The quantification of low-probability–high-consequences events: part I. A generic multi-risk approach

Dynamic risk processes, which involve interactions at the hazard and risk levels, have yet to be clearly understood and properly integrated into probabilistic risk assessment. While much attention has been given to this aspect lately, most studies remain limited to a small number of site-specific multi-risk scenarios. We present a generic probabilistic framework based on the sequential Monte Carlo Method to implement coinciding events and triggered chains of events (using a variant of a Markov chain), as well as time-variant vulnerability and exposure. We consider generic perils based on analogies with real ones, natural and man-made. Each simulated time series corresponds to one risk scenario, and the analysis of multiple time series allows for the probabilistic assessment of losses and for the recognition of more or less probable risk paths, including extremes or low-probability–high-consequences chains of events. We find that extreme events can be captured by adding more knowledge on potential interaction processes using in a brick-by-brick approach. We introduce the concept of risk migration matrix to evaluate how multi-risk participates to the emergence of extremes, and we show that risk migration (i.e., clustering of losses) and risk amplification (i.e., loss amplification at higher losses) are the two main causes for their occurrence.     

长江流域降水极值的变化趋势

依据1960-2005年长江流域147个气象站逐日降水,ECHAM5/MPI-OM气候模式模拟的长江流域79个格点20世纪实验期(1941-2000年)以及未来3种排放情景(SRES-B1,A1B,A2)下21世纪前50年逐日降水数据,建立年最大强降水和汛期<1.27 mm/d的最长干旱持续天数序列。运用广义极值分布,广义帕雷托分布,广义逻辑分布与韦克比分布等4种分布函数定量拟合了长江流域降水极值的概率分布。研究表明:韦克比分布函数能够较好地拟合长江流域降水极值的概率分布。在3种排放情景下,未来降水极值的重现期呈现不同的空间分布特征。长江流域,尤其是中下游大部地区,1951-2000年间的50年一遇强降水和干旱事件,在2001-2050年间发展成为25年一遇降水极值事件。未来气候变暖条件下,降水极值重现期出现的这种变化趋势,将会对水资源趋势产生重大的影响。     

About the observed and future changes in temperature extremes over India

An attempt is made in the present study to analyse observed and model simulated temperature extremes over Indian region. Daily maximum and minimum temperature data at 121 well-distributed stations for the period 1970–2003 have been used to study the observed changes in objectively defined values of temperature extremes. In addition, an assessment of future scenarios of temperature extremes associated with increase in the concentration of atmospheric greenhouse gases is done using simulations of a state-of-the-art regional climate modelling system known as PRECIS (Providing Regional Climate for Impact Studies) performed to generate the climate for the present (1961–1990) and future projections for the period 2071–2100. Observational analysis done with 121 stations suggests the widespread warming through increase in intensity and frequency of hot events and also with decrease in frequency of cold events. More than 75% stations show decreasing trend in number of cold events and about 70% stations show increasing trend in hot events. Percentage of stations towards the warming through intensity indices of highest maximum temperature, lowest minimum temperature is 78 and 71% stations, respectively. Remaining stations show opposite trends, however, most of them are statistically insignificant. Observational analysis for India as a whole also shows similar results. Composite anomalies for monthly temperature extremes over two equal parts of the data period show increase (decrease) in the frequency of hot (cold) events for all months. In general, PRECIS simulations under both A2 and B2 scenarios indicate increase (decrease) in hot (cold) extremes towards the end of twenty-first century. Both show similar patterns, but the B2 scenario shows slightly lower magnitudes of the projected changes. Temperatures are likely to increase in entire calendar year, but the changes in winter season are expected to be prominent. Diurnal temperature range is expected to decrease in winter (JF) and pre-monsoon (MAM) months.     

Characterization and assessment of the devastating natural hazards across the Canadian Prairie Provinces from 2009 to 2011

From 2009 to 2011, the Canadian Prairies were subjected to exceptionally variable precipitation regimes, ranging between record drought and unprecedented flooding. Adjacent regions concurrently experienced droughts and floods, and individual areas transitioned rapidly from pluvial to drought conditions and vice versa. Such events had major impacts; for example, damages from floods in the Assiniboine River Basin (ARB) have exceeded $1 billion, and forest fires ravaged the town of Slave Lake, Alberta. This study first characterizes, and then assesses, these devastating natural hazards in terms of their physical processes (across multiple spatial and temporal scales) related to both the spatially contrasting precipitation states and rapid temporal transitions between these states. Subtle differences in large-scale atmospheric flow had marked impacts on precipitation. Primary factors controlling the distribution and amount of precipitation included the location and persistence of key surface and upper-air features, as well as their interaction. Additionally, multiple events—rather than individual extremes—were responsible for the flooding over the Saskatchewan River Basin and the ARB. Very heavy rainfall events (≥25 mm d^?1) accounted for up to 55 % of warm season rain at some locations, and the frequency of heavy rainfall events was critical for determining whether a region experienced drought or pluvial conditions. This study has increased our knowledge of the characteristics, impacts and mechanisms of rapidly transitioning disparate precipitation states on the Canadian Prairies and will aid in better understanding both past and projected future hydro-climatic extremes in the region.     

YANGTZE DISCHARGE MEMORY

We present a review on studies focusing on memories in hydrological time series in the Yangtze Basin based on observational and reconstructed historical data.Memory appears as scaling of power spectra,S(f)～f-β,with 0 <β≤ 1.The presence of scaling is noteworthy in daily river discharge time series:1)from weeks to a couple of years,power spectra follow flicker noise,that is β≈ 1;2)beyond years,spectral scaling appraaclTes β≈0.3.In historical time series of floods and draughts,power spectra also shows scaling with β≈ 0.38 ～0.52.Furthermore,a 70-year peak is detected in historical maritime events series,which also appears in other past climate indicators.Presence of memory in these hydrological time series implies clustering of extremes and scaling of their recurrence times,therefore,probabilistic forecast potential for extremes can be derived.On the other hand,although several physical processes,for example,soil moisture storage and high intermittency of precipitation,have been suggested to be the possible candidates contributing to the presence of long term memory,they remain open for future research.     

Expected impacts of climate change on extreme climate events

An overview of the expected change of climate extremes during this century due to greenhouse gases and aerosol anthropogenic emissions is presented. The most commonly used methodologies rely on the dynamical or statistical downscaling of climate projections, performed with coupled atmosphere–ocean general circulation models. Either of dynamical or of statistical type, downscaling methods present strengths and weaknesses, but neither their validation on present climate conditions, nor their potential ability to project the impact of climate change on extreme event statistics allows one to give a specific advantage to one of the two types. The results synthesized in the last IPCC report and more recent studies underline a convergence for a very likely increase in heat wave episodes over land surfaces, linked to the mean warming and the increase in temperature variability. In addition, the number of days of frost should decrease and the growing season length should increase. The projected increase in heavy precipitation events appears also as very likely over most areas and also seems linked to a change in the shape of the precipitation intensity distribution. The global trends for drought duration are less consistent between models and downscaling methodologies, due to their regional variability. The change of wind-related extremes is also regionally dependent, and associated to a poleward displacement of the midlatitude storm tracks. The specific study of extreme events over France reveals the high sensitivity of some statistics of climate extremes at the decadal time scale as a consequence of regional climate internal variability.     

A 1286‐year hydro‐climate reconstruction for the Balkan Peninsula

We present a June–July drought reconstruction based on the standardized precipitation index (SPI) for the Balkan Peninsula over the period 730–2015 CE. The reconstruction is developed using a composite Pinus heldreichii tree‐ring width chronology, from a high‐elevation network of eight sites in the Pindus Mountains in northwest Greece, composed of living trees and relict wood. The dataset includes the ring width series of Europe's currently oldest known living tree, dendrochronologically dated to be more than 1075 years old. The spatial coverage of the reconstruction is improved by using an averaged gridded SPI data target derived from a response field that is located north of the study region. Justification for this approach includes the remoteness of instrumental data, the spatial variability of precipitation and synoptic scale circulation patterns. Over the past 1286 years, there have been 51 dry and 43 pluvial events. The driest year during the 1286‐year‐long period was 1660 and the wettest year was 1482. Comparison with shorter reconstructions and documentary evidence validates the new reconstruction, and provides additional insight into socioeconomic impacts and spatial patterns of extreme events. Fifty‐nine of 72 previously undescribed extremes occurred prior to the 17th century. The new reconstruction reveals long‐term changes in the number of extremes, including substantially fewer drought and pluvial events in the 20th century. Additional tests on the long‐term effects of age structure, replication and covariance changes support the heteroscedastic nature of the reconstructed hydro‐climatic extremes.     

Recent trends in pre-monsoon daily temperature extremes over India

Extreme climate and weather events are increasingly being recognized as key aspects of climate change. Pre-monsoon season (March–May) is the hottest part of the year over almost the entire South Asian region, in which hot weather extremes including heat waves are recurring natural hazards having serious societal impacts, particularly on human health. In the present paper, recent trends in extreme temperature events for the pre-monsoon season have been studied using daily data on maximum and minimum temperatures over a well-distributed network of 121 stations for the period 1970–2005. For this purpose, time series of extreme temperature events have been constructed for India as a whole and seven homogeneous regions, viz., Western Himalaya (WH), Northwest (NW), Northeast (NE), North Central (NC), East coast (EC), West coast (WC) and Interior Peninsula (IP).     

Trends in Blizzards at Selected Locations on the Canadian Prairies

Climate Change is anticipatedto result in alterations in cyclone activity over the northern hemisphere. Cyclones in their passage across the open prairie of western Canada spawn one of the more extreme weather events that occur in that part of the country; blizzards. Numerous studies of individual blizzards are available. The objective of this study of blizzards is to identify trends in their seasonal occurrence, in seasonal blizzard weather element extremes, and discuss the results in the context of climate change. Criteria used in western Canada to define a blizzard event during the period of study were applied to the archive of hourly weather data for locations within the Prairie Ecozone. Blizzard events were extracted for the period 1953–1997 and analyzed for trends in seasonal occurrence. Results of this analysis are presented which illustrate a significant downward trend for weather observing locations in the more westerly part of the prairies. This trend is consistent with results found by others that indicate a decrease in cyclone frequency over western Canada. No significant trend was found in the more central and eastern locations. No significant trend was evident in seasonal extremes of blizzard weather elements at most locations.     

Climate extremes: an observation and projection of its impacts on food production in ASEAN

Climate change alters global food systems, especially agriculture and fisheries—significant aspects of the livelihoods and food security of populations. The 2014 IPCC Fifth Assessment Report identified Southeast Asia as the most vulnerable coastal region in the world, and highlighted the potential distribution of impacts and risks of climate change in the region. While climate hazards may differ across geographical regions, the impact of climate extremes on food production will affect marginal farmers, fishers and poor urban consumers disproportionately, as they have limited capacities to adapt to and recover from extreme weather events. Governments and other stakeholders need to respond to climate extremes and incorporate adaptation into national development plans. Unfortunately, there is still limited peer-review publication on the subject matter. This paper presents some findings from research on observed and projected loss and damage inflicted by climate extremes on agricultural crops in Southeast Asia.     

Research frontiers in climate change: Effects of extreme meteorological events on ecosystems

Climate change will increase the recurrence of extreme weather events such as drought and heavy rainfall. Evidence suggests that modifications in extreme weather events pose stronger threats to ecosystem functioning than global trends and shifts in average conditions. As ecosystem functioning is connected with ecological services, this has far-reaching effects on societies in the 21st century. Here, we: (i) present the rationale for the increasing frequency and magnitude of extreme weather events in the near future; (ii) discuss recent findings on meteorological extremes and summarize their effects on ecosystems and (iii) identify gaps in current ecological climate change research.     

Synoptic features associated with dust transition processes from North Africa to Asia

Aerosol index data from the total ozone mapping spectrometer satellite and reanalysis data from the National Center for Environmental Prediction and the National Center for Atmospheric Research are useful in the study of synoptic properties of the dust storms that carry dust from North Africa to Asia during the spring season for the period 1979 to 2006. In this study, we analyzed the synoptic properties of dust cases that pass through the transition zone between North Africa and Asia. We identified the dust cases to study by looking, inside transition zone, at events with an aerosol index greater than 2. We then divided the identified cases, depending on the spread and strength of the dust inside the transition zone, into seven categories ranging from weak events to moderate events to violent events. We found the common synoptic characteristics in all these categories as follows: The high pressure belt located over northern Africa allows the low pressure belt located over the South African Sahara to move northward; a pressure gradient between these two atmospheric systems directs from south to north; an increase in the pressure gradient leads to increased in both of the event’s dust and the amount of dust moves to North Africa from the Sahara; an additional pressure gradient between the western Azores high pressure system and the low pressure system located over the Arabian Peninsula directs from west to east; the stronger the pressure gradient, the greater the amount of dust in the event and moving a large amount of dust from Northeast Africa to Asia. To verify that these characteristics capture the essence of dust events from North Africa to Asia, we checked if they were also common to two additional extremes categories and two extremes events. The results confirmed the continued existence of these common characteristics.     

全球气候变化及其影响

全球气候变化及其对社会与自然系统产生的影响已日益受到全世界各国政府与广大民众的关注。与天气和气候有关的灾害给人类生命财产造成的损失日益增大,社会与生态系统似乎变得日趋脆弱。人们关心刚刚过去的20世纪的天气与气候发生了什么变化,更希望了解未来的21世纪,人类居住的地球会出现什么样的气候情景。根据一些国家和地区的观测记录、研究成果以及科学家们对气候变化的评估与预测展望,对全球气候变化问题进行概括。首先阐明20世纪地区性气候变化的事实;并根据政府间气候变化委员会(IPCC)科学技术报告中关于20世纪全球气候变化进行的总结性评估以及对21世纪全球气候变化的预测,作为阐述过去与未来全球气候变化的主要依据。同时,还介绍了一些科学家对IPCC关于全球气候变化的结论所持的不同观点或质疑。还就气候变化对社会与自然系统可能产生的影响略作论述。     

Effects of different soil and water conservation measures on hydrological extremes and flood processes in the Yanhe River,Loess Plateau,China

The runoff and sediment load of the Loess Plateau have changed significantly due to the implementation of soil and water conservation measures since the 1970s. However, the effects of soil and water conservation measures on hydrological extremes have rarely been considered. In this study, we investigated the variations in hydrological extremes and flood processes during different periods in the Yanhe River Basin (a tributary of the Loess Plateau) based on the daily mean runoff and 117 flood event data from 1956 to 2013. The study periods were divided into reference period (1956–1969), engineering measures period (1970–1995), and biological control measures period (1996–2013) according to the change points of the annual streamflow and the actual human activity in the basin. The results of the hydrological high extremes (HF1_max, HF3_max, HF7_max) exhibit a decreasing trend (P?<?0.01), whereas the hydrological low extremes (HBF1_min, HBF3_min, HBF7_min) show an increasing trend during 1956–2013. Compared with the hydrological extremes during the reference period, the hydrological high extremes increased during the engineering measures period at low (<?15%) and high frequency (>?80%), whereas decreased during the biological control measures period at almost all frequencies. The hydrological low extremes generally increased during both the engineering measures and biological control measures periods, particularly during the latter period. At the flood event scale, most flood event indices in connection with the runoff and sediment during the engineering measures period were significantly higher than those during the biological control measures period. The above results indicate that the ability to withstand hydrological extremes for the biological control measures was greater than that for the engineering measures in the studied basin. This work reveals the effects of different soil and water conservation measures on hydrological extremes in a typical basin of the Loess Plateau and hence can provide a useful reference for regional soil erosion control and disaster prevention policy-making.

     

Synchronous variability changes in Alpine temperature and tree-ring data over the past two centuries

The understanding of extremes and their temporal distribution is useful in characterizing the behaviour of the climate system, and necessary for understanding their social and economic costs and risks. This task is analogous to the study of pointer years in dendrochronological investigations. Commonly used dendroclimatological methods, however, tend to result in an equalization of variance throughout the record by normalizing variability within moving windows. Here, we analyse a larger network of high-elevation temperature-sensitive tree sites from the European Alps processed to preserve the relative frequency and magnitude of extreme events. In so doing, temporal changes in year-to-year tree-ring width variability were found. These decadal length periods of increased or decreased likelihood of extremes coincide with variability measures from a long-instrumental summer temperature record representative of high-elevation conditions in the Alps. Intervention analysis, using an F-test to identify shifts in variance, on both the tree-ring and instrumental series, resulted in the identification of common transitional years. Based on a well-replicated network of sites reflecting common climatic variation, our study demonstrates that the annual growth rings of trees can be utilized to quantify past frequency and amplitude changes in extreme variability. Furthermore, the approach outlined is suited to address questions about the role of external forcing, ocean-atmosphere interactions, or synoptic scale changes in determining patterns of observed extremes prior to the instrumental period.     

Decreasing precipitation extremes at higher temperatures in tropical regions

It has been often accepted that rising troposphere temperatures will lead to higher precipitation intensities. This argument is based on the Clausius?CClapeyron (C?CC) relation, which indicates an increase in atmospheric moisture storage capacity of approximately 7?% K^?1. However, recent studies carried out in mid-latitude regions indicate that changes in precipitation intensity as a function of temperature do not necessarily follow the C?CC relation. This study aimed to evaluate the correlation between precipitation extremes and temperature in tropical regions, using measured data obtained at low latitude ranges over Brazil. The results indicate that, at daily timescale, the C?CC relation alone is unlikely to explain the relation between precipitation extremes and temperatures in tropical regions. Additional aspects, such as moisture availability and the duration of precipitation events, should be further analyzed to allow a comprehensive understanding of the relationship between temperature and precipitation intensity. Moreover, we show that in tropical regions, higher temperatures may reduce the magnitude of extreme precipitation events at daily timescales, independent of the season of the year.     

Integrating hydrologic modeling and land use projections for evaluation of hydrologic response and regional water supply impacts in semi-arid environments

Semi-arid environments are generally more sensitive to urbanization than humid regions in terms of both hydrologic modifications and water resources sustainability. The current study integrates hydrologic modeling and land use projections to predict long-term impacts of urbanization on hydrologic behavior and water supply in semi-arid regions. The study focuses on the Upper Santa Clara River basin in northern Los Angeles County, CA, USA, which is undergoing rapid and extensive development. The semi-distributed Hydrologic Simulation Program Fortran (HSPF) model is parameterized with land use, soil, and channel characteristics of the study watershed. Model parameters related to hydrologic processes are calibrated at the daily time step using various spatial configurations of precipitation and parameters. Potential urbanization scenarios are generated on the basis of a regional development plan. The calibrated (and validated) model is run under the proposed development scenarios for a 10 year period. Results reveal that increasing development increases total annual runoff and wet season flows, while decreases are observed in existing baseflow and groundwater recharge during both dry and wet seasons. As development increases, medium-sized storms increase in both peak flow and overall volume, while low and high flow events (extremes) appear less affected. Urbanization is also shown to decrease natural recharge and, when considered at the regional scale, may result in a loss of critical water supply to Southern California. The current study provides a coupled framework for a decision support tool that can guide efforts involved in regional urban development planning and water supply management.     

Shifting Economic Impacts from Weather Extremes in the United States: A Result of Societal Changes,Not Global Warming

Loss values from extremes in the U.S. and elsewhere have been more qualitativethan quantitative, but recent pressures for better information have led to newassessments and better estimates of financial losses from extremes. These pressureshave included concerns over potential impacts of more extremes due to global warmingfostered by ever increasing costs to the insurance industry and government from weather extremes; plus a series of massive losses during the past 15 years (drought of 1988–1989,Hurricane Andrew in 1992, and Midwestern 1993 floods). These recent assessmentsattempted to adjust data for societal changes over time and thus derived new and betterestimates of losses for seven major extremes than existed previously. Three extremeshave annual average losses in excess of a billion dollars (1998 dollars) includinghurricanes ($4.2 billion), floods ($3.2 billion), and severe local storms ($1.6 billion).One extreme and its adjusted losses exhibit upward trends (floods), but all others showno increases with time or temporal decreases (hail, hurricanes, tornadoes, and severethunderstorms). Annual national losses during 1950–1997 from the three major extremes, plus four others (hail, tornadoes, winter storms, and wind storms), collectively reveal no upward or downward trend over time, with an average annual loss of $10.3 billion. The quality loss values do not indicate an increase as has been postulated for global warming. The good news is that better estimates of impacts now exist, but the bad news is that they are still estimates and do not include sizable unmeasured losses. If accurate data on the economic impacts from weather extremes are seen as important for scientific research and policy-making for global warming, the U.S. needs a continuing program to adequately measure losses from weather extremes.     

A probabilistic approach for estimating return period of extreme annual rainfall in different cities of Punjab

Multi-day rainfall events are an important cause of recent severe flooding in Pakistan, and any change in the magnitude of such events may have severe impact upon urban structures such as dams, urban drainage systems, and flood. This article uses statistical distributions to define extremes of annual rainfall of different cities of Punjab (Lahore, Murree, Sialkot, and Jhelum) with given return periods. Our calculations suggest that general extreme value is the best-fitted distribution for the extreme annual rainfall of different cities of Punjab. Our calculations show that different cities of Punjab have 5 years return period for receiving more than 100 mm daily rainfall. While they have 30 years return period for receiving more than 200 mm daily rainfall. This asks for construction of new dams in Pakistan.     

Climate change and increased risk for the insurance sector: a global perspective and an assessment for the Netherlands

Climate change is projected to increase the frequency and severity of extreme weather events. As a consequence, economic losses caused by natural catastrophes could increase significantly. This will have considerable consequences for the insurance sector. On the one hand, increased risk from weather extremes requires assessing expected changes in damage and including adequate climate change projections in risk management. On the other hand, climate change can also bring new business opportunities for insurers. This paper gives an overview of the consequences of climate change for the insurance sector and discusses several strategies to cope with and adapt to increased risks. The particular focus is on the Dutch insurance sector, as the Netherlands is extremely vulnerable to climate change, especially with regard to extreme precipitation and flooding. Current risk sharing arrangements for weather risks are examined while potential new business opportunities, adaptation strategies, and public–private partnerships are identified.