scholarly journals Climatological Characteristics and Observed Trends of Tropical Cyclone–Induced Rainfall and Their Influences on Long-Term Rainfall Variations in Hong Kong

2015 ◽  
Vol 143 (6) ◽  
pp. 2192-2206 ◽  
Author(s):  
Richard C. Y. Li ◽  
Wen Zhou ◽  
Tsz Cheung Lee
Keyword(s):  
Hong Kong ◽  
Tropical Cyclone ◽  
Rainfall Variability ◽  
Daily Rainfall ◽  
Extreme Value Analysis ◽  
Total Rainfall ◽  
Value Analysis ◽  
Rainfall Frequency ◽  
Rainfall Variations

Abstract This study examines the climatological features of tropical cyclone (TC) rainfall in Hong Kong in association with different TC-related parameters, and investigates the changes in TC rainfall, non-TC rainfall, and total rainfall during the past few decades in Hong Kong. On average, rainfall induced by TCs can account for about 25% of the total precipitation during summer and fall, and the contribution can be even greater in extreme cases. Composite analysis suggests that extreme TC rainfall is often related to TCs in closer proximity to Hong Kong, with higher intensity, and is associated with stronger convection and moisture convergence in the vicinity of Hong Kong. Evaluations of the observed trends of different rainfall indices suggest that the rainfall variability in Hong Kong is considerably affected by the TC rainfall, which has a decreasing trend in frequency and intensity in recent decades. Taking out the TC rainfall from the total rainfall reveals that there is an increasing trend in daily rainfall frequency and intensity for non-TC rainfall in Hong Kong. Moreover, time-dependent generalized extreme value analysis of non-TC rainfall also reveals an increase in the return values of the maximum daily rainfall in Hong Kong. Results of this study suggest that, in order to obtain a more comprehensive picture of the long-term rainfall variations in Hong Kong, the contributions of TC rainfall should definitely be taken into account in the analysis.

scholarly journals WIND WAVE FREQUENCIES IN A TROPICAL CYCLONE REGION

1978 ◽  
Vol 1 (16) ◽  
pp. 3
Author(s):  
Rodney J. Sobay
Keyword(s):  
Tropical Cyclone ◽  
Continental Shelf ◽  
Wind Wave ◽  
Wave Climate ◽  
Extreme Value Analysis ◽  
Local Wind ◽  
Value Analysis ◽  
Coral Sea ◽  
Wave Conditions

Australia's Coral Sea coast from Bundaberg north to Cape York has a wind wave climate that is almost unique. The coastline is afforded unparalleled protection from the 1900 km Great Barrier Reef, yet it lies in a tropical cyclone region and must expect recurrent intense wind and wave conditions. The Great Barrier Reef is a continuous chain of quite separate coral reef clusters located near the edge of the continental shelf. The separate reefs are often exposed at low tide, the inner fringe of the clusters ranges from 10 km offshore north of Cairns to 200 km offshore south of Rockhampton and the outer fringe is typically some 50 km further offshore, beyond which the ocean bed drops rapidly away. Incident wave energy from the Coral Sea is invariably dissipated on the outer edge of the Reef and wave conditions on the continental shelf can reasonably be considered due to local wind conditions. The Reef imposes an effective fetch limitations on wave generation over the continental shelf and there is, as a consequence, a moderately rapid response of wave conditions to changes in local wind conditions. A pronounced diurnal variation in the wind climate is reflected also in the wave climate and the stability of the region's tropical climate leads to frequent calm to slight sea conditions. This stability however is occasionally exploded by the generation and passage of a tropical cyclone in mid to late summer. Large waves can be generated by the intense winds of the tropical cyclone (hurricane or typhoon), often an order of magnitude greater than those in response to non-cyclonic events. The rational design of coastal structures and the rational pursuit of coastal zone management requires appropriate estimates of the frequency of occurrence of waves of various heights. Ideally such information is obtained from an extreme value analysis of long term wave records at the particular site in question. Permanent wave recording programs unfortunately have only become common practice in the present decade and wave records, if they exist at all for a particular site, are rarely long enough to allow a satisfactory extreme value analysis. It is clear, in the Australian context at least, that historical wave data alone is not yet sufficient to derive satisfactory estimates of long term wave frequencies. The alternative is system modelling. Wind is a major meteorological variable and its long term recording has been a standard meteorological practice now for over half a century.

scholarly journals Long-Term and Seasonal Trends in Global Wave Height Extremes Derived from ERA-5 Reanalysis Data

2020 ◽  
Vol 8 (12) ◽  
pp. 1015
Author(s):  
Alicia Takbash ◽  
Ian R. Young
Keyword(s):  
Southern Hemisphere ◽  
Wave Height ◽  
Significant Wave Height ◽  
Reanalysis Data ◽  
Extreme Value Analysis ◽  
Winter Storms ◽  
Value Analysis ◽  
Weather Forecasts ◽  
Significant Wave

A non-stationary extreme value analysis of 41 years (1979–2019) of global ERA5 (European Centre for Medium-Range Weather Forecasts Reanalysis) significant wave height data is undertaken to investigate trends in the values of 100-year significant wave height, Hs100. The analysis shows that there has been a statistically significant increase in the value of Hs100 over large regions of the Southern Hemisphere. There have also been smaller decreases in Hs100 in the Northern Hemisphere, although the related trends are generally not statistically significant. The increases in the Southern Hemisphere are a result of an increase in either the frequency or intensity of winter storms, particularly in the Southern Ocean.

Comparison of the Long-Term Trends of the Largest Waves in the Ice-Free Arctic Waters From Different Reanalysis Products

2018 ◽  
Author(s):  
Takuji Waseda ◽  
Takehiko Nose ◽  
Adrean Webb
Keyword(s):  
Arctic Ocean ◽  
The Arctic ◽  
Extreme Value Analysis ◽  
Positive Trend ◽  
Value Analysis ◽  
The Arctic Ocean ◽  
Ship Route ◽  
Long Term Trends ◽  
Horizontal Grid

The long-term trends of the expected largest waves in the ice-free Arctic waters from Laptev to Beaufort Seas was studied analyzing the ERA-interim reanalysis from 1979 to 2016. The analysis showed that the positive trend is largest in October and increased almost 70 cm in 38 years. For ships navigating the Northern Ship Route, it is important to know what the possible largest waves to expect during its cruise. In view of conducting the extreme value analysis, the uncertainty of the largest wave needs to be validated. However, the observation in the Arctic Ocean is limited. We, therefore, rely on the reanalysis wave products in the Arctic Ocean, whose uncertainty is yet to be determined. ERA-Interim and ERA-5 are compared in the Laptev, the East Siberian, Chukchi and Beaufort Seas. The comparison is relevant as the two products differ in its horizontal grid resolution and availability of the satellite altimeter significant wave height data assimilation. During 2010–2016 when the ERA5 is available, only a small difference from ERA-Interim was detected in the mean. However, the expected largest waves in the domain tended to be large for the ERA-5, 8% normalized bias. The tendency was quite similar with a high correlation of 0.98.

scholarly journals Smoothing of 70-Year Daily Rainfall Data Based on Moving Average and Weighted average Technique

2019 ◽  
Vol 8 (6) ◽  
pp. 1407-1410
Keyword(s):  
Moving Average ◽  
Daily Rainfall ◽  
Rainfall Data ◽  
Extreme Value Analysis ◽  
Cyclic Pattern ◽  
Simple Method ◽  
Value Analysis ◽  
Rainfall Analysis ◽  
Daily Rainfall Data ◽  
South West Monsoon

An extreme value analysis of rainfall for Thanjavur town in Tamil Nadu was carried out using 70 years of daily rainfall data. Moving average method is a simple method to understand rainfall trend of the selected station. The analysis has been carried out for monthly, seasonal and annual rainfalls. No other graphical methods such as Ordinate graph, Bar diagram, Chronological chart will describe about the trend or cyclic pattern. By smoothening out the extreme variations and indicating the trend or cyclic pattern is known as moving average curve. Through this moving average curve, it is possible to understand the trend which can be used in the future years. From the results of annual wise rainfall analysis, based on 3-year, 5-year, 10-year moving average, it is found that there is no persistent regular cycle is visible and where as in 30-year, 40-year, 50-year moving average a horizontal linear trend has been observed. In Winter season, Summer season, North-East monsoon, South- West monsoon wise rainfall analysis, for 3-year, 5-year, 10-year moving average denote no apparent trend or cyclicity where as in 30-year, 40-year, 50- year moving average a horizontal linear cycle has been noticed. It is clear from the study that there is no large variation of rainfall that had been occurred in the Thanjavur city based on selected years of analysis.

Tropical Cyclone– and Monsoon-Induced Rainfall Variability in Taiwan

2010 ◽  
Vol 23 (15) ◽  
pp. 4107-4120 ◽  
Author(s):  
Jau-Ming Chen ◽  
Tim Li ◽  
Ching-Feng Shih
Keyword(s):  
Tropical Cyclone ◽  
South China Sea ◽  
South China ◽  
Rainfall Variability ◽  
The South China Sea ◽  
Upward Motion ◽  
The South ◽  
Total Rainfall ◽  
China Sea ◽  
Anomalous Cyclone

Abstract This study investigates the interannual variability of tropical cyclone (TC)- and monsoon-induced rainfall (P) in Taiwan during July–September for the period 1950–2002. To examine the relative effects of TCs and monsoons, local rainfall in Taiwan is separated into two subcomponents: TC rainfall (PTC) and seasonal monsoon rainfall (PSM). The former is induced by TC passage across Taiwan, while the later is caused by large-scale monsoon circulation. Climatologically, PTC and PSM accounts for 47.5% and 52.5% of total rainfall in Taiwan, respectively, showing a comparable contribution. On an interannual time scale, PTC and PSM anomalies tend to vary inversely. Two dominant rainfall variability types are found in Taiwan: enhanced PTC but suppressed PSM (T+S−) and suppressed PTC but enhanced PSM (T−S+). The T+S− type features a low-level anomalous cyclone and enhanced upward motion southeast of Taiwan. This favorable environmental condition leads to more TC formation in the region. TCs are further steered by mean southeasterly flows toward Taiwan to increase PTC (T+). As Taiwan is located in the western boundary of the anomalous cyclone, anomalous northeasterly water vapor fluxes hinder moisture supplies from the South China Sea into Taiwan, resulting in decreased PSM (S−). The T−S+ type concurs with an anomalous cyclone over Taiwan. Its center enhances upward motion and moisture fluxes from the South China Sea into Taiwan, yielding increased PSM (S+). Meanwhile, weak relative vorticity anomalies occur to the southeast of Taiwan, suppressing TC formation in the region. Mean southerly steering flows tend to drive more TCs toward Japan and the North Pacific, resulting in decreased TC frequency and PTC in Taiwan (T−). The present approach provides a new perspective for studying and predicting interannual rainfall variability via the separation of rainfall into TC- and monsoon-induced rainfall subcomponents, rather than looking solely at total rainfall. The result shows that there are two ways to significantly increase total rainfall in Taiwan (T+S− and T−S+), but there is only one way to decrease it (T−S−). The composites of circulation anomalies based on two rainfall indexes have more significant and coherent dynamic patterns than those sorted based on the total rainfall index.

Squall Detection and Analysis From Historical Satellite Data

2019 ◽  
Author(s):  
L. Renac ◽  
D. P. Hurdle ◽  
F. J. M. Enet ◽  
J. De Vroom
Keyword(s):  
Satellite Data ◽  
Measurement Data ◽  
Extreme Value Analysis ◽  
Intermediate Water ◽  
Design Data ◽  
Value Analysis ◽  
Design Values ◽  
The Impact ◽  
Long Term Measurement

Abstract Thunderstorms and squalls (fronts of contiguous thunderstorms) are associated with short but intense local winds that have a great impact on operability or design conditions for moored ship operations in the coastal zone. The brevity and local scale of such events makes them difficult to capture using standard measurement data and usually requires dedicated long-term measurement campaigns. Because the standard measurements available are usually based on 10-minute averages taken once an hour, such data is often not available. In the absence of conventional measured data, the use of satellite data can provide useful design data if analyzed and applied with caution. We present two case studies (West Africa and Brazil) where squalls have been identified in satellite data and used for extreme value analysis (EVA) to support the design of intermediate water depth mooring systems. The detection of squalls is confirmed with satellite imagery and the handling of this data for the EVA is presented in detail with assumptions made and the sensitivity of the results to these assumptions. The impact on design values is also discussed for both geographic locations.

scholarly journals Interdecadal Changes in Summertime Tropical Cyclone Precipitation over Southeast China during 1960–2009

2015 ◽  
Vol 28 (4) ◽  
pp. 1494-1509 ◽  
Author(s):  
Richard C. Y. Li ◽  
Wen Zhou
Keyword(s):  
Tropical Cyclone ◽  
Rainfall Intensity ◽  
Principal Component ◽  
Dominant Mode ◽  
Intensity Change ◽  
Boreal Summer ◽  
Total Rainfall ◽  
Southeast China ◽  
Rainfall Frequency ◽  
Rainfall Anomalies

Abstract This study examines the changes in tropical cyclone (TC) precipitation and the associated contributing factors over southeast China during 1960–2009. Climatologically, TC rainfall accounts for approximately 20%–40% of the total rainfall over southeast China during boreal summer, and the contribution can even reach 50% for some of the coastal provinces, such as Guangdong, Fujian, Zhejiang, and Hainan. The dominant mode of TC rainfall reveals a dipole pattern over southern southeast China (SSC) and eastern southeast China (ESC), and the associated principal component time series exhibits remarkable interdecadal variations, with two potential change points being identified in the late 1970s and early 1990s. These interdecadal shifts in TC rainfall are also found to be synchronous with two regime shifts in total rainfall, and they can account for more than 40% of the total rainfall anomalies over the coastal regions of southeast China. To discover the dominant factors responsible for the interdecadal variations, the overall TC rainfall anomalies are broken down into three different components (rainfall frequency, rainfall intensity, and nonlinear terms) based on a new empirical statistical approach. It is found that the interdecadal variation in TC precipitation over SSC is controlled predominantly by changes in TC rainfall intensity as well as TC rainfall frequency, while that over ESC depends mainly on the intensity and the nonlinear terms. Further examination of the TC passage frequency (TPF) suggests that the significant reduction in TPF and TC rainfall frequency over SSC during 1979–92 is associated mainly with suppressed TC genesis (negative genesis effect), while the increase in TPF and TC rainfall frequency during 1993–2009 can be attributed primarily to the enhanced passage probability (positive track effect) over SSC. Meanwhile, variations in TC rainfall intensity seem to be unrelated to the TC’s own intensity change.

A Comparison of Methods for Assessing the Lifetime Reliability of a Moored FPSO

2004 ◽  
Author(s):  
Andrew J. Grime ◽  
R. S. Langley
Keyword(s):  
Reliability Analysis ◽  
Offshore Structures ◽  
Extreme Value Analysis ◽  
Design Codes ◽  
Short Term ◽  
Safety Level ◽  
Value Analysis ◽  
Design Storm ◽  
Current Design

Current design codes for floating offshore structures are based on measures of short-term reliability. That is, a design storm is selected via an extreme value analysis of the environmental conditions and the reliability of the vessel in that design storm is computed. Although this approach yields valuable information on the vessel motions, it does not produce a statistically rigorous assessment of the lifetime probability of failure. An alternative approach is to perform a long-term reliability analysis in which consideration is taken of all sea states potentially encountered by the vessel during the design life. Although permitted as a design approach in current design codes, the associated computational expense generally prevents its use in practice. A new efficient approach to long-term reliability analysis is presented here, the results of which are compared with a traditional short-term analysis for the surge motion of a representative moored FPSO in head seas. This serves to illustrate the failure probabilities actually embedded within current design code methods, and the way in which design methods might be adapted to achieve a specified target safety level.

Predictive groundwater flood hazard mapping in lowland karst

2020 ◽  
Author(s):  
Owen Naughton ◽  
Ted McCormack ◽  
Joan Campanya
Keyword(s):  
Flood Hazard ◽  
Flood Frequency ◽  
Flood Frequency Analysis ◽  
Extreme Value Analysis ◽  
Hazard Mapping ◽  
Stochastic Weather Generator ◽  
Value Analysis ◽  
Extreme Flood ◽  
Flood Maps

<p>The management of karst geohazards requires new and novel strategies to address the complexities inherent in karst systems and the challenges posed by a changing climate. The often rapid and widespread interaction between surface and subsurface hydrology can leave karst terrains uniquely susceptible to flooding from groundwater sources. Quantifying the frequency and magnitude of such flooding is a key step in the management of flood risk. Here, we present a novel interdisciplinary approach developed for predictive groundwater flood hazard mapping in the lowland karst plains of Ireland. This approach ties together direct and earth observation-derived hydrograph data, hydrological modelling, stochastic weather generation and extreme value analysis to generate predictive groundwater flood maps for qualifying sites.</p><p>The first step in the approach was the collection of hydrological data for sites susceptible to groundwater flooding. A monitoring network of 50 sites was established in late 2016 to provide baseline data over a 30-month period. Additionally, a methodology for delineating historic flood extents and water elevations from multi-temporal Copernicus Sentinel-1 Synthetic Aperture Radar (SAR) imagery was developed. This allowed hydrograph generation for ungauged sites, whilst also allowing observations of the 2015/2016 extreme flood event at gauged sites which predated monitoring. Next, site-specific hydrological models capable of constructing flood hydrographs from antecedent rainfall and soil moisture conditions were calibrated for 393 sites using a combination of observed and SAR hydrographic data (mean NSE: 0.81). A stochastic weather generator calibrated on 70-year meteorological records was used to generate long-term synthetic rainfall data for each site. These stochastic series, together with long-term average evapotranspiration, were used as input to the site models to produce long-term hydrological series from which annual maxima series were derived. Thereafter, flood frequency analysis was used to estimate predictive flood levels and generate predictive flood maps. This novel applied approach has significantly improved our fundamental scientific understanding of groundwater flooding as a geohazard, whilst also informing regional planning and development to limiting future flood vulnerability.</p>

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