High Intensity Precipitation Events Research Articles

Incorporation crisis lifecycle theory into full-stage flash drought spatio-temporal pattern identification and risk analysis

Compared to conventional slow-developing droughts, the characteristics and drivers of flash droughts are often more complex. This complexity challenges global drought early warning systems, leading to severe losses in crop yields during flash drought events. To address this problem, our study introduces the Full Life Cycle Flash Drought Identification Framework (FLCFDIF), which incorporates crisis lifecycle theories to link the lifecycle progression of flash droughts with corresponding risk management measures. The results indicate significant differences in the risk characteristics of flash drought events are observed between monsoon and non-monsoon regions of China, with flash droughts in monsoon regions erupting more rapidly, lasting longer, and recovering more slowly than flash droughts in non-monsoon areas. Flash droughts typically feature negative precipitation anomalies and positive anomalies in maximum temperature and evapotranspiration during the progression of the droughts. However, the high-intensity precipitation events that drive flash drought recovery primarily occur during the termination phase rather than the previously assumed recovery phase. Therefore, employing a 40% soil moisture percentile as a threshold for determining the end of flash droughts can reduce disturbances from low-intensity precipitation events and establish a link between flash droughts and seasonal droughts. In Southeast China, the probability of flash droughts transitioning to seasonal droughts is approximately 10%. In future flash drought risk management, it is crucial to integrate the four stages of flash drought progression (development, duration, recovery, and termination) and implement timely emergency response actions, including warning, assessment, mitigation, and monitoring, to address the environmental impacts of flash drought events.

Drainage water management, woodchip bioreactor, and saturated riparian buffer as stacked conservation practices for improving crop yields and water quality

Stacking edge-of-field practices may improve nutrient removal from crops. To examine the effects of stacking edge-of-field conservation practices, a woodchip bioreactor (WBR) and saturated riparian buffer (SRB) were installed in series by intercepting tile flow from a field having a drainage water management system. Nutrient monitoring from 5 years evaluated nutrient export annually and based on the precipitation intensity. Drainage water was monitored for total suspended solids (TSS), nitrate-N, total-P, total-N, and ortho-P at the inlet and outlet of WBR and control structure of SRB. Nutrient export reductions of WBR and SRB were determined for precipitation events that were categorized as low <12.7 mm, mid 12.7–25.4 mm, high 25.4–50.8 mm, and very high >50.8 mm. Over the five seasons, nitrate-N export was reduced 88 % at the WBR outlet and 78 % at SRB outlet when used in a stacked series configuration. The efficacy of edge-of-field practices was affected by the intensity of precipitation events. The low and mid-intensity precipitation events generated 67 % of the total discharge from the subsurface drainage system which accounted for 74 % of the influent nitrate-N. During low and mid-intensity precipitation events, discharge was reduced by 58–65 %, nitrate-N was reduced by 49–88 % and total-P was reduced by 65–73 % by using stacked practice of WBR and SRB. During high and very high-intensity precipitation events only nitrate-N export was reduced by 61–66 %. This indicates that when designing stacked edge-of-the-field practices the cumulative effect of the practices and their performance during different precipitation events should be taken into account when managing conservation practice-based cropping systems.

Quantile-Regression-Ensemble: A Deep Learning Algorithm for Downscaling Extreme Precipitation

Global Climate Models (GCMs) simulate low resolution climate projections on a global scale. The native resolution of GCMs is generally too low for societal-level decision-making. To enhance the spatial resolution, downscaling is often applied to GCM output. Statistical downscaling techniques, in particular, are well-established as a cost-effective approach. They require significantly less computational time than physics-based dynamical downscaling. In recent years, deep learning has gained prominence in statistical downscaling, demonstrating significantly lower error rates compared to traditional statistical methods. However, a drawback of regression-based deep learning techniques is their tendency to overfit to the mean sample intensity. Extreme values as a result are often underestimated. Problematically, extreme events have the largest societal impact. We propose Quantile-Regression-Ensemble (QRE), an innovative deep learning algorithm inspired by boosting methods. Its primary objective is to avoid trade-offs between fitting to sample means and extreme values by training independent models on a partitioned dataset. Our QRE is robust to redundant models and not susceptible to explosive ensemble weights, ensuring a reliable training process. QRE achieves lower Mean Squared Error (MSE) compared to various baseline models. In particular, our algorithm has a lower error for high-intensity precipitation events over New Zealand, highlighting the ability to represent extreme events accurately.

Simulation of Long-Term Water Erosion in Rainfed Croplands of Eastern Washington

Highlights Water erosion in the inland Pacific Northwest was modeled with WEPP for the past (1940–1982) and present (1983–2020). Water erosion decreased from past to present in the study watersheds. Major factors are increased adoption of conservation practices and decrease in large precipitation events. Abstract. Water erosion is an ongoing problem in eastern Washington due to its hilly terrain, highly erodible silt loam soils, rain on thawing soil, and the prevalence of conventional tillage. The region is characterized by a Mediterranean-type climate with warm, dry summers and cool, wet winters. Three distinct precipitation zones, with annual totals low (&amp;lt;380 mm), intermediate (380–460 mm), and high (&amp;gt;460 mm), dictate the area’s crop rotations. A unique 43-year (1940–1982) dataset of winter erosion measured on multiple agricultural fields in Whitman County, eastern Washington, by Verle Kaiser, a USDA Soil Conservation Service agronomist, showed annual erosion rates averaging 53.8 Mg ha-1, far exceeding the current Natural Resources Conservation Service tolerable limit of 11 Mg ha-1 yr–1 for the soils in the area. Kaiser’s field data allowed us to compare the historical field-measured erosion rates with those simulated by the WEPP (Water Erosion Prediction Project) model. Anthropogenic factors, such as tillage and crop rotation, change with time. Conservation tillage, including reduced- and no-till, has been increasingly adopted in eastern Washington since the mid-1980s. The specific objectives of this study were to (1) apply the WEPP model to simulate soil erosion in eastern Washington and evaluate the interactive effects of climate and management, in addition to topography and soil, on water erosion in the study area, and (2) compare the simulation results with Kaiser’s historical field dataset and elucidate the long-term soil erosion trend. The WEPPcloud interface was used to delineate a watershed within each precipitation zone of the study area. Climate inputs were divided into two periods: the past (1939–1982) and the present (1983–2020). Erosion has noticeably decreased from the past to the present, with WEPP simulated annual erosion averaging 13.5, 34.5, and 52.6 Mg ha-1 for the past, and 9.5, 14.1, and 15.5 Mg ha-1 for the present, in the selected watersheds in the low-, intermediate-, and high-precipitation zones, respectively. The decreasing trend was primarily due to the increased adoption of conservation tillage and crop rotation, as well as a decrease in the number of high-intensity precipitation events in the present climate. Keywords: Inland Pacific Northwest, Soil erosion by water, Temporal trend, WEPP.

Evaluation of High-Intensity Precipitation Prediction Using Convolutional Long Short-Term Memory with U-Net Structure Based on Clustering

Recently, Asia has experienced significant damage from extreme precipitation events caused by climate change. Improving the accuracy of quantitative precipitation forecasts over wide regions is essential to mitigate the damage caused by precipitation-related natural disasters. This study compared the predictive performances of a global model trained on the entire dataset and a clustered model that clustered precipitation types. The precipitation prediction model was constructed by combining convolutional long short-term memory with a U-Net structure. Research data consisted of precipitation events recorded at 10 min intervals from 2017 to 2021, utilizing radar data covering the entire Korean Peninsula. The model was trained on radar precipitation data from 30 min before the current time (t − 30 min, t − 20 min, t − 10 min, and t − 0 min) to predict the precipitation after 10 min (t + 10 min). The prediction performance was assessed using the root mean squared error and mean absolute error for continuous precipitation data and precision, recall, F1 score, and accuracy for the presence or absence of precipitation. The research findings indicate that, with sufficient training data for each precipitation type, models trained on clustered precipitation types outperform those trained on the entire dataset, particularly for predicting high-intensity precipitation events.

Population dynamics in Taiwan from the Neolithic to early historic periods (5000–100 cal BP): Linking cultural developments and environmental change

To reconstruct population dynamics in Taiwan between 5000 and 100 cal BP, we analysed spatial-temporal changes in archaeological site abundance and size (area). The results suggest that population growth was discontinuous throughout the study region and that the main spatial differences in population trends were between eastern/northern and western Taiwan. Comparison of settlement data shows that population trends in Taiwan and different regions in continental China were partly parallel. We contrast these data with political, economic, settlement, and climatic developments in continental China, when considering possible factors that influenced these demographic relationships. In addition, we examined published palaeoenvironmental time series from the broader study region to explore human-environment interactions. This revealed that proxy records of human activities (agriculture, deforestation) correlate with the derived trends in site abundance and area. Furthermore, we hypothesise that the inferred sparse settlement in eastern Taiwan during 2700–1800 cal BP is related to climate change. An increase in seasonal rainfall and high-intensity precipitation events in late summer and autumn, due to long-term changes in summer monsoon precipitation and El Niño–Southern Oscillation intensity, likely resulted in unfavourable hydrological conditions for crop cultivation in this part of the study region.

Analysis of the Asymmetric Characteristic of Extreme Rainfall Erosivity in 8 Provinces of Southern China during 1961–2020

The roles of rainfall with various intensities in hydraulic erosion processes are obviously different. In-depth knowledge about the spatiotemporal variation in extreme rainfall erosivity is critical for soil erosion risk assessment and formulation of response measures. In the period of 1961–2020, more than 390,000 erosive rainfall data from 212 meteorological stations were collected to explore the erosion characteristics of different intensities of rainfall erosivity across southern China. The asymmetric characteristic of extreme rainfall erosion was analyzed and expressed by an asymmetric change index (ACI) defined in this study. Correlation analysis was applied to study the impact of global extreme climate events on the ACI. The results showed that different patterns of precipitation had evident asymmetric characteristics in rainfall erosivity, and fewer high-intensity precipitation events contributed to much higher total rainfall erosivity, particularly for rainstorms (≥100 mm). The ACI of the rainfall erosivity exhibited evident spatial heterogeneity; insignificant increasing trends were found in the ACIs for heavy rainfall, torrential, and rainstorm erosivities over the past 60 years. The change rate of ACI varied greatly on both monthly and interdecadal scales, and the ACI of rainstorms showed the maximum linear increasing trend on the long-time scale. There were significantly high correlations between the ACI and erosive rainfall days and the ACI and erosive rainfall (p &lt; 0.01), and the correlation coefficients were relatively higher from May to October, where the precipitation was concentrated. Additionally, the El Niño-Southern Oscillation and tropical cyclones clearly influenced the spatiotemporal distribution of the ACI and rainfall erosivity but were limited to specific periods and regions. These results could provide a reference for extreme soil erosion event monitoring and control in southern China.

The utility of using Volunteered Geographic Information (VGI) for evaluating pluvial flood models

Pluvial floods are increasingly threatening urban environments worldwide due to human-induced climate change. High-resolution, state-of-the-art pluvial flood models are urgently needed to inform climate change adaptation and disaster risk reduction measures but are generally not empirically tested because of the rarity of local high-intensity precipitation events and the lack of monitoring capabilities. Volunteered Geographic Information (VGI) collected by professionals, non-professionals and citizens and made available on the internet can be used to monitor the dynamic extent of a pluvial flood during and after an extreme rain event but is sometimes considered to be unreliable. In this paper, we explore the general utility of VGI to evaluate the performance of pluvial flood models and gain new insights to improve these models. As background for our research, we use the capital city of Budapest, which recently suffered three heavy rainfall events in just five years (2015, 2017 and 2020). For each pluvial flood event, we collected photographic evidence from different online media sources and estimated the associated water depths at various locations in the city from the image context. These were compared with the results of a 2D pluvial flood model that has been shown to provide comparable results to other state-of-the-art inundation models and is easily transferred to other urban areas due to its reliance on open data sources. We introduce a general methodology for comparing VGI with model data by probing different spatial resolutions. Our findings highlight untapped potential and fundamental challenges in using VGI for model evaluation. It is proposed that VGI may become an essential tool and improve the confidence in model-based risk assessments for climate change adaptation and disaster risk reduction.

Field Investigation and Finite Element Analysis of Landslide-Triggering Factors of a Cut Slope Composed of Granite Residual Soil: A Case Study of Chongtou Town, Lishui City, China

Landslides caused by excavations and precipitation events are widespread types of slope failures in southwest Zhejiang, China, in areas with granite residual soil. Investigations of the effect of high precipitation on the hydrological response, stability, and evolutionary mechanism of cut slopes in granite soil areas are lacking. The characteristics of historical landslides in Chongtou Town in southwestern Zhejiang were summarized, and a typical slope was selected for analysis. The hydraulic and mechanical properties of the residual soil and fully weathered granite were tested, and the surface displacements on the slope were monitored. Geo-studio was utilized to establish a coupled seepage-deformation model to validate the numerical method and investigate the landslide-triggering factors of the cut slope. The results showed nearly all historical landslides in Chongtou Town were triggered by precipitation events, and the slide bodies consisted of residual soil and fully weathered granite with similar geotechnical properties. The simulated and measured horizontal displacements were in good agreement, indicating the reliability of the established model and parameters. The stability coefficient decreased with an increase in the gradient or height of the cut slope. The critical height values were 5.3 m, 5.5 m, 5.7 m, 6.0 m, and 6.3 m at slopes of 60°, 65°, 70°, 75°, and 80°, respectively. Long-term torrential rain and short-term high-intensity precipitation events are likely to trigger landslides when the precipitation event lasts longer than 26 h and 78 h, respectively. The landslide formation includes four stages: slope evolution, formation of unloading zone at slope foot, migration and loss of soil particles, and instability of the cut slope. The findings can be used to prevent and manage landslides on cut slopes in areas with granite residual soil.

Using Water Stable Isotopes and Cross-Correlation Analysis to Characterize Infiltration of Precipitation through Unsaturated Zone at the Velika Gorica Site of Zagreb Aquifer

The unsaturated zone plays a crucial role in the hydrological cycle and is a key factor in modeling and understanding hydrological processes. It regulates water transfer from the land surface to the groundwater while providing protection, transfer, and attenuation of potential groundwater contaminants. This research presents the first results of continuous in situ monitoring of all soil horizons of the Eutric Cambisols and the remaining unsaturated zone of the Zagreb aquifer (Velika Gorica well field). The Zagreb aquifer is the main source of potable water for the inhabitants of the City of Zagreb and Zagreb County, which is protected by the Republic of Croatia. Cross-correlation analysis and water stable isotopes (δ2H and δ18O) were used to investigate whether there is a hydraulic connection between precipitation and groundwater, the approximate duration of percolation, and whether there are indicators that suggest the presence of preferential flow or processes such as water mixing and/or evaporation. The cross-correlation analysis showed and confirmed the assumption of the presence of preferential flow with average lag times ranging from 1.59 up to 3.63 h. The results also indicate that low organic matter content may contribute to higher lag times associated with precipitation infiltration. It was found that only high-intensity precipitation events allow effective infiltration, and that the amount of infiltration depends on the water content of the soil at the beginning of each precipitation event. The isotopic results showed that the isotopic composition of the soil water in the first three soil horizons follows the one of precipitation, while deuterium excess confirmed that the sampled water is mobile water and that an evaporation process is possible in the A horizon. The results also show that suction cups can be used to determine the isotopic signature of both bulk and mobile water, depending mainly on the granulometric composition of the material in which they are installed.

Moderate precipitation reduction enhances nitrogen cycling and soil nitrous oxide emissions in a semi-arid grassland.

The ongoing climate change is predicted to induce more weather extremes such as frequent drought and high-intensity precipitation events, causing more severe drying-rewetting cycles in soil. However, it remains largely unknown how these changes will affect soil nitrogen (N)-cycling microbes and the emissions of potent greenhouse gas nitrous oxide (N2 O). Utilizing a field precipitation manipulation in a semi-arid grassland on the Loess Plateau, we examined how precipitation reduction (ca. -30%) influenced soil N2 O and carbon dioxide (CO2 ) emissions in field, and in a complementary lab-incubation with simulated drying-rewetting cycles. Results obtained showed that precipitation reduction stimulated plant root turnover and N-cycling processes, enhancing soil N2 O and CO2 emissions in field, particularly after each rainfall event. Also, high-resolution isotopic analyses revealed that field soil N2 O emissions primarily originated from nitrification process. The incubation experiment further showed that in field soils under precipitation reduction, drying-rewetting stimulated N mineralization and ammonia-oxidizing bacteria in favor of genera Nitrosospira and Nitrosovibrio, increasing nitrification and N2 O emissions. These findings suggest that moderate precipitation reduction, accompanied with changes in drying-rewetting cycles under future precipitation scenarios, may enhance N cycling processes and soil N2 O emissions in semi-arid ecosystems, feeding positively back to the ongoing climate change.

Spatial allocation of LID practices with a water footprint approach

Urban water problems due to stormwater have been aggravated by the higher frequency of high-intensity precipitation events and the increase of paved surfaces. However, with appropriate stormwater management practices, such as low-impact development (LID), stormwater can provide an additional urban water resources rather than cause damage. This study aims to apply a water footprint to location determination of LID practices in the urban area. The LID planning procedure was demonstrated with the highest population density region in Taipei, Taiwan. In order to improve the spatial resolution of LID allocation, the “first-level dissemination area” with 450 residents was used as a spatial unit. The performance of LID practices was then evaluated with the simulation using the Storm Water Management Model (SWMM). Three LID practices, rainwater harvesting systems, permeable pavements, and bioretention systems, were selected. After the water footprint accounting, ten sites were suggested for LID implementation. The runoff reduction rate reached up to 65 % by rainwater harvesting systems or at least 3 % by permeable pavements. This study provides a simpler and more effective approach to ways of integrating an urban water footprint into LID planning and stormwater management in urban areas.

Geo-Hydrological Events and Temporal Trends in CAPE and TCWV over the Main Cities Facing the Mediterranean Sea in the Period 1979–2018

The Mediterranean region is regarded as the meeting point between Europe, Africa and the Middle East. Due to favourable climatic conditions, many civilizations have flourished here. Approximately, about half a billion people live in the Mediterranean region, which provides a key passage for trading between Europe and Asia. Belonging to the middle latitude zone, this region experiences high meteorological variability that is mostly induced by contrasting hot and cold air masses that generally come from the west. Due to such phenomenon, this region is subject to frequent intensive precipitation events. Besides, in this complex physiographic and orographic region, human activities have contributed to enhance the geo-hydrologic risk. Further, in terms of climate change, the Mediterranean is a hot spot, probably exposing it to future damaging events. In this framework, this research focuses on the analysis of precipitation related events recorded in the EM–DAT disasters database for the period 1979–2018. An increasing trend emerges in both event records and related deaths. Then a possible linkage with two meteorological variables was investigated. Significant trends were studied for CAPE (Convective Available Potential Energy) and TCWV (Total Column Water Vapor) data, as monthly means in 100 km2 cells for 18 major cities facing the Mediterranean Sea. The Mann–Kendall trend test, Sen’s slope estimation and the Hurst exponent estimation for the investigation of persistency in time series were applied. The research provides new evidence and quantification for the increasing trend of climate related disasters at the Mediterranean scale: recorded events in 1999–2018 are about four times the ones in 1979–1998. Besides, it relates this rise with the trend of two meteorological variables associated with high intensity precipitation events, which shows a statistically significative increasing trend in many of the analysed cities facing the Mediterranean Sea.

Sensitivity Analysis for Effect of Changes in Input Data on Hydrological Parameters and Water Balance Components in the Catchment Area of Hungarian Lowland

Abstract Extreme weather and climate changes are emerging more frequently in Central Europe, Hungary, and in the near future the increase in prolonged droughts, high-intensity precipitation events and the temporal variations of precipitation are expected, which may increase the magnitude of local water damages (OVF, 2016). As a result of climate change, these extreme weather events will be more frequent, however it is difficult to predict them, as until now insufficient amount of observations are available on smaller watercourses and on refined territorial water balances. For the future assessment of the environmental and economic impacts of climate change, it is essential to explore the integrated relationship of evapotranspiration, runoff, infiltration, surface and subsurface waters, and other hydrological processes, which can fundamentally describe regionally the water management conditions. In this research, an earlier study (DHI Hungary 2019) on the catchment area of the main canal of the Dong-ér Brook is pursued to continue the development of the MIKE SHE model in a more complex manner. Within the frame of the present study, the relationship between the individual hydrological parameters, the water balance components and extreme precipitation events (drought, heavy rainfall events) for the entire drainage basin have been examined, besides, the expected effects of the predicted temperature rise on the water balance is evaluated. Using data from 2018 as reference, the sensitivity of the changes in daily precipitation and daily mean temperature has been assessed to estimate the effects of the future climate change on hydrological parameters and water balance components.

Recharge and Infiltration Mechanisms of Soil Water in the Floodplain Revealed by Water-Stable Isotopes in the Upper Yellow River

The stable isotopes (δD and δ18O) in soil water allow tracing of the flow and transportation of water in the soil. However, there are few studies on the use of soil water stable isotopes to explore the soil water in the floodplain, especially in determining the soil water source and infiltration mechanism. The Bayesian mixing model (MixSIAR) was integrated with the line conditioned excess (lc-excess) of stable isotopes (δD and δ18O) in precipitation, soil water (0–150 cm), river water, and groundwater to determinate the source and recharge mechanisms of two different soil profile types in the floodplain of the upper Yellow River in Lanzhou, China. The results showed that soil water below 80 cm was affected by river water recharge, affecting soil water content and stable isotopic composition at S1 sampling points (profile parallel to river water); this effect was not observed at S2 (profile is higher than the river water) sampling points. The isotopic compositions of the soil water sources at the two sampling points (S1: δD = −77.41‰, δ18O = −11.01‰; S2: δD = −74.02‰, δ18O = −10.56‰) were depleted more than those in the long-term amount-weighted precipitation isotopes (δD = −56.30‰, δ18O = −8.17‰). The isotope signatures of soil water sources are similar to the isotope characteristics of some high-intensity precipitation events (≥30 mm/day), indicating that soil water originates from a fraction of the total precipitation. The piston flow (60%) and the preferential flow (40%) coexist, but soil moisture and rainfall intensity will affect the sequence of the two infiltration methods. This study provides insights for understanding the hydrological process of the upper Yellow River and evaluating groundwater quality and protecting the floodplain environment.

When does a parsimonious model fail to simulate floods? Learning from the seasonality of model bias

ABSTRACT Identifying situations where a hydrological model yields poor performance is useful for improving its predictive capability. Here we applied an evaluation methodology to diagnose the weaknesses of a parsimonious rainfall-runoff model for flood simulation. The GR5H-I hourly lumped model was evaluated over a large set of 229 French catchments and 2990 flood events. Model bias was calculated considering different streamflow time windows, from calculations using all observations to analyses of individual flood events. We then analysed bias across seasons and against several flood characteristics. Our results show that although GR5H-I had good overall performance, most of the summer floods were underestimated. In summer and autumn, compensations between flood and recession periods were identified. The largest underestimations of flood volumes were identified when high-intensity precipitation events occurred, especially under low soil moisture conditions.

The role of superficial geology in controlling groundwater recharge in the weathered crystalline basement of semi-arid Tanzania

Study regionLittle Kinyasungwe River Catchment, central semi-arid Tanzania. Study focusThe structure and hydraulic properties of superficial geology can play a crucial role in controlling groundwater recharge in drylands. However, the pathways by which groundwater recharge occurs and their sensitivity to environmental change remain poorly resolved. Geophysical surveys using Electrical Resistivity Tomography (ERT) were conducted in the study region and used to delineate shallow subsurface stratigraphy in conjunction with borehole logs. Based on these results, a series of local-scale conceptual hydrogeological models was produced and collated to generate a 3D conceptual model of groundwater recharge to the wellfield. New hydrological insights for the regionWe propose that configurations of superficial geology control groundwater recharge in dryland settings as follows: 1) superficial sand deposits act as collectors and stores that slowly feed recharge into zones of active faulting; 2) these fault zones provide permeable pathways enabling greater recharge to occur; 3) ‘windows’ within layers of smectitic clay that underlie ephemeral streams may provide pathways for focused recharge via transmission losses; and 4) overbank flooding during high intensity precipitation events increases the probability of activating such permeable pathways. These conceptual models provide a physical basis to improve numerical models of groundwater recharge in drylands, and a conceptual framework to evaluate strategies (e.g., Managed Aquifer Recharge) to artificially enhance the availability of groundwater resources in these regions.

The “Problem” of New Orleans and Diminishing Sustainability of Mississippi River Management—Future Options

Climate change forcings are having significant impacts in coastal Louisiana today and increasingly affect the future of New Orleans, a deltaic city mostly below sea level, which depends on levee and pumps to protect from a host of water-related threats. Precipitation has increased in the Mississippi River basin generally, increasing runoff, so that in recent years the Mississippi River has been above flood stage for longer periods of time both earlier and later in the year, increasing the likelihood that hurricane surge, traditionally confined to summer and fall, may compound effects of prolonged high water on river levees. The Bonnet Carré Spillway, just upstream of New Orleans has been operated more often and for longer periods of time in recent years than ever before in its nearly 100-year history. Because all rain that falls within the city must be pumped out, residents have been exposed to interior flooding more frequently as high-intensity precipitation events can occur in any season. A sustainable path for New Orleans should involve elevating people and sensitive infrastructure above flood levels, raising some land levels, and creating water storage areas within the city. Management of the lower Mississippi River in the future must include consideration that the river will exceed its design capacity on a regular basis. The river must also be used to restore coastal wetlands through the use of diversions, which will also relieve pressure on levees.

Testing hypotheses on signatures of precipitation variability in the river and floodplain deposits of the Paleogene San Juan Basin, New Mexico, U.S.A.

ABSTRACTMuch progress has been made in recent years towards a set of recognition criteria for river discharge variability in river channel deposits, and thus sedimentary proxies for precipitation variability. Despite this progress, there is currently no consensus on how different styles of discharge variability are reflected in river sedimentary records, and whether variable-discharge river records from different climate types can be distinguished. Herein, river discharge and precipitation variability in the Paleogene is investigated using associations between river channel and floodplain deposits across the Paleocene–Eocene boundary from the Paleocene upper Nacimiento Formation and the early Eocene San Jose Formation in the San Juan Basin, New Mexico, USA.The succession is identified as deposits of variable-discharge river systems based on shared channel-deposit characteristics with modern and ancient variable-discharge river systems and the proposed facies models, in addition to alternations of poorly drained and well-drained floodplain deposits and/or slickensides indicating alternating wet–dry cycles. A long-term stratigraphic trend toward increasingly well-drained floodplain deposits is also observed and hypothesized to indicate successively more arid conditions from the Paleocene into the early Eocene. Comparisons with modern rivers from various climate zones suggest a long-term shift from a monsoonal climate in the Paleocene, to a fluctuating subhumid climate, ultimately leading to semiarid to arid conditions in the early Eocene. These observations suggest that floodplain deposits may be a better indicator of ambient climate, whereas channel deposits are records for frequency and magnitude of high-intensity precipitation events. Therefore, the existing facies models for variable-discharge rivers that consider only channel facies may not capture critical information needed to make accurate interpretations of paleoclimatic conditions. This study also adds to a growing body of evidence from geologic records of mid-latitude Paleogene river systems suggesting increases in the magnitude or variability of river discharge coinciding with established climate perturbations.

Flood Hazard Assessment in Madeira (Portugal) – The Case Study of Machico

This study aims to carry out a proper flood risk assessment in Machico’s main watercourse and purpose at least two different flood mitigation measures to prevent major impacts over the watershed. Furthermore, the assessment addresses the need for structural-measures — i.e. detention basins — towards mitigating flood hazards under high-intensity and short-duration precipitation events. It became possible to morphometrically characterize all the watersheds using empirical equations to gather specific parameters and indexes. A proper articulation between the hydrological and the spatial analysis using geographic information systems was then carried out. According to many parameters calculated the watershed of Machico proved to assume a very large-size and to be highly prone to flash floods. The spatial analysis took into consideration the watershed’s Fill Rate using both Dutch and the Ternary Phase Diagram methods and allowed us to define criteria towards the establishment of detention basins as a valid flood mitigation measure. Finally, it was clear that the watershed corresponding to Machico’s main watercourse induces the need to further implement either a detention basin or to modify the roughness coefficient of its river channel. Moreover, the comparison between the results obtained with DROTA’s Flood Risk Report, allows us to consider this study’s outcome both satisfactory and valid.