Low-lying Coastal Zones Research Articles

Identifying global hotspots where coastal wetland conservation can contribute to nature-based mitigation of coastal flood risks

Low-lying coastal zones are increasingly exposed to flood risks due to global change including sea level rise, increasing storm intensity and growing coastal population densities. Local to regional-scale studies have demonstrated that conservation or restoration of coastal wetland ecosystems, such as salt marshes and mangroves, provides nature-based risk mitigation, as these wetlands have the natural capacity to mitigate the impacts of storm surges and related flood risks. Yet, it is unknown how important this nature-based mitigation of coastal flood risks is on a global scale. Here we present the results of a global-scale GIS model assessing the global distribution of inland surface areas and population numbers exposed to storm surges that would first propagate through tidal wetlands before they reach the inhabited land, and hence that would receive storm surge mitigation by the mangrove forests and salt marshes. Further our model quantifies the distance travelled by a storm surge through the tidal wetlands as a measure of the magnitude of storm surge mitigation. Results show that on a worldwide scale, about 30% of the flood-exposed low-lying coastal plain benefits from nature-based storm surge mitigation by tidal wetlands, with the largest areas located in deltas (e.g. Pearl River, Yangtze, Mekong) and estuaries (e.g. Elbe). Areas protected by large wetlands, where a storm surge would first propagate through >5 km of tidal wetlands before it reaches vulnerable land and people, are located in river deltas such as of the Guayas (Ecuador), Mississippi (USA) and Ganges-Brahmaputra (India and Bangladesh). About 35% of the global flood-exposed coastal population receives nature-based storm surge mitigation. The majority of that population (80%) is located in five countries, i.e. China, Vietnam, the Netherlands, India and Germany. Areas more exposed to extreme storm surges (Eastern America, Caribbean Sea, Eastern Asia) include hotspot areas where storm surges are travelling through wider tidal wetlands generating higher risk mitigation, as for example in the Mississippi delta, Chesapeake bay, Ganges-Brahmaputra delta or Yangtze delta. Our global assessment aims to increase general awareness on the capacity of nature-based coastal flood risk mitigation, and to stimulate further local scale analyses in support of its wider application around the world.

An indicator-based approach to assess social vulnerability of coastal areas to sea-level rise and flooding: A case study of Bandar Abbas city, Iran

The sea-level rise (SLR) resulting from climate change and flooding will threaten residents living in low-lying coastal zones in the coming decades. In this regard, evaluating social vulnerability as a significant component of flood risk reduction is necessary. Indicators, in conjunction with multi-criteria decision-making (MCDM) methods, have been recently employed to quantify social vulnerability. In the present study, an indicator-based approach was developed to assess social vulnerability to SLR and flooding in Bandar Abbas city coastal district, southern Iran. To build a social vulnerability index (SoVI) indicators were firstly categorized in, exposure, sensitivity, and adaptive capacity components. Indicators were then weighted using MCDM methods (i.e., analytical hierarchy process (AHP) and fuzzy AHP models). Subsequently, an additive weighting model was employed to produce social vulnerability maps at the block level, and under different combined flooding scenarios in 2050 and 2100. Results showed that using the fuzzy AHP does not necessarily change the ranks of indicators and components compared to the AHP model. However, the spatial extents of social vulnerability were entirely different for both models due to differences in indicators weight. It confirms that using the AHP model as a simplified method can be acceptable when determining indicators and components weight is required. Although, in the case of identifying the detailed spatial extents of social vulnerability using the fuzzy AHP might be appropriate. For all scenarios, using the AHP and fuzzy AHP model, most districts were classified as medium and low vulnerable, respectively. Moreover, the impact of SLR resulting from climate change was significantly evident in the eastern and western parts, where more districts were recognized as highly and very highly vulnerable in the worst-case scenario (S4-2100). The results of this study provide valuable comparative information that can be employed by decision-makers in coastal planning and risk reduction at local scales.

A global exploration of tidal wetland creation for nature-based flood risk mitigation in coastal cities

Coastal cities around the world are increasingly exposed to flood risks due to climate change, resulting sea level rise and more intense storm surges as well as due to growing coastal population densities and land subsidence. Nature-based risk mitigation, consisting of conservation or creation of coastal ecosystems that have the natural capacity to adapt to sea level rise and to mitigate storm surges, is increasingly proposed, but real-live implementation is yet limited to specific local cases. Our study presents a global scale analysis of the surface areas available for potential creation or restoration of tidal wetlands (salt marshes and mangrove forests) in front of 135 highly populated, flood-exposed coastal cities, as part of nature-based or hybrid strategies to buffer against coastal flood risks. Our results reveal that 34% (4 600 km2) of the total land area within the influence zone of storm surge propagation between the sea and the cities is potentially available for tidal wetlands creation. Those areas mainly correspond to rural areas with a low population density such as croplands, paddy fields or vegetated areas and to water bodies. The key factors influencing the area potentially available for tidal wetlands creation are the geomorphology and the population density, as 60% (8 300 km2) of the land area below mean high tide in front of the studied cities is urbanized or densely populated. Cities located along deltas or estuaries and in bays and lagoons (e.g. Hamburg, Guayaquil, Tianjin, Portland or San Jose) have generally larger low-lying coastal zones and consequently larger potentially available areas for salt marshes and mangrove forests restoration or creation for coastal flood risks mitigation. Our results contribute to increasing evidence and awareness of the possibilities of nature-based mitigation of coastal flood risks by restoring and creating tidal wetlands in front of flood-exposed coastal cities around the world.

Increased coastal wave hazard generated by differential wind and wave direction in hyper-tidal estuaries

Wave overtopping and subsequent coastal flood hazard is strongly controlled by wind and water levels, and is especially critical in hyper-tidal estuaries where even small changes in wave heights can be catastrophic if they are concurrent with high spring tide. Wave hazard in estuaries is largely attributed to high amplitude shorter period, locally generated wind waves; while low amplitude longer period waves rarely impact low-lying coastal zones up-estuary. Here, the effect of wind and wave properties on up-estuary wave propagation and the sensitivity of significant wave height are investigated numerically along the shoreline of the Severn Estuary, southwest England, as an example. Representative values for wind speed and direction, wave height, period and direction are used to identify key combinations of factors that define the wave hazard generation. High amplitude, short period wind waves are sensitive to opposing winds, with a steepening effect that varies along the estuary shoreline, highlighting the effect of estuarine geometry on wave hazard. Low amplitude, long period wind waves respond with maximum variability in significant wave height to strong winds resulting in their propagation further up-estuary. Our results advance current understanding of the compound interaction between wind and waves, and identify critical conditions maximizing the hazard and hazard variability along the shoreline. The outcomes from this research can help to avoid economic losses from operational downtime in ports and harbors, inform sustainable coastal sea defense design and understand how wave hazard may vary under future climate due to changing storm tracks. Results can also be applied to the design of coastal infrastructure and facilitation of emergency response planning.

Characterizing the Indian Ocean sea level changes and potential coastal flooding impacts under global warming

The Indian Ocean which is home to many islands and the low-lying coastal zones have attracted considerable attention due to regional sea level changes. In this study, we examine regional changes in sea level of the Indian Ocean and potential coastal flooding impacts by using tide gauge data. Various interpolation methods are evaluated to predict values at locations where data is unavailable. Based on the cross-validation analysis, the radial basis function is identified as the most optimal interpolation method and is used to analyze the spatial patterns of sea level changes. The analysis reveals that Bangladesh, Seychelles, and Cocos (Keeling) Islands have relatively high rates of sea level rise. These regions would thus be highly vulnerable to coastal flooding induced by the accelerating sea level rise in future decades, posing significant threats to coastal communities and ecosystems. Flooding impacts are examined through inundation mapping in a geographic information system (GIS) environment. In addition, relationships between regional factors (sea surface temperature, air temperature, and vertical land motions) affecting sea level rise are investigated. Our findings indicate that vertical land motion is an important factor affecting sea level changes for the regions of Seychelles and Cocos Islands. There is a strong relationship between air temperature and sea level rise for all studied regions. This study is a first attempt to examine regional changes in sea level of the Indian Ocean and potential coastal flooding impacts by using tide gauge data. The methods used in this study can be applied to other coastal regions around the world.

Uncertainty in estuarine extreme water level predictions due to surge-tide interaction.

Storm surge is often the greatest threat to life and critical infrastructures during hurricanes and violent storms. Millions of people living in low-lying coastal zones and critical infrastructure within this zone rely on accurate storm surge forecast for disaster prevention and flood hazard mitigation. However, variability in residual sea level up-estuary, defined here as observed sea level minus predicted tide, can enhance total water levels; variability in the surge thus needs to be captured accurately to reduce uncertainty in site specific hazard assessment. Delft3D-FLOW is used to investigate surge variability, and the influence of storm surge timing on barotropic tide-surge propagation in a tide-dominant estuary using the Severn Estuary, south-west England, as an example. Model results show maximum surge elevation increases exponentially up-estuary and, for a range of surge timings consistently occurs on the flood tide. In the Severn Estuary, over a distance of 40 km from the most upstream tide gauge at Oldbury, the maximum surge elevation increases by 255%. Up-estuary locations experience short duration, high magnitude surge elevations and greater variability due to shallow-water effects and channel convergence. The results show that surge predictions from forecasting systems at tide gauge locations could under-predict the magnitude and duration of surge contribution to up-estuary water levels. Due to the large tidal range and dynamic nature of hyper-tidal estuaries, local forecasting systems should consider changes in surge elevation and shape with distance up-estuary from nearby tide gauge sites to minimize uncertainties in flood hazard assessment.

Reprint of Changes in coastal dune systems on the Catalan shoreline (Spain, NW Mediterranean Sea). Comparing dune landscapes between 1890 and 1960 with their current status

The aim of this paper is to assess the changes that have occurred in coastal dune landscapes in Catalonia (Spain, NW Mediterranean Sea) over the last decades. Data from photographic, cartographic, and documentary sources between 1890 and 1960 have been examined and contrasted with the current status of dunes. Our analysis measures the historical transformation of the coastal dune system according to type of transformation (disappeared dunes, dunes smaller in size and dunes that have undergone few changes) and land cover changes surrounding the beaches.At this time in Catalonia, the most extensive coastal dune systems are located in Empordà county (Roses Bay and Baix Ter Bay) and the Ebro Delta. The results reflect that the loss of dune habitat during recent decades has affected more than 90% of the Catalan beaches assessed, 60% of which have disappeared and 30% reduced in size. The most affected province is Barcelona, where disappearance of dunes has affected over 80% of beaches and no beaches present almost untouched dunes; Girona and Tarragona have also been seriously affected, with dunes disappearing from 60% to 40% of the beaches assessed, respectively. However, on a minority of beaches along the Catalan shoreline, a few dunes remain almost untouched (10%).Land cover changes surrounding the beaches show that dune habitats have been drastically reduced due to human pressure, especially urbanization and tourism-related processes. A multiple correspondence analysis (MCA) has shown that the dune systems that have disappeared are located in non-protected areas and low-lying coastal zones, whereas dunes that have become smaller in size or undergone few changes are located in protected natural areas and on cliffed coasts.

Index based multi-criteria approach to coastal risk assesment

The present study focuses on the quantification of coastal risks associated with erosion and inundation accelerated by sea level rise and extreme storms events in the specific conditions of micro-tidal semi-enclosed seas. The main objective is to develop a measure that characterises climate-related external hazards, the exposure (of people and assets at risk of being damaged) and vulnerability of human and natural systems. This is accomplished by means of adaption of the concept of nondimensional coastal risk (or resilience) index (CRI), as a function of coastal vulnerability and exposure indices, to the conditions of sedimentary shores of the eastern Baltic Sea and testing its suitability for low-lying coastal zones considering their environmental and socio-economic characteristics. The study area is an about 45 km long coastal section of Lithuania in the south-eastern Baltic Sea. We introduce a set of locally relevant coastal vulnerability and exposure variables, apply an Analytical Hierarchy Process to calculate the criteria weights and GIS multi-criteria evaluation approach to calculate the CRI values. The coastal segments with high vulnerability often have low values of the exposure index. About 11% of the study area is under very high risk. The largest CRI values occur at a certain distance from the touristic or industrial spots near Klaipėda, around the Palanga pier and to the north of Sventoji. These coastal sectors are highly populated areas that suffer from sediments deficit due to coastal engineering structures.

Changes in coastal dune systems on the Catalan shoreline (Spain, NW Mediterranean Sea). Comparing dune landscapes between 1890 and 1960 with their current status

The aim of this paper is to assess the changes that have occurred in coastal dune landscapes in Catalonia (Spain, NW Mediterranean Sea) over the last decades. Data from photographic, cartographic, and documentary sources between 1890 and 1960 have been examined and contrasted with the current status of dunes. Our analysis measures the historical transformation of the coastal dune system according to type of transformation (disappeared dunes, dunes smaller in size and dunes that have undergone few changes) and land cover changes surrounding the beaches.At this time in Catalonia, the most extensive coastal dune systems are located in Empordà county (Roses Bay and Baix Ter Bay) and the Ebro Delta. The results reflect that the loss of dune habitat during recent decades has affected more than 90% of the Catalan beaches assessed, 60% of which have disappeared and 30% reduced in size. The most affected province is Barcelona, where disappearance of dunes has affected over 80% of beaches and no beaches present almost untouched dunes; Girona and Tarragona have also been seriously affected, with dunes disappearing from 60% to 40% of the beaches assessed, respectively. However, on a minority of beaches along the Catalan shoreline, a few dunes remain almost untouched (10%).Land cover changes surrounding the beaches show that dune habitats have been drastically reduced due to human pressure, especially urbanization and tourism-related processes. A multiple correspondence analysis (MCA) has shown that the dune systems that have disappeared are located in non-protected areas and low-lying coastal zones, whereas dunes that have become smaller in size or undergone few changes are located in protected natural areas and on cliffed coasts.

Vertical accuracy evaluation of SRTM-GL1, GDEM-V2, AW3D30 and CartoDEM-V3.1 of 30-m resolution with dual frequency GNSS for lower Tapi Basin India

Shuttle Radar Topography Mission (SRTM-GL1), Advanced Space Borne Thermal Emission and Reflection Radiometer- Global DEM (GDEM-V2), recently released Advanced Land Observing Satellite (‘DAICHI’) DEM (AW3D30) and Indian National Cartosat-1 DEM v3 (CartoDEM-V3.1) provide free topographic data at a 30-m resolution for Indian peninsula. In this research study, the vertical accuracy of DEM is evaluated for above data-sets and compared with high accuracy dual frequency GNSS of a millimetre accuracy. The extensive field investigation is carried out using a stratified random fast static DGPS survey for collecting 117 high accuracy ground control points in a predominantly agriculture catchment. Further, the effect of land cover, slope and low-lying coastal zone on DEM vertical accuracy was also analysed and presented in this study.

Social work models for climate adaptation: the case of small islands in the Caribbean

Small Island Developing States (SIDS) are widely recognised as being very vulnerable to the impacts of climate change. In some manner, climate change will impact on the livelihoods of most individuals in the twenty-first century. Some of the risks for small islands are risk of death, injury, ill-health or disrupted livelihoods in low-lying coastal zones due to storm surges, coastal flooding, and sea level rise. The Intergovernmental Panel on Climate Change suggests that in small islands, which have diverse physical and human attributes, community-based adaptation has been shown to generate larger benefits when delivered in conjunction with other developmental activities. One of the adaptive responses suggested is to improve the efficacy of traditional community coping strategies; this can be facilitated by social work intervention at the macro-level. The role of social workers in SIDS can impact on sustainable development and towards improved livelihoods of a country’s human resources. According to the Council on Social Work Education, the purpose of the social work profession is to promote human and community well-being. This purpose is put into practice through a quest for social and economic justice, the prevention of conditions that limit human rights, the elimination of poverty and the enhancement and quality of life for all persons. Key strategies by which social workers can promote sustainable development include building relations with communities, helping individuals to deepen their understanding of sustainable development, and assisting them to develop and work towards goals and objectives that lead towards the integration and improvement of economic, social and environmental outcomes.

Density-driven vertical transport of saltwater through the freshwater lens on the island of Baltrum (Germany) following the 1962 storm flood

Due to the growing vulnerability of low-lying coastal zones to flooding by seawater, there is a current need for studies of the impact of such inundations on fresh groundwater resources. The knowledge from the literature is biased towards tropical atoll environments, and only few studies specifically investigated the effect of density-driven downward flow, even though its importance is widely acknowledged. The present study is based on previously unpublished hydrochemical data collected on the island of Baltrum following a devastating storm in 1962, which uniquely show the impact of seawater inundation on a freshwater lens in a siliciclastic aquifer. The field data show that about 3kg of Cl per m2 of inundated land area, or 18cm of seawater, infiltrated, and that elevated salinities persisted at the measurement depths of 4 and 6m for at least 4years, and at least for 6years at greater depths. Numerical models support the assertion that the shape of the measured salinographs, i.e. an initial sharp rise in the salt concentration with time, followed by a continually-slowing decrease, must be attributed to density-driven salt fingering. Models that did not consider density effects fail to simulate the observed patterns. Transient recharge, model dimension and lateral flow modify the details of the simulation results, but in all models density-driven vertical flow dominates the overall system behaviour. The diminishing importance of density-driven flow at greater depths, however, in combination with slow recharge-driven flow rates prolongs flushing times, and enhances the risk of brackish-water up-coning when pumping is resumed too soon.

Rapid risk assessment of wetland degradation and loss in low-lying coastal zone of Shanghai, China

ABSTRACTCoastal wetlands are facing an increasingly high risk of degradation and loss due to a wide variety of human activities and natural processes. Human encroachment, including land reclamation, drainage, and introduction of invasive species, has direct negative effects on wetlands, mainly through changes in hydrology and vegetation. Additionally, accelerated sea level rise (SLR) can result in flooding of wetlands in low-lying coastal zones. In this study, we present a rapid risk assessment method for coastal wetland loss and degradation. The main stress factors, i.e., urban sprawl, agriculture, coastal erosion, and SLR, have been examined and quantified through remote sensing and geographic information system spatial analysis. A weighted factor-based linear model has been used to evaluate the spatial risk levels of wetland loss. The proposed methodology is applied to the low-lying coastal wetlands of Hangzhou Bay in Shanghai, China. The results show that the regions closer to the sea have relatively higher risk levels on the landward side of the coastline, but relatively low risk levels on the seaward side of the coastline. This work emphasizes the need to sustainably use and protect wetlands in order to reduce disaster risks and contribute to the improvement of human well-being.

Application of a Coupled Vegetation Competition and Groundwater Simulation Model to Study Effects of Sea Level Rise and Storm Surges on Coastal Vegetation

Global climate change poses challenges to areas such as low-lying coastal zones, where sea level rise (SLR) and storm-surge overwash events can have long-term effects on vegetation and on soil and groundwater salinities, posing risks of habitat loss critical to native species. An early warning system is urgently needed to predict and prepare for the consequences of these climate-related impacts on both the short-term dynamics of salinity in the soil and groundwater and the long-term effects on vegetation. For this purpose, the U.S. Geological Survey’s spatially explicit model of vegetation community dynamics along coastal salinity gradients (MANHAM) is integrated into the USGS groundwater model (SUTRA) to create a coupled hydrology–salinity–vegetation model, MANTRA. In MANTRA, the uptake of water by plants is modeled as a fluid mass sink term. Groundwater salinity, water saturation and vegetation biomass determine the water available for plant transpiration. Formulations and assumptions used in the coupled model are presented. MANTRA is calibrated with salinity data and vegetation pattern for a coastal area of Florida Everglades vulnerable to storm surges. A possible regime shift at that site is investigated by simulating the vegetation responses to climate variability and disturbances, including SLR and storm surges based on empirical information.

Vulnerability of artisanal fishing communities to flood risks in coastal southwest Nigeria

The vulnerability of coastal communities to climate change risks is an important development issue for Africa's low-lying coastal zones. Frequent floods resulting from climate change, sea-level rise and other human-induced environmental stressors have become a major concern in the coastal zone of Nigeria. This article draws upon conceptual issues in vulnerability and livelihoods to examine the multi-scale causes of current vulnerability of artisanal fishing communities in the Ogun coastal area of southwest Nigeria to flood risks. Fisher folk in the study area are highly vulnerable to the increasing incidence of floods as virtually all aspects of their livelihoods are impacted. Adaptive capacity which is influenced by existing socio-economic and institutional contexts at different scales is examined. Projected changes in climate for Nigeria's coastal zone and future socio-economic conditions of artisanal fishers suggest higher vulnerability in the future.

Vulnerability assessment of the coastal wetlands in the Yangtze Estuary, China to sea-level rise

Sea-level rise (SLR) caused by global climate change will have significant impacts on the low-lying coastal zone. The coastal wetlands in the Yangtze Estuary, with their low elevation, are particularly sensitive to SLR. In this study, the potential impacts of SLR on the coastal wetlands in the Yangtze Estuary were analyzed by adopting the SPRC (Source–Pathway–Receptor–Consequence) model. Based on the SPRC model and IPCC vulnerability definition, an indicator system for vulnerability assessment on the coastal wetlands to SLR was developed, in which the rate of SLR, subsidence rate, habitat elevation, mean daily inundation duration of habitat and sedimentation rate were selected as the key indicators. A spatial assessment method based on a GIS platform was established by quantifying each indicator, calculating the vulnerability index and grading the vulnerability. Vulnerability assessment, based on the projection of SLR rates from the present trend (0.26 cm/yr) and IPCC's A1F1 scenario (0.59 cm/yr), were performed for three time periods: short-term (2030s), medium-term (2050s) and long-term (2100s). The results indicated that in the 2030s, 6.6% and 9.0% of the coastal wetlands were within the grade of low vulnerability under the scenarios of present trend and A1F1, respectively. In the 2050s, the percentage of coastal wetlands within the grades of low and moderate vulnerability increases to 9.8% and 0.2%, 9.5% and 1.0% under the scenarios of present trend and A1F1, respectively. In the 2100s, 8.1% and 3.0% of the coastal wetlands were within the grade of low vulnerability, 0.8% and 2.8% were within the grade of moderate vulnerability under the scenarios of present trend and A1F1, respectively. The percentage of coastal wetlands within the grade of high vulnerability increases significantly, amounting to 2.3% and 6.9% under the scenarios of present trend and A1F1, respectively. The application of the SPRC model, the methodology developed and the results could assist with the objective and quantitative assessment of the vulnerability of coastal wetlands undergoing the impacts of SLR elsewhere. Without proper mitigation measures, the potential decrease in the area and loss of habitats and ecosystem services from the wetlands is inevitable. Based on the results of this study, mitigation measures should be considered for securing the future of the coastal wetlands in the Yangtze Estuary, which include the management of sedimentation, rehabilitation and re-creation of wetland habitat, reduction of land subsidence and control of reclamation.

General considerations and highlights of low-lying coastal zones: passive continental margins from the poles to the tropics

Abstract This Special Publication presents 23 papers that examine comparable, predominantly siliciclastic coastal zones of low-lying passive trailing-continental margins (primarily east Americas) from polar areas to the equator. The objective is to establish similarities and major differences among them. This introductory paper outlines major contributions of the various papers, but will also highlight coastal differences and briefly add information not fully treated by others. This is done in three parts: (a) some basic concepts are stressed, such as the importance of ‘coastal zone’ (total landscape) in the north–south comparison and the variable climates; (b) a review is made of the component materials of the coasts, such as difference in sediments owing to source rocks, weathering and geological history (glaciations), and in flora and fauna such as burrowing organisms; and (c) a few classical examples are reported from warm zones, such as Galveston Island and the Sapelo Island marshes, but the focus is on less well-known environments of cold areas – those most impacted by climate change. Each component of the coastal zone can develop diagnostic characteristics, but the entire assemblage of sedimentary and biological features is what uniquely defines present environments and allows identification of ancient coastal zones.

Coastal changes in the Sendai area from the impact of the 2011 Tōhoku-oki tsunami: Interpretations of time series satellite images, helicopter-borne video footage and field observations

A combination of time-series satellite imagery, helicopter-borne video footage and field observation is used to identify the impact of a major tsunami on a low-lying coastal zone located in eastern Japan. A comparison is made between the coast protected by armoured ‘engineered’ sea walls and the coast without. Changes are mapped from before and after imagery, and sedimentary processes identified from the video footage. The results are validated by field observations. The impact along a ‘natural’ coast, with minimal defences, is erosion focussed on the back beach. Along coasts with hard engineered protection constructed to defend against erosion, the presence of three to six metre high concrete-faced embankments results in severe erosion on their landward faces. The erosion is due to the tsunami wave accelerating through a hydraulic jump as it passes over the embankment, resulting in the formation of a ditch into which the foundations collapse. Engineered coastal defences are thus found to be small defence against highly energetic tsunami waves that overtop them.There is little erosion (or sedimentation) of the whole beach, and where active, it mainly forms V-shaped channels. These channels are probably initiated during tsunami inflow and then further developed during tsunami backflow. Tsunami backflow on such a low lying area takes place energetically as sheet flow immediately after tsunami flooding has ceased. Subsequently, when the water level landward of the coastal dune ridges falls below their elevation, flow becomes confined to rivers and breaches in the coast formed during tsunami inflow. Enigmatic, short lived, ‘strand lines’ are attributed to the slow fall of sea level after such a major tsunami. Immediately after the tsunami coastal reconstruction begins, sourced from the sediment recently flushed into the sea by tsunami backflow.

Coastal hazard mapping in the Cuddalore region, South India

It is estimated that nearly one-third of India’s population lives on the coast and is dependent on its resources. Shoreline erosion, storm surges and extreme events have resulted in severe loss of human life, damage to ecosystems and to property along the coast of India. Studies carried out in the Cuddalore region of South India reveal that this low-lying coastal zone, which suffered significant erosion during the last century, has been severely affected by the tsunami of 2004, storm floods and cyclones. In response to these impacts, a variety of coastal defense measures and adaptation strategies have been implemented in the region, although with only limited success. In order to inform future coastal planning in this region, the work reported here identifies a composite hazard line, seaward of which coastal flooding events will have a return interval of less than 1 in 100 years. The area landward of the coastal hazard line will be unaffected by 100 years of coastal erosion at present day rates. The study directly supports the Integrated Coastal Zone Management (ICZM) Plan of the Tamil Nadu State through the identification and assessment of coastal hazards and the overall vulnerability to coastal flooding and erosion. The key results from this pilot study will be used directly by the State of Tamil Nadu in the protection of the coastal livelihoods, better conservation measures and sustainable development along the coast. This study is a step toward mapping the hazard line for the entire coast of India that helps protect human lives and property.

Climate Change and Sea-Level Rise: Impact On Agriculture Along Andhra Pradesh Coast—A Geomatics Analysis

Climate change due to anthropogenic forcing through escalating greenhouse gas emissions and destruction of carbon sinks by deforestation is leading to floods and droughts affecting agriculture production. Global warming induces steric as well as eustatic rise in sea-level, by thermal expansion and addition of ice-melt water, respectively. Although the IPCC (2007) estimated a maximum possible sea-level rise of about 59 cm, more recent estimates show a global average rise of ≥1 m by the 2100 AD. The low-lying coastal zones are more vulnerable to rising sea levels as they face submergence or saltwater intrusion which affects the agriculture activities. Geomatics-based models on the possible impact of the predicted sea-level rise on coastal agriculture are necessary to initiate appropriate mitigation plans. The present study is an attempt in this direction taking the Andhra Pradesh (AP) coast as an example. The land use / land cover of the AP coast was mapped through the interpretation of IRS-P6 LISS III imagery from 2008. SRTM digital elevation models coupled with landform evidences have been used to interpolate contours at 0.5 m interval, although highly approximate, for the entire coastal region. If the sea level rises by 1.0 m, about 4040 km2 area including the present intertidal wetlands as well as the land between the present and future high tide lines would be affected along the entire 1030-km-long AP coast displacing about 1.67 million inhabitants and their economic activities, in about 351 revenue villages. The low-lying Krishna-Godavari delta region in the central part of the AP coast would be the worst affected zone as 2205 km2 of its area including about 1593 km2 under various types of agricultural activities is lying within the future high tide limit of 2.5 m elevation.