Typhoon Rainstorm Research Articles

Analysis of Dual-Polarimetric Radar Variables and Quantitative Precipitation Estimators for Landfall Typhoons and Squall Lines Based on Disdrometer Data in Southern China

Typhoon rainstorms often cause disasters in southern China. Quantitative precipitation estimation (QPE) with the use of polarimetric radar can improve the accuracy of precipitation estimation and enhance typhoon defense ability. On the basis of the observed drop size distribution (DSD) of raindrops, a comparison is conducted among the DSD parameters and the polarimetric radar observation retrieved from DSD in five typhoon and three squall line events that occurred in southern China from 2016 to 2017. A new piecewise fitting method (PFM) is used to develop the QPE estimators for landfall typhoons and squall lines. The performance of QPE is evaluated by two fitting methods for two precipitation types using DSD data collected. Findings indicate that the number concentration of raindrops in typhoon precipitation is large and the average diameter is small, while the raindrops in squall line rain have opposite characteristics. The differential reflectivity (ZDR) and specific differential phase (KDP) in these two precipitation types increase slowly with the reflectivity factor (ZH), whereas the two precipitation types have different ZDR and KDP in the same ZH. Thus, it is critical to fit the rainfall estimator for different precipitation types. Enhanced estimation can be obtained using the estimators for specific precipitation types, whether the estimators are derived from the conventional fitting method (CFM) or PFM, and the estimators fitted using the PFM can produce better results. The estimators for the developed polarimetric radar can be used in operational QPE and quantitative precipitation foresting, and they can improve disaster defense against typhoons and heavy rains.

Typhoon triggered operation tunnel debris flow disaster in coastal areas of SE China

Typhoons have inflicted significant damage and loss of life to China, a large number of typhoon–rainstorm–debris flow–tunnel accidents occur in the southeastern coastal areas each year. Considering the disaster prevention and mitigation decision-making of disaster accidents in coastal areas and the reduction of regional economic losses, this Express Letter presents some typical accident scenes and rescue measures in recent years and analyses the hazard mechanism from three aspects. On this basis, we propose some suggestions such as the monitoring and early-warning system, which can provide a few references for reducing disaster losses and improving disaster treatments.

A Case Study of a Regional Torrential Rain Caused by Typhoon in North China

By using the NCEP/GFS analysis data, CIMISS data, JMA and China’s Typhoon Networks, heavy rainstorm occurred in east of North China associated with Typhoon Damrey from August 3rd to 4th, 2012 was analyzed. Results show during Damrey was going nearby Tianjin City and Hebei province of China, heavy rainstorm was observed in the cities of Qinhuangdao and Tangshan. The southerly jet stream from the southern side of the subtropical high and the periphery of Typhoon Saola is the conveyor belt for water vapor and energy, which enables Damrey to maintain for a long time and provide water vapor and heat conditions for rainfall in east of North China. The structure of Damrey caused a strong updraft in east of North China with a K-index greater than 35°C, which provided a favorable condition for the heavy rainstorm. The typhoon rainstorms in North China are the result of the interaction of the westerly, subtropical and tropical systems. In this heavy rain period, there was an obvious interaction between subtropical and tropical systems. This study has investigated the interaction between the northwestern Pacific typhoon and the North China heavy rainstorm, including the circulation characteristics of the typhoon and North China before and after the regional heavy rainstorm. Additionally, the climate background provides a reliable basis for the heavy rain forecast.

Investigation and monitoring on a rainfall-induced deep-seated landslide

The ground movement of Xiashan village landside of Zhejiang province, China, commenced in 1958 due to typhoon rainstorms followed by two subsequent slips in 1989 and 2001. The reactivation of the large-scale landslide has become a serious concern to the safety of a nearby reservoir and the local villagers. A pilot testing program was established in 2007 using a variety of landslide monitoring facilities. The slope is of a chair-shaped form with Quaternary residual soil overlying the Pliocene sedimentary and basalt layers. The pilot test program included GPS, inclinometers of conventional and fixed types, piezometer, and rain gauge. Two potential sliding planes were identified in the inclinometers showing the possible slip mode along more than one bedding plane. A shallow slip surface dipping a low angle (10°) lies in the residual soil, while a deep slip surface is located along the weak plane within the Pliocene strata. The piezometer reading indicated high groundwater level and a certain level of correlation with the displacement velocity. A critical groundwater depth was determined, and its usage as a warning threshold was discussed. In view of the very important location about an existing dam, it is strongly recommended that surface and internal drainage facilities be provided to ensure the long-term stability of the landslide.

An objective prediction model for typhoon rainstorm using particle swarm optimization: neural network ensemble

A nonlinear ensemble prediction model for typhoon rainstorm has been developed based on particle swarm optimization-neural network (PSO-NN). In this model, PSO algorithm is employed for optimizing the network structure and initial weight of the NN with creating multiple ensemble members. The model input of the ensemble member is the high correlated grid point factors selected from the rainfall forecast field of Japan Meteorological Agency numerical prediction products using the stepwise regression method, and the model output is the future 24 h rainfall forecast of the 89 stations. Results show that the objective prediction model is more accurate than the numerical prediction model which is directly interpolated into the stations, so it can better been implemented for the interpretation and application of numerical prediction products, indicating a potentially better operational weather prediction.

Medium-scale natural disaster risk scenario analysis: a case study of Pingyang County, Wenzhou, China

A series of empirical studies involving typhoon rainstorm and flood risk scenario analysis were carried out on a medium spatial scale, covering Pingyang County. Considering a rainstorm/water-logging conversion process, active flooding submergence and per unit area values (million yuan/km2), two typical risk scenarios (50- and 100-year frequency) were simulated and analyzed. The study revealed that high-risk areas distributed across the towns of Aojiang, Qiancang and Xiaojiang, with a maximum submerged depth of 4.61 m for a 100-year flood hazard. In the case of a disaster loss rate >65 %, the potential maximum loss could be more than 10 million yuan/km2. For medium-scale disaster risk, more attention must be paid to catastrophic events, which have a low probability of occurrence but would induce great losses. An amended risk formula could determine the degree of priority for responses to hazards of equal risk value better. In Pingyang County, the 50-year flood risk for Kunyang, Aojiang, Qiancang and Xiaojiang is greater than that of 100-year events for the next 50 years. However, these areas should give priority to their responses to 100-year disaster events during the next 100 years. In addition, the attention of disaster risk should vary in different spatial regions.

Large-scale natural disaster risk scenario analysis: a case study of Wenzhou City, China

Based on the analysis and calculation of the hazard intensity of typhoon rainstorms and floods as well as the vulnerability of flood receptors and the possibility of great losses, risk scenarios are proposed and presented in Wenzhou City, Zhejiang Province, China, using the Pearson-III model and ArcGIS spatial analyst tools. Results indicate that the elements of risk scenarios include time–space scenarios, disaster scenarios, and man-made scenarios. Ten-year and 100-year typhoon rainstorms and flood hazard areas are mainly concentrated in the coastal areas of Wenzhou City. The average rainfall across a 100-year frequency is 450 mm. The extreme water depth of a 100-year flood is 600 mm. High-vulnerability areas are located in Yueqing, Pingyang, Cangnan, and Wencheng counties. The average loss rate of a 100-year flood is more than 50%. The greatest possible loss of floods shows an obvious concentration-diffusion situation. There is an area of about 20–25% flood loss of 6–24 million Yuan RMB/km2 in the Lucheng, Longwan and Ouhai districts. The average loss of a 100-year flood is 12 million Yuan RMB/km2, and extreme loss reaches 49.33 million Yuan RMB/km2. The classification of risk scenario may be used for the choice of risk response priorities. For the next 50 years, the 10-year typhoon rainstorm-flood disaster is the biggest risk scenario faced by most regions of Wenzhou City. For the Yueqing, Ruian, and Ouhai districts, it is best to cope with a 100-year disaster risk scenario and the accompanying losses.

Design Hyetograph for Typhoon Rainstorms in Taiwan

The design flood can be determined by transposing the design storm observed in the region surrounding the project and converting the storm to flow by use of a simple rainfall-runoff relation or a watershed runoff model. In this study, a design hyetograph in a double-triangular shape of 48 h duration was derived from rainfall intensity-duration-frequency curve to represent the time distribution of severe typhoon rainstorms. The design floods generated by performing a rainfall-runoff model using design hyetographs as inputs were verified using the flow records from 17 watersheds in Taiwan. The result indicated that the generated design discharge using the proposed hyetograph for specified return periods were close to the discharge obtained from frequency analysis using flow records. The proposed design hyetograph can be applied to areas that are usually threatened by typhoon rainstorms.

Hydrometeorological and landuse attributes of debris flows and debris floods during typhoon Toraji, July 29–30, 2001 in central Taiwan

The 921 Chi-Chi earthquake, a 7.5 M earthquake with center located near Chi-Chi of Nan Tou County occurred on September 21, 1999 and caused more than 2400 fatalities and totaling billions of dollars losses due to destruction and damages to private and public buildings, roads, bridges and hydraulic structures in central Taiwan. This 921 Chi-Chi earthquake also triggered close to 26,000 landslides with a total area of 15,977 ha and severely disturbed mountain slopes, thus setting the conditions for occurrence of more landslides and other related disasters. Post-earthquake watershed restoration works progressed without disruptions by major typhoon rainstorms until July 29–30, 2001 when typhoon Toraji hit eastern and central Taiwan with heavy rainfall having peak hourly intensity exceeding 70 mm/h. This rainstorm caused several major debris flows and debris floods that destroyed or severely damaged dams, roads, bridges, dikes and houses, in addition to causing 103 casualties, 111 missing (presumed dead), 189 injured. This study (1) explores the characteristics and impacts of debris flows/floods and (2) investigates hydrometeorological and land use attributes of debris flows and debris floods associated with this typhoon Toraji in central Taiwan. Debris floods, different from more familiar debris flows, are extreme peak streamflows containing large quantities of muds, rocks and debris normally occurring in third and fourth order watersheds. Data analysis and field investigations revealed that the disastrous debris flows and debris floods during typhoon Toraji were essentially caused by very heavy rainfalls on inherently unstable mountain slopes that were loosened further earlier by the 921 Chi-Chi earthquake. The extremely intense rainfall of typhoon Toraji provided not only additional materials by creating new and reactivating or enlarging old landslides but also high peak stream flows required for occurrence of debris flows and debris floods. The destruction and damaging power of debris flows and debris floods witnessed during typhoon Toraji suggests that the effectiveness of engineering structures for disaster prevention is limited. For disaster mitigation, it is required to have more comprehensive strategies such as (1) land use zoning that regulates and restricts human encroachment on hazardous areas and (2) implementation of evacuation drills and relocation plan for people currently living in the hazardous zones.