Effects Of Typhoons Research Articles

Developing and understanding cascading effects scenario of typhoons in coastal mega-cities from system perspectives for disaster risk reduction: A case study of shenzhen, China

Coastal mega-cities provide spaces of economic and social activities in contemporary China. Due to the cumulated effects of rapid urbanization and climate change, typhoon disasters always trigger serious cascading effects by affecting interrelated urban elements in high-density urban areas, thereby amplifying disastrous consequences. Developing cascading effects scenarios of typhoons, as well as understanding cause–effect relationships among the involved cascading events is essential to designing disaster risk reduction strategies in coastal mega-cities. However, high uncertainty of the natural hazards and the increasing complexity of coastal mega-cities present challenges to develop and understand cascading effects of typhoons. This research proposes an innovative approach to develop, model, and analyze cascading effects scenario of typhoon disasters in Shenzhen, China for providing insights of disaster risk reduction from system perspectives. First, considering the uncertainty of typhoons and complexity of the study area, the cascading effects scenario of typhoon disasters is developed by encoding hazard transitions triggered by historical cases, in combination with expert judgment. A network approach based on Social Network Analysis is employed to model, visualize, and analyze cascading effects scenarios of typhoons aiming to explore the underlying complexity of typhoon disasters. Finally, disaster risk reduction strategies are designed and evaluated from network analysis perspectives. This research increases the understanding of the evolution process of cascading effects triggered by typhoons in rapid-urbanizing mega-cities from system perspectives. Furthermore, it provides insights of designing effective disaster risk reduction strategies for urban governments to improve sustainability and resilience of coastal mega-cities to typhoon disasters.

Effects of typhoon and upwelling on Chlorophyll-a distribution in the northeastern coast of Hainan during Summer.

Typhoons or upwelling are thought to promote higher phytoplankton chlorophyll-a (Chl-a) concentration in many previous studies. However, the combined effects of typhoons and upwelling have been less studied in the South China Sea. Based on satellite remote sensing data, we investigated potential contributions of temperature-characterizing upwelling and typhoon events to Chl-a changes in the Hainan northeast area. Results showed that the Chl-a concentration was 0.80 mg m-3 at the coastal upwelling index (CUI) of 1.7°C in the summer of 2020 when there were no typhoons crossing the area. The CUI (1.01°C) of typhoon-influenced period in 2019 was 0.21°C higher than that of typhoon-free period in 2019. And the Chl-a also increased from 0.70 mg m-3 to 0.99 mg m-3. In comparison, during the typhoon-free period, with the higher CUI, there was the higher concentration of Chl-a. In addition, the typhoon affected Chl-a concentration is significantly higher than that in the other two typhoon-free periods of 2019 and 2020. Though the typhoon has a limited effect on the upwelling intensity, the Chl-a concentration is much higher than when the upwelling acts alone. This is due to the combined effect of typhoon (vertical mixing and runoff) and upwelling. The above results indicate that upwelling dominated the changes in Chl-a concentration in the Hainan northeast upwelling area during the typhoon-free period. In contrast, strong vertical mixing and runoff dominated the changes of Chl-a concentration during the typhoon-influenced period in the above area.

Indirect Effects of Binary Typhoons on an Extreme Rainfall Event in Henan Province, China From 19 to 21 July 2021. 3. Sensitivities to Microphysics Schemes

AbstractPrevious numerical studies have focused on the direct impact of microphysics schemes on multiscale atmospheric systems that produce rainfall. However, the indirect impact of microphysics schemes on the key large‐scale circulation around areas of extreme rainfall has not yet been examined systematically. We used the ARW‐WRF (Advanced Research WRF (Weather Research and Forecasting) Model) to simulate the extreme rainfall event in Henan province, China from 19 to 21 July 2021. Experiments were conducted to investigate the sensitivity of the simulation to the three popular double‐moment microphysics parameterizations: the Thompson, Morrison and WDM6 (WRF Double‐Moment 6‐Class Microphysics Schemes). We found significant sensitivity to the microphysics parameterization, with the maximum precipitation varying by up to 400 mm and the area‐averaged precipitation by 33 mm. The Thompson and Morrison microphysics schemes produced the largest amount of precipitation, whereas the WDM6 scheme produced the smallest amount of precipitation. The simulated southerly flow varied substantially between the different microphysics schemes. This is due to the ability of the microphysics schemes to produce latent heat, which enhances the southerly flow, leading to more intense precipitation. The higher the parameterized latent heat, the stronger and more obvious the southerly flow over southern Henan province, with the WDM6 scheme simulating a much weaker southerly flow and the Thompson scheme producing the strongest southerly flow. These results indicate that the indirect effects on the key circulation patterns can be just as sensitive to the formulation of the microphysics scheme as the direct effects on extreme rainfall. These results may help to improve the prediction of extreme rainfall events.

Berthing Capacity Evaluation of Fishing Port Prone to Typhoons: A Case Study of Shengsi Fishing Port

Typhoons and other extreme weather events frequently strike offshore fishing ports. Therefore, an objective and realistic assessment of the berthing capacity of fishing ports are critical to offshore production safety and the safe management of fishing ports to minimize typhoon effects. We integrated the MIKE 21 spectral wave (SW) and Holland wind models to recreate typhoon wave characteristics during the transit of Typhoon In-Fa and further analyzed the berthing capacity of the Shengsi fishing port (SFP) under different recurrence periods and route impacts. We planned the mooring area realistically and upgraded the marine fisheries production safety and security system. The model’s major wave heights and water levels are consistent with the actual observations, and the d-trend model evaluation demonstrates that our model performs well. The berthing capacity of the SFP was accurately calculated based on the significant wave height and stable mooring conditions for fishing vessels. The effective berthing area within SFP reached 5.88 km2 during the typhoon transit, accounting for 89.3% of the harbor area. A total of 5,154 fishing vessels, comprising 492 large-sized fishing vessels, 2,334 medium-sized fishing vessels, and 1,328 small-sized fishing vessels, could be moored. The berthing capacity under the impact of typhoons with varying recurrence periods is boosted by 10% compared with that of a 100a typhoon. When under the influence of typhoons with distinct trajectories, the wider the sheltered area of SFP is due to the topography sheltering effect, the more southerly the typhoon path is. This article examines the impact of alternative typhoon routes and return periods on fishing port sheltering capacity. The MIKE 21 SW wave and the Holland typhoon models are adopted to simulate the wave characteristics of the waters surrounding the fishing ports during the occurrence of the typhoon to analyze the fishing ports’ berthing capability. This report can be a reference for disaster reduction and offshore fishing port berthing management.

Suspended sediment dynamics and influencing factors during typhoons in Hangzhou Bay, China

Hangzhou Bay is located in China on the south side of the Changjiang Estuary and is vulnerable to extreme weather, such as typhoons in the summer and autumn. In this study, a three dimensional suspended sediment numerical model was developed that considers the dynamic factors of advection, mixing, wave, and sediment-induced stratification to simulate and analyze the effect of typhoons on water and sediment transport in Hangzhou Bay. The model validations show that the model can sufficiently reproduce the variability of the suspended sediment concentration (SSC) during typhoon conditions. The simulation results show that the high SSC in the bottom layer was mainly distributed in the leading edge of the south coast, and generally exceeded 10 kg·m−3. During typhoons, the water and suspended sediment transport in Hangzhou Bay presented a pattern of "north-landward and south-seaward" circulation, which promoted the convergence of suspended sediment in the center part of the bay. During Typhoon Rumbia in 2018, the water and sediment flux across the section from Nanhui Cape to Qiqu Archipelago (NQ section) increased by 18.13% and 265.75%, respectively, compared with those before the typhoon. The wave-induced bottom shear stress during typhoons has a very significant impact on the bottom SSC. The sensitivity experiments show that the wave-induced bottom shear stress greatly promotes the sediment resuspension during typhoons, which indirectly makes the sediment-induced stratification stronger than the direct effect of waves on the vertical mixing. The strong winds brought by typhoons mainly enhanced the vertical mixing, which has a stronger effect on surface SSC than waves. The suppression of vertical mixing by sediment-induced stratification during typhoons should not be ignored, especially for high turbidity coastal waters, such as Hangzhou Bay.

Mechanism of oceanic eddies in modulating the sea surface temperature response to a strong typhoon in the western North Pacific

Eddies are ubiquitous mesoscale dynamics in oceans worldwide that prominently influence the upper ocean. Specifically, the presence of preexisting eddies can modulate oceanic responses to passing typhoons, for which the underlying mechanism requires further investigation. In 2013, Typhoon Soulik traveled over 2,000 km in the western North Pacific, encountering multiple eddies, offering a suitable opportunity for investigating the impact of eddies on typhoon-induced upper ocean responses. A coupled ocean-atmosphere model was developed for this event, and the simulations were validated with multiple observations. The surface cold wake after Typhoon Soulik was successfully reproduced by the coupled model, showing a multicore structure, which was due to the preexisting mesoscale cyclonic eddies along the typhoon path. An experimental case excluding eddies was also tested in the numerical model. The comparison between the control and experimental cases revealed that sea surface cooling was enhanced by eddies via the vertical mixing and horizontal advection of eddy-related currents. In particular, vertical mixing enhanced sea surface cooling beneath the typhoon center due to the stronger vertical stratification within the preexisting cyclonic oceanic eddies. The eddy-related current with a horizontal temperature gradient contributed to advection, enhancing sea surface cooling at the cooling center and leading to a rightward-shifted pattern of enhanced sea surface cooling. This study enriches the understanding of the complex upper ocean dynamics under the combined effects of typhoons and eddies.

Typhoon Effects on the Vertical Chlorophyll Distribution on the Northern Shelf of the South China Sea

AbstractTyphoon Merbok passed through the northern South China Sea and landed near the Pearl River Estuary in June 2017. Field observations showed that the chlorophyll‐a (Chla) concentration in the bottom/subsurface chlorophyll maximum (BCM/SCM) layer decreased in both nearshore and offshore regions after Merbok. In addition, the BCM/SCM layer became shallower in the nearshore region and deeper in the offshore region after Merbok. A coupled physical‐biogeochemical model was applied to investigate the driving mechanism for this Chla change. During the typhoon, the spatial movement of plume water was responsible for the surface Chla change in the nearshore region, and vertical mixing increased Chla in the upper layer and decreased it in the SCM layer in the offshore region. Shortly after the typhoon, surface Chla increased and bottom Chla decreased in the nearshore region, which was associated with strengthened bottom flow and vertical mixing. When the typhoon‐induced mixing decreased, upwelling tended to shoal the BCM layer in the nearshore region, and phytoplankton production increased Chla in the BCM layer. In the offshore region, vertical mixing was the dominant mechanism for Chla redistribution during the typhoon, which decreased Chla in the SCM layer and resulted in a deeper SCM layer. A few days after the typhoon, phytoplankton production also contributed to the Chla change particularly in the subsurface layer, which was stronger in the nearshore region than that in the offshore region. These findings may contribute to the understanding of phytoplankton dynamics in response to typhoons in coastal areas.

Wave–current interaction by Typhoon Fongwong on saline water intrusion and vertical stratification in the Yangtze River Estuary

Saline water intrusion and vertical stratification are two important phenomena in estuaries, and thereby inextricably related to water mixing. In this study, a coupled 3D current-wave-salinity transport modeling is used to evaluate the effects of strong wind, wave and current on salt intrusion and water mixing in the Yangtze River Estuary (YRE) during typhoon Fongwong (2014). The model is validated by the measured wave height and period, tidal level, current velocity and salinity data. The model results show that: 1) wave-current interaction (WCI) during the typhoon period increased the current velocity and tidal level while decreased the air pressure, causing a storm surge by 1.2 m in the YRE; 2) the strong waves and winds strengthened the salinity intrusion in the YRE and the North Branch (NB) presented evident changes. After typhoon passage, the high saline water did not flush out immediately, indicating the typhoon effects were a fast process but the recovery of two weeks was slow; 3) The effect of the WCI showed a significant increase of water mixing and destratification during the typhoon event. Similar to the salinity intrusion, the process of regaining stratification needed a relatively long time. This research highlights that the WCI effects are important in the typhoon period on the hydrodynamics and salinity variation in the horizontal and vertical directions.

Development of a Typhoon Damage Prediction Function and Rating System Using Typhoon Characteristics and Tracks

In this study, a typhoon exposure index (TEI) was developed that can identify the effects of typhoons on the Korean Peninsula, allowing the development of a typhoon damage prediction function using TEI and rainfall data, based on which a new typhoon rating system is proposed that takes likely damage into consideration. TEI takes a value inversely proportional to the distance from the center of a typhoon to a district and proportional to the maximum wind speed in the center of a typhoon. In the rainfall data, a variable identified using principal component analysis was introduced to resolve the issue of multicollinearity between the maximum rainfall and duration. The typhoon damage prediction function for all typhoons showed good predictive precision, and the predictive precision for typhoons passing through the East Sea and making landfall in the South Sea was higher than for all typhoons. Since the KMA typhoon rating system cannot represent the degree of disaster risk on the Korean Peninsula by track, a new typhoon rating system considering with damage was developed using TEI and rainfall data.

Insignificant effects of eddies and typhoons on the biogeochemistry of the tropical northwest Pacific Ocean

We investigated the effects of eddies and typhoons on the biogeochemistry of the tropical northwest Pacific by examining the distribution of nutrients, dissolved oxygen (DO), chlorophyll-a (Chl-a), gross primary production (GPP), dissolved organic carbon (DOC), and fluorescent dissolved organic matter (FDOM). Water samples were collected from anticyclonic and cyclonic eddies in September 2019 and 2020, and before and after the passage of a Category 2 typhoon in 2019. The study region was characterized by a deep nitracline (~150 m), which was deeper than both the pycnocline (~50 m) and the FDOM-depleted layer (~75 m). A subsurface chlorophyll maximum layer was observed at 100–150 m depth. No clear differences in Chl-a, DO, GPP, DOC, and FDOM were observed for the anticyclonic and cyclonic eddies, indicating that the eddies did not have a significant influence on biological production. Similarly, there were no discernable changes in Chl-a concentrations or other biogeochemical parameters after the passage of the typhoon, which induced water mixing to a depth of ~60 m. We conjecture that the nutrient-depleted layer was too deep for any eddy- or typhoon-induced vertical mixing to cause upwelling of nutrients to the euphotic zone. Our results imply that the disturbances caused by mesoscale processes in the upper layer of the highly oligotrophic northwest Pacific may have a smaller effect than in oceans in other parts of the world.

Short-term effects of tropical cyclones on the incidence of dengue: a time-series study in Guangzhou, China

BackgroundLimited evidence is available about the association between tropical cyclones and dengue incidence. This study aimed to examine the effects of tropical cyclones on the incidence of dengue and to explore the vulnerable populations in Guangzhou, China.MethodsWeekly dengue case data, tropical cyclone and meteorological data during the tropical cyclones season (June to October) from 2015 to 2019 were collected for the study. A quasi-Poisson generalized linear model combined with a distributed lag non-linear model was conducted to quantify the association between tropical cyclones and dengue, controlling for meteorological factors, seasonality, and long-term trend. Proportion of dengue cases attributable to tropical cyclone exposure was calculated. The effect difference by sex and age groups was calculated to identify vulnerable populations. The tropical cyclones were classified into two levels to compare the effects of different grades of tropical cyclones on the dengue incidence.ResultsTropical cyclones were associated with an increased number of dengue cases with the maximum risk ratio of 1.41 (95% confidence interval 1.17–1.69) in lag 0 week and cumulative risk ratio of 2.13 (95% confidence interval 1.28–3.56) in lag 0–4 weeks. The attributable fraction was 6.31% (95% empirical confidence interval 1.96–10.16%). Men and the elderly were more vulnerable to the effects of tropical cyclones than the others. The effects of typhoons were stronger than those of tropical storms among various subpopulations.ConclusionsOur findings indicate that tropical cyclones may increase the incidence of dengue within a 4-week lag in Guangzhou, China, and the effects were more pronounced in men and the elderly. Precautionary measures should be taken with a focus on the identified vulnerable populations to control the transmission of dengue associated with tropical cyclones.Graphical

Typhoon Wave Simulation Responses to Various Reanalysis Wind Fields and Computational Domain Sizes

A fully coupled tide-surge-wave model was developed to study the influence of different computational domains on typhoon wave characteristics in the waters surrounding Taiwan. Three typhoons were selected as study cases: Meranti, Malakas, and Megi, which successively impacted Taiwan in September 2016. Superposition of the CFSV2 winds blended with ERA5 winds onto the tide-surge-wave model yielded optimum simulations of typhoon waves. Storm wave responses along the eastern shelf of Taiwan resulting from three typhoons were examined in four model domains. The first domain (D01) was primarily situated in the region where giant waves were generated. The second domain (D02) covered an area extending from 114° E to 130° E and 19° N to 29° N. The third domain (D03) southwardly included the entire Bashi Channel, from longitudes of 111° E to 135° E and latitudes of 18° N to 30° N. The fourth domain (D04) was the largest among the four computational domains; it extended from longitudes of 105° E to 140° E and latitudes of 15° N to 31° N. The simulated sea state responses indicated that the smaller computational domains were inadequate for typhoon-driven storm wave computation purposes, although the areas of D01 and D02 reached approximately 0.75 and 1.38 million km2, respectively, encompassing all of Taiwan Island and adjacent waters. Our results suggest that utilizing at least D03 or a larger model domain (e.g., D04) is essential to account for the remote wind effect of typhoons on wave simulations in Taiwanese waters.

Market response to typhoons: The role of information and expectations

AbstractDamages from tropical storms are enormous and predicted to increase with climate change. This study uses high‐frequency data to investigate typhoons' effects through information channels on Taiwan's wholesale vegetable market during the 1996–2014 period. We first identify effects on prices and quantities during storms' striking periods and further separate price effects into those due, respectively, to supply and demand shifts. The results show that for typhoons that make landfall, prices rise significantly during the striking period, and the decomposition results indicate that most of the price effects during periods with warnings but no landfall are due to demand shifts, which supports evidence of precautionary purchases by consumers. However, during the landfall period, the price effect is mainly driven by decreased supply. In addition, we find that typhoon effects differ between specific vegetables, and the magnitude of precautionary purchase is correlated with expected damage to those vegetables. Consumers also make more precautionary purchases when they face higher‐intensity typhoons or learn typhoons will make landfall within 24 h, and such prior information related to intensity or landfall urgency can also amplify early harvest effects by farmers.

Temporal Variation Analysis of Rice Yield in the Jiangsu Province, China: Application of Decision Support System for Agrotechnology Transfer Model

The accuracy of grain yield estimation is critical for national food security. Because of the comprehensive influence of spatial differentiation conditions, such as temperature, precipitation, soil, rice variety, and irrigation, yield estimation requires integrated modeling that is based on dynamic conditions. These dynamic conditions include geographical background, biological factors, and human impact. Most existing studies focus on the observation and analysis of external factors; only a few reports on yield simulations are coupled with nature, management, and crop growth mechanism. Our study incorporates the crop growth mechanism of rice, along with data of rice varieties, soil, meteorology, and field management, to determine the rice yield in Jiangsu province, China. In addition, we have used a decision support system for the agrotechnology transfer model, along with Coupled Model Intercomparison Project data and geographic information system technology. Our results showed that: (1) A calibrated variety genetic coefficient could simulate rice biomass value (flowering stage, maturity stage, and yield) reasonably. The values of NRMSE (Normalized Root Mean Square Error) between the simulated and measured values after parameter calibration are all less than 10%, the values of d(index of agreement) are all close to 1, the simulated value of yield is in good agreement with the measured value. (2) A linear correlation between the meteorological elements and yield was observed. The linear correlation had regional differences. Notably, an increase in precipitation was conducive to the increase in yield. Except at the Huaiyin site, the other sites showed that the temperature rise could potentially lead to reduced production. We found that an increase in solar radiation was unfavorable to the production of rice in the northern and western sites in the Jiangsu province, whereas it was conducive in the southern and eastern sites. (3) Our study predicted the rice yield from typical sites in the Jiangsu province from 2019 to 2060 in the wake of climate change while excluding the extreme effects of diseases, pests, typhoons, and floods. The order of average yield per unit area is as follows: Xinghua site (8212.76 kg/ha) > Huaiyin site (7912.70 kg/ha) > Gaoyou site (7440.98 kg/ha) > Gaochun site (7512.29 kg/ha) > Ganyu site (7460.88 kg/ha) > Yixing site (7167.00 kg/ha). Notably, the average yields from the Xinghua and Huaiyin sites were higher than that from the Jiangsu province (7617.77 kg/ha). The fluctuation of the yield per unit area at each site was generally consistent with the fluctuation in the overall yield, showing a downward trend and tends to be stable. The dispersion of yield per unit area indicates that Gaochun had the most stable yield per unit area followed by Xinghua, Ganyu, Yixing, Huaiyin, and Gaoyou. The yield per unit area of the Huaiyin and Gaoyou sites was unstable and portrayed the biggest fluctuations. Future studies need to focus on how to deal with spatial variation and carry out adaptive verification to make the simulation results applicable to more dimensions.

Observational study of typhoon effects on the oval-shaped 330 m high Zhuhai Center Tower

This paper investigates typhoon-induced wind effects on a skyscraper based on 72-h-long field measurement records. In this large-scale monitoring study, the wind field characteristics surrounding the monitored building are first investigated using climate records collected by a moveable laser radar wind profiler that was temporarily fixed next to the tall building during Typhoon Cempaka, which could avoid adverse impacts caused by interference at the building top or the terrain effects through measurements from an anemometer atop the building or a meteorological observation tower that could be far away from the monitored building. Subsequently, the wind-excited cladding pressures and structural responses of the monitored skyscrapers are analysed according to measurements by pressure transducers, accelerometers and velocimeters, and the pressure distribution characteristics and structural dynamic properties are estimated by spectral analysis and the random decrement technique. Ultimately, provided the oval-shaped appearance and spiral configuration of the Zhuhai Center Tower, the results derived in this study are compared with those of other supertall buildings in terms of several aspects of concern, including the distribution features of wind pressures and acceleration response and amplitude-dependent characteristics of modal parameters, which would further the understanding of wind effects on tall buildings with various cross sections and building shapes. This study aims to provide comprehensive reference information for the wind-resistant design of high-rise buildings in tropical cyclone-prone regions.

Response of Temperature to Successive Typhoons in the South China Sea

Typhoons are serious natural disasters in coastal areas. During the summer of 2011, successive typhoons Nesat and Nalgae appeared in the South China Sea, providing a unique opportunity for us to study the response of the upper ocean to successive typhoons. We comprehensively use satellite data and COAWST model data to explore the effects of successive typhoons on the temperature structure of the South China Sea. Nesat caused the sea surface temperature to decrease by up to 4.4 °C on the right side of the typhoon path, and the ensuing Nalgae caused the temperature to decrease by up to 2.2 °C. Because Nesat had already cooled the ocean, the response to Nalgae was more to the left of the track than one would normally expect. The upwelling dominates the change in subsurface temperature. Based on the increase caused by Nesat, the isotherm was further raised by Nalgae. The isotherm rising amplitude is larger in the upper and deeper layer and is smaller in the middle layer in the depth range of 0–200 m. Heat budget analysis indicates that in the area close to the typhoon path, vertical diffusion is the main reason for the decrease in ocean surface temperature, while total advection suppresses the decrease in temperature. In the area with a larger distance from the typhoon path, vertical diffusion and total advection lead to the decrease in ocean surface temperature, and total advection will gradually contribute more to temperature change and become the dominant factor. On the right side of the typhoon track, the reduction of the contribution rate of vertical diffusion with distance from typhoon track is slower than that on the left side of the typhoon track. Whether Nesat or Nalgae, the intensity and depth of effects of vertical diffusion on the right side of typhoon path are greater than those on the left side of typhoon path, and the near-inertial periodic oscillation of local temperature change rate is more obvious. When the vertical diffusion is weak, the influence of vertical advection and horizontal advection is deeper. Moreover, the near-inertial periodic oscillation of the local temperature change occurs in lower depth after Nalgae passed through than that after Nesat. The typhoon intensity of the two typhoons shows the opposite change: the first typhoon increases, and the second typhoon weakens. Therefore, the special case of successive typhoons should be fully considered in typhoon prediction to improve accuracy.

Post-typhoon forest damage estimation using multiple vegetation indices and machine learning models

The frequency and intensity of typhoons have increased due to climate change. These climate change-induced disasters have caused widespread damage to forests. Evaluation of the effects of typhoons on forest ecosystems is often complex and challenging, mainly because of their sporadic nature. In this paper, we compared existing forest damage estimation techniques with the goal of identifying their respective advantages and suitable use cases. We considered Hokkaido in northern Japan as a case study, where three typhoons successively struck in 2016 and led to forest destruction. Forest damage was estimated from Landsat 8 imagery by three approaches, namely using vegetation damage indices (DVDI, DNDVI and ΔEVI), using supervised classification with Random Forest (RF) and Support Vector Machines (SVM) and finally by using the commercial CLASlite software with built-in methods to detect forest disturbance. Machine learning classifiers obtained the highest damage assessment accuracy, but intensive computation and complex processing steps were required. The RF and SVM classifiers gave the highest accuracies when using Fractional Cover as a predictor variable (Overall Accuracy = 80.36% in both cases, and ROC AUC values of 0.89 and 0.88, respectively.) Among the vegetation damage indices, DNDVI produced the highest accuracy (AUC = 0.85, OA = 77.68%).The most damaged areas were on the windward slopes, where forest patches were exposed to the brunt of the typhoon winds. Forest damage also peaked at the highest elevations in the study area, possibly representing exposed hilltops. Methods and findings presented in this study can help stakeholders to implement more effective forest damage monitoring after typhoons and other extreme weather events in the future.

Indirect Effects of Binary Typhoons on an Extreme Rainfall Event in Henan Province, China From 19 to 21 July 2021: 2. Numerical Study

AbstractAn extreme precipitation event over Henan province, China from 19 to 21 July 2021 led to flood disasters in this region and widespread concern about the subsequent loss of life and livelihoods. We conducted numerical simulations to examine the impacts of typhoons In‐fa (2021) and Cempaka (2021) on this extreme rainfall event. The control simulation reasonably reproduced the motion of typhoons In‐fa and Cempaka and the associated distribution and amount of extreme rainfall. Sensitivity experiments were conducted in which typhoon In‐fa was artificially moved in both northerly and westerly directions in the initial conditions. The results indicated that the southerly flow between typhoon Cempaka and Henan, which determined the structure and distribution of the extreme rainfall event, was sensitive to the motion of typhoon In‐fa. Numerical experiments that removed typhoon Cempaka confirmed that both the movement of In‐fa and its interaction with Cempaka were closely associated with southerly flows and had a significant effect on the extreme precipitation event. In the absence of typhoon Cempaka, although typhoon In‐fa still had a remote effect on precipitation, the effect was much smaller than in the presence of Cempaka. Our simulation of this extreme rainfall event in Henan and the associated sensitivity experiments are consistent with the results of previous studies of multiple tropical cyclones, which showed that interactions among multiple tropical cyclones can lead to changes in their outer circulation that affect extreme precipitation events.

Intraseasonal interactive effects of successive typhoons characterize canopy damage of forests in Taiwan: A remote sensing-based assessment

Wind gusts and rainfall from tropical cyclones can heavily damage forest canopies, leading to abrupt changes in forest structure and tree demography. Although many studies have shown that successive tropical cyclones can interact with each other through residual effects, the role of past disturbances is unclear because they may lead to damage amplification of the second cyclone because of weakened forest structure, or damage reduction of the second cyclone because of previous damage to susceptible trees. We investigated the interaction between consecutive cyclones between 2001 and 2017 for five well-conserved forests in Taiwan, which experiences an average of 1.75 typhoons annually. Using MODIS imagery, we computed the typhoon-induced change of a canopy vegetation index, the Normalized Difference Infrared Index (NDII). The effects of successive typhoons were assessed separately for typhoons occurring within a single year (annual analysis) and within two consecutive years (biennial analysis). We used mixed effect models of reductions in NDII, a measurement of canopy damage, in relation to target and past typhoon characteristics and damage magnitude. NDII reduction induced by preceding typhoons was slightly more important and statistically significant in explaining the variation in NDII reduction associated with the target typhoon in the annual than in the biennial analysis, where the effect was non-significant. Canopy damage did not always decrease across typhoons occurring within the same season, however, for most successive typhoons in the biennial analysis, the second cyclone caused equal or less canopy damage (16 out of 21 typhoon pairs). These results support the idea that residual interactive effects of previous typhoons decrease quickly over time and rarely last for several typhoon seasons for Taiwanese forests, contributing to their high resistance to frequent typhoon disturbance.

Numerical modelling of storm surge, nutrient pollution and saltwater intrusion in a large estuary with typhoon effects

A coupled modelling framework, consisting of the storm surge model and the European Regional Seas Ecosystem Model (ERSEM), has been established to examine hydrodynamics process during Typhoon Hagupit and its role on nutrient and salinity dynamics in the Pearl River Estuary (PRE). The accuracy of modelling framework was reasonably validated against measured typhoon wind, storm tide, and water quality data. Further analysis suggests Hagupit significantly increases water levels in the PRE. Meanwhile, the seaward residual currents apparently and chaotically change. The phosphate and dissolved inorganic nitrogen concentrations decrease by 0.2–1.8 and 20–88.6 μmol/L in the most area from the downstream of narrow river channels to offshore region due to the variations of hydrodynamics, while small difference was detected in upstream narrow channels and open sea. By contrast, salinity distribution showed opposite variation. Statistically, the typhoon winds alleviated the averaged nutrient pollution in the whole PRE, while causing serious saltwater intrusion.