Yr Return Research Articles

Risk of Extreme Precipitation under Nonstationarity Conditions during the Second Flood Season in the Southeastern Coastal Region of China

Abstract This study analyzes the variation and risk changes of extreme precipitation under nonstationarity conditions using the Generalized Additive Models for Location, Scale, and Shape (GAMLSS) and the Mann–Kendall (MK) test. The extreme precipitation series is extracted from the observations during the second flood season (July–September) from 1960 to 2012 derived from 86 meteorological stations in the southeastern coastal region of China. The trend of mean (Mn) and variance (Var) of extreme precipitation is detected by MK. Ten large-scale circulation variables and four greenhouse gases are selected to construct a climate change index and a human activity index, which are based on principal component analysis. The recurrence risk of extreme precipitation is calculated by GAMLSS while considering climate changes and human activities. The results demonstrate that the nonstationarity characteristic of extreme precipitation is widespread in this region. A significant increasing trend of Mn is found in Shanghai, eastern Zhejiang, and northern and southern Fujian. An enhanced Var is found in eastern Guangdong. A significant positive correlation exists between climate changes/human activities and Mn/Var, especially in Zhejiang and Fujian. Generally, the contribution of climate changes and human activities to Mn is greater than it is to Var. In this region, the precipitation amount of high-frequency (2-yr return period) and low-frequency (100-yr return period) events increases from inland to coastal and from north to south. The government should pay careful attention to these trends because the intensity of extreme precipitation events and their secondary disasters could result in serious losses.

Drought in the Southeastern USA: an assessment of downscaled CMIP5 models

CR Climate Research Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials CR 74:251-262 (2018) - DOI: https://doi.org/10.3354/cr01502 Drought in the Southeastern USA: an assessment of downscaled CMIP5 models Johanna Engström1,*, David Keellings2 1Department of Geography, University of Florida, Gainesville, Florida 32611, USA 2Department of Geography, University of Alabama, Tuscaloosa, Alabama 35487, USA *Corresponding author: joem@ufl.edu ABSTRACT: The Southeastern USA has been repeatedly affected by severe droughts that have impacted the environment and economy of the region. In this study, the ability of 32 downscaled Coupled Model Intercomparison Project Phase 5 (CMIP5) models, downscaled using localized constructed analogs (LOCA), to simulate historical observations of dry spells from 1950 to 2005 are assessed using Perkins skill scores and significance tests. The analysis is split between cold and warm seasons based on timing of agricultural planting and harvesting dates of key crops. The models generally simulate the distribution of dry days well but there are significant differences between the ability of the best- and worst-performing models, particularly when it comes to the upper tail of the distribution. Only the top models provide a good estimate of extreme dry-spell lengths with simulations of 20 yr return values within ±5 d of observed values across the region. The findings provide guidance on selection of a suitable model ensemble for assessment of future drought risk in the Southeastern USA. KEY WORDS: Drought · Localized constructed analogs · LOCA climate models · Precipitation · Southeastern USA Full text in pdf format PreviousNextCite this article as: Engström J, Keellings D (2018) Drought in the Southeastern USA: an assessment of downscaled CMIP5 models. Clim Res 74:251-262. https://doi.org/10.3354/cr01502 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in CR Vol. 74, No. 3. Online publication date: February 28, 2018 Print ISSN: 0936-577X; Online ISSN: 1616-1572 Copyright © 2018 Inter-Research.

Estimation of Design Flood Hydrographs for Osun River at Iwo Control Station in Osun State, Nigeria

The unit and storm hydrographs for the catchment of Osun River at Iwo station Osun State, Nigeria were developed. Soil Conservation Service (SCS) and Snyder’s unit hydrograph methods were used to develop synthetic hydrographs for the catchment, while the SCS Curve Number method was used to estimate excess rainfall values from rainfall depth of different return periods. The peak storm flows obtained based on the unit hydrograph ordinates using convolution procedures determined by SCS for rainfall events of 10yr, 20yr, 50yr, 100yr and 200yr return periods for the catchment vary from 819.87 m3/s to 1681.34 m3/s, while those based on Snyder’s method for the catchment vary from 551.41m3/s to 1134.86 m3/s . The statistical analysis at 5% level of significance indicated that there were significant differences in the two methods. The analysis showed that the total peak flows for different return periods obtained from SCS method is higher than that of Snyder’s method by 33.16%. SCS method was recommended for use on the watershed since it incorporates most major hydrological and morphological characteristics of the basins like the watershed area, main channel length, river channel slope and watershed slope.

Projected increases in the annual flood pulse of the Western Amazon

The impact of a changing climate on the Amazon basin is a subject of intensive research because of its rich biodiversity and the significant role of rainforests in carbon cycling. Climate change has also a direct hydrological impact, and increasing efforts have focused on understanding the hydrological dynamics at continental and subregional scales, such as the Western Amazon. New projections from the Coupled Model Inter-comparison Project Phase 5 ensemble indicate consistent climatic warming and increasing seasonality of precipitation in the Peruvian Amazon basin. Here we use a distributed land surface model to quantify the potential impact of this change in the climate on the hydrological regime of the upper Amazon river. Using extreme value analysis, historical and future projections of the annual minimum, mean, and maximum river flows are produced for a range of return periods between 1 and 100 yr. We show that the RCP 4.5 and 8.5 scenarios of climate change project an increased severity of the wet season flood pulse (7.5% and 12% increases respectively for the 100 yr return floods). These findings agree with previously projected increases in high extremes under the Special Report on Emissions Scenarios climate projections, and are important to highlight due to the potential consequences on reproductive processes of in-stream species, swamp forest ecology, and socio-economy in the floodplain, amidst a growing literature that more strongly emphasises future droughts and their impact on the viability of the rainforest system over greater Amazonia.

Future Projections of Extreme Ocean Wave Climates and the Relation to Tropical Cyclones: Ensemble Experiments of MRI-AGCM3.2H*

Abstract Future projections of extreme ocean surface wave climates were carried out with single-model ensemble experiments of the atmospheric global climate model MRI-AGCM3.2H. The ensemble experiments of MRI-AGCM3.2H consist of four future sea surface temperature (SST) ensembles and three perturbed physics (PP) ensembles. This study showed that future changes in extreme wave heights strongly depend on the global climate model (GCM) performance to simulate tropical cyclones (TCs), indicating a need to acknowledge that results in a study that employs a low-performance model are not able to account for extreme waves associated with TCs (TC waves). The spatial distribution of future changes in non-TC extreme wave heights on the global scale was similar to that for mean wave heights; namely, wave heights increase over the middle-to-high latitudes in the Southern Ocean and central North Pacific and decrease over midlatitudes and the North Atlantic, although the magnitude of future changes for extreme wave heights is greater than for mean wave heights. The variance of future changes mainly depends on differences in physics among PP ensemble experiments rather than differences in SST ensembles. The 10-yr return wave heights of TC waves over the western North Pacific showed either an increase or a decrease of 30% for different regions, maximally. The spatial distribution of future changes in TC waves can be explained by an eastward shift of TC tracks.

Use of radar QPE for the derivation of Intensity–Duration–Frequency curves in a range of climatic regimes

Summary Intensity–Duration–Frequency (IDF) curves are widely used in flood risk management because they provide an easy link between the characteristics of a rainfall event and the probability of its occurrence. Weather radars provide distributed rainfall estimates with high spatial and temporal resolutions and overcome the scarce representativeness of point-based rainfall for regions characterized by large gradients in rainfall climatology. This work explores the use of radar quantitative precipitation estimation (QPE) for the identification of IDF curves over a region with steep climatic transitions (Israel) using a unique radar data record (23 yr) and combined physical and empirical adjustment of the radar data. IDF relationships were derived by fitting a generalized extreme value distribution to the annual maximum series for durations of 20 min, 1 h and 4 h. Arid, semi-arid and Mediterranean climates were explored using 14 study cases. IDF curves derived from the study rain gauges were compared to those derived from radar and from nearby rain gauges characterized by similar climatology, taking into account the uncertainty linked with the fitting technique. Radar annual maxima and IDF curves were generally overestimated but in 70% of the cases (60% for a 100 yr return period), they lay within the rain gauge IDF confidence intervals. Overestimation tended to increase with return period, and this effect was enhanced in arid climates. This was mainly associated with radar estimation uncertainty, even if other effects, such as rain gauge temporal resolution, cannot be neglected. Climatological classification remained meaningful for the analysis of rainfall extremes and radar was able to discern climatology from rainfall frequency analysis.

Regional climate projection over South Korea simulated by the HadGEM2-AO and WRF model chain under RCP emission scenarios

This study assesses the regional climate projection newly generated within the framework of the national downscaling project in South Korea. To obtain fine-scale climate information (12.5 km), dynamical downscaling of the HadGEM2-AO global projections forced by the representative concentration pathway (RCP4.5 and RCP8.5) scenarios is performed using the Weather Research and Forecasting (WRF) modeling system. Changes in temperature and precipitation in terms of long-term trends, daily characteristics and extremes are presented by comparing two 30 yr periods (2041−2070 vs. 2071−2100) in which increasing rates of emission forcing between the RCP4.5 and RCP8.5 scenarios are relatively similar and quite different, respectively. The temperature increase presents a relevant trend, but the degree of warming varies in different periods and emission scenarios. While the temperature distribution from the RCP8.5 projection is continuously shifted toward warmer conditions by the end of the 21st century, the RCP4.5 projection appears to stabilize warming in accordance with emission forcing. This shift in distribution directly affects the magnitude of extremes, which enhances extreme hot days but reduces extreme cold days. Precipitation changes, however, do not respond monotonically to emission forcing, as they exhibit less sensitivity to different emission scenarios. An enhancement of high intensity precipitation and a reduction of weak intensity precipitation are discernible, implying an intensified hydrologic cycle. Changes in return levels of annual maximum precipitation suggest an increased probability of extreme precipitation with 20 yr and 50 yr return periods.

Calculation and Evaluation of an Air-Freezing Index for the 1981–2010 Climate Normals Period in the Coterminous United States

AbstractThe air-freezing index (AFI) is a common metric for determining the freezing severity of the winter season and estimating frost depth for midlatitude regions, which is useful for determining the depth of shallow foundation construction. AFI values represent the seasonal magnitude and duration of below-freezing air temperature. Departures of the daily mean temperature above or below 0°C (32°F) are accumulated over each August–July cold season; the seasonal AFI value is defined as the difference between the highest and lowest extrema points. Return periods are computed using generalized extreme value distribution analysis. This research replaces the methodology used by the National Oceanic and Atmospheric Administration to calculate AFI return periods for the 1951–80 time period, applying the new methodology to the 1981–2010 climate normals period. Seasonal AFI values and return period values were calculated for 5600 stations across the coterminous United States (CONUS), and the results were validated using U.S. Climate Reference Network temperature data. Return period values are typically 14%–18% lower across CONUS during 1981–2010 versus a recomputation of 1951–80 return periods with the new methodology. For the 100-yr (2 yr) return periods, about 59% (83%) of stations show a decrease of more than 10% in the more recent period, whereas 21% (2%) show an increase of more than 10%, indicating a net reduction in winter severity that is consistent with observed climate change.

Resource availability shapes fire‐filtered savannas

AbstractQuestionsHumid savannas can be considered fire‐filtered landscapes because fire is very frequent (<10 yr return intervals) and only fire‐resistant species can occur. This flammable vegetation can be functionally heterogeneous, structurally and floristically patchy. We hypothesized that resource availability (mainly water and nutrient availabilities) accounted for most of the functional and phylogenetic spatial structure of communities across these savanna landscapes.LocationEmas National Park, central Brazil.MethodsWe used individual‐based functional trait, phylogenetic and environmental data combined with spatial information to assess the main drivers and mechanisms of community functional change (turnover) in a large fire‐filtered savanna landscape. We used Mantel correlograms and a maximum rank correlation approach to assess the spatial structure and the subset of landscape factors that best predict compositional, phylogenetic, species‐based and individual‐based functional community turnovers and the mechanism by which they do operate.ResultsCommunities were spatially structured across the landscape, presenting functional convergence at shorter distances and divergence at larger distances. All of the turnover metrics presented unique spatial structures and were correlated with a unique set of landscape predictors. Soil texture accounted for the largest fraction of the spatial structure, but soil N availability, pH, altitude and fire frequency were also important.ConclusionsOur results support the idea that the patchy distribution of water and nutrients mediated by clay content shape community membership in fire‐filtered savannas, whereas current variations in fire frequency interact with resource availability to shift community attributes from species average trait values (intraspecific variability).

MODELLING EXTREME SEA LEVELS DUE TO SEA LEVEL RISE AND STORM SURGE IN THE SETO INLAND SEA, JAPAN

The extreme sea level due to storm surge and future sea-level rise (SLR) in the year of 2050 and 2100 are estimated by using ensemble empirical mode decomposition (EEMD) and extreme value analysis (EVA) with long-term sea level records in and around the Seto Inland Sea, Japan. Ensemble empirical mode decomposition, an adaptive data analysis method, can separate the tidal motions and the non-linear trend from the sea level records to reconstruct the storm surge levels, and then the reconstructed storm surge levels are applied to statistical model, EVA, to obtain the extreme storm surges at 95% confidence interval in the target return periods. The SLR trend at Tokuyama in the Seto Inland Sea obtained from EEMD is 3.58 mm/yr over 1993-2010, which is slightly larger than the recent altimetry-based global rate of 3.3 ± 0.4 mm/yr over 1993-2007. The resulting SLR in 2050 and 2100 estimated are 0.18 m and 0.49 m, respectively. The 30-, 50-, and 100-yr return levels at Tokuyama obtained by EVA are 1.30 m, 1.43 m and 1.64 m. Therefore, the extreme sea level in 2050 and 2100 due to future SLR and storm surge with 100-yr return level would be 1.82 m (1.35 m ~ 2.26 m with 95% confidence intervals) and 2.13 m (1.75 m ~ 3.10 m with 95% confidence intervals), respectively. The SLR is not only due to mass and volume changes of sea water, but also due to other factors such as local subsidence, river discharge and sediments, and vegetation effect. The non-linear trend of SLR, which is the residue from EEMD, can be regarded as a final consequential sea level after considering those factors and their nonlinearity. The combined EEMD-EVA method can be useful tool not only for the extreme sea level estimation under climate change, but also for many cases in coastal engineering and hydrology.

Distribution characteristics of the intensity and extreme intensity of tropical cyclones influencing China

To address the deficiency of climatological research on tropical cyclones (TCs) influencing China, we analyze the distributions of TCs with different intensities in the region, based on the best-track TC data for 1949–2011 provided by the Shanghai Typhoon Institute. We also present the distributions of 50- and 100-yr return-period TCs with different intensities using the Gumbel probability distribution. The results show that TCs with different intensities exert distinctive effects on various regions of China and its surrounding waters. The extreme intensity distributions of TCs over these different regions also differ. Super and severe typhoons mainly influence Taiwan Island and coastal areas of Fujian and Zhejiang provinces, while typhoons and TCs with lower intensities influence South China most frequently. The probable maximum TC intensity (PMTI) with 50- and 100-yr return periods influencing Taiwan Island is below 890 hPa; the PMTI with a 50-yr return period influencing the coastal areas of Fujian and Zhejiang provinces is less than 910 hPa, and that with a 100-yr return period is less than 900 hPa; the PMTI with a 50-yr return period influencing the coastal areas of Hainan, Guangdong, and the northern part of the South China Sea is lower than 930 hPa, and that with a 100-yr return period is less than 920 hPa. The results provide a useful reference for the estimation of extreme TC intensities over different regions of China.

Projected Tasman Sea Extremes in Sea Surface Temperature through the Twenty-First Century

AbstractOcean climate extremes have received little treatment in the literature, aside from coastal sea level and temperatures affecting coral bleaching. Further, it is notable that extremes (e.g., temperature and precipitation) are typically not well represented in global climate models. Here, the authors improve dynamically downscaled ocean climate model estimates of sea surface temperature (SST) extremes in the Tasman Sea off southeastern Australia using satellite remotely sensed observed extreme SSTs and the simulated marine climate of the 1990s. This is achieved using a Bayesian hierarchical model in which the parameters of an extreme value distribution are modeled by linear regression onto the key marine climate variables (e.g., mean SST, SST variance, etc.). The authors then apply this fitted model, essentially a form of bias correction, to the marine climate projections for the 2060s under an A1B emissions scenario. They show that the extreme SSTs are projected to increase in the Tasman Sea in a nonuniform way. The 50-yr return period extreme SSTs are projected to increase by up to 2°C over the entire domain and by up to 4°C in a hotspot located in the central western portion of the Tasman Sea, centered at a latitude ~500 km farther south than the projected change in mean SST. The authors show that there is a greater than 50% chance that annual maximum SSTs will increase by at least 2°C in this hotspot and that this change is significantly different than that which might be expected because of random chance in an unchanged climate.

Statistical evaluation on storm sewer design criteria under climate change in Seoul, South Korea

This study conducted statistical analysis under both stationary and non-stationary climate using rainfall data measured in Seoul, South Korea. The 50 year annual maximum rainfall data were analysed with generalised extreme value distribution and Gumbel distribution. Possible rainfall changes were predicted with nonstationary forms of the two distributions, considering time variable location parameters. The current storm sewer design criteria were assessed by reflecting climate change implications and expected lifetime performance. Expected return periods were reduced to 4.67, 8.66, 19.16 and 23.53 years for the current 10 min - 5, 10, 30 and 50 years. The newly suggested design criteria of 5, 10, 30 and 50 yr return period storm events were 5.3, 12, 48 and 107 years for the 10 min duration for a 50 year lifetime expectancy.

Precipitation downscaling in Canadian Prairie Provinces using the LARS-WG and GLM approaches

Two stochastic precipitation simulation models, namely the Long Ashton Research Station weather generator (LARS-WG) and a Generalized Linear Model-based weather generator (GLM-WG), are evaluated for downscaling daily precipitation at four selected locations (Banff, Calgary, Saskatoon and Winnipeg) in the Canadian Prairies. These weather generators model precipitation occurrence and amount components separately. Large-scale climate variables (including mean temperature, sea level pressure and relative humidity, derived from National Centers for Environmental Prediction reanalysis data) and observed precipitation records are used to calibrate and validate GLM-WG, while only observed precipitation records are used to calibrate and validate LARS-WG. A comparison of common statistical properties (i.e. annual/monthly means, variability of daily and monthly precipitation and monthly proportion of dry days) and characteristics of drought and extreme precipitation events derived from simulated and observed daily precipitation for the calibration (1961–1990) and validation (1991–2003) periods shows that both weather generators are able to simulate most of the statistical properties of the historical precipitation records, but GLM-WG appears to perform better than LARS-WG for simulating precipitation extremes and temporal variability of drought severity indices. For developing projected changes to precipitation characteristics, a change factor approach based on Canadian Global Climate Model (CGCM) simulated current (1961–1990) and future (2071–2100) period precipitation is used for driving simulations of LARS-WG, while for driving GLM-WG simulations, large-scale predictor variables derived from CGCM current and future period outputs are used. Results of both weather generators suggest significant increases to the mean annual precipitation for the 2080s. Changes to selected return levels of annual daily precipitation extremes are found to be both location- and generator-dependent, with highly significant increases noted for Banff with LARS-WG and for both Banff and Calgary with GLM-WG. Overall, 5- and 10-yr return levels are associated with increases (with the exception of Winnipeg) while 30- and 50-yr return levels are associated with site-dependent increases or decreases. A simple precipitation-based drought severity index suggests decreases in drought severity for the 2080s.

풍재위험도지수를 이용한 특수건물 진단

The wind-induced disaster risk index (WRI) is developed to inspect the safety against windstorm for the specific buildings, approximately 34,000 buildings, distributed over South Korea. WRI for a specific building is based on the wind damage band which calculates an average damage probability with the strong wind exerted on it and makes the damage probability take an variation due to its characteristics. The strong wind is defined as the wind speed extracted from the wind hazard map that is a set of 10-min averaged winds of 100-yr return period over South Korea. The building characteristics is invested by three categories including 4 of the environmental variables, 5 of the roof variables, and 8 of the wall variables. We took a survey for 724 of the specific buildings. According to the results of WRIs for the sample in the corresponding rate zones for wind and flood insurance, the more the rate zone is high, the more WRIs increase in general. In comparison of WRIs to occupancy, WRIs show a tendency of increasement in the order of apartment, commercial, and industrial buildings.

A modelling study of long term green roof retention performance

This paper outlines the development of a conceptual hydrological flux model for the long term continuous simulation of runoff and drought risk for green roof systems. A green roof's retention capacity depends upon its physical configuration, but it is also strongly influenced by local climatic controls, including the rainfall characteristics and the restoration of retention capacity associated with evapotranspiration during dry weather periods. The model includes a function that links evapotranspiration rates to substrate moisture content, and is validated against observed runoff data. The model's application to typical extensive green roof configurations is demonstrated with reference to four UK locations characterised by contrasting climatic regimes, using 30-year rainfall time-series inputs at hourly simulation time steps. It is shown that retention performance is dependent upon local climatic conditions. Volumetric retention ranges from 0.19 (cool, wet climate) to 0.59 (warm, dry climate). Per event retention is also considered, and it is demonstrated that retention performance decreases significantly when high return period events are considered in isolation. For example, in Sheffield the median per-event retention is 1.00 (many small events), but the median retention for events exceeding a 1 in 1 yr return period threshold is only 0.10. The simulation tool also provides useful information about the likelihood of drought periods, for which irrigation may be required. A sensitivity study suggests that green roofs with reduced moisture-holding capacity and/or low evapotranspiration rates will tend to offer reduced levels of retention, whilst high moisture-holding capacity and low evapotranspiration rates offer the strongest drought resistance.

A strategy to address the task of seismic micro-zoning in landslide-prone areas

Abstract. As concerns landslide prevention and mitigation policies at the urban scale, the ability of Geographical Information Systems (GIS) to combine multi-layered information with high precision enables technicians and researchers to devote efforts in managing multiple hazards, such as seismically induced instability in urbanized areas. As a matter of fact, many villages in the Italian Apennines, placed near high-energy seismic sources, are characterized by active sliding that are seasonally remobilized by rainfall. GIS tools can be useful whether accurate Digital Elevation Models (DEM) are available and detailed mechanical and hydraulic characterization of superficial deposits over significant portion of the urban territory is undertaken. Moreover, the classic methods for estimating the seismic-induced permanent displacements within natural slopes are drawn from the generalization of Newmark's method. Such method can be applied to planar sliding mechanism that can be considered still valid wherever shallow landslides are generated by an earthquake. The failure mechanism depends on the mechanical properties of the superficial deposits. In this paper, the town of Castelfranci (Campania, southern Italy) has been studied. This small town, hosting two thousand inhabitants, suffers from the seasonal reactivation of landslides in clayey soil deposits due to rainfall. Furthermore, the site is seismically classified by means of the peak ground acceleration (PGA) equal to 0.246 g with respect to a 475 yr return period. Several studies on the evolution of slopes have been undertaken at Castelfranci and maps have been drawn at the urban scale not taking into any account the seismic hazard. This paper shows possible seismically induced hazard scenarios within the Castelfranci municipal territory aimed at microzonation of level 2, by estimating the slope permanent displacements comparable to those caused by the strongest historical seismic event that hit this area: the 1980 Irpinia earthquake. To this aim, geotechnical characterization of local soils collected over the last 25 yr by local technicians have been used to predict possible permanent displacements by means of Newmark's sliding block approach. Two simplified relationships relating peak ground acceleration and Arias intensity to permanent displacements have been used and compared. Although similar results are drawn, the two analyses point out the most hazardous sectors of the Castelfranci urban area.

Extreme winds over Europe in the ENSEMBLES regional climate models

Abstract. Extreme winds cause vast amounts of damage every year and represent a major concern for numerous industries including construction, afforestation, wind energy and many others. Under a changing climate, the intensity and frequency of extreme events are expected to change, and accurate projections of these changes will be invaluable to decision makers and society as a whole. This work examines four regional climate model downscalings over Europe following the SRES A1B scenario from the "ENSEMBLE-based Predictions of Climate Changes and their Impacts" project (ENSEMBLES). It investigates the projected changes in the 50 yr return wind speeds and the associated uncertainties. This is accomplished by employing the peaks-over-threshold method with the use of the generalised Pareto distribution. The models show that, for much of Europe, the 50 yr return wind is projected to change by less than 2 m s−1, while the uncertainties associated with the statistical estimates are larger than this. In keeping with previous works in this field, the largest source of uncertainty is found to be the inter-model spread, with some locations showing differences in the 50 yr return wind of over 20 m s−1 between two different downscalings.

Nonlinear response of fixed jacket offshore platform under structural and wave loads

The structural design requirements of an offshore platform subjected to wave induced forces and moments in the jacket can play a major role in the design of the offshore structures. For an economic and reliable design; good estimation of wave loadings are essential. A nonlinear response analysis of a fixed offshore platform under structural and wave loading is presented, the structure is discretized using the finite element method, wave plus current kinematics (velocity and acceleration fields) are generated using 5th order Stokes wave theory, the wave force acting on the member is calculated using Morison's equation. Hydrodynamic loading on horizontal and vertical tubular members and the dynamic response of fixed offshore structure together with the distribution of displacement, axial force and bending moment along the leg are investigated for regular and extreme conditions, where the structure should keep production capability in conditions of the 1-yr return period wave and must be able to survive the 100-yr return period storm conditions. The result of the study shows that the nonlinear response investigation is quite crucial for safe design and operation of offshore platform.

Seismic risk assessment of architectural heritages in Gyeongju considering local site effects

Abstract. A seismic risk assessment is conducted for cultural heritage sites in Gyeongju, the capital of Korea's ancient Silla Kingdom. Gyeongju, home to UNESCO World Heritage sites, contains remarkable artifacts of Korean Buddhist art. An extensive geotechnical survey including a series of in situ tests is presented, providing pertinent soil profiles for site response analyses on thirty cultural heritage sites. After the shear wave velocity profiles and dynamic material properties were obtained, site response analyses were carried out at each historical site and the amplification characteristics, site period, and response spectrum of the site were determined for the earthquake levels of 2400 yr and 1000 yr return periods based on the Korean seismic hazard map. Response spectrum and corresponding site coefficients obtained from site response analyses considering geologic conditions differ significantly from the current Korean seismic code. This study confirms the importance of site-specific ground response analyses considering local geological conditions. Results are given in the form of the spatial distribution of bedrock depth, site period, and site amplification coefficients, which are particularly valuable in the context of a seismic vulnerability study. This study presents the potential amplification of hazard maps and provides primary data on the seismic risk assessment of each cultural heritage.