scholarly journals Compound Flooding: Dependence at Sub-daily Scales Between Extreme Storm Surge and Fluvial Flow

2021 ◽  
Vol 7 ◽  
Author(s):  
Peter E. Robins ◽  
Matt J. Lewis ◽  
Mariam Elnahrawi ◽  
Charlotte Lyddon ◽  
Neil Dickson ◽  
...  
Keyword(s):  
Sea Level ◽  
River Flow ◽  
Response Times ◽  
High Tide ◽  
Sea Levels ◽  
Hourly Data ◽  
Fluvial Response ◽  
Compound Events ◽  
Phase Data ◽  
Flooding Events

Estuaries are potentially exposed to compound flooding where weather-driven extreme sea levels can occur synchronously with extreme fluvial discharge to amplify the hazard. The likelihood of compound flooding is difficult to determine due to multiple interacting physical processes operating at sub-daily scales, and poor observation records within estuaries with which to determine potential future probabilistic scenarios. We hypothesize that fluvial extremes can occur within the peak of the surge in small/steep catchments because of rapid runoff times, whilst the length-scale in larger/flatter catchments will result in fluvial and marine extremes being out-of-phase. Data (15 min river flow and hourly sea level) spanning 40 years were analyzed to assesses the behaviour and timings of fluvial and sea level extremes in two contrasting estuaries: Humber and Dyfi (United Kingdom). Compound events were common in the Dyfi, a small/steep catchment on Britain’s west coast with fast fluvial response times. Almost half of the 937 skew-surge events (95th-percentile) occurred within a few hours of an extreme fluvial peak, suggesting that flood risk is sensitive to the storm timing relative to high tide—especially since flows persisted above the 95th-percentile typically for less than 12 h. Compound events were more frequent during autumn/winter than spring/summer. For the Humber, a larger/flatter catchment on the east coast with slower fluvial response times, extreme fluvial and skew-surge peaks were less frequent (half as many as the Dyfi) and compound events were less common (15% of events co-occurred). Although flows in the Humber persisted above the 95th-percentile for typically between one and 4 days, hence overlapping several high tides and possibly other surges. Analysis of 56 flooding events across both estuaries revealed: 1) flooding is more common in the Dyfi than Humber; 2) Dyfi flooding is driven by 99th-percentile flows lasting hours and co-occurring with a 95th percentile skew-surge; 3) Humber flooding was driven by 95th-percentile flows lasting days, or surge-driven—but rarely co-occurring. Our results suggest that compound flooding studies require at least hourly data (previous analyses have often used daily-means), especially for smaller systems and considering the potential intensification of rainfall patterns into the future.

scholarly journals Compounding effects of sea level rise and fluvial flooding

2017 ◽  
Vol 114 (37) ◽  
pp. 9785-9790 ◽  
Author(s):  
Hamed R. Moftakhari ◽  
Gianfausto Salvadori ◽  
Amir AghaKouchak ◽  
Brett F. Sanders ◽  
Richard A. Matthew
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Hazard Assessment ◽  
Failure Probability ◽  
River Flow ◽  
Flood Hazard ◽  
High Tide ◽  
Probability Method ◽  
Flood Hazards ◽  
Flood Hazard Assessment

Sea level rise (SLR), a well-documented and urgent aspect of anthropogenic global warming, threatens population and assets located in low-lying coastal regions all around the world. Common flood hazard assessment practices typically account for one driver at a time (e.g., either fluvial flooding only or ocean flooding only), whereas coastal cities vulnerable to SLR are at risk for flooding from multiple drivers (e.g., extreme coastal high tide, storm surge, and river flow). Here, we propose a bivariate flood hazard assessment approach that accounts for compound flooding from river flow and coastal water level, and we show that a univariate approach may not appropriately characterize the flood hazard if there are compounding effects. Using copulas and bivariate dependence analysis, we also quantify the increases in failure probabilities for 2030 and 2050 caused by SLR under representative concentration pathways 4.5 and 8.5. Additionally, the increase in failure probability is shown to be strongly affected by compounding effects. The proposed failure probability method offers an innovative tool for assessing compounding flood hazards in a warming climate.

Interactions of extreme river flows and sea levels for coastal flooding

2020 ◽  
Author(s):  
Peter Robins ◽  
Lisa Harrison ◽  
Mariam Elnahrawi ◽  
Matt Lewis ◽  
Tom Coulthard ◽  
...  
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
West Coast ◽  
Flood Risk ◽  
Coastal Flooding ◽  
Relative Timing ◽  
The West ◽  
Sea Levels ◽  
Flooding Hazards ◽  
Fluvial Response

<p>Coastal flooding worldwide causes the vast majority of natural disasters; for the UK costing £2.2 billion/year. Fluvial and surge-tide extremes can occur synchronously resulting in combination flooding hazards in estuaries, intensifying the flood risk beyond fluvial-only or surge-only events. Worse, this flood risk has the potential to increase further in the future as the frequency and/or intensity of these drivers change, combined with projected sea-level rise. Yet, the sensitivity of contrasting estuaries to combination and compound flooding hazards at sub-daily scales – now and in the future – is unclear. Here, we investigate the dependence between fluvial and surge interactions at sub-daily scales for contrasting catchment and estuary types (Humber vs. Dyfi, UK), using 50+ years of data: 15-min fluvial flows and hourly sea levels. Additionally, we simulate intra-estuary (<50 m resolution) sensitivities to combination flooding hazards based on: (1) realistic extreme events (worst-on-record); (2) realistic events with shifted timings of the drivers to maximise flooding; and (3) modified drivers representing projected climate change.</p><p>For well-documented flooding events, we show significant correlation between skew surge and peak fluvial flow, for the Dyfi (small catchment and estuary with a fast fluvial response on the west coast of Britain), with a higher dependence during autumn/winter months. In contrast, we show no dependence for the Humber (large catchment and estuary with a slow fluvial response on the east coast of Britain). Cross-correlation results, however, did show correlation with a time lag (~10 hours). For the Dyfi, flood extent was sensitive to the relative timing of the fluvial and surge-tide drivers. In contrast, the relative timing of these drivers did not affect flooding in the Humber. However, extreme fluvial flows in the Humber actually reduced water levels in the outer estuary, compared with a surge-only event. Projected future changes in these drivers by 2100 are likely to increase combination flooding hazards: sea-level rise scenarios predicted substantial and widespread flooding in both estuaries. However, similar increases in storm surge resulted in a greater seawater influx, altering the character of the flooding. Projected changes in fluvial volumes were the weakest driver of estuarine flooding. On the west coast of Britain containing many small/steep catchments, combination flooding hazards from fluvial and surges extremes occurring together is likely. Moreover, high-resolution data and hydrodynamic modelling are necessary to resolve the impact and inform flood mitigation methodology.</p>

scholarly journals Timescales of emergence of chronic flooding in the major economic center of Guadeloupe

2021 ◽  
Vol 21 (2) ◽  
pp. 703-722
Author(s):  
Gonéri Le Cozannet ◽  
Déborah Idier ◽  
Marcello de Michele ◽  
Yoann Legendre ◽  
Manuel Moisan ◽  
...  
Keyword(s):  
Sea Level ◽  
Tide Gauge ◽  
Ground Motions ◽  
Weather Conditions ◽  
Coastal Zones ◽  
Tide Gauge Records ◽  
Sea Levels ◽  
Vertical Ground Motions ◽  
Vertical Ground ◽  
Flooding Events

Abstract. Sea-level rise due to anthropogenic climate change is projected not only to exacerbate extreme events such as cyclones and storms but also to cause more frequent chronic flooding occurring at high tides under calm weather conditions. Chronic flooding occasionally takes place today in the low-lying areas of the Petit Cul-de-sac marin (Guadeloupe, West Indies, French Antilles). This area includes critical industrial and harbor and major economic infrastructures for the islands. As sea level rises, concerns are growing regarding the possibility of repeated chronic flooding events, which would alter the operations at these critical coastal infrastructures without appropriate adaptation. Here, we use information on past and future sea levels, vertical ground motion, and tides to assess times of emergence of chronic flooding in the Petit Cul-de-sac marin. For RCP8.5 (Representative Concentration Pathway 8.5; i.e., continued growth of greenhouse gas emissions), the number of flood days is projected to increase rapidly after the emergence of the process so that coastal sites will be flooded 180 d a year within 2 decades of the onset of chronic flooding. For coastal locations with the lowest altitude, we show that the reconstructed number of floods is consistent with observations known from a previous survey. Vertical ground motions are a key source of uncertainty in our projections. Yet, our satellite interferometric synthetic-aperture radar results show that the local variability in this subsidence is smaller than the uncertainties in the technique, which we estimate to be between 1 (standard deviation of measurements) and 5 mm/yr (upper theoretical bound). Despite these uncertainties, our results imply that adaptation pathways considering a rapid increase in recurrent chronic flooding are required for the critical port and industrial and commercial center of Guadeloupe. Similar processes are expected to take place in many low-elevation coastal zones worldwide, including on other tropical islands. The method used in this study can be applied to other locations, provided tide gauge records and local knowledge of vertical ground motions are available. We argue that identifying times of emergence of chronic flooding events is urgently needed in most low-lying coastal areas, because adaptation requires decades to be implemented, whereas chronic flooding hazards can worsen drastically within years of the first event being observed.

scholarly journals Assessing the Uncertainty in Projecting Local Mean Sea Level from Global Temperature

2014 ◽  
Vol 53 (9) ◽  
pp. 2163-2170 ◽  
Author(s):  
Peter Guttorp ◽  
Alex Januzzi ◽  
Marie Novak ◽  
Harry Podschwit ◽  
Lee Richardson ◽  
...  
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Climate Model ◽  
Global Climate ◽  
Global Climate Model ◽  
High Tide ◽  
Deterministic Models ◽  
Total Uncertainty ◽  
Sea Levels ◽  
Global Sea Level

AbstractThe process of moving from an ensemble of global climate model temperature projections to local sea level projections requires several steps. Sea level was estimated in Olympia, Washington (a city that is very concerned with sea level rise because parts of downtown are barely above mean highest high tide), by relating global mean temperature to global sea level; relating global sea level to sea levels at Seattle, Washington; and finally relating Seattle to Olympia. There has long been a realization that accurate assessment of the precision of projections is needed for science-based policy decisions. When a string of statistical and/or deterministic models is connected, the uncertainty of each individual model needs to be accounted for. Here the uncertainty is quantified for each model in the described system and the total uncertainty is assessed in a cascading effect throughout the system. The projected sea level rise over time and its total estimated uncertainty are visualized simultaneously for the years 2000–2100, the increased uncertainty due to each of the component models at a particular projection year is identified, and estimates of the time at which a certain sea level rise will first be reached are made.

scholarly journals Some Pitfalls of the Semiempirical Method Used to Project Sea Level

2015 ◽  
Vol 28 (9) ◽  
pp. 3779-3785 ◽  
Author(s):  
Mirko Orlić ◽  
Zoran Pasarić
Keyword(s):  
Sea Level ◽  
Transfer Functions ◽  
Response Times ◽  
Semiempirical Method ◽  
First Century ◽  
Third Century ◽  
Sea Levels ◽  
Level Data ◽  
Related Response ◽  
Twenty First Century

Abstract Three variants of the semiempirical method for sea level projection are considered. They differ in assuming that the response of sea level to temperature forcing is equilibrium, inertial, or a combination of the two. All variants produce a successful regression of the temperature and sea level data, albeit with controlling parameters that differ among the cases. The related response times vary considerably, with a realistic value (~50 yr) obtained only if both the equilibrium and the inertial dynamics are taken into account. A comparison of sea levels projected by using the three variants shows that the time series are similar through the middle of the twenty-first century but they radically diverge by the end of the twenty-third century. This result is interpreted with the aid of the underlying transfer functions. It suggests that one should be cautious when using the semiempirical method to project sea level beyond the twenty-first century.

Future estuarine circulation patterns characterization based on a hydrodynamic models ensemble

2021 ◽  
Author(s):  
Isabel Iglesias ◽  
José Luís Pinho ◽  
Ana Bio ◽  
Paulo Avilez-Valente ◽  
Willian Melo ◽  
...  
Keyword(s):  
Sea Level ◽  
River Flow ◽  
Extreme Values ◽  
Numerical Models ◽  
Point Of View ◽  
Sea Levels ◽  
Flood Peak ◽  
Climate Change Effects ◽  
Hydrodynamic Behaviour ◽  
Rising Sea Levels

<p>Estuarine regions are strategically important from an environmental, economic, and social point of view. To reduce vulnerability and increase resilience, it is crucial to know their dynamics that usually are poorly understood. Numerical models have proven to be an appropriate tool to improve this knowledge and simulate scenarios for future conditions. However, as the modelling results may be inaccurate, the application of the ensembles technique can be very useful in reducing possible uncertainties. In the EsCo-Ensembles project, this technique is proposed to improve hydrodynamic predictions for two Portuguese estuaries: Douro and Minho.</p><p>Two already validated numerical models (openTELEMAC-MASCARET and Delft3D), which have demonstrated their ability to accurately describe estuarine hydrodynamic patterns and water elevation for river flow in normal and extreme conditions, were applied. Several scenarios for climate change effects were defined including river flood peak flows for the 100 and 1000 year return periods and sea level extreme values for RCPs 4.5 and 8.5 in 2100.</p><p>The results demonstrated a clear difference between the hydrodynamic behaviour of the two estuaries. Model outcomes for the Minho estuary, which is dominated by the tide and therefore by oceanographic conditions, show a pronounced effect of rising sea levels on estuarine hydrodynamics. Whereas, for the Douro estuary, which is heavily dominated by the river flow, the effect of the sea level rise is hardly noticeable during flood events.</p><p>These and further results of this ongoing project are expected to (i) provide a complete hydrodynamic characterization of the two estuaries; (ii) evaluate future trends; (iii) estimate the flood risks associated with extreme events and (iv) demonstrate that the combined use of different models reduces their uncertainty and increases the confidence and consistency of the forecasts.</p><p><strong>Acknowledgements: </strong>To the Strategic Funding UIDB/04423/2020 and UIDP/04423/2020 (FCT and ERDF) and to the project EsCo-Ensembles (PTDC/ECI-EGC/30877/2017, NORTE 2020, Portugal 2020, ERDF and FCT). The authors also want to acknowledge the data provided by EDP, IH and Confederación Hidrográfica Miño-Sil.</p>

scholarly journals Analysis on the Extreme Sea Levels Changes along the Coastline of Bohai Sea, China

Atmosphere ◽  
2018 ◽  
Vol 9 (8) ◽  
pp. 324 ◽  
Author(s):  
Jianlong Feng ◽  
Delei Li ◽  
Hui Wang ◽  
Qiulin Liu ◽  
Jianli Zhang ◽  
...  
Keyword(s):  
Sea Level ◽  
Bohai Sea ◽  
High Tide ◽  
Tide Gauges ◽  
Mean Sea Level ◽  
Sea Levels ◽  
The Bohai Sea ◽  
Extreme Sea Levels ◽  
The Mean

Using hourly sea level data from four tide gauges, the changes of the extreme sea level in the Bohai Sea were analyzed in this work. Three components (i.e., mean sea level, tide and surge) as well as the tide–surge interaction were studied to find which component was important in the changes of extreme sea levels. Significant increasing trends exist in the mean sea level at four tide gauges from 1980 to 2016, and the increase rate ranges from 0.2 to 0.5 cm/year. The mean high tide levels show positive trends at four tide gauges, and the increasing rate (0.1 to 0.3 cm/year) is not small compared with the long-term trends of the mean sea levels. However, the mean tidal ranges show negative trends at Longkou, Qinhuangdao and Tanggu, with the rate from about −0.7 to −0.2 cm/year. At Qinhuangdao and Tanggu, the annual surge intensity shows explicit long-term decreasing trend. At all four tide gauges, the storm surge intensity shows distinct inter-annual variability and decadal variability. All four tide gauges show significant tide–surge interaction, the characteristics of the tide–surge interaction differ due to their locations, and no clear long-term change was found. Convincing evidence implies that the extreme sea levels increase during the past decades from 1980 to 2016 at all tide gauges, with the increasing rate differing at different percentile levels. The extreme sea level changes in the Bohai Sea are highly affected by the changes of mean sea level and high tide level, especially the latter. The surge variation contributes to the changes of extreme sea level at locations where the tide–surge interaction is relatively weak.

scholarly journals Insuring property under climate change

2017 ◽  
Vol 13 (4) ◽  
Author(s):  
Belinda Storey ◽  
Ilan Noy
Keyword(s):  
Climate Change ◽  
New Zealand ◽  
Sea Level ◽  
Housing Stock ◽  
High Tide ◽  
Storm Surges ◽  
Intergovernmental Panel ◽  
Sea Levels ◽  
The Antarctic ◽  
Emissions Scenario

Climate change will increasingly create severe risks for  New Zealand’s coastal housing stock. Even a small amount of sea level rise will substantially exacerbate the costs of flooding and storm surges (Parliamentary Commissioner for the Environment, 2015). Under the Intergovernmental Panel on Climate Change’s (IPCC) three mitigation scenarios, global average sea levels are likely to rise by between 28cm and 73cm by 2100 (above the 1986–2005 average). Under the IPCC’s high emissions scenario the sea level is likely to rise by between 52cm and 98cm by 2100 (IPCC, 2013). Only collapse of parts of the Antarctic ice sheet, if triggered, could cause the sea level to rise substantially above these ranges. Some regions in New Zealand (including the main urban centres) have high enough quality geographic data to infer the number of homes at risk. In those regions, there are over 43,000 homes within 1.5m of the present average spring high tide and over 8,000 within 50cm.

scholarly journals Flooding in Central Chile: Implications of Tides and Sea Level Increase in the 21st Century

2018 ◽  
Vol 10 (12) ◽  
pp. 4335 ◽  
Author(s):  
Octavio Rojas ◽  
María Mardones ◽  
Carolina Martínez ◽  
Luis Flores ◽  
Katia Sáez ◽  
...  
Keyword(s):  
Sea Level ◽  
21St Century ◽  
Salt Marshes ◽  
River Mouth ◽  
Global Scale ◽  
Residential Areas ◽  
Central Chile ◽  
Sea Levels ◽  
Level Increase ◽  
Flooding Events

Coastal floods have become a serious problem on a global scale, increasing in frequency or magnitude due to natural conditions, and exacerbated by socioeconomic factors. This investigation analyzes the role of tides and average sea levels on the development and intensity of flooding in the lower section of the Andalién River, located toward the southern extreme of the coast of central Chile and northeast of Concepción, the country’s second most populous city. Numerical simulation (1D) was used in five modeled scenarios to determine potential flooding areas, demonstrating the influence of tides in flooding processes as far away as 7.3 km from the river mouth, which is reinforced by the fact that 57% of flooding events occur during syzygies. Further, a climate change-induced sea level rise of 60 cm from current levels by the end of the 21st century would produce a 4% increase in flood-prone areas, with 17% of flooding affecting the current built-up area and 83% of floodplains and salt marshes. Efforts must be made to protect or conserve these latter areas in order to increase natural resilience, given the high costs of implementing structural measures to protect future residential areas.

scholarly journals Leaf Enzyme and Plant Productivity Responses to Environmental Stress Associated with Sea Level Rise in Two Asian Mangrove Species

Forests ◽  
2019 ◽  
Vol 10 (3) ◽  
pp. 250 ◽  
Author(s):  
Xiaobo Lv ◽  
Donghai Li ◽  
Xiaobo Yang ◽  
Mengwen Zhang ◽  
Qin Deng
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Synergistic Effects ◽  
High Tide ◽  
Mangrove Forests ◽  
Mangrove Species ◽  
Sea Levels ◽  
Tidal Flooding ◽  
Seawater Salinity ◽  
Flooding Time

As the only forests situated at the transition between land and sea, mangrove forests are one of the first ecosystems vulnerable to rising sea levels. When the sea level rises, plants are exposed to increased salinity, as well as tidal flooding. The responses of mangrove forests to changing sea levels depend on the synergistic effects of tidal flooding and salinity on plants, especially seedlings. The focus of this paper is to assess the ability of different tide position on mangrove Aegiceras corniculatum (A. corniculatum) and Bruguiera sexangula (B. sexangula) seedlings to withstand tidal flooding and seawater salinity, and to investigate the effects of tidal flooding and salinity on plant growth. To accomplish this, a controlled experiment was initiated to examine the synergistic effects of tidal flooding and salinity on the growth and physiology of A. corniculatum and B. sexangula seedlings subjected to four tidal flooding times and four levels of salinity over a course of six months. The results showed that the biomass and antioxidant enzymes of A. corniculatum and B. sexangula seedlings were significantly affected by the increase in salinity and flooding time. Changes in biomass, SOD, and CAT activity of A. corniculatum seedlings show that they are more adapted to grow in an environment with high salinity and long flooding time than B. sexangula. Our results show that species growing in middle- to low-tide levels were better adapted to sea level rise than those growing at high-tide levels.

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