全球干旱/半干旱区年代尺度干湿变化研究的进展及思考

干旱/半干旱区气候变化研究一直是广泛关注的前沿科学问题,尤其是气候干湿变化规律及未来的发展趋势。过去大量的研究揭示了全球不同干旱/半干旱区的干湿变化事实和机理,取得了一系列重要进展,IPCC第6次评估报告明确指出未来全球干旱化将加剧,但也存在诸多问题没有得到一致的认识。本文将对全球变暖背景下有关干旱/半干旱区年代尺度干湿变化,特别是年代尺度干旱研究进行梳理,系统评述当前相关研究的现状并提出干旱/半干旱区研究所面临的关键科学问题。     

干旱半干旱区土壤湿度数值模拟研究进展

总结和回顾了干旱半干旱地区土壤湿度研究在区域气候变化研究过程中的重要性,详尽描述了干旱半干旱区土壤湿度数值模拟的研究现状。在过去几十年里,大型地面观测试验计划的开展、卫星遥感监测能力的加强促进了干旱半干旱地区陆面模式模拟土壤湿度能力的提高,推动了干旱半干旱地区土壤湿度数值模拟的研究进程。尤其是干旱半干旱地区气候观测站的建立,积累了长期宝贵的连续性观测数据,增强了检验卫星反演方法的能力,促进了陆面模式的参数化改进。近年来随着气象学、生态学以及水文学、土壤学等学科之间交叉合作的加强,气候变化背景下土壤湿度对碳、氮循环的影响研究得到越来越多的重视,尤其在干旱半干旱地区,局地碳通量和水分供应存在密切联系。因此,未来半干旱地区土壤湿度的研究不仅要开展观测计划,积累长期连续的高质量数据,改进卫星反演能力和模式参数化方案,而且要进一步深化和加强学科交叉内容的研究,分析气候变化背景下土壤湿度在生态学、水文学、土壤学等学科的变化形式和特点,多角度、多方向地开展和改进干旱半干旱地区土壤湿度的数值模拟研究。     

2008年夏季中国干旱-半干旱区陆面主要物理参数的平均特征

采用2008年7-9月观测的中国干旱-半干旱区试验观测协同与集成研究资料,选取12个测站(涵盖不同气候环境区的草地、农田、果林和森林等下垫面)比较分析了干旱-半干旱区的动力、热力和水汽粗糙度长度、总体输送系数、反照率以及土壤热传导率和热扩散率的夏季平均特征,并与陆面模式的理论参考值进行了对比。结果表明,植被下垫面的水、热特性和植被高度对主要陆面参数有重要影响,但植被下垫面的土壤热传导率和扩散率与下垫面类型之间无明显关系。动力学粗糙度长度与下垫面的植被高度呈正相关关系,无论是稳定还是不稳定层结下,动量拖曳系数都随着植被高度的增大而增大,而反照率随植被高度的增加而降低。在研究区的下垫面中,草地下垫面动力学粗糙度长度的实测值比模式理论参考值偏小,但农田和果林下垫面的实测值比理论参考值偏大;草地下垫面动量拖曳系数理论的参考值比实测值高,但其他下垫面的实测值高于理论参考值;实测反照率处于可见光反照率和近红外光反照率之间,但反照率的理论参考值比实测值偏高。     

甘肃干旱半干旱地区气候特征对农业生产的影响

提要根据1951—1990年的光能、气温、降水和风等气象资料,对甘肃干旱半干旱地区的主要气候特征进行了比较详细的分析,并阐述了这些气候特征对农业生产的利弊影响。     

东亚、北非干旱半干旱区边界层高度的特征研究

采用再分析资料ERA-20C对东亚、北非干旱半干旱区一百多年边界层高度(Boundary Layer Height,BLH)的时空变化特征进行比较研究,结果揭示了两个地区不同气候区BLH空间分布和时间变化的差异性。结果表明,BLH的空间分布与气候干湿程度密切相关,同时受海拔以及河流、湖泊分布等的影响;干旱区、半干旱-半湿润过渡区的BLH在东亚和北非均为升高趋势;极端干旱区、干旱-半干旱过渡区、半干旱区的BLH在东亚为升高趋势,在北非为降低趋势;极端干旱区对干旱半干旱区整体BLH年际变化贡献最小,东亚为11. 05%,北非为3. 68%;东亚半干旱区年际变化贡献最大23. 74%,北非半干旱-半湿润过渡区年际变化贡献最大28. 89%。两个地区BLH的变化均包含周期为60年、30年、10年、5～7年和2～4年的振荡,在长时间尺度的周期变化中,两个地区的BLH基本呈反位相关系,在短时间尺度的周期变化中,呈反位相、同位相交替转换的关系; BLH的长期变化趋势,东亚各季节均为升高趋势,北非只有冬季为升高趋势; BLH年际变化,夏季占主导地位,东亚年际变化贡献率是58. 50%,北非年际变化贡献率是57. 52%,北非秋季年际变化贡献率是东亚地区的2倍多。     

我国干旱半干旱区降水的特征分析

利用聚类分析对全国160站1951～1992年的年降水标准化资料做分析,结果可划分为两大区——干旱半干旱区和非干旱区,在此基础上进行降水区划及降水分布型研究,得出我国干旱半干旱区大致分成9个小区以及它的3种年降水分布型式。     

中国干旱半干旱区洪涝灾害的初步分析

中国干旱半干旱区的洪涝灾害是一个尚未引起人们重视的重大科学问题,这主要是因为干旱半干旱区对洪涝灾害的防范意识比较薄弱。而极端降水事件的次数、强度和持续时间与干旱半干旱区的洪涝灾害有密切联系,直接影响该区域洪涝灾害及其次生地质灾害的次数与严重程度。以干旱半干旱区的极端降水事件为切入点,分析了中国干旱半干旱区的极端降水事件次数和极端降水量的变化特征,旨在为干旱半干旱区的洪涝灾害研究提供科学依据。结果表明,进入21世纪以来,中国110°E以西的干旱半干旱区极端降水事件的日数有所增多,而110°E以东的区域日数都有所减少。干旱半干旱区极端降水量的变化也呈现出西增东减的分布,大部分干旱半干旱区的极端降水量变化占总降水量变化的40%以上,一部分地区能达到50%,甚至100%-200%。从季节变化来看,春季天山以北、新疆南部、甘肃敦煌和内蒙古包头以北地区极端降水量增加较多,夏季110°E以西的干旱半干旱区极端降水量均增大明显,秋季陕西榆林、内蒙古鄂尔多斯、包头和呼和浩特等地极端降水量增大较明显。     

利用GLDAS资料分析黄土高原半干旱区土壤湿度对气候变化的响应

利用GLDAS资料分析了1948~2010年黄土高原半干旱区气温、降水和土壤湿度的变化趋势,并重点讨论了气温和降水对土壤湿度的影响和相对贡献。结果表明:近60 a来黄土高原半干旱区整体呈现暖干化趋势,增温速率明显高于全球平均增温速率;不同深度的土壤湿度的长期变化均呈减小趋势,且年际间变化明显。不同深度的土壤湿度和气温呈负相关关系,并随着土壤加深,两者的相关性加强;土壤湿度和降水则呈正相关关系,相关关系最大出现在表层土壤。通过分析气温和降水在不同季节对土壤湿度的相对贡献发现,春季和冬季气温对土壤湿度的相对贡献较降水显著,秋季恰好相反,夏季气温和降水对土壤湿度的相对贡献大小相当。对比不同深度层降水、气温对土壤湿度的相对贡献得出,降水对浅层土壤湿度有显著作用,而气温对深层土壤湿度的作用更明显。     

海南岛干湿概况与干旱发生特征

利用气象干湿气候等级指标对海南岛进行了逐月的划分,并分析干旱发生的特征.结果表明:从11月份开始海南岛进入旱季,干旱区从西部东方县开始逐渐向东扩展;1到3月份全岛均处于干旱状态;从4月份开始,干旱区逐步向西退缩.海南岛一年四季均有干旱发生,冬春季节为季节性干旱,夏秋两季降水的时间分布不均会发生短暂干旱.     

东亚干旱半干旱区空中水资源研究进展

系统回顾了近年来中外对东亚干旱半干旱区空中水资源方面的主要研究进展,主要包括大气水汽、云的分布特征、空中水资源的降水转化率及其影响因子等。东亚干旱半干旱区西部及东部水汽含量较中部高,背风坡水汽含量较迎风坡高,季风区及山脉地区云水资源高于盆地、沙漠上空。20世纪80年代中期以后,东亚干旱半干旱区对流层底部的水汽显著增多,其中夏季增加最为明显。在全球气候变化背景下,中国西北部分地区云水路径总体呈现上升趋势,同时呈现"东正西负"的东西向变化差异以及"北正南负"的反相位特征。大气环流、地表温度、下垫面地表特征等因子通过影响东亚干旱半干旱区的水汽输送及蒸散,进而改变东亚干旱半干旱区空中水资源,空中水资源的改变通过影响辐射收支、不同高度云量及第2次相变产生的云水含量进而对局地温度和降水产生影响。以往研究中,大部分主要针对东亚干旱半干旱区大气中的水汽含量和云平均状态的分布与变化特征,而与降水相关联的空中水资源的变化特征目前仍不清楚,有待系统深入地研究。      

Land-Air Interaction over Arid/Semi-arid Areas in China and Its Impact on the East Asian Summer Monsoon. Part I： Calibration of the Land Surface Model （BATS） Using Multicriteria Methods

To improve the land surface simulation in the arid and semi-arid areas of northern China, the observational data from two field experiments in Dunhuang and Tongyu are used to optimize the parameters in the land surface model, BATS, through calibration with the multicriteria method. Sensitivity analysis to the parameters in Dunhuang and Tongyu indicates that different parameters need to be calibrated in two sites with different environmental and climate regimes. Comparison of observed sensible heat flux, latent heat flux, and ground surface temperature with the simulated ones shows the simulations with the optimized parameters have been substantially improved. Especially, the holistic simulations with the calibration of the parameter values are much closer to the observations in the arid region (Dunhuang), and the energy partition with the calibrated parameters can also be simulated well in the semi-arid region (Tongyu). Whole results demonstrate that the parameter calibration of the land surface model is important when the model is to be used to investigate the land-air interaction.     

全球增暖背景下中国干湿气候带变化规律研究

用中国区域561个气象站1961—2010年的逐日气象资料,计算了多时间尺度的湿润指数。用ArcGIS软件平台对站点的降水量和湿润指数进行反距离加权插值,得到其空间分布图,进而分别从全球气候变暖背景下和年代际两个角度分析了湿润指数与干湿气候带界线的变化特征。结果表明:在气候变暖背景下,新疆的极干旱区范围缩小;内蒙东部半干旱区东伸增大,西部干旱区南移扩大;山东半湿润区南移扩大;陕西半干旱区加大,湿润区缩小。从年代际变化而言,湿润指数和干湿气候带界线分布有明显的区域特征。东北地区总体呈现干湿交替特征;1970s起,西北地区总体趋湿;华北东南部持续趋干;新疆南部(极干旱区)持续趋湿;南方地区在2000s四川南部和贵州中南部趋干,出现部分半干旱区。另外,根据中国农业区划方案,分别计算7个一级农业类型区湿润指数。发现7大农业区50 a来湿润指数都呈下降趋势(青藏区除外),尤其西南地区在2000s湿润指数下降最为显著,其主要原因是2001年以来该地区潜在蒸散增加和降水偏少造成的。     

Recent progress in studies on land cover change and its regional climatic effects over China during historical times

The recent progresses on the reconstruction of historical land cover and the studies on regional climatic effects to temperature,precipitation,and the East Asian Monsoon across China were reviewed.Findings show that the land cover in China has been significantly modified by human activities over the last several thousands years,mainly through cropland expansion and forest clearance.The cropland over traditional Chinese agricultural areas increased from 5.32×105 km2 in the mid-17th century to 8.27×105 km2 in...     

An overview of dry-wet climate variability among monsoon-westerly regions and the monsoon northernmost marginal active zone in China

Climate in mainland China can be divided into the monsoon region in the southeast and the westerly region in the northwest as well as the intercross zone, i.e., the monsoon northernmost marginal active zone that is oriented from Southwest China to the upper Yellow River, North China, and Northeast China. In the three regions, dry-wet climate changes are directly linked to the interaction of the southerly monsoon flow on the east side of the Tibetan Plateau and the westerly flow on the north side of the Plateau from the inter-annual to inter-decadal timescales. Some basic features of climate variability in the three regions for the last half century and the historical hundreds of years are reviewed in this paper. In the last half century, an increasing trend of summer precipitation associated with the enhancing westerly flow is found in the westerly region from Xinjiang to northern parts of North China and Northeast China. On the other hand, an increasing trend of summer precipitation along the Yangtze River and a decreasing trend of summer precipitation along the monsoon northernmost marginal active zone are associated with the weakening monsoon flow in East Asia. Historical documents are widely distributed in the monsoon region for hundreds of years and natural climate proxies are constructed in the non-monsoon region, while two types of climate proxies can be commonly found over the monsoon northernmost marginal active zone. In the monsoon region, dry-wet variation centers are altered among North China, the lower Yangtze River, and South China from one century to another. Dry or wet anomalies are firstly observed along the monsoon northernmost marginal active zone and shifted southward or southeastward to the Yangtze River valley and South China in about a 70-year timescale. Severe drought events are experienced along the monsoon northernmost marginal active zone during the last 5 centuries. Inter-decadal dry-wet variations are depicted by natural proxies for the last 4--5 centuries in several areas over the non-monsoon region. Some questions, such as the impact of global warming on dry-wet regime changes in China, complex interactions between the monsoon and westerly flows in Northeast China, and the integrated multi-proxy analysis throughout all of China, are proposed.     

中国中东部地区不同气候背景下城市乡村气温差异研究

本文利用中国中东部424个气象站常规观测资料与再分析气象资料,研究了1981—2014年中国中东部地区(京津冀、黄淮和长三角)不同气候背景下城市和乡村的气温差异(ΔT_(城乡))。研究发现,中国中东部ΔT_(城乡)昼夜基本皆为正,北部的京津冀和南部的长三角地区ΔT_(城乡)存在显著昼夜差异:白天长三角地区ΔT_(城乡)大于京津冀地区;夜间则反之,京津冀地区ΔT_(城乡)大于长三角地区;黄淮地区昼夜ΔT_(城乡)特征介于前两个区域之间。分析发现,各地区昼夜ΔT_(城乡)与城市和乡村的地表温差(ΔT_(d城乡))有很好的相关关系。城市规模不是造成南北方昼夜ΔT_(城乡)差异的原因。结合大气热源(汇)Q_1和水汽汇Q_2等要素进一步分析其物理机制发现,大气热源(汇)Q_1是表征南北方ΔT_(城乡)昼夜差异的较好物理指标:(1)白天,南方乡村和城市比北方乡村和城市Q_1皆较大,但南北方城市下垫面类型类似导致其Q_2基本相同,而南方乡村地表蒸散发强烈、地表大气升温较慢,使得南方地区ΔT_(城乡)大于北方地区ΔT_(城乡);(2)夜间,北方乡村地区Q_1负值绝对值高于南方乡村、也高于北方城市,即北方乡村感热降温显著强于南方乡村和北方城市,而南北方城市Q_1值基本相同,使得北方地区ΔT_(城乡)大于南方地区ΔT_(城乡)。本文研究结果表明,高温湿润地区白天城乡温差更大,而低温干燥地区夜间城乡温差更大。     

The influence of land surface changes on regional climate in Northwest China

Land surface changes effect the regional climate due to the complex coupling of land-atmosphere interactions. From 1995 to 2000, a decrease in the vegetation density and an increase in ground-level thermodynamic activity has been documented by multiple data sources in Northwest China, including meteorological, reanalysis from European Centre for Medium-Range Weather Forecasts （ECMWF）, National Oceanic and Atmospheric Administration＇s （NOAA） Advanced Very High Resolution Radiometer （AVHRR） and TIROS Operational Vertical Sounder （TOVS） satellite remote sensing data. As the ground-level thermodynamic activity increases, humid air from the surrounding regions converge toward desert （and semi-desert） regions, causing areas with high vegetation cover to become gradually more arid. Furthermore, land surface changes in Northwest China are responsible for a decrease in total cloud cover, a decline in the fraction of low and middle clouds, an increase in high cloud cover （due to thermodynamic activity） and other regional climatic adaptations. It is proposed that, beginning in 1995, these cloud cover changes contributed to a ＂green- house＂ effect, leading to the rapid air temperature increases and other regional climate impacts that have been observed over Northwest China.     

Study on climatic characteristics of China-influencing tropical cyclones

Analysis of the climatic characteristics of the tropical cyclones that affect China yields several interesting features. The frequency of these tropical cyclones tended to decrease from 1951 to 2005, with the lowest frequency in the past ten years. The decrease in the frequency of super typhoons is particularly significant. The main season of tropical cyclone activities is from May to November, with an active period from July to September. There are three obvious sources of these tropical cyclones and they vary with seasons and decades. Their movement has also changed with seasons. On average, these tropical cyclones affect China for 5.6 months annually and the period of influence decreases in the past decades. An analysis of daily data indicates that the days of typhoon influence are shorter in winter and spring and longer in summer. The frequency of tropical cyclones is the largest over southeastern China, decreasing northwestward. Taiwan is the region that is affected by tropical cyclones most frequently. The average annual precipitation associated with tropical cyclones has also decreased gradually northwestward from southeastern China.     

西北干旱区极端高温时空变化特征分析

利用1961—2010年西北干旱区83个气象观测站的日气温资料,通过线性倾向率、百分位法及Mann-Kendall法得出西北干旱区极端高温的具体变化特征。用百分位法对西北干旱区日气温数据进行处理,确定极端高温指标的阈值,得出极端高温强度和极端高温事件的频率。结论如下:自1989年开始,西北干旱区年极端高温呈显著上升趋势,空间上西部大于东部,局部地区盆地南缘大于北缘;极端高温日数呈明显的上升趋势;四季极端高温均有上升趋势,秋季增长率最高、冬季最低,秋季极端高温日数增长速率最大;季极端高温及高温日数高值区分布在西北干旱区西北和东南部的盆地边缘,干旱区沙漠边缘及戈壁区;西北干旱区年、季极端高温日数均与年平均气温相关性突出。     

辽宁短期气候变化的波动理论研究

通过近50 a的资料分析得知,气候形成三大因子太阳辐射、大气环流和地理环境年际间的异常波动是引起短期气候变化的根本原因,也是气候灾害年诊断预测的物理依据。运用波动理论不仅能诊断当年的气候灾害,还能开展3～5 a的气候趋势滚动预测。