Morakot Research Articles

Disaster investigation and analysis of Typhoon Morakot

Typhoon Morakot first struck Taiwan on 6 August 2009, which led to a much more serious disaster than the notorious ‘August 7th Flood’ which occurred 50 years previously; it broke records for almost all meteorological observing data with an estimated rainfall in five days surpassing Taiwan's annual average rainfall of 2500 mm. Such a huge amount of rainfall caused more serious damage than the 921 earthquake. The typhoon left 620 people dead, 80 people missing, and over NT$90 billion in total direct property losses in 2009. Therefore, within one week after the disaster, the National Science Council requested the National Science and Technology Center for Disaster Reduction to investigate the disasters caused by Typhoon Morakot and to carry out a comprehensive investigation to better understand the type, numbers, and scale of the disasters. Meanwhile, this investigation also aims to better understand the causes and to spot potentially dangerous areas. Our key focuses include: flooding, water facilities, landslides, debris flows, bridges, traffic, and agricultural losses. Finally, based on an intensive investigation, analysis, and review results, we hope to develop both short-term and long-term countermeasures for future disaster prevention reference.

A Strategy of Sustainable Environment Management: The Case Study of Wutai Township in Taiwan

After Typhoon Morakot in 2009, the Taiwanese government relocated three indigenous villages to the lowland, leading to changes in traditional lifestyles and customs. Using the Wutai community as a case study, this paper suggests a strategy for sustainable post-disaster indigenous development . The paper focuses on two issues, the traditional land use of Rukai people in Wutai Township and their methods used regarding village relocation, afforestation and mountain patrol after Typhoon Morakot. Our research found that about 73.0% of locals who agree with afforestation in Aboriginal territory, 54.3% would like to sign a contract with the government which lasts more than twenty years, and 84.5% wish to be included in mountain patrol. Therefore, we propose that a mountain patrol foundation be established, to be responsible for the recruitment of mountain patrol members, planning afforestation, and conservation. Moreover, through the foundation, a mountain academy might be established, which could handle dynamic activities and systematize disciplines so as to link traditional environmental knowledge and modern conservation skills. Also, the foundation could help the local communities to develop eco-tourism and other related industries to increase local incomes and conservation funds, as a step towards sustainable development.

FLO-2D simulation of mudflow caused by large landslide due to extremely heavy rainfall in southeastern Taiwan during Typhoon Morakot

Daniau Village in Daniau Creek Watershed, Taitung County, Taiwan, sustained damages from landslides and mudflows during Typhoon Morakot in 2009. The purpose of this study is to adopt the FLO-2D numerical model recognized by Federal Emergency Management Agency (FEMA) to simulate the mudflow, and the Daniau Village was used as a case study, along with rainfall and digital terrain data for this simulation. On the basis of sediment yields, the residual sediment volume in the landslide area was determined to be 33,276 m 3 by comparison of digital elevation models (DEMs) and by using the universal soil loss equation (USLE). In addition, this study performed a hydrological frequency analysis of rainfall to estimate the flow discharge as conditions of the simulation. Results of disaster surveys were collected to compare with outputs of the numerical model. Results of the simulation conducted with FLO-2D indicated that if the countermeasure was not destroyed, the drainage work would function without overflow. This study aimed to review the effectiveness of countermeasure on the basis of simulation results obtained by using the model to provide references for future disaster prevention and resident evacuation plans.

Late Holocene episodic river aggradation along the Lao-nong River (southwestern Taiwan): An application to the Tseng-wen Reservoir Transbasin Diversion Project

The Tseng-wen Reservoir Transbasin Diversion Project (the Tseng-wen Project), currently the largest water-resources scheme in Taiwan, aims at constructing a tunnel system across the mountains to divert the water of the Lao-nong River to the Tseng-wen Reservoir, the largest reservoir in the island. This project was suspended, however, because the constructed tunnel entrance on the side of the Lao-nong River has been buried by the 20–30m aggradation of the river during 2009 Typhoon Morakot, which triggered extensive landslides/debris flows and killed >400 people in southwestern Taiwan. To understand the river history and help assess the risk to the project, the fluvial/debris-flow sequences exposed along the 5km-long river reach upstream of the buried tunnel entrance were examined, and a total of 38 radiocarbon dates were obtained for chronological constraints. The study is limited by the intrinsic uncertainties of the dates and by the likelihood that much of the stratigraphic evidence has been eroded away or remains unexposed. Even so, this study identified 9 pre-historical aggradation events in the past 2ka, each of which had a magnitude comparable to, or greater than, the 2009 event. The most recent event occurred <200 BP. The event of 0.8ka (or younger) aggraded the river to 120m above the 2008 level. These ancient events were sourced mainly from the alternate growth of fan systems from 3 tributaries, two of which contributed to the 2009 event. There are still 3 other such fan-building tributaries joining the studied river reach, and 8 more farther upstream, that must have supplied vast amounts of sediment to the trunk river. In sum, although dominated by incision over long term in response to rapid tectonic uplift, the studied river is subject to short-term, large-scale aggradation, far beyond the coping capacity of the Tseng-wen Project as originally designed. For this and other mountain rivers in Taiwan, future engineering plans should consider the risk of significant river aggradation.

Large-scale simulation of watershed mass transport: a case study of Tsengwen reservoir watershed, southwest Taiwan

We present the large-scale simulation of watershed mass transport, including landslide, debris flow, and sediment transport. A case study of Tsengwen reservoir watershed under the extreme rainfall triggered by typhoon Morakot is conducted for verification. This approach starts with volume-area relation with landslide inventory method to predict temporal and regional landslide volume production and distribution. Then, debris flow model, Debris-2D, is applied to simulate the mass transport from hillslope to fluvial channel. Finally, a sediment transport model, NETSTARS, is used for hydraulic and sediment routing in river and reservoir. Near the water intake at the reservoir dam, the simulated sediment concentration is in good agreement with the measured one. The proposed approach gives good prediction and should help the management of reservoir operation and disaster prevention.

Typhoon Morakot meteorological analyses

Typhoon Morakot yielded record-breaking precipitation and caused severe disasters in Southern Taiwan in early August 2009. This event revealed the desperate need for extreme rainfall and disaster prediction. The multiscale analysis on circulations demonstrates that Typhoon Morakot not only developed in a monsoon trough, which is a large-scale system in favor of the development of convection systems, it was also involved with complicated features of different scales that included typhoon circulation itself, the circulation of northwestward-propagating 10–30-day oscillation, and the circulation of northward-propagating 40–50-day oscillation. The other remarkable features of Typhoon Morakot are: the asymmetric structure of convection, less damage occurred near the typhoon center than at the fringes, and the record-breaking torrential rain in the mountain areas of south Taiwan induced by the flows on the south fringe of the typhoon. The causes of disastrous precipitation from Typhoon Morakot can be stated as: (1) a large-scale environment in favor of convection development and a plentiful vapor supply provided by strong southwesterly flow, (2) the interaction between topography, typhoon circulation, and large-scale circulation resulting in the heavy rainfall in the mountains of Southern Taiwan, and (3) the weakening of steering flow slowed down Morakot's translation speed before it made landfall and extended the duration of heavy precipitation.

Crisis Communication Failure: A Case Study of Typhoon Morakot

In 2009, Typhoon Morakot was the deadliest typhoon to impact Taiwan in recorded history. Around 700 people were either killed or lost in the catastrophe, while damage to agricultural, public construction and business losses amounted to NT$110 billion (US$3.5 billion). The purpose of this study is to examine the crisis with Typhoon Morakot and how governmental agencies respond to the needs of the citizens. Throughout the stages, three main themes of Taiwanese government’s response to Typhoon Morakot emerged: 1) ignoring the warning signs in pre-crisis stage, 2) failure in crisis response in crisis stage, and 3) taking corrective actions in post-crisis stage. The findings demonstrate a need to develop culturally and ethnically competent crisis response to minority population. It is important to note that the necessity of community participation during reconstruction is essential.

Exploring the spatial patterns of disaster impacts caused by Typhoon Morakot

Geographic context is recognized as an important factor in explaining the potential vulnerability and damage from disasters. However, the spatial dimension of disaster damages is not always taken into account in traditional damage assessment. This article aims to provide a comprehensive methodology that incorporates multivariable analysis with a spatial statistical autocorrelation analysis model in order to assess damages caused by Typhoon Morakot. Three watersheds are selected as the case study site with the consideration of complexity among these divergent affected areas. Spatial autocorrelation analysis was utilized to measure localized hotspots of damage. The grouping maps of affected areas were constructed using cluster analysis. The geographic characteristics of these damages were further compared among the three watersheds. Finally, we discuss the underlying factors that result in the variability of spatial patterns associated with damage, and explain how the findings can make a contribution to policy making and recovery plan implementation regarding typhoon risk reduction.

High-resolution quantitative precipitation forecasts and simulations by the Cloud-Resolving Storm Simulator (CReSS) for Typhoon Morakot (2009)

Summary Typhoon Morakot (2009) struck Taiwan during 7–9 August 2009, and brought extreme rainfall up to 2855 mm and the worst damages in the past 50 years. The operational models showed deficiency and serious under-prediction in rainfall amount at real time. This study demonstrates that the Cloud-Resolving Storm Simulator (CReSS), a state-of-the-art, high-resolution model, at a grid size of 3 km and starting as early as 0000 UTC 4 August, can successfully simulate and reproduce the event with high accuracy, including the distribution and timing of heavy rainfall in Taiwan. In the simulation starting at 0000 UTC 6 August, for example, the threat scores for 24-h rainfall for 8 August (with extreme amounts >1450 mm) reach 0.8–0.4 even at thresholds of 100–500 mm. This result is only possible due to small track error and the phase-locking mechanism of the Taiwan topography to heavy rainfall. Furthermore, real-time forecast and hindcast integrations of the CReSS model show that high-quality quantitative precipitation forecasts (QPFs) with peak total amount 67–80% of the true value are also obtained from initial conditions at 0000 UTC 6 August, which is about 2 days prior to the beginning of the heaviest rainfall in southern Taiwan. In these integrations, typhoon track errors in the global model forecasts used as boundary conditions are the major error source that prevent more ideal QPF results before and at 1200 UTC 5 August. When properly configured, it is believed that other similar cloud-resolving models can achieve comparable performance. Thus, the importance of and potential benefits from deterministic high-resolution forecasts is stressed, which may give an extended lead-time when the track error is small. With potentially longer time window for emergency action just prior to extreme rainfall events when it matters the most, such forecasts may ultimately lead to reduced losses in lives and properties.

Typhoon Morakot: Key Findings from the Journal TAO for Improving Prediction of Extreme Rains at Landfall

T yphoon Morakot (2009) was one of the deadliest typhoons to impact Taiwan in the past 50 years. It brought catastrophic damage to Taiwan, leaving 673 people dead and 26 others missing. This slow-moving storm produced huge amounts of rainfall, peaking at 2,965 mm (116.73 in.) in 4 days (7–10 August 2009), and caused enormous mudslides and severe flooding throughout southern Taiwan. One massive mudslide devastated the entire Shiaolin village, killing approximately 500 people in this village alone. The estimated agricultural losses amounted to roughly NT$16.4 billion (about US$550 million). Morakot also caused widespread damage in China and the Philippines. Improving forecasting techniques and early warning systems for landfalling tropical cyclones (TCs) has thus become one of the most important tasks facing scientists and governmental agencies. Since this extreme rainfall event, there have been extensive studies focusing on its record-breaking amount of rainfall from various scientific and forecast perspectives. Accordingly, a conference named “The International Workshop on Typhoon Morakot (2009),” summarized by C.-S. Lee and colleagues in a 2011 article, was held on 25–26 March 2010 in Taipei, Taiwan, during which various aspects of TCs were communicated and discussed. The conference specifically aimed to identify gaps in our understanding of TCs and to discuss advanced forecast guidance tools required to improve warnings of these extreme precipitation and flooding events. The community went a step further to propose a special issue to the journal Terrestrial, Atmospheric and Oceanic Sciences (TAO) in order to provide a comprehensive summary of Morakot and other extreme rainfall events associated with landfalling TCs. The special issue, “Typhoon Morakot (2009): Observation, Modeling, and Forecasting Applications,” was published in December 2011 and covered observation analyses of circulations and structures, mesoscale model simulations, data assimilation techniques, and practical forecast verification and guidance. Key findings and consensuses in this special issue are carried out from approaches of statistics, observations, and numerical simulations, and are summarized below.

Investigation of the Hsien-du-Shan rock avalanche caused by typhoon Morakot in 2009 at Kaohsiung county, Taiwan

The Hsien-du-shan rock avalanche at Kaohsiung County, Taiwan, was triggered by heavy rainfall brought by Typhoon Morakot in 2009. Heavy rainfall began on the day of August 6, and continued to the morning of August 9 when the slope failure and landslide occurred. In this post-event investigation, physical, mechanical, and hydraulic properties of the rocks/soils at this large landslide site are evaluated. The in situ hydraulic conductivity of the soils at the source area was found to be too low (k=1.48×10−6m/s) for rainfall to vertically infiltrate to the deep sliding surface, which was found to have a maximum depth of 85.6m. The post-failure simulations using discontinuous deformation analysis (DDA) suggest that the geometry of the sliding surface governs the failure behavior, and two continuous progressing failures likely occurred at the beginning of the Hsien-du-shan rock avalanche.Slope deformation was observed by the local residents before the Hsien-du-shan rock avalanche occurred as a geomorphologic precursor. In addition, water accumulation along the sliding surface governs the behavior of the sliding surface. Therefore, in the future, an early warning system of a rock avalanche can be developed by simultaneously applying high-resolution airborne LiDAR to detect slope deformation and using geo-electric measurements to image the infiltration of surface water to the sliding surface.

Loss Curve Analysis of a Debris Flow: A Case Study on the Daniao Tribe

The post-disaster recovery from a debris flow imposes a heavy financial burden on a government; thus, it is necessary for governmental agencies use their limited resources effectively. In this study, we focus on the loss curve assessment, the framework of which includes hazard simulation, exposure evaluation and loss assessment. A numerical program named DEBRIS-2D is used to simulate debris flow hazards of different scale. Then, the latest land usage data and the economic loss model are factored in for exposure and loss assessment. In August 2009, Typhoon Morakot hit Taiwan and horrendous disasters resulted, including large-scale landslides and debris flows. The Daniao tribe in Taitung in eastern Taiwan was hit by one of these debris flows, with a debris-flow volume in excess of 500,000 m3, which was beyond the scope of any recovery plan. We simulate the hazards of the debris flow in different volumes and build the loss curve in relation. Notably, the practice of assessing damage caused by such disasters can help in assessing possible losses before they occur, thus allowing governments to take the necessary precautionary measures.

The necessary and sufficient condition for GM(1, 1) grey prediction model

The grey theory demonstrates the optimal and unique ability of performing fitting predictions using small data sets and limited information to allow fast, concise, accurate, and effective predictions and understand future trends. The GM(1,1) model within the grey theory is used frequently by scholars as a prediction tool. To enhance the accuracy of GM(1,1) prediction, numerous studies have provided satisfactory results on revised grey prediction models. However, because the sufficient and necessary condition of GM(1,1) model that the grey development coefficient should not equal zero is neglected, singular phenomena occur when computers are used to calculate matrix values to obtain the grey development coefficient a. Additionally, if it is neglected that a should not equal zero and the result is substituted into the prediction equation, a meaningless predictive value is obtained. In this paper, we will demonstrate scientific and effective procedures to solve this singular phenomenon of GM(1,1) prediction model with the practical cases and show its application in forecasting the moving path of the typhoon MORAKOT.

Observations of a freshwater pulse induced by Typhoon Morakot off the northern coast of Taiwan in August 2009

Author Posting. © Sears Foundation for Marine Research, 2013. This article is posted here by permission of Sears Foundation for Marine Research for personal use, not for redistribution. The definitive version was published in Journal of Marine Research 71 (2013): 19-46, doi:10.1357/002224013807343452.

Numerical Study of Cold Dome Variability induced by Typhoon Morakot (2009) off Northeastern Taiwan

Numerical Study of Cold Dome Variability induced by Typhoon Morakot (2009) off Northeastern Taiwan

Nutrient supply in the Southern East China Sea after Typhoon Morakot

Author Posting. © Sears Foundation for Marine Research, 2013. This article is posted here by permission of Sears Foundation for Marine Research for personal use, not for redistribution. The definitive version was published in Journal of Marine Research 71 (2013): 133-149, doi:10.1357/002224013807343425.

High-Resolution Modeling of Typhoon Morakot (2009): Vortex Rossby Waves and Their Role in Extreme Precipitation over Taiwan

AbstractA high-resolution nonhydrostatic numerical model, the Advanced Regional Prediction System (ARPS), was used to simulate Typhoon Morakot (2009) as it made landfall over Taiwan, producing record rainfall totals. In particular, the mesoscale structure of the typhoon was investigated, emphasizing its associated deep convection, the development of inner rainbands near the center, and the resultant intense rainfall over western Taiwan.Simulations at 15- and 3-km grid spacing revealed that, following the decay of the initial inner eyewall, a new, much larger eyewall developed as the typhoon made landfall over Taiwan. Relatively large-amplitude wave structures developed in the outer eyewall and are identified as vortex Rossby waves (VRWs), based on the wave characteristics and their similarity to VRWs identified in previous studies.Moderate to strong vertical shear over the typhoon system produced a persistent wavenumber-1 (WN1) asymmetric structure during the landfall period, with upward motion and deep convection in the downshear and downshear-left sides, consistent with earlier studies. This strong asymmetry masks the effects of WN1 VRWs. WN2 and WN3 VRWs apparently are associated with the development of deep convective bands in Morakot’s southwestern quadrant. This occurs as the waves move cyclonically into the downshear side of the cyclone. Although the typhoon track and topographic enhancement contribute most to the record-breaking rainfall totals, the location of the convective bands, and their interaction with the mountainous terrain of Taiwan, also affect the rainfall distribution. Quantitatively, the 3-km ARPS rainfall forecasts are superior to those obtained from coarser-resolution models.

Community Resilience after Disaster in Taiwan: A Case Study of Jialan Village with the Strengths Perspective

This article examines community resilience in disaster recovery in Jialan Village, where many families lost their homes when Typhoon Morakot struck Taiwan in 2008. In-depth interviews were conducted with policymakers, social workers, resource coordinators, and leaders of the local aboriginal community. The main findings were (a) the village's recovery was due to the effective use and coordination of community resources; (b) partnership building between the public and private sectors was crucial in the community's recovery; and (c) the recovery was enhanced by values such as a strong sense of mutual help, good physical health, positive attitudes, and autonomy.

Performance evaluation of radar and satellite rainfalls for Typhoon Morakot over Taiwan: Are remote-sensing products ready for gauge denial scenario of extreme events?

summary This study evaluated rainfall estimates from ground radar network and four satellite algorithms with a relatively dense rain gauge network over Taiwan Island for the 2009 extreme Typhoon Morakot at various spatiotemporal scales (from 0.04 to 0.25 and hourly to event total accumulation). The results show that all the remote-sensing products underestimate the rainfall as compared to the rain gauge measurements, in an order of radar (� 18%), 3B42RT (� 19%), PERSIANN-CCS (28%), 3B42V6 (� 36%), and CMORPH (� 61%). The ground radar estimates are also most correlated with gauge measurements, having a correlation coefficient (CC) of 0.81 (0.82) at 0.04 (0.25) spatial resolution. For satellite products, CMORPH has the best spatial correlation (0.70) but largely underestimates the total rainfall accumulation. Compared to microwave ingested algorithms, the IR-dominant algorithms provide a better estimation of the total rainfall accumulation but poorly resolve the temporal evolution of the warm cloud typhoon, especially for a large overestimation at the early storm stage. This study suggests that the best performance comes from the ground radar estimates that could be used as an alternative in case of the gauge denial. However, the current satellite rainfall products still have limitations in terms of resolution and accuracy, especially for this type of extreme typhoon.

Critical rainfall for typhoon-induced debris flows in the Western Foothills, Taiwan

Typhoon Morakot devastated Taiwan during August 6–11, 2009, with a maximum total rainfall of 2884mm, causing >22,000 cases of slope failures. Rainfall thresholds for debris flow initiation are investigated using the hourly intensity vs. duration (I–D), hourly intensity vs. cumulative rainfall (I–R), and daily rainfall vs. antecedent daily rainfall (ADR) index methods. Among the 39 well-documented cases, 32 sites with known date and time of debris flow initiation were focused. Results reveal that debris flows and debris avalanches occur under a very wide range of rainfall characteristics, with return periods ranging from several years to 200years, indicating that the empirical rainfall threshold alone is insufficient for an effective debris flow prediction system. A consistent pattern of all I–R paths for the investigated sites shows the combined effect of rainfall characteristics and inherent stability features of the slopes, suggesting that the I–R path is potentially useful in facilitating debris flow predictions. It is also suggested that empirical rainfall thresholds should be calibrated using physical models against specific slope conditions to increase the accuracy of debris flow predictions.