivistic approach, relying on empirical facts (sensual empiricism). The research methodology used is purely qualitative descriptive, focusing on an in-depth understanding related to the characteristics, context, and research subjects. Data collection methods include Guest Tour and comparative techniques. The results of this study show that the characteristics of drainage infrastructure in the study area form a network pattern. The types of channels in the study area are primary channels, secondary channels, and tertiary channels. They consist of artificial channels with open concrete construction, located above the ground with a combined drainage system. While most of the physical conditions are good, some exhibit minor damage. A significant portion of the drainage water is stagnant. Flood-prone areas constitute 41%, areas with infrequent flooding are at 43%, and areas that have never experienced flooding are at 16%. Management recommendations for the study area include providing green open spaces, creating biopore infiltration holes, constructing detention and retention ponds, using paving blocks/grass blocks, conducting maintenance (normalization and rehabilitation) of drainage, and involving the community in each management aspect.

The Impact of Flood Frequency on the Heterogeneity of Floodplain Surface Soil Properties

Floodplain soils are subject to quasi-periodic flood disturbances. This flooding serves to enrich floodplain soils, increasing their fertility and often making them ideal locations for agriculture. However, what is less well understood is how the frequency of flooding impacts on soil fertility and the diversity of soil character. This study investigates how flood frequency influences the heterogeneity (assessed using 26 physical and geochemical soil properties) of floodplain soils in a semi-arid floodplain wetland system in New South Wales, Australia. The study includes an investigation of soil properties across four flood frequency (or disturbance frequency) categories ranging from frequent through to infrequent flood disturbance. Thirty samples were collected from each zone and the physical and geochemical soil data were analyzed using a suite of univariate and multivariate statistical tests. The results show that sites subject to an intermediate level of flood disturbance have a greater level of diversity in soil properties than those sites subject to frequent flood disturbances. These results reflect those of the Intermediate Disturbance Hypothesis, an ecological theory that posits the highest biological diversity will also be found in intermediately disturbed environments and suggests that there might be physical habitat drivers of biological diversity in intermediately disturbed floodplains.

Evolution of sediment grain-size profiles on a sheltered, continental shelf in response to punctuated flood deposition

The evolution and preservation of flood deposits on continental shelves offshore river mouths is influenced by the dynamic relationship between punctuated discharge events and post-deposition processes. These short-term dynamic changes at the seafloor that ultimately shape the sedimentary record are difficult to monitor and not well understood. The aim of this study was to examine how punctuated deposition of flood sediments from a coastal river on the continental shelf, biological mixing and winnowing interplay in shaping grain size profiles and their transient evolution, and the preservation of flood layers in the sedimentary record. For this end an observations-based model was devised for the northern shelf of the sheltered, hyper-arid Gulf of Aqaba-Eilat, where infrequent floods from ephemeral rivers occur ∼ yr−1 and there is low physical perturbation by currents and waves in between, conditions that facilitate the examination of grain size profiles' evolution in time. The model shows that in between floods mixing and winnowing shape grain size profiles in the seafloor, causing the sediment to coarsen from the top down and shape a subsurface peak of the fine flood-sediments. Over longer time periods, without additional floods, mixing and winnowing gradually erase the peak of fines, coarsening the entire mixed layer thus nulling the flood layers' chances of preservation. This important role of winnowing near the sediment surface is missing in previous studies. Concurrently, our modelling suggests that long-term positive sedimentation, usually estimated on the years' time-scale, is comprised of a series of short-term, steep sediment deposition events brought by the punctuated floods (lasting hours to days) and followed by a gradual (months to years' time-scale) winnowing of finer sediments (erosion). These high-resolution dynamics that were captured by the model and included short-term flood depositions and their reoccurrence, could not be deduced from the long-term sedimentary records.

The behaviour of property prices when affected by infrequent floods

The reduction in property values following a major flood event is significant to individuals, communities and governments alike. Property owners who purchase properties just before a major flood risk significant personal loss on their largest single asset. The costs of a major event are shared across communities through government funded recovery efforts in the short term, and changes to insurance premiums and house values in the long term. Designing protections, adaptations and insurance mechanisms that can equitably ameliorate future impacts requires a detailed understanding of how flood risk affects property prices. This paper explores patterns of discounting of property prices following infrequent flooding events. It relates property value discounting in response to floods to various theories of market behaviour. There are alternative behavioural theories which explain why agents may react in this manner. We use a behavioural framework proposed in earlier literature to construct econometric measurements that provide the opportunity to make statistical inferences on whether the expected behaviours are supported by the data. The patterns found are consistent with a market where buyers are either unaware of the risk of flood or unable to evaluate it probabilistically.

Evaluation and Mitigation of Flash Flood Risks in Arid Regions: A Case Study of Wadi Sudr in Egypt

Flash floods threaten the lives of people and properties in different regions around the world, especially in arid and semi-arid regions due to infrequent flood events. The current study aims to assess the geomorphological parameters of Wadi Sudr, South Sinai in Egypt to evaluate flash flood risks and provide adequate mitigation methods. This study presents an integrated method that combines geographic information system (GIS) and watershed modeling system (WMS) with HEC-HMS to visualize and assess flood events in the study area. Different morphologic parameters of the watershed were determined, including linear, areal, and relief parameters. GIS was used to analyze the satellite images and determine the characteristics of the valley to get the extension and number of stream orders in the valley, then WMS was used to estimate rainstorms and basin characteristics, as well as estimate the amount of rain that causes flooding. HEC-HMS program was used for hydrological demonstration and precipitation overflow estimation. The morphometric analysis provided a quantitative portrayal of the Wadi Sudr watershed. Wadi Sudr has 4029 streams connected with seventh order of streams spread over an area of 547.45 km2. Based on the results of morphologic and hydraulic parameters of the watershed, two locations of protection dams were suggested. A comparison between the two locations was made to select the best location based on some criteria, including storage capacity, water depth behind the dam, width and shape of the valley, and the area covered by water stored in the reservoir. The comparison between the two locations showed that the first location is more appropriate for dam construction based on the examined criteria. The valley shape in the first location is more regular than in the second. The first location provided higher storage capacity and water depth in front of the dam than the second. The area covered by water and the width of the valley is less than the second. The stability of the dam at the first site could be higher and the cost of construction could cost be less than the second due to these reasons. A comparison was made using the weighted linear combination (WLC) method, which consists of 13 criteria to determine the suitability index (SI) in order to select the best location from the proposed locations. SI proved that the first location is better than the second. The designed dam in the selected site could be cost-efficient to protect the study area from flood risks and harvesting water that can be used in different purposes. This methodology can be applied in different areas for mitigating flash flood risks.

Simulation-based assessment of inundation risk potential considering the nonstationarity of extreme flood events under climate change

The projected increase in the frequency of extreme rainfall events with climate change has serious implications for flood risk management. This study developed a novel method to evaluate future flood inundation risk in the Kakehashi River basin, Japan. First, a pseudo global warming (PGW) method and ensemble simulation techniques were combined to develop rainfall projections with different return periods, based on the Weather Research and Forecasting (WRF) model. Second, runoff analyses were performed for the target river basin, and inundation simulations, including levee breaches, were conducted at high spatial resolution (40 × 40 m). Finally, the potential inundation risk for the river basin was estimated. Rainfall simulation results indicated intensification of short-duration heavy rainfall events. The PGW ensemble simulations indicated that extreme rainfall scenarios with long return periods (>1000 years, based on current conditions) are likely to occur more frequently in the future, highlighting the possibility of flood intensification. Regardless of the length of return period, areas with infrequent flooding but large inundation depth and those with more frequent flooding but small inundation depth were classified as high risk. The proposed method provides a baseline framework for future flood risk assessments and the results highlight the importance of incorporating (currently) rare heavy rainfall events in future flood management evaluation and planning.

Antecedent Topography and Sediment Dispersal: The Influence of Geologically Instantaneous Events on Basin Fill Patterns

AbstractFavorable topographic gradients and channel bed aggradation are often cited as primers for river channel avulsion. Sylhet Basin in Bangladesh subsides relatively rapidly and presents a topographically favorable channel course for the Brahmaputra River. Holocene occupations of this region remained routed along the basin's western margin, depositing tens of meters of amalgamated channel sands but leaving the central basin under‐filled. The localized backwater effect from a seasonal lake that forms in Sylhet Basin, referred to as a “hydraulic barrier,” has been proposed as a mechanism for keeping the channel pinned to the western margin. Using a 1‐D channel profile model and a 2‐D depth‐averaged hydrodynamic model, we test the preferred flow path between two possible channel courses under a range of physical conditions. Results show that the hydraulic barrier interpretation is implausible unless water depths are increased beyond the physical dimensions of Sylhet Basin. Reducing topographic slope along the two pathways does not sufficiently enhance the local backwater to steer the channel to the basin center. Only the introduction of a scoured antecedent channel along the western margin induces a strong preference for bypass of the central basin. These results corroborate field evidence that Holocene outburst floods scoured a paleochannel that became the preferred course for the Brahmaputra within Sylhet Basin in the mid to late Holocene. We conclude that modification of basin topography by large, infrequent flood events can exert a persistent influence on channel steering that is comparable to previously documented effects of monsoon variability and tectonic deformation.

Controls on carbon dioxide and methane fluxes from a low-center polygonal peatland in the Mackenzie River Delta, Northwest Territories

Growing season surface–atmosphere exchange of carbon dioxide and methane were quantified at Fish Island, a wetland site in the lower northeast Mackenzie River Delta, Northwest Territories, Canada. The terrain consists of low-center polygonal tundra and is subject to infrequent flooding in high water years. Carbon dioxide and methane fluxes were continuously measured using eddy covariance and the relevance of different environmental controls were identified using neural networks. Net daily carbon dioxide uptake peaked in mid-July before gradually decreasing and transitioning to net daily emissions by September. Variations in light level and temperature were the main controls over diurnal net carbon dioxide uptake, whereas thaw depth and phenology were the main seasonal controls. Methane emissions measured at Fish Island were higher than comparable studies on river delta sites in the Arctic and were influenced by the interaction of a large number of factors including thaw and water table depth, soil temperatures, and net radiation. Spikes in methane emissions were associated with strong winds and turbulence. The Fish Island tundra was a net sink for carbon during the growing season and methane emissions only slightly reduced the overall sink strength.

Do we prioritize floodplains for development and farming? Mapping global dependence and exposure to inundation

Global wetlands and floodplains offer benefits and perils alike for human society. For example, humans rely on natural flood cycles for fisheries and agriculture, yet flooding also caused nearly one trillion USD in damage in the past 30 years and impacts millions of people every year. Looking forward, altered flow regimes or increased drought conditions are expected to affect the natural inundation cycle and its ecosystem services. The current and potential future impacts of flooding and drying events warrant increasing efforts to quantify our dependence and exposure within flooded areas, since any change from current inundation patterns is expected to have consequences for those who rely on regular flood occurrences. This paper provides a baseline global assessment of the dependence and exposure of human populations, urban areas, roads, and agriculture on current inundation patterns. The analysis uses a spatially explicit inundation map at ∼500 m resolution (GIEMS-D15) derived from satellite remote sensing to represent flooding extents and overlays it with current population and land use maps. We find that 35% of the analyzed population, or 2.0 billion people, live inside areas that are prone to inland flooding, which comprise only 12% of the land surface area (excluding marine coastal areas), confirming that population densities within inundation zones are about three-times above global average. Likewise, 35% of urban areas potentially experience regular, seasonal, or infrequent flooding. Agriculture shows a similar pattern with 24% of the world’s cropland in areas of recurring inundation. Finally, we estimate that 18% of the global road network is exposed to inundation during high water periods. These global estimates demonstrate a preferential tendency of human populations, infrastructure, and agriculture to be co-located within inundation areas, making related anthropogenic activities highly susceptible to future changes in flood regimes. The results are intended to offer a suite of first-order estimates as partial input to more holistic risk and vulnerability assessments and to ultimately improve environmental planning and policy at large scales.

Hydrological, geomorphic and sedimentological responses of an alpine basin to a severe weather event (Vaia storm)

To achieve a reliable analysis of the impacts induced in mountain basins by large and infrequent floods, all their main components, from the spatial-temporal distribution of meteorological agents to the hydrological, geomorphic and sedimentological response should be considered. Comprehensive study of the hydro-geomorphic responses is extremely valuable to increase the awareness of large floods, especially, in highly populated mountain areas. Such type of investigation requires a solid and wide dataset, which is why only few studies had the chance to describe the response in such a holistic way. This work comprehensively analyzed the high magnitude/low frequency Vaia event, a severe storm that affected northeastern Italy in October 2018 and thus the Rio Cordon study basin. The 80 h precipitation registered in the basin showed a total rainfall equal to 29.8% of the mean annual precipitation. The temporal distribution of rainfall presented two phases, i.e., a first characterized by moderate but persistent precipitation and a second more intense, exhibiting recurrence intervals over 50 years. A combination of indirect methods permitted the reconstruction of the hydraulic forcing acted in the Rio Cordon. Despite the implicit uncertainty, these methods clearly highlighted the high magnitude expressed by October 2018 flood, which generated a unit peak discharge equal to 3.3 m3 s−1 km−2 and a peak of unit stream power of 3865 W m−2, i.e., the highest hydraulic forcing conditions ever observed in 34 years. In terms of geomorphic changes, the use of pre- and post-event LiDAR data stressed out a moderate response of the hillslopes, where the (re)activation of the sediment sources was limited. Only few of these acted as sediment supplier to the main channel. The channel network instead, exhibited an evident response, with the Rio Cordon severely altered by wide lateral widening, deep streambed incision and armouring removal. The hydraulic and geomorphic forcing generated by October 2018 flood caused extensive streambed remobilization and boulder mobility that, in turn, induced the transport of a massive sediment volume. In this sense, the match between bedload observed and bedload predicted suggested the outstanding hydraulic forcing occurred and the quasi-unlimited supply conditions acted during the flood. The long-lasting monitoring program maintained in the Rio Cordon basin provided the rare opportunity to compare two high magnitude/low frequency floods and their induced effects. The September 1994 and October 2018 events were caused by different rainfall conditions, which resulted in different hydrological- and, especially, geomorphic- and sedimentological-responses. Particularly, the October 2018 flood induced an unprecedented alteration on the fluvial system, the effects of which could persist over the long-term.

Foliar elemental microprobe data and leaf anatomical traits consistent with drought tolerance in

In food-productive river basins, ecosystems reliant on natural flows are affected by climate change and water removal. One such example is Australia’s Murray–Darling Basin (MDB), to which the ecologically important black box tree Eucalyptus largiflorens (Myrtaceae) is unique. Little is known about its mineral nutrition and response to flooding. A field study conducted at Hattah Kulkyne National Park on the MDB examined nutrient and Al distribution in mature and young foliage of trees whose status varied with respect to the presence of surface floodwaters. Black box is also of interest due to emerging evidence of its capacity to accumulate high foliar salt concentrations. Here, cryo scanning electron microscopy alone (SEM), combined with energy dispersive spectroscopy (SEM-EDS) and X-ray fluorescence (XRF) spectroscopy were applied to evaluate leaf anatomy and elemental patterns at the cellular and whole-leaf levels. Variation in whole-leaf elemental levels across flooded and dry trees aligned with known nutritional fluctuations in this drought-tolerant species reliant on occasional infrequent flooding. The microprobe data provide evidence of drought tolerance by demonstrating that extended conditions of lack of water to trees do not elicit leaf anatomical changes nor changes to leaf cellular storage of these elements. Foliar Na concentrations of ~2000–6000 mg kg–1 DW were found co-localised with Cl in mesophyll and dermal cells of young and mature leaves, suggesting vacuolar salt disposal as a detoxification strategy.

The effect of flood intermittency on bifurcations in fluviodeltaic systems: Experiment and theory

AbstractThe dimensions and organization of deltaic islands and channels dictate delta morphology. This study presents experimental results modelling deposition at a river mouth and flow bifurcation around delta islands. Mouth bar formation and channel bifurcation is achieved in a laboratory setting by alternating input of suspended load transport and bedload transport. These two modes of transport produce two characteristic deposits with different advection lengths. Suspended load transport creates a steep deposit far from the inlet, while bedload creates a low angle, levéed deposit near the inlet. This study found that flow bifurcations occur where the proximal and distal deposits encroach on one another; and determined that there is a relationship between the frequency of suspended load transport and the length to channel bifurcation. Frequent flooding causes shorter length to bifurcations, whereas infrequent flooding causes greater length to bifurcations. This work overturns the hitherto understood mechanism of bifurcation location as a function of only high‐transport conditions. Instead, the interactions between the sediment transport and deposition from normal flow and large‐scale flooding events dictate delta island morphology.

Storm surge risk assessment for the insurance system: A case study in Tokyo Bay, Japan

With the renewal of the basic disaster management plan in Japan, the transferring flood risk itself to insurance carriers is promoted by the Japanese government. An insurance company to which flood risks are transferred must assess infrequent flood risks to manage the overall risk of the company. Insurance systems may reach peak risk condition when a high wind coincides with a high storm surge level. However, there are few studies on the assessment of storm surges using stochastic approaches for Japan. This study suggests the procedure of stochastic storm surge risk assessment with low calculation load and applies it to the Tokyo Bay coast in Japan, a region exposed to large storm surges.Risk mapping and economic losses on the Tokyo Bay coast due to extreme flooding caused by storm surges are predicted for exceedance probability using stochastic approaches. Data on one thousand modeled typhoons passing through Tokyo Bay are extracted using a probabilistic tropical cyclone model over 10,000 years. Flooding due to storm surges is calculated with a validated numerical storm surge model. Next, a storm surge risk map that indicates inundation depth for a representative exceedance probability is created from the results of a series of stochastic hazard calculations. The inundation depth data sets for 1000 typhoons—along with the spatially distributed assets and values and damage functions provided by the Japanese government for Tokyo Bay—are used to estimate the economic loss from typhoons for corresponding exceedance probability. From the risk mapping, it was found that the storm surge risk in Chiba and Kanagawa prefectures is relatively high for exceedance probabilities and the economic losses estimated for the exceedance probability of 0.005 are 158.4 and 91.5 billion Japanese yen for the private and commercial sectors respectively along the Tokyo Bay coast. Moreover, the effect of the astronomical tide on the exceedance probability is evaluated using a neural network. However, it was found that the randomly determined astronomical tide does not have a significant influence on the exceedance probability targeted for insurance purposes when losses over 10,000 years are investigated.

“It Will Never Happen Again”: The Myth of Flood Immunity in Brisbane

ABSTRACTAlthough scholarship shows how collective memory aids community resilience to hazards, sociopolitical forces erode this transformative potential. A study of Brisbane River floods highlights the entanglement of memory with a myth of flood immunity, created by community faith in dams to prevent flooding, infrequent floods, drought and hydrological misunderstandings, and upheld by floodplain development perceived as an economic booster. When flooding threatened the myth of immunity in 2011, the event was framed as dam mismanagement to deflect attention from poor land use practices and government culpability. This myth endures, leaving South East Queensland no more resilient for unpredictable but certain future flooding.

Alluvial fan aggradation/incision history of the eastern Tibetan plateau margin and implications for debris flow/debris-charged flood hazard

This paper reconstructs the Quaternary aggradation and incision history of a debris flow/debris-charged flood-affected valley in order to detect the impact of climate on alluvial fan dynamics. We used optically stimulated luminescence (OSL) dating of quartz to determine the ages of alluvial fan terraces. Comparison between the aggradation and incision history and regional climatic records suggests that aggradation occurred in cold and/or dry climates, whereas incision is a feature of warm and wet climates. Cold climates lead to enhanced frost shattering, and dry climates cause deteriorated vegetation. Both effects caused surplus sediment, which was transported by infrequent flood discharges to form alluvial fan/terrace deposits. Incision during wet and warm climates is due to increased vegetation cover and an increase in the frequency of flood discharges. This relationship between climate and valley evolution is applied to assess future changes in the present active channel by considering recent climatic records. The results show that the valley channel is expected to experience net incision if the average temperature continues increasing while precipitation maintains at a constant level.

Changes in Community-Level Riparian Plant Traits over Inundation Gradients, Colorado River, Grand Canyon

Comparisons of community-level functional traits across environmental gradients have potential for identifying links among plant characteristics, adaptations to stress and disturbance, and community assembly. We investigated community-level variation in specific leaf area (SLA), plant mature height, seed mass, stem specific gravity (SSG), relative cover of C4 species, and total plant cover over hydrologic zones and gradients in years 2013 and 2014 in the riparian plant community along the Colorado River in the Grand Canyon. Vegetation cover was lowest in the frequently inundated active channel zone, indicating constraints on plant establishment and production by flood disturbance and anaerobic stress. Changes in trait values over hydrologic zones and inundation gradients indicate that frequently inundated plots exhibit a community-level ruderal strategy with adaptation to submergence (high SLA and low SSG, height, seed mass, C4 relative cover), whereas less frequently inundated plots exhibit adaptation to drought and infrequent flood disturbance (low SLA and high SSG, height, seed mass, C4 relative cover). Variation in traits not associated with inundation suggests niche differentiation and multiple modes of community assembly. The results enhance understanding of future responses of riparian communities of the Grand Canyon to anticipated drying and changes in hydrologic regime.

An approach for the determination of precipitation input for worst-case flood modelling

ABSTRACTThere is a lack of suitable methods for creating precipitation scenarios that can be used to realistically estimate peak discharges with very low probabilities. On the one hand, existing methods are methodically questionable when it comes to physical system boundaries. On the other hand, the spatio-temporal representativeness of precipitation patterns as system input is limited. In response, this paper proposes a method of deriving spatio-temporal precipitation patterns and presents a step towards making methodically correct estimations of infrequent floods by using a worst-case approach. A Monte Carlo approach allows for the generation of a wide range of different spatio-temporal distributions of an extreme precipitation event that can be tested with a rainfall–runoff model that generates a hydrograph for each of these distributions. Out of these numerous hydrographs and their corresponding peak discharges, the physically plausible spatio-temporal distributions that lead to the highest peak discharges are identified and can eventually be used for further investigations.Editor A. Castellarin; Associate editor E. Volpi