Large Typhoons Research Articles

Impact evaluation of typhoons and remediation works on spatiotemporal evolution of air dose rate in two riverside parks in Fukushima, Japan after the Dai-ichi nuclear power plant accident

This study elucidated the impacts of typhoon events and remediation works on the spatiotemporal evolution of the air dose rate in riverside areas frequented by residents. Spatial distribution of the air dose rate and radiocesium concentration in the sediments were measured in two riverside parks located near each other in Fukushima Prefecture, Japan, for 2015–2020. The air dose rates measured by walk surveys were interpolated using ordinary kriging to generate air dose rate maps, to facilitate a comparison between the results at different points in time during the measurement campaigns. After the typhoons that occurred during 2015–2018, the air dose rate near the riverside in one park decreased, but not in the other, because the erosion and sediment deposition patterns differed between them. This could be due to the presence of a dam upstream, which serves a flood mitigation function. However, the extreme event of typhoon Hagibis in 2019 dropped the air dose rates near the riversides in both parks. In contrast to the typhoon events which affected the riverside areas, remediation works such as decontamination undertaken during 2015–2019 reduced the air dose rates around the garden and lawn areas which are frequently used as recreational sites. Modeling the temporal evolutions in the air dose rates for the entire area of the riverside parks revealed that 35% of the reduction was caused by physical decay of radiocesium on average, 14% by vertical migration of radiocesium in the soil through precipitation, and 51% by the three typhoons and remediation works during 2015–2019. The contribution of 20% from the strongest typhoon Hagibis highlights the fact that floods resulting from large typhoons are effective in causing natural attenuation of air dose rates in riverside parks.

The Huapinghsu Channel/Mienhua Canyon System as a Sediment Conduit Transporting Sediments From Offshore North Taiwan to the Southern Okinawa Trough

By examining bathymetric and seismic reflection data in the shelf-slope region offshore northeast of Taiwan, the morphology of the Huapinghsu Channel/Mienhua Canyon System was refined and the occurrence of axial incision in the major erosional trough of the Mienhua Canyon was identified. The Huapinghsu Channel extends from its head at a water depth of 120 m seaward across the shelf-slope region and merges with the Mienhua Canyon before finally emptying into the Southern Okinawa Trough. This review with a new idea illustrates this channel/canyon system as a sediment conduit transporting sediments from western Taiwan rivers to the Southern Okinawa Trough. Within the proximal reach of the Mienhua Canyon, in situ suspended particles were found associated with bottom nepheloid layers, which transport resuspended particles along the canyon course, and eventually into the Southern Okinawa Trough even during sea-level highstand. The shelf area around the channel head is subject to the influence of frequent occurrences of large typhoons and seasonal migrations of oceanic currents. Numerical examinations indicate that the flow velocities related with large waves or currents satisfy the critical values to the threshold of the motion of fine sand, implying gravity flows occur around the channel head, sweep unconsolidated sediments in the channel head, or even incise the channel floor at the present day. In this paper, sea level changes from the Last Glacial Maximum (LGM, ∼21 ka BP) to the present and sediment input to the head of the Huapinghsu Channel head are considered the major factors in the control of the Huapinghsu Channel/Mienhua Canyon system, which functions as a sediment conduit in the study area. Tectonics and climate are the minor factors that contribute to shelf sediment transport to the Southern Okinawa Trough via this channel/canyon system.

Proposing a Method to Analyze Slope Displacement Using the Distance Image Data of Depth Camera

Sediment disasters have occurred with higher frequencies in recent years because of local heavy rains caused by line-shaped precipitation systems and torrential rains accompanying large typhoons. Since rescue operators are constantly under physical risk at disaster sites, there is a need for technologies to predict the occurrence of secondary disasters. The authors research the measurement of slope displacements by focusing on a depth camera that is readily deployable, can be easily set up, and enables monitoring of an extensive area but does not require expert knowledge to carry out measurements. In this process, we confirmed the difficulty of measuring slope changes preceding failure when the depth camera (DC) is set at a distance because of the large measurement errors caused by the limited depth resolution and poor measurement conditions under rainfall. In this study, we propose a new method for analyzing depth image data obtained by a depth camera and verify its validity for displacement measurements. After comparing the previous and proposed methods, we could confirm that the latter enables one to detect slope changes from minute deformations. When compared with the results of extensometers that directly measured the slope, we found that the results displayed similar tendencies of increase. Therefore, by measuring displacements preceding a slope failure using a depth camera and analyzing the depth image data acquired using the proposed method, we found that it is possible to detect minute changes that precede slope failures.

Estimation of the non-exceedance probability of extreme storm surges in South Korea using tidal-gauge data

Abstract. Global warming, one of the most serious aspects of climate change, can be expected to cause rising sea levels. These have in turn been linked to unprecedentedly large typhoons that can cause flooding of low-lying land, coastal invasion, seawater flows into rivers and groundwater, rising river levels, and aberrant tides. To prevent typhoon-related loss of life and property damage, it is crucial to accurately estimate storm-surge risk. This study therefore develops a statistical model for estimating such surges' probability based on surge data pertaining to Typhoon Maemi, which struck South Korea in 2003. Specifically, estimation of non-exceedance probability models of the typhoon-related storm surge was achieved via clustered separated peaks-over-threshold simulation, while various distribution models were fitted to the empirical data for investigating the risk of storm surges reaching particular heights. To explore the non-exceedance probability of extreme storm surges caused by typhoons, a threshold algorithm with clustering methodology was applied. To enhance the accuracy of such non-exceedance probability, the surge data were separated into three different components: predicted water level, observed water level, and surge. Sea-level data from when Typhoon Maemi struck were collected from a tidal-gauge station in the city of Busan, which is vulnerable to typhoon-related disasters due to its geographical characteristics. Fréchet, gamma, log-normal, generalized Pareto, and Weibull distributions were fitted to the empirical surge data, and the researchers compared each one's performance at explaining the non-exceedance probability. This established that Weibull distribution was better than any of the other distributions for modelling Typhoon Maemi's peak total water level. Although this research was limited to one city on the Korean Peninsula and one extreme weather event, its approach could be used to reliably estimate non-exceedance probabilities in other regions where tidal-gauge data are available. In practical terms, the findings of this study and future ones adopting its methodology will provide a useful reference for designers of coastal infrastructure.

Control of radiocesium recontamination by plant removal along a decontaminated riverside in Fukushima, Japan

The accident at the Fukushima Dai-ichi Nuclear Power Plant in March 2011 resulted in the widespread deposition of radiocesium in and around Fukushima prefecture. Riversides have an additional contamination risk through deposition of material containing radiocesium transported from upstream. In our previous research (Nishikiori and Suzuki, 2017) we developed a decontamination method in a river bank in 2014; however, the decontaminated site had a recontamination risk. In this study, we evaluated the effectiveness of plant removal as a countermeasure against recontamination because plants favor the deposition of highly-contaminated fine particles. Although suspended solids with high radiocesium concentrations were transported, under plant-removal conditions (2015–2016), sediment deposited in the flood channel was sandy with low radiocesium concentrations. In 2017, one year after the plant recovery, somewhat muddy sediment with high radiocesium concentrations was deposited during medium rainfall events; the plant biomass would explain the amount of fine sediment that was deposited. Additionally, large typhoons introduced sandy sediment even on the densely vegetated flood channel. Thereby, the air dose rates did not increase during the observation period. Plant removal may control the deposition of highly contaminated sediments and be an effective countermeasure for recontamination in the flood channel.

Dependence of Probabilistic Quantitative Precipitation Forecast Performance on Typhoon Characteristics and Forecast Track Error in Taiwan

Abstract This study investigates the probabilistic quantitative precipitation forecast (PQPF) performance of typhoons that affected Taiwan during 2011–16. In this period, a total of 19 typhoons with a land warning issued by the Central Weather Bureau (CWB) are analyzed. The PQPF is calculated using the ensemble precipitation forecast data from the Taiwan Cooperative Precipitation Ensemble Forecast Experiment (TAPEX), and the verification data, verification thresholds, and typhoon characteristics are obtained from the CWB. The overall PQPF performance of TAPEX has an acceptable reliability and discrimination ability, and the higher probability error is distributed at the mountainous area of Taiwan. The PQPF performance is significantly influenced by typhoon characteristics (e.g., typhoon tracks, sizes, and forward speeds). The PQPFs for westward-moving, large, or slow typhoons have higher reliability and discrimination ability, and lower-probability error than those for northward-moving, small, or fast typhoons, except for similar reliability between fast and slow typhoons. Because northward-moving or small typhoons have larger forecast track error, and their PQPF performance is sensitive to the accuracy of the forecast track, a higher probability error occurs than that for westward-moving or large typhoons. Furthermore, because there is no difference in track error between fast and slow typhoons, the larger track spread for slow typhoons increases the rainfall forecast spread and reduces the probability error. The orientation of Taiwan’s topography and the topographic effect also influence and increase the distribution and value of probability error for northward-moving, small, or fast typhoons. In summary, forecast track characteristics are influenced by typhoon characteristics and further affect the PQPF performance.

Dynamics of an old evergreen coppice in southwestern Japan with special focus on a typical coppice species (Castanopsis cuspidata) and a climax species (Distylium racemosum)

We investigated stand dynamics of an abandoned evergreen coppice (c.a. 100 years old) over the course of 21 years in south Kyushu, Japan. The study stand showed a change in species composition from being dominated by Castanopsis cuspidata to Distylium racemosum, that is, from a typical coppice species to a typical climax species of the region. However, the relative dominance of Castanopsis spp. appeared to remain very high in the study stand compared to that in the Aya Research Site, a typical old-growth forest in the region, due to abundant C. cuspidata canopy trees of coppice origin. This suggests that the species composition of the study stand remained distinct from that of climax forests in the region. On the other hand, D. racemosum did not show a significant change in diameter at breast height (DBH) class frequency distribution from 1996 to 2017, probably due to the slow growth of this species. However, generalized linear models (GLMs) were used to identify the factors affecting better DBH growth of this species in the gap, indicating the potential for further development of the population structure when small trees are released from suppression of canopy trees. This suggests, inversely, that the development of the D. racemosum population was heavily suppressed by abundant C. cuspidata canopy trees of coppice origin that survived to the age of nearly 100 years. Further, large typhoons are suggested to cause severe canopy disturbances that remove canopy trees of C. cuspidata, which might be important for promoting further forest succession, even for a nearly 100-year-old evergreen old coppice.

Large tsunamis reset growth of massive corals

Corals at Ishigaki Island, Japan, are characterized by their high species diversity. Not only are they struck by storm waves generated annually by typhoons, the corals, especially the massive ones, in the fringing reef were buffeted by huge tsunami waves with a run-up height of ca. 30 m in 1771 Meiwa tsunami and its predecessors at few hundred-year intervals. We present field survey and numerical results demonstrating that such near-field large tsunamis could have reset the growth of massive corals, a phenomenon which large typhoons have not caused. Our field survey revealed that the massive corals in the lagoon are not attached to the bedrock but are instead located on the sandy sea bottom. Therefore, those are movable of sufficiently large wave inundated in the lagoon. Our numerical results further showed that the maximum velocity of the tsunami at the reef edge, calculable as < 21.2 m/s at the study area, is still high in the shallow lagoon, perhaps generating sufficiently strong hydrodynamic force to devastate the massive corals in the shallow lagoon entirely, as well as some presumed damages on tabular and branching corals on the reef crest and reef slope. This numerical result is consistent with the observed fact that even a 9-m long Porites boulder (about 220 t) was cast ashore by the 1771 tsunami. The sizes of the presently living massive corals of Porites spp. are consistent with our hypothesis that they started to grow after the latest 1771 tsunami event. At the coral reefs of high tsunami-risk countries, severe destruction of corals by large tsunami waves should be considered for their growth history because, depending on the bathymetry, coral characteristics, and tsunami hydrodynamic features, tsunamis can radically alter coral habitats.

Modeling the Effectiveness of Infrastructure and Travel Demand Management Measures to Improve Traffic Congestion during Typhoons

Many commuters find themselves stranded during natural disasters like typhoons. In the Tokai region in Japan, many road sections become heavily congested during typhoons, with some commuters reporting homebound trips taking more than four times longer than usual because of road flooding at several locations. Although large typhoons are considered extreme events (in terms of magnitude), they occur frequently (i.e., several times per year), substantiating the need for better preparedness. Nonetheless, it is impossible to predict exactly which roads are going to be flooded during a typhoon. As a result, in this study, a stochastic modeling approach was used that assigns a failure probability to each road segment based on climate model outputs for the region. Using this stochastic model, the travel time reliability between any given origin–destination pair can be determined. By applying this model to the road network of the Tokai region, two major measures were identified that could be implemented to reduce severe congestion during a typhoon. First, targeted infrastructure management measures can be implemented to strengthen heavily used roads, thus reducing the failure probability of major roads. Second, travel demand management measures can be implemented, such as asking commuters to leave their workplace or school one or two hours after their normal departure time. Overall, it was found that strengthening heavily used roads has a bigger impact in relieving congestion than delaying departure time, but that combining both strategies achieves the best results.

Landslide-driven drainage divide migration

Research Article| February 23, 2018 Landslide-driven drainage divide migration Maxwell P. Dahlquist; Maxwell P. Dahlquist 1Department of Earth Sciences, University of Southern California, Los Angeles, California 90089, USA Search for other works by this author on: GSW Google Scholar A. Joshua West; A. Joshua West 1Department of Earth Sciences, University of Southern California, Los Angeles, California 90089, USA Search for other works by this author on: GSW Google Scholar Gen Li Gen Li 1Department of Earth Sciences, University of Southern California, Los Angeles, California 90089, USA Search for other works by this author on: GSW Google Scholar Author and Article Information Maxwell P. Dahlquist 1Department of Earth Sciences, University of Southern California, Los Angeles, California 90089, USA A. Joshua West 1Department of Earth Sciences, University of Southern California, Los Angeles, California 90089, USA Gen Li 1Department of Earth Sciences, University of Southern California, Los Angeles, California 90089, USA Publisher: Geological Society of America Received: 19 May 2017 Revision Received: 20 Nov 2017 Accepted: 05 Feb 2018 First Online: 23 Feb 2018 Online Issn: 1943-2682 Print Issn: 0091-7613 © 2018 Geological Society of America Geology (2018) 46 (5): 403–406. https://doi.org/10.1130/G39916.1 Article history Received: 19 May 2017 Revision Received: 20 Nov 2017 Accepted: 05 Feb 2018 First Online: 23 Feb 2018 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Maxwell P. Dahlquist, A. Joshua West, Gen Li; Landslide-driven drainage divide migration. Geology 2018;; 46 (5): 403–406. doi: https://doi.org/10.1130/G39916.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Drainage divide migration reorganizes river basins, redistributing erosive energy and contributing to feedbacks between tectonics, erosion, and climate. However, the conditions governing divide migration and the time scales on which it occurs are poorly understood. By connecting channels to hillslopes in steep landscapes, landslides are expected to play a central role in divide migration and landscape evolution. In this study, we examine landslides triggered by three events (two earthquakes and a tropical cyclone), seeking insight into controls on divide migration. Of the ∼100,000 landslides triggered, we mapped 365 that caused a divide to migrate, resulting in a total exchange of ∼2 km2 between basins from ∼82,000 km2 affected by landsliding. By applying several proposed metrics for divide stability based on river channel morphology, we use our database of divide migrations to test for the role of landslides in coupling between channels and divides. We find that, at the time scale of a single landslide-generating event, patterns of area gain and loss between basins are consistent with landscapes progressing toward steady state, as inferred from channel metrics. We also propose a metric to quantify divide migration, area exchange, and the contribution of an event toward topographic steady state. Restricting our analysis to the main drainage divide, and using estimates of recurrence interval and the rate of topographic evolution in Taiwan, we calculate that landslides triggered by large typhoons account for a minimum of 12%–15% of southern Taiwan’s progress toward steady state. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

LONG-TERM TOPOGRAPHIC CHANGES AROUND SAND SPIT AND IMPACT OF EXTRAORDINARY HIGH WAVES DURING TYPHOONS

Around the Mihono-matsubara sand spit in Suruga Bay in Japan, the beach was eroded owing to the decrease in the fluvial sand supply from the Abe River triggered by excess riverbed mining before 1967, together with the discharge of sand into the deep sea via a steep slope near the tip of the sand spit. As a measure against beach erosion, an artificial headland (HL) composed of two detached breakwaters and the breakwaters (BWs) placed along the shoreline have been constructed along with beach nourishment, but the beach is barely maintained by these measures. In 2013, two large typhoons hit the coast, causing rapid beach changes around the structures, and these beach changes were superimposed on the long-term topographic changes that have occurred over a long time as a geomorphological process. In this study, their impact to the beaches was investigated on the basis of the field data.

Large-scale Disasters on World Heritage and Cultural Heritage in Japan: Significant Impacts and Sustainable Management Cases

On 11 March 2011, the East Japan Great Earthquake occurred off the east coast of Japan. This magnitude 9 earthquake caused a tsunami of 8–9 m in height, which subsequently reached an upstream height of up to 40 m, causing extensive damage over a 500-km span along the east coast of Japan. Damage was caused to 295 National Cultural Properties of Japan, most of which was due to the associated tsunamis rather than the earthquake. Particularly, significant damage was seen in the coastal cultural landscapes. In addition, Japan has extremely large typhoons every year. In recent years, it has not been unusual to see typhoon-caused storms, heavy rains and flooding, causing intensive damage such as landslides to World Heritage properties and their buffer zones. Such damage is seen in the pilgrimage routes of the “Sacred Sites and Pilgrimage Routes in the Kii Mountain Range” and in the natural elements of their associated cultural landscapes. The author presents a report on the damage from the East Japan Great Earthquake and other disasters on World Heritage and cultural heritage, and on their increasing occurrence in Japan. A discussion on remedial measures and the need for sustainable protection and management for World Heritage and other significant heritage is included.

Collaborative Resilience to Episodic Shocks and Surprises: A Very Long-Term Case Study of Zanjera Irrigation in the Philippines 1979–2010

This thirty-year case study uses surveys, semi-structured interviews, and content analysis to examine the adaptive capacity of Zanjera San Marcelino, an indigenous irrigation management system in the northern Philippines. This common pool resource (CPR) system exists within a turbulent social-ecological system (SES) characterized by episodic shocks such as large typhoons as well as novel surprises, such as national political regime change and the construction of large dams. The Zanjera nimbly responded to these challenges, although sometimes in ways that left its structure and function substantially altered. While a partial integration with the Philippine National Irrigation Agency was critical to the Zanjera’s success, this relationship required on-going improvisation and renegotiation. Over time, the Zanjera showed an increasing capacity to learn and adapt. A core contribution of this analysis is the integration of a CPR study within an SES framework to examine resilience, made possible the occurrence of a wide range of challenges to the Zanjera’s function and survival over the long period of study. Long-term analyses like this one, however rare, are particularly useful for understanding the adaptive and transformative dimensions of resilience.

Characteristics of Wave Grouping and Freak Wave Observed by Two Typhoons

Two large typhoons destroyed a concrete detached breakwater on the Suruga Coast, Shizuoka Prefecture, Japan in 2013. Although the Typhoon Man-yi, recorded a lower wave height than the other Typhoon Wipha, significant damage to the structure was observed by Typhoon Man-yi. It appeared that the significant wave height alone cannot describe the extreme wave field caused by typhoon appropriately. This study investigates typhoon wave characteristics with an objective to extract essential wave parameters influential to the stability of coastal structures. The relationships among various parameters were examined regarding the nonlinearity and the irregularity of nearshore waves, such as power spectrum, occurrence of freak waves, skewness and kurtosis, wave grouping and distribution of wave height. It is concluded that the occurrence of freak wave had strong correlation with the kurtosis μ4 and the groupiness factor GF. The nonlinearity parameter П1/3 was found to be a good parameter in the early detection of catastrophic wave field.

On tropical cyclone size and intensity changes associated with two types of long-lasting rainbands in monsoonal environments

Tropical cyclones (TCs) in a monsoonal environment may have heavy rain events separate from the eyewall rainfall. Two types of long-lasting rainbands in western North Pacific TCs interacting with the East Asia summer monsoon during 1999–2009 are identified and the effects of these rainbands on TC size and intensity changes are examined. For all of the south-type Outer Mesoscale Convective Systems as defined in our previous study, the TC intensification rate is decreased but the rate of size change is not modified. Long-lasting south-type Enhanced Rainbands (ERBs) that develop between 100 and 300 km radii and move cyclonically are associated with significant TC size increases. Seventy percent of very large typhoons had an ERB during the period when they intensified from tropical storms to typhoons.

Spatiotemporal analysis of vegetation index after typhoons in the mountainous watershed

An extensive land cover change was triggered by a series of typhoons, especially Typhoon Morakot in 2009 in Taiwan. The normalized difference vegetation index (NDVI) series from multiple satellite images were applied to monitor the change processes of land cover. This study applied spatiotemporal analysis tools, including empirical orthogonal functions (EOF), and multiple variograms in analyzing space–time NDVI data, and detected the effects of large chronological disturbances in the characteristics of land cover changes. Spatiotemporal analysis delineated the temporal patterns and spatial variability of NDVI caused by these large typhoons. Results showed that mean of NDVI decreased but spatial variablity of NDVI increased after typhoons in the study area. The EOF can clarify the major component of NDVI variations and identify the core area of the NDVI changes. Various approaches showed consistent results that Typhoon Morakot significantly lowered the NDVI in land cover change process. Furthermore, the spatiotemporal analysis is an effective monitoring tool, which advocates the use of the index for the quantification of land cover change and resilience.

Seasonal variations in the nitrogen isotope composition of Okinotori coral in the tropical western Pacific: A new proxy for marine nitrate dynamics

[1] To demonstrate the utility of coral skeletons as a recorder of nitrate dynamics in the surface ocean, we collected coral skeletons of Porites lobata and determined their nitrogen isotope composition (δ15Ncoral) from 2002 to 2006. Skeletons were collected at Okinotori Island in southwestern Japan, far from any sources of terrestrial nitrogen. Nitrogen isotope compositions along the growth direction were determined at 800 μm intervals (∼1 month resolution) and compared against the skeletal carbon isotope composition (δ13Ccoral-carb), barium/calcium ratio (Ba/Ca), and Chlorophyll-a concentration (Chl-a). From 2002 to 2004, ratios of the δ15Ncoral varied between +0.8 and +8.3‰ with inverse variation to SST (r = −0.53). Ba/Ca ratios and Chl-a concentrations were also observed to be high during seasons with low SST. These results suggested that the vertical mixing that occurs during periods of low SST carries nutrients from deeper water (δ15NDIN; +5∼+6‰) to the sea surface. In 2005 onward, δ15Ncoral and Ba/Ca ratios also had positive peaks even in high SST during periods of transient upwelling caused by frequent large typhoons (maximum wind speed 30 m/s). In addition, low δ15Ncoral (+0.8∼+2.0‰) four months after the last typhoon implied nitrogen fixation because of the lack of typhoon upwelling through the four years record of δ15Ncoral. Variations in the δ13Ccoral-carb and δ15Ncoral were synchronized, suggesting that nitrate concentration could control zooxanthellae photosynthesis. Our results suggested that δ15Ncoral holds promise as a proxy for reconstructing the transport dynamics of marine nitrate and thus also a tool for estimating nitrate origins in the tropical and subtropical oceans.

Metabolic changes and the resistance and resilience of a subtropical heterotrophic lake to typhoon disturbance

We studied how typhoon strength affects the daily dynamics of ecosystem metabolism of a subtropical alpine lake in Taiwan. We identified proximal agents of typhoon disturbance and assessed the resistance (the extent of change induced by a disturbance) and resilience (the rate of recovery after a disturbance) of lake metabolism to them. Gross primary production (GPP), ecosystem respiration (ER), and net ecosystem production were estimated from high-frequency dissolved oxygen data provided by an instrumented buoy. Typhoons resulted in significantly lower GPP (3%–81% decrease), and higher ER (7%–828% increase) compared with immediately before the events, and thus the lake became more heterotrophic (28%–852% increase in heterotrophy). The resistance and resilience of lake metabolism depended on the intensity of the typhoon. Smaller typhoons (with average daily accumulated precipitation (ADAP) &lt; 200 mm·day–1) had greater effects on lake metabolism than medium (ADAP = 200–350 mm·day–1) and large (ADAP &gt; 350 mm·day–1) typhoons. However, metabolism also recovered more quickly after smaller typhoons than after medium or larger typhoons. Typhoon effects on ecosystem metabolism is likely mediated by the magnitude and duration of typhoon-induced changes in lake mixing, the quantity and quality of dissolved organic carbon, and the biomass of primary producers.

Numerical Simulation Model for Storm Surge Inundation Incorporating Accurate Estimation of Transition Process from Overtopping to Overflow

A numerical simulation model for storm surge inundation has been developed. Inundation simulation method induced by transition process from overtopping to overflow is incorporated into this model. Convenient estimation method for this transition process is based on the equations produced by Goda(1975a). Several parameters in the Goda's equations are revaluated by numerical wave simulations of the transition process from overtopping to overflow. These simulations are performed by using VOF method (CADMAS-SURF). According to these simulation results accurate flow rates over the coastal dikes are estimated at the time of storm surge. With this simulation model high storm surges generated by large typhoons around the coasts of Japan can be reproduced. This paper presents the outline of the simulation model for storm surge inundation.

Remote sensing data with the conditional latin hypercube sampling and geostatistical approach to delineate landscape changes induced by large chronological physical disturbances.

This study applies variogram analyses of normalized difference vegetation index (NDVI) images derived from SPOT HRV images obtained before and after the ChiChi earthquake in the Chenyulan watershed, Taiwan, as well as images after four large typhoons, to delineate the spatial patterns, spatial structures and spatial variability of landscapes caused by these large disturbances. The conditional Latin hypercube sampling approach was applied to select samples from multiple NDVI images. Kriging and sequential Gaussian simulation with sufficient samples were then used to generate maps of NDVI images. The variography of NDVI image results demonstrate that spatial patterns of disturbed landscapes were successfully delineated by variogram analysis in study areas. The high-magnitude Chi-Chi earthquake created spatial landscape variations in the study area. After the earthquake, the cumulative impacts of typhoons on landscape patterns depended on the magnitudes and paths of typhoons, but were not always evident in the spatiotemporal variability of landscapes in the study area. The statistics and spatial structures of multiple NDVI images were captured by 3,000 samples from 62,500 grids in the NDVI images. Kriging and sequential Gaussian simulation with the 3,000 samples effectively reproduced spatial patterns of NDVI images. However, the proposed approach, which integrates the conditional Latin hypercube sampling approach, variogram, kriging and sequential Gaussian simulation in remotely sensed images, efficiently monitors, samples and maps the effects of large chronological disturbances on spatial characteristics of landscape changes including spatial variability and heterogeneity.