A projection of extreme climate events in the 21st century over east Asia using the community climate system model 3

A series of coupled atmosphere-ocean-land global climate model (GCM) simulations using the National Center for Atmospheric Research (NCAR) Community Climate System Model 3 (CCSM3) has been performed for the period 1870–2099 at a T85 horizontal resolution following the GCM experimental design suggested in the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4). First, a hindcast was performed using the atmospheric concentrations of three greenhouse gases (CO₂, CH₄, N₂O) specified annually and globally on the basis of observations for the period 1870–1999. The hindcast results were compared with observations to evaluate the GCM’s reliability in future climate simulations. Second, climate projections for a 100-year period (2000–2099) were made using six scenarios of the atmospheric concentrations of the three greenhouse gases according to the A1FI, A1T, A1B, A2, B1, and B2 emission profiles of the Special Report on Emissions Scenarios. The present CCSM simulations are found to be consistent with IPCC’s AR4 results in the temporal and spatial distributions for both the present-day and future periods. The GCM results were used to examine the changes in extreme temperatures and precipitation in East Asia and Korea. The extreme temperatures were categorized into warm and cold events: the former includes tropical nights, warm days, and heat waves during summer (June–July–August) and the latter includes frost days, cold days, and cold surges during winter (December–January–February). Focusing on Korea, the results predict more frequent heat waves in response to future emissions: the projected percentage changes between the present day and the late 2090s range from 294% to 583% depending on the emission scenario. The projected global warming is predicted to decrease the frequency of cold extreme events; however, the projected changes in cold surge frequency are not statistically significant. Whereas the number of cold surges in the A1FI emission profile decreases from the present-day value by up to 24%, the decrease in the B1 scenario is less than 1%. The frequency and intensity of extreme precipitation events year-round were examined. Both the frequency and the intensity of these events are predicted to increase in the region around Korea. The present results will be helpful for establishing an adaptation strategy for possible climate change nationwide, especially extreme climate events, associated with global warming.     

基于ECHAM5模式预估2050年前中国旱涝格局趋势

 利用ECHAM5/MPI-OM气候模式输出的2001-2050年逐月降水量资料,考虑IPCC采用的3种排放情景（A2：温室气体高排放情景;A1B:温室气体中排放情景;B1：温室气体低排放情景）,计算其标准化降水指数,分析了中国2050年前3种排放情景下的旱涝格局。结果表明：3种情景下旱涝趋势空间分布不同,其中A2情景下旱涝格局同1961-2000年观测到的旱涝格局相似,均存在一条由东北向西南的干旱带;而A1B和B1情景下旱涝格局则发生了很大的变化,尤其B1情景下出现了"北涝南旱"的格局。未来50 a干旱面积在A2情景下呈略增加趋势;A1B和B1情景下为减少趋势。3种情景下干旱频率的空间分布也各不相同。     

Projections of Extreme Rainfall in Hong Kong in the 21st Century

The possible changes in the frequency of extreme rainfall events in Hong Kong in the 21st century wereinvestigated by statistically downscaling 30 sets of the daily global climate model projections (involvinga combination of 12 models and 3 greenhouse gas emission scenarios,namely,A2,A1B,and B1) of theFourth Assessment Report of the Intergovernmental Panel on Climate Change.To cater for the intermittentand skewed character of the daily rainfall,multiple stepwise logistic regression and multiple stepwise linearregression were employed to develop the downscaling models for predicting rainfall occurrence and rainfallamount,respectively.Verification of the simulation of the 1971-2000 climate reveals that the models ingeneral have an acceptable skill in reproducing past statistics of extreme rainfall events in Hong Kong.Theprojection results suggest that,in the 21st century,the annual number of rain days in Hong Kong is expectedto decrease while the daily rainfall intensity will increase,concurrent with the expected increase in annualrainfall.Based on the multi-model scenario ensemble mean,the annual number of rain day is expected todrop from 104 days in 1980-1999 to about 77 days in 2090-2099.For extreme rainfall events,about 90% ofthe model-scenario combinations indicate an increase in the annual number of days with daily rainfall 100mm (R100) towards the end of the 21st century.The mean number of R100 is expected to increase from 3.5days in 1980-1999 to about 5.3 days in 2090-2099.The projected changes in other extreme rainfall indicesalso suggest that the rainfall in Hong Kong in the 21st century may also become more extreme with moreuneven distributions of wet and dry periods.While most of the model-emission scenarios in general projectconsistent trends in the change of rainfall extremes in the 21st century,there is a large divergence in theprojections among different model/emission scenarios.This reflects that there are still large uncertainties inmodel simulations of future extreme rainfall events.     

Projection of Extreme Temperatures in Hong Kong in the 21st Century

The possible changes in the frequency of extreme temperature events in Hong Kong in the 21st century were investigated by statistically downscaling 26 sets of the daily global climate model projections (a combination of 11 models and 3 greenhouse gas emission scenarios, namely A2, A1B, and B1) of the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. The models’ performance in simulating the past climate during 1971–2000 has also been verified and discussed. The verification revealed that the models in general have an acceptable skill in reproducing past statistics of extreme temperature events. Moreover, the models are more skillful in simulating the past climate of the hot nights and cold days than that of the very hot days. The projection results suggested that, in the 21st century, the frequency of occurrence of extremely high temperature events in Hong Kong would increase significantly while that of the extremely low temperature events is expected to drop significantly. Based on the multi-model scenario ensemble mean, the average annual numbers of very hot days and hot nights in Hong Kong are expected to increase significantly from 9 days and 16 nights in 1980–1999 to 89 days and 137 nights respectively in 2090–2099. On the other hand, the average annual number of cold days will drop from 17 days in 1980–1999 to about 1 day in 2090–2099. About 65 percent of the model-scenario combinations indicate that there will be on average less than one cold day in 2090–2099. While all the model-emission scenarios in general have projected consistent trends in the change of temperature extremes in the 21st century, there is a large divergence in the projections between difierent model/emission scenarios. This reflects that there are still large uncertainties in the model simulation of the future climate of extreme temperature events.     

CMIP5模式集合对中国区域性低温事件的模拟与预估

基于CMIP5逐日最低气温的模拟和预估数据,对中国区域性低温事件进行了研究。通过对中国区域性低温事件的历史模拟显示,模式集合的结果低估了中国区域性低温事件的变化趋势,但能够反映出与观测结果相同的减弱趋势,且比单个模式的结果更稳定,其空间分布与观测结果相似度也较高。在此基础上,采用模式集合方案对不同排放情景下（RCP2.6, RCP4.5, RCP8.5）的中国区域性低温事件进行了预估。结果显示,在RCP2.6排放情景下,中国区域性低温事件的减弱趋势较为缓和;在RCP4.5排放情景下,中国区域性低温事件呈现出显著的减弱趋势;在RCP8.5排放情景下,中国区域性低温事件的减弱趋势更明显。温室气体的排放可能主要影响中国区域性低温事件的强度和发生频次,对其空间分布影响较小。     

Forecasting the effects of global warming on radial growth of subalpine trees at the upper and lower distribution limits in central Japan

Effects of global warming on radial growth were examined for the subalpine tree species Abies veitchii (1600–2200 m?a.s.l.), A. mariesii (2000–2500 m?a.s.l.) and Betula ermanii (1600–2500 m?a.s.l.) in central Japan, by using dendrochronological techniques. Chronologies of tree-ring widths were examined for the three species and of maximum latewood densities for the two Abies species at their upper and lower distribution limits (total 10 chronologies). We developed multiple regression models to reproduce these chronologies from the monthly mean temperature and sum of precipitation. Of the 10 chronologies, growth-climate relations could not be modeled for tree-ring width chronologies of the three species at their lower distribution limits because of low correlation. Annual mean temperature and annual sum of precipitation will increase about 3 °C and 100 mm, respectively, by 2100 in central Japan, according to 18 climatic change scenarios (6 general circulation models ×3 greenhouse gasses emission scenarios). We predicted tree-ring widths and maximum latewood densities by substituting 18 climatic change scenarios into the growth-climate models. Maximum latewood densities and tree-ring widths of A. mariesii at the upper and lower distribution limits increased by 2100. The rates of the increase tended to be greater for scenarios with more greenhouse gas emission. By contrast, maximum latewood densities of A. veitchii and tree-ring widths of B. ermanii were unchanged by 2100, irrespective of the three greenhouse gas emission scenarios. This study showed that radial growth of the three species responds differently to global warming and their responses are predictable by dendrochronological models.     

Extreme precipitation over the Maritime Alps and associated weather regimes simulated by a regional climate model: Present-day and future climate scenarios

Summary We use the regional climate model RegCM nested within time-slice atmospheric general circulation model experiments to investigate the possible changes of intense and extreme precipitation over the French Maritime Alps in response to global climate change. This is a region with complex orography where heavy and/or extended precipitation episodes induced catastrophic floods during the last decades. Output from a 30-year simulation of present-day climate (1961–1990) is first analysed and compared with NCEP reanalysed 700 hPa geopotential heights (Z700) and daily precipitation observations from the Alpine Precipitation Climatology (1966–1999). Two simulations under forcing from the A2 and B2 IPCC emission scenarios for the period 2071–2100 are used to investigate projected changes in extreme precipitation for our region of interest. In general, the model overestimates the annual cycle of precipitation. The climate change projections show some increase of precipitation, mostly outside the warm period for the B2 scenario, and some increase in the variability of the annual precipitation totals for the A2 scenario. The model reproduces the main observed patterns of the spatial leading EOFs in the Z700 field over the Atlantic-European domain. The simulated large scale circulation (LSC) variability does not differ significantly from that of the reanalysis data provided the EOFs are computed on the same domain. Two similar clusters of LSC corresponding to heavy precipitation days were identified for both simulated and observed data and their patterns do not change significantly in the climate change scenarios. The analysis of frequency histograms of extreme indices shows that the control simulation systematically underestimates the observed heavy precipitation expressed as the 90^th percentile of rainday amounts in all seasons except summer and better reproduces the greatest 5-day precipitation accumulation. The main hydrological changes projected for the Maritime Alps consist of an increase of most intense wet spell precipitation during winters for both scenarios and during autumn for the B2 scenario. Case studies of heavy precipitation events show that the RegCM is capable to reproduce the physical mechanisms responsible for heavy precipitation over our region of interest.     

西南地区持续性气候事件的未来变化预估

利用RegCM4.0区域气候模式单向嵌套BCC_CSM1.1模式输出资料进行连续积分获得的模拟预估数据,对西南地区未来2025-2055年在两种温室气体排放情景下持续性干期和持续湿期事件的特征及其相对于历史基准期的变化进行了预估分析。结果表明,最长持续干期和湿期在RCP4.5和RCP8.5两种情景下的变化趋势不一致,RCP8.5情景下的最长湿期和持续湿期事件的发生频次相较RCP4.5并没有大幅增加,而是比RCP4.5情景具有更高的年际变率特征。相对于历史基准期,两种情景下的最长持续性气候事件的日数和发生频次在西南地区的东南部区域显著性增加,而在川西高原地区显著减少。对于持续干期发生的频次FCDD和最长持续湿期而言,四川中部以及四川、云南和贵州三省邻接处在RCP4.5情景下表现为显著增加的区域在RCP8.5情景下转变为显著减少。未来几十年西南地区持续性湿期和干期的分布特征可能更加趋于不均匀。     

Effects of climate change on snow accumulation and melting in the Broye catchment (Switzerland)

The study used a daily step conceptual hydrological model to examine the effects of climate change on snowfall accumulation and on snow cover melting in the Broye catchment (moderate relief- altitude from 400 to 1500 m a.s.l.). Five elevation bands representing a range of climatic conditions were used together with three realistic climate change scenarios based loosely on GCM's predictions and which reflect feasible changes by extending time periods. For a very moderate climate change (rise in air temperature of ca 1 °C), possibly in a near future, the reduction of snow cover duration, mean water equivalent and monthly maximum water equivalent is the most sensitive in the lower part of the catchment and during the first and last months of the snow season. In the higher part of the basin and during the colder months January and February, similar reduction rates can be expected in case of larger climate changes. The floods due to the melting of snow cover are lower. Sometimes rainfall, considered as snow in the present day conditions, generates additional floods during the winter season. For winter sports resorts below 1500 m a.s.l., even the very moderate climatic change scenario (temperature rise around 1 °C) leads to economically very difficult conditions. Finally, a climatic change detection index based on snow cover duration is proposed.     

Projected hydroclimate changes over Andean basins in central Chile from downscaled CMIP5 models under the low and high emission scenarios

This study examines the projections of hydroclimatic regimes and extremes over Andean basins in central Chile (～ 30–40° S) under a low and high emission scenarios (RCP2.6 and RCP8.5, respectively). A gridded daily precipitation and temperature dataset based on observations is used to drive and validate the VIC macro-scale hydrological model in the region of interest. Historical and future simulations from 19 climate models participating in CMIP5 have been adjusted with the observational dataset and then used to make hydrological projections. By the end of the century, there is a large difference between the scenarios, with projected warming of ～ + 1.2 °C (RCP2.6), ～ +?3.5 °C (RCP8.5) and drying of ～ ? 3% (RCP2.6), ～ ? 30% (RCP8.5). Following the strong drying and warming projected in this region under the RCP8.5 scenario, the VIC model simulates decreases in annual runoff of about 40% by the end of the century. Such strong regional effect of climate change may have large implications for the water resources of this region. Even under the low emission scenario, the Andes snowpack is projected to decrease by 35–45% by mid-century. In more snowmelt-dominated areas, the projected hydrological changes under RCP8.5 go together with more loss in the snowpack (75–85%) and a temporal shift in the center timing of runoff to earlier dates (up to 5 weeks by the end of the century). The severity and frequency of extreme hydroclimatic events are also projected to increase in the future. The occurrence of extended droughts, such as the recently experienced mega-drought (2010–2015), increases from one to up to five events per 100 years under RCP8.5. Concurrently, probability density function of 3-day peak runoff indicates an increase in the frequency of flood events. The estimated return periods of 3-day peak runoff events depict more drastic changes and increase in the flood risk as higher recurrence intervals are considered by mid-century under RCP2.6 and RCP8.5, and by the end of the century under RCP8.5.     

CMIP6情景中主要温室气体和气溶胶排放强度的时空分布特征分析

基于不同共享社会经济路径（Shared Socioeconomic Pathways, SSPs）形成的8组最新的未来可能情景（SSPx-y情景）,被用于第六次耦合模式比较计划（CMIP6）,以据此来预估未来气候变化的可能幅度和趋势。本文主要对比分析了8组SSPx-y新情景中主要温室气体和气溶胶排放数据的基准年排放强度分布、未来排放强度的时空变化、以及在6个典型区域排放强度的逐年变化等特征。结果表明:二氧化碳（CO₂）、甲烷（CH₄）、黑碳（BC）、二氧化硫（SO₂）在基准年的排放强度高值区都位于东亚和南亚。相比于基准年,2100年CO₂和CH₄在高和低辐射强迫情景下表现出的排放强度变化有显著差异。此外,所有情景下2100年的BC和SO₂全球平均排放强度都弱于基准年的排放强度。在时间变化上,随着生物质能碳捕获与封存技术的不断进步,所有地区在4组不超过3.4 W/m2的低辐射强迫情景下,CO₂排放强度到2100年都呈现负值。其中,南美洲的负排放最强,2100年在SSP5-3.4情景下该地区的排放强度为－0.3 kg m－2 a－1。最后,对比东亚和南亚排放强度的逐年变化可以发现,在各情景所描述的未来发展过程中,东亚的减排行动的成效都要好于南亚。     

CMIP6-WACCM模式对北半球反气旋型Rossby波破碎趋势的预估

利用CMIP6中的CESM2-WACCM模式逐日资料，预估未来2020—2099年SSP2-4.5、SSP3-7.0和SSP5-8.5三种不同排放情景下北半球对流层顶附近反气旋型Rossby波破碎（Anticyclonic Rossby Wave Breaking， AWB）的空间分布、发生频率、水平尺度、对称结构及其长期趋势。总体而言，未来四个季节AWB都在北太平洋和北大西洋有高频区。夏季北太平洋高频区发生频数显著多于北大西洋高频区，其他三季相反。两高频区在三种不同情景下，AWB物质经向输送通常以对称输送为主，但北太平洋区内冬、春、秋三季在SSP2-4.5情景下AWB物质向极净输送，北大西洋区内夏季在SSP2-4.5和SSP5-8.5情景下AWB物质向赤道净输送。未来的长期趋势显示，两高频区内各季节的AWB发生频数、水平尺度和物质向极输送主要呈减小（减少）趋势，且温室气体排放量越大，减小趋势越显著。在SSP5-8.5情景下，北太平洋夏季AWB总面积变化趋势为-365.5个1°×1°标准经纬度网格/10 a，该变化由区域内AWB平均尺度减小（-2.7个标准化网格/10 a）和发生频率减少（-1.9个/10 a）共同导致；该区域的向极输送率变化率为-0.016 5/10 a。北大西洋秋季AWB发生频数变化率为-2.3个/10 a，导致其总面积则以-440.4个标准化网格/10 a的速度减小。     

Climate change impacts on forest fire potential in boreal conditions in Finland

The aim of this work was to study the forest fire potential and frequency of forest fires under the projected climate change in Finland (N 60°–N 70°). Forest fire index, generally utilized in Finland, was used as an indicator for forest fire potential due to climatological parameters. Climatic scenarios were based on the A2 emission scenario. According to the results, the forest fire potential will have increased by the end of this century; as a result of increased evaporative demand, which will increase more than the rise in precipitation and especially in southern Finland. The annual number of forest fire alarm days is expected to increase in southern Finland to 96–160 days by the end of this century, compared to the current 60–100 days. In the north, the corresponding increase was from 30 to 36 days. The expected increase in the annual frequency of forest fires over the whole country was about 20% by the end of this century compared to the present day. The greatest increase in the frequency of fires, per 1,000 km², was in the southernmost part of the country, with six to nine fires expected annually per 1,000 km² at the end of this century, meaning a 24–29% increase compared to the present day frequencies.     

两种温室气体排放情景下中国汛期江淮暴雨低涡特征研究

本文基于一个水平分辨率为50 km的区域气候模式RegCM4(Regional Climate Model,version 4.0)的模拟与预估结果,对我国汛期江淮暴雨低涡在气候变化背景下的统计特征与合成结构进行分析,进一步对两种温室排放情景下未来中国汛期的江淮暴雨低涡特征进行预估。结果表明:RegCM4模式对环境要素及低涡都具有一定的模拟能力,低涡的伸展高度、生命期及暴雨位置模拟结果与观测较为接近,但模拟的低涡个数、最大暖区高度以及温、湿要素分布均比实际略偏低,而风速和低涡的强度模拟则偏强;在未来两种温室排放情景预估方面, RCP4.5(Representative Concentration Pathways,简称RCP)典型浓度排放情景下,暴雨低涡数量比例减少,强度减弱,但低涡发展高度仍以850 hPa为主,生命期多为2 d以内,低涡雨区分布及最大暖区高度均与历史时段相近;RCP8.5情景下,暴雨低涡比例明显大于RCP4.5情景,低涡发展高度以700 hPa为主,生命期达3 d的增多,强度增强,最大暖区厚度范围显著伸展。两种情景下均有低涡中温度锋区减弱,而湿度锋区增强,但RCP8.5情景减弱与增强更显著,显示更高的温室气体排放将导致未来出现更强的暴雨低涡,造成伴随暴雨的低涡灾害性天气的增加,因此应进一步深化对低涡暴雨灾害性天气发展趋势的研究。     

Climate-change effects on extreme precipitation in central Europe: uncertainties of scenarios based on regional climate models

Observations as well as most climate model simulations are generally in accord with the hypothesis that the hydrologic cycle should intensify and become highly volatile with the greenhouse-gas-induced climate change, although uncertainties of these projections as well as the spatial and seasonal variability of the changes are much larger than for temperature extremes. In this study, we examine scenarios of changes in extreme precipitation events in 24 future climate runs of ten regional climate models, focusing on a specific area of the Czech Republic (central Europe) where complex orography and an interaction of other factors governing the occurrence of heavy precipitation events result in patterns that cannot be captured by global models. The peaks-over-threshold analysis with increasing threshold censoring is applied to estimate multi-year return levels of daily rainfall amounts. Uncertainties in scenarios of changes for the late 21st century related to the inter-model and within-ensemble variability and the use of the SRES-A2 and SRES-B2 greenhouse gas emission scenarios are evaluated. The results show that heavy precipitation events are likely to increase in severity in winter and (with less agreement among models) also in summer. The inter-model and intra-model variability and related uncertainties in the pattern and magnitude of the change is large, but the scenarios tend to agree with precipitation trends recently observed in the area, which may strengthen their credibility. In most scenario runs, the projected change in extreme precipitation in summer is of the opposite sign than a change in mean seasonal totals, the latter pointing towards generally drier conditions in summer. A combination of enhanced heavy precipitation amounts and reduced water infiltration capabilities of a dry soil may severely increase peak river discharges and flood-related risks in this region.     

Assessing the impact of climate change on representative field crops in Israeli agriculture: a case study of wheat and cotton

Climate changes, associated with accumulation of greenhouse gases, are expected to have a profound influence on agricultural sustainability in Israel, a semi-arid area characterized by a cold wet winter and a dry warm summer. Accordingly this study explored economic aspects of agricultural production under projected climate-change scenarios by the “production function” approach, as applied to two representative crops: wheat, as the major crop grown in Israel’s dry southern region, and cotton, representing the more humid climate in the north. Adjusting outputs of the global climate model HadCM3 to the specific research locations, we generated projections for 2070–2100 temperatures and precipitations for two climate change scenarios. Results for wheat vary among climate scenarios; net revenues become negative under the severe scenario (change from −145 to −273%), but may increase under the moderate one (−43 to +35%), depending on nitrogen applied to the crop. Distribution of rain events was found to play a major role in determining yields. By contrast, under both scenarios cotton experiences a considerable decrease in yield with significant economic losses (−240 and −173% in A2 and B2 scenarios, respectively). Additional irrigation and nitrogen may reduce farming losses, unlike changes in seeding dates.     

全球升温1.5℃和2.0℃情景下中国乡村振兴核心区极端降水的变化特征北大核心CSCD

中国乡村振兴核心区生态环境较脆弱,暴雨洪涝等气象灾害频发,在此背景下,定量、科学地评估乡村振兴核心区全球升温情景下极端降水的变化特征,能够为乡村振兴核心区防止因灾返贫策略等的制定提供一定的科学依据。本研究基于CMIP6(Coupled Model Intercomparison Project Phase 6)气候模式下不同SSPs-RCPs(Shared Socioeconomic Pathways-Representative Concentration Pathways)组合情景模拟数据,对全球升温1.5℃和2.0℃情景下中国乡村振兴核心区极端降水事件频次、强度和持续时间的变化特征进行了分析。结果表明:(1)相对于基准期(1995~2014年),全球升温1.5℃情景下,乡村振兴核心区受极端降水影响明显增大,面积占比60.91%的区域极端降水频次增加,面积占比88.19%的区域极端降水强度增强,面积占比81.07%的区域极端降水持续时间增加;(2)全球升温2.0℃情景下,乡村振兴核心区三项极端降水指标变化与升温1.5℃情景下相似,相对于基准期有增加趋势,极端降水频次、强度和持续时间面积占比分别为55.78%、85.24%、79.33%;(3)从空间角度分析,全球升温1.5℃和2.0℃情景下,乡村振兴核心区中西部相较东部可能更易受极端降水的影响,西藏片区频次和持续时间增加显著,尤其值得关注;(4)当全球升温从1.5℃到2.0℃情景,乡村振兴核心区整体极端降水特征的变化未表现出明显增减趋势及空间特征。相比1.5℃较基准期的变化,2.0℃情景下极端降水频次、强度、持续时间的增加区域范围均缩小,但平均增幅均变大,对于发生极端降水事件的乡村振兴核心区区域而言可能面临更大的风险。     

“一带一路”区域未来气候变化预估

利用耦合模式比较计划第5阶段(CMIP5)提供的18个全球气候模式的模拟结果,预估了3种典型浓度路径(RCP2.6、RCP4.5、RCP8.5)下“一带一路”地区平均气候和极端气候的未来变化趋势。结果表明:在温室气体持续排放情景下,“一带一路”地区年平均气温在未来将会持续上升,升温幅度随温室气体浓度的增加而加大。在高温室气体排放情景(RCP8.5)下,到21世纪末期,平均气温将普遍升高5℃以上,其中北亚地区升幅最大,南亚和东南亚地区升幅最小。对于降水的变化,预估该区域大部分地区的年降水量将增加,其中西亚和北亚增加最为明显,而且在21世纪中期,RCP2.6情景下的增幅要比RCP4.5和RCP8.5情景下的偏大,而在21世纪后期,RCP8.5情景下降水的增幅比RCP2.6和RCP4.5情景下的偏大。未来极端温度也将呈升高的趋势,增温幅度高纬度地区大于低纬度地区、高排放情景大于低排放情景。而且在高纬度区域,极端低温的增暖幅度要大于极端高温的增幅。连续干旱日数在北亚和东亚总体呈现减少趋势,而在其他地区则呈增加趋势。极端强降水在“一带一路”区域总体上将增强,增强最明显的地区位于南亚、东南亚和东亚。     

Projected 21st century snowfall changes over the French Alps and related uncertainties

Snowfall changes in mountain areas in response to anthropogenic forcing could have widespread hydrological, ecological and economic impacts. In this paper, the robustness of snowfall changes over the French Alps projected during the 21st century and the associated uncertainties are studied. In particular, the role of temperature changes on snowfall changes is investigated. Those issues are tackled through the analysis of the results of a very large ensemble of high-resolution regional climate projections, obtained either through dynamical or statistical downscaling. We find that, at the beginning and at the end of the cold season extending from November to March (included), temperature change is an important source of spread in snowfall changes. However, no link is found between temperature and snowfall changes in January and February. At the beginning and at the end of the cold season, the rate of change in snowfall per Kelvin does not depend much on the bias correction step, the period or the greenhouse gas scenario but mostly on the downscaling method and the climate models, the latter uncertainty source being dominant.     

FUTURE CHANGE OF PRECIPITATION EXTREMES OVER THE PEARL RIVER BASIN FROM REGIONAL CLIMATE MODELS

Based on RegCM4, a climate model system, we simulated the distribution of the present climate (1961-1990) and the future climate (2010-2099), under emission scenarios of RCPs over the whole Pearl River Basin. From the climate parameters, a set of mean precipitation, wet day frequency, and mean wet day intensity and several precipitation percentiles are used to assess the expected changes in daily precipitation characteristics for the 21st century. Meanwhile the return values of precipitation intensity with an average return of 5, 10, 20, and 50 years are also used to assess the expected changes in precipitation extremes events in this study. The structure of the change across the precipitation distribution is very coherent between RCP4.5 and RCP8.5. The annual, spring and winter average precipitation decreases while the summer and autumn average precipitation increases. The basic diagnostics of precipitation show that the frequency of precipitation is projected to decrease but the intensity is projected to increase. The wet day percentiles (q90 and q95) also increase, indicating that precipitation extremes intensity will increase in the future. Meanwhile, the 5-year return value tends to increase by 30%-45% in the basins of Liujiang River, Red Water River, Guihe River and Pearl River Delta region, where the 5-year return value of future climate corresponds to the 8- to 10-year return value of the present climate, and the 50-year return value corresponds to the 100-year return value of the present climate over the Pearl River Delta region in the 2080s under RCP8.5, which indicates that the warming environment will give rise to changes in the intensity and frequency of extreme precipitation events.