Collating Historic Weather Observations for the East Asian Region： Challenges, Solutions, and Reanalyses

1. IntroductionHistoric instrumental weather observations, made on land or at sea from as early as the 17th century （e.g.,Camuffo et al.,2010）,are integral to extending our understanding of the decadal and centennial variations of Earth＇s climate and for comparison with paleo-proxy data.

Third assessment on impacts of climate change on tropical cyclones in the Typhoon Committee Region——Part Ⅰ:Observed changes, detection and attribution

Published findings on climate change impacts on tropical cyclones(TCs)in the ESCAP/WMO Typhoon Committee Region are assessed.We focus on observed TC changes in the western North Pacific(WNP)basin,including frequency,intensity,precipitation,track pattern,and storm surge.Results from an updated survey of impacts of past TC activity on various Members of the Typhoon Committee are also reported.Existing TC datasets continue to show substantial interdecadal variations in basin-wide TC frequency and intensity in the WNP.There has been encouraging progress in improving the consensus between different datasets concerning intensity trends.A statistically significant northwestward shift in WNP TC tracks since the 1980s has been documented.There is low-to-medium confidence in a detectable poleward shift since the 1940s in the average latitude where TCs reach their peak intensity in the WNP.A worsening of storm inundation levels is believed to be occurring due to sea level rise-due in part to anthropogenic influence-assuming all other factors equal.However,we are not aware that any TC climate change signal has been convincingly detected in WNP sea level extremes data.We also consider detection and attribution of observed changes based on an alternative Type II error avoidance perspective.

THE LONG TERM VARIATIONS OF TROPICAL CYCLONE ACTIVITY IN THE SOUTH CHINA SEA AND THE VICINITY OF HONG KONG

This study examines the long-term variations of tropical cyclone(TC) frequency and intensity in the South China Sea(SCS) and the vicinity of Hong Kong from 1961 to 2010 based on the best track data of four main weather agencies in the western North Pacific, namely the Hong Kong Observatory, China Meteorological Administration, Regional Specialized Meteorological Center Tokyo and Joint Typhoon Warning Center of the United States. To account for the discrepancy in the best track data between agencies, the maximum sustained wind speeds are standardized to the 10-minute average before data analysis. Moreover, a sensitivity assessment based on three different data scenarios is also conducted to study the uncertainty in trend analysis due to the discrepancy in the datasets from various agencies. The results show that, likely modulated by the El Ni?o Southern Oscillation and the Pacific Decadal Oscillation, there exist strong inter-annual and inter-decadal variations in the TC frequency in the SCS and the vicinity of Hong Kong.For the long-term trend, all dataset/scenario combinations depict a decrease in the TC frequency in the SCS and the vicinity of Hong Kong during the study period, but the trend is not statistically significant at 5% level for most of the datasets. As for the TC intensity, the discrepancy between weather agencies remains very substantial even when the difference in the wind speed averaging period is accounted for. The large differences in the available datasets do not allow for a reliable detection of the long-term trend of the TC intensity in the SCS. The study of the TC impacts on Hong Kong reveals that there is no significant trend on the TC-induced extreme rainfall in Hong Kong. The extreme high winds associated with TCs within 500 km range of Hong Kong have no significant trend at Waglan Island(offshore island) while those of the urban station at Kai Tak have a signifi-cant decreasing trend.

Third assessment on impacts of climate change on tropical cyclones in the Typhoon Committee Region-Part Ⅱ:Future projections

This paper assesses published findings on projections of future tropical cyclone(TC)activity in the ESCAP/WMO Typhoon Committee Region under climate change scenarios.This assessment also estimates the projected changes of key TC metrics for a 2℃anthropogenic global warming scenario for the western North Pacific(WNP)following the approach of a WMO Task Team,together with other reported findings for this region.For projections of TC genesis/frequency,most models suggest a reduction of TC frequency,but an increase in the proportion of very intense TCs over the WNP in the future.However,some individual studies project an increase in WNP TC frequency.Most studies agree on a projected increase of WNP TC intensity over the 21 st century.All available projections for TC related precipitation in the WNP indicate an increase in TC related precipitation rate in a warmer climate.Anthropogenic warming may also lead to changes in TC prevailing tracks.A further increase in storm surge risk may result from increases in TC intensity.The most confident aspect of forced anthropogenic change in TC inundation risk derives from the highly confident expectation of further sea level rise,which we expect will exacerbate storm inundation risk in coastal regions,assuming all other factors equal.

A REVIEW ON THE LONG TERM VARIATIONS OF TROPICAL CYCLONE ACTIVITY IN THE TYPHOON COMMITTEE REGION

A review on the long term variations of tropical cyclone(TC) activity in the Typhoon Committee region was conducted based on the assessments of IPCC, IWTC and ESCAP/WMO Typhoon Committee and a number of recent publications. The results reveal strong inter-annual and inter-decadal variations in the TC activity over the western North Pacific(WNP). Analysis of available TC data since 1950 s indicates that most of the TC datasets depict a decreasing trend, and some statistically significant, in the annual number of TCs and typhoons in the WNP. For TC intensity, differences in TC databases for the WNP do not allow a convincing detection of a long term trend in this basin. Climate model projections suggest a noticeable decrease in the frequency of the WNP TCs in the 21 st century. Some of the model simulations also report an increase in the number of intense TCs and the TC potential intensity in the WNP in a warmer climate. Looking forward, data homogeneity in TC databases and uncertainties in model simulation are two main hurdles hindering the determination of the past and future trends of TC activity in this basin. Inter-agency co-operations are urgently required to improve the homogeneity and consistency of TC databases in the WNP. Continuous research would also be needed to further our understanding of the influence of natural variability and anthropogenic warming on the TC activity in the WNP.

Assessment of the damages and direct economic loss in Hong Kong due to Super Typhoon Mangkhut in 2018

Super Typhoon Mangkhut hit Hong Kong on September 16,2018,necessitating the issuance of the highest tropical cyclone warning signal,No.10 Hurricane Signal.Packing ferocious winds and record-breaking storm surge,Mangkhut brought the most serious and widespread destruction to the territory in the recent three decades.A series of post event information search,field visits and damage surveys has been conducted by the Hong Kong Observatory(HKO)and the findings on the damages and impacts caused by Mangkhut in different parts of the territory are documented in this paper.Moreover,by analyzing the economic loss data reported by various government departments,public utilities and organizations in Hong Kong and the statistics on insurance claims from the Hong Kong Federation of Insurers(HKFI),the estimated direct economic loss due to Mangkhut in Hong Kong is about HK$4.60 billion,which is about 3.8 times to that of Super Typhoon Hato in 2017.On the contrary,in the Guangdong-Hong Kong-Macao Greater Bay Area,the estimated direct economic loss due to Hato is significantly higher than that of Mangkhut.This could be attributed to the early and effective warnings for Mangkhut,increased public awareness and typhoon preparedness for Mangkhut in 2018 since the fierce attack of Hato in 2017,and infrastructure enhancement of the major impact areas.

IMPACTS OF CLIMATE CHANGE ON TROPICAL CYCLONES IN THE WESTERN NORTH PACIFIC BASIN. PART Ⅱ: LATE TWENTY-FIRST CENTURY PROJECTIONS

This paper reviews the latest studies on the relationship between projected late 21 st century climate changes and tropical cyclone(TC) activity in the western North Pacific(WNP) basin, which is the region of the United Nations Economic and Social Commission for Asia and the Pacific(ESCAP)/World Meteorological Organization(WMO) Typhoon Committee members. Existing studies of projected changes of TC activity in this basin, such as frequency, intensity, precipitation, genesis location and track pattern are summarized, based on an assumed A1 B future climate change scenario. A review of available studies on projected future changes in WNP landfalling TC activity is also included.While it remains uncertain whether there has been any detectable human influence on tropical cyclone frequency, intensity, precipitation, track, or related aggregated storm activity metrics in the basin, modeling studies suggest changes in future tropical cyclone activity for the WNP basin. More models project decreases than increases in tropical storm frequency(range-70% to +60%);most studies project an increase in the TC intensity(range-3% to +18%);and all six available studies that include the WNP basin project increases in TC precipitation rates(range +5 to +30%).

IMPACTS OF CLIMATE CHANGE ON TROPICAL CYCLONES IN THE WESTERN NORTH PACIFIC BASIN. PART Ⅰ: PAST OBSERVATIONS

This paper reviews the current state of the science on the relationship between climate change and historical tropical cyclone(TC) activity in the western North Pacific(WNP) basin, which is the region of the ESCAP/WMO Typhoon Committee members. Existing studies of observed changes of TC activity in this basin, such as frequency, intensity, precipitation, genesis location and track pattern are summarized. Results from a survey on impacts of past TC activity on various members of Typhoon Committee are reported, along with a review of studies of past WNP landfalling TCs.With considerable interannual and interdecadal variations in the TC activity in this basin, it remains uncertain whether there has been any detectable human influence on tropical cyclone frequency, intensity, precipitation, track, or related aggregated storm activity metrics. Also, the issues of homogeneity and consistency of best track data sets in the WNP further add uncertainty to relevant research studies. Observations indicate some regional shifts in TC activity in the basin, such as a decreasing trend in TC occurrence in part of the South China Sea and an increasing trend along the east coast of China during the past 40 years. This change is apparently related to local circulation changes in the eastern Asia and WNP, though the cause of the circulation changes remains unknown.

TRAINING AND RESEARCH UNDER THE TYPHOON COMMITTEE

The ESCAP/WMO Typhoon Committee Training and Research Coordination Group(TRCG),formerly known as the Typhoon Research Coordination Group,has served Members of the Typhoon Committee for more than 20 years.As evident from the change of its name,TRCG has since extended its scope of activities from research to training with a view to bridging the technological gap and enhancing forecasting capability among Members as the development of technology continues to gather pace in recent decades.While the Typhoon Committee right from its early days has been visionary in establishing the three components of meteorology,hydrology and disaster risk reduction(DRR)within its organizational structure,the need for closer collaboration and synergy among the three components has become even apparent and critical as we enter the age of Big Data and face up to the multi-faceted impacts and environmental issues brought about by climate change.As such,TRCG in recent years has also taken on the responsibility of promoting cross-cutting research and training activities in support of the Committee’s Strategic Plan.This paper summarizes the initiatives undertaken by TRCG and the challenges that lie ahead.