中国近46年来冬半年日降水变化特征分析

中国总体冬半年降水总量、日降水强度以及强降水日数都有不同程度的增加趋势。西北地区的变化相对显著,其平均降水量、降水日数及日降水强度都呈增加趋势,特别是20世纪80年代后期发生跃变。华北和中部地区降水总量趋于减少。南方3区多为增加趋势,其中东南和华南与冬季风及欧亚遥相关型有显著的负相关关系,而西南地区日降水参数则与温度和北极涛动指数显著相关。东北地区降水指标没有明显的一致趋势。     

早新生代温室气候及冰期气候转型的模拟研究

早新生代是地质史上最后一个温室气候期,随后南极冰盖形成,地球进入到晚新生代冰期。温室气候的成因和冰期气候转型的机制一直是国际相关学界关注的问题。评述国际上对此开展的古气候模拟,反映了早新生代温室气候受到了海洋和大陆的地理位置、暖海洋温盐环流和海洋热输送、太阳辐射和大气CO2浓度变化的作用和影响。古气候模拟还反映了早新生代温室气候转向冰期气候,受到了大洋通道改变和高原构造隆起、大气成分变化以及海陆生态系相互的作用和反馈。这些古气候模拟试验锁定在气候变化的关键时段和重要驱动因子,对测试地球内外驱动力和地球各圈层反馈作用提供了重要的科学依据;温室气候以及趋向冰期气候的模拟研究对探讨气候变化内在机制、预测未来气候具有重要意义。      

2023年秋季我国气候异常特征及成因分析

利用NCEP/NCAR再分析数据集和中国2400个站的气候观测数据,对2023年秋季我国气候异常特征及其成因进行分析。2023年秋季全国平均气温为1961年以来历史同期最高;全国平均降水量接近常年同期,但空间分布不均且季节内变化明显。秋季欧亚中高纬环流呈“两槽一脊”型,造成我国气温显著偏高;9月呈“两脊一槽”型,巴尔喀什湖低槽活动导致西北地区降水增多;10月呈“两槽一脊”型,导致北方地区偏暖加强;11月呈“西高东低”型,东路冷空气增强,东北地区气温偏低、降水偏多。西太平洋副热带高压总体较常年偏强、偏西,脊线9月异常偏北、10月偏南、11月接近常年。印缅槽9月显著偏强,10—11月接近常年。9月印缅槽偏强与副热带高压异常偏北共同导致了长江中下游以北至黄河下游地区多雨;10—11月东部地区水汽条件整体偏差。9—10月近海台风频繁活动,造成华南地区降水偏多。2023年秋季我国气候受到大气季节内变化的显著作用,热带海温异常的影响不典型。     

2023年全球重大天气气候事件

2023年,全球平均气温比工业化前高出约1.45℃(±0.12℃),是有观测记录以来最热的一年。全球海平面继续上升,且全球平均海平面达到了有卫星记录(1993年至今)以来的最高水平,反映了持续的海洋变暖以及冰川和冰盖的融化。北极海冰面积仍远低于常年值,南极海冰面积创下历史新低。巴基斯坦、中国京津冀地区、意大利、巴西圣保罗州北部沿海地区、新西兰北岛等地遭受暴雨洪涝灾害,非洲西北部、中国云南、中美洲和南美洲北部发生严重干旱,南欧、北美、南美、东亚和南亚等地遭遇创纪录高温热浪,欧洲和北美等地遭遇寒流和暴风雪侵袭,强对流天气频繁袭击世界各处,全球热带气旋活动频繁。     

Variability of temperature,salinity and tidally‐averaged density in the middle estuary of the St Lawrence

Abstract

Surveys in the Middle Estuary of the St Lawrence have yielded a data base consisting of more than 15,000 T‐S pairs distributed over 62 13‐h profiling stations. Although the T‐S curves at each station are remarkably linear, the variability of the slopes and intercepts of the lines is considerable. The means and standard deviations of the temperature and salinity at each individual station are not explicable in terms of linear combinations of the parameters for location in the Estuary, the upstream water properties, the phase of the spring‐neap cycle and the tidal energies.

It is shown that the tidally‐averaged density structure is separable into horizontal and vertical components and that its vertical variation over the whole Estuary may be explained by any one of three different functional forms. However, its horizontal variation is not explicable in terms of linear combinations of the parameters mentioned in the paragraph above.

Plots of the horizontal variations in temperature, salinity or density may only be meaningful if the data are collected synoptically, and even then cannot be considered to be accurate over time‐scales longer than one tidal cycle.     

Investigation into the daily precipitation variability in the Yangtze River Delta,China

In this article, by using the daily precipitation data measured at 58 meteorological stations, spatial and temporal variability of daily precipitation including zero rainfall values (called “precipitation”) and without zero rainfall values (called “rain”) and four precipitation extrema (P₀, P₂₀, P₅₀, and P₁₀₀ representing the daily precipitation with the magnitude smaller than 0.1 mm, bigger than 20 mm, 50 mm, and 100 mm per day, respectively) in the Yangtze River Delta (YRD) during 1958–2007 were analyzed, and the effects of urbanization were further investigated. Results indicate that (i) differing from the downward trends in 1958–1985, daily precipitation and rain in 1986–2007 show slowly downward trends in the mid YRD but show upward trends in the northern and southern YRD. (ii) Spatial and temporal variability of the rain is more complex than daily precipitation. Both of them become smaller but show more obvious fluctuations in 1986–2007. (iii) Urbanizations cause not only the urban rainfall island problem but also more obvious fluctuations of rain intensity in the mid YRD, reflecting more uncertainty of daily precipitation variability. (iv) Urbanizations have little effects on the variability of P₀ and P₁₀₀ but cause notable increases of P₂₀ and P₅₀. (v) The spatial variability of daily precipitation and precipitation extrema in 1958–1985 clearly shows a breakpoint at 30°20′N latitude, but the breakpoint disappears afterward because of the effects of urbanization. Copyright © 2012 John Wiley & Sons, Ltd.     

Paleoclimate studies and natural-resource management in the Murray-Darling Basin I: past,present and future climates

This paper provides an incisive review of paleoclimate science and its relevance to natural-resource management within the Murray-Darling Basin (MDB). The drought of 1997–2010 focussed scientific, public and media attention on intrinsic climate variability and the confounding effect of human activity, especially in terms of water-resource management. Many policy and research reviews make statements about future planning with little consideration of climate change and without useful actionable knowledge. In order to understand future climate changes, modellers need, and demand, better paleoclimate data to constrain their model projections. Here, we present an insight into a number of existing long-term paleoclimate studies relevant to the MDB. Past records of climate, in response to orbital forcing (glacial–interglacial cycles) are found within, and immediately outside, the MDB. High-resolution temperature records, spanning the last 10⁵ years, exist from floodplains and cave speleothems, as well as evidence from lakes and their associated lunettes. More recently, historical climate records show major changes in relation to El Niño–Southern Oscillation cycles and decadal shifts in rainfall regimes. A considerable body of research currently exists on the past climates of southeastern Australia but, this has not been collated and validated over large spatial scales. It is clear that a number of knowledge gaps still exist, and there is a pressing need for the establishment of new paleoclimatic research within the MDB catchment and within adjacent, sensitive catchments if past climate science is to fulfil its potential to provide policy-relevant information to natural-resource management into the future.     

Sensitivity of streamflow from a Himalayan catchment to plausible changes in land cover and climate

Global climate change will likely increase temperature and variation in precipitation in the Himalayas, modifying both supply of and demand for water. This study assesses combined impacts of land‐cover and climate changes on hydrological processes and a rainfall‐to‐streamflow buffer indicator of watershed function using the Soil Water Assessment Tool (SWAT) in Kejie watershed in the eastern Himalayas. The Hadley Centre Coupled Model Version 3 (HadCM3) was used for two Intergovernmental Panel on Climate Change (IPCC) emission scenarios (A2 and B2), for 2010–2099. Four land‐cover change scenarios increase forest, grassland, crops, or urban land use, respectively, reducing degraded land. The SWAT model predicted that downstream water resources will decrease in the short term but increase in the long term. Afforestation and expansion in cropland will probably increase actual evapotranspiration (ET) and reduce annual streamflow but will also, through increased infiltration, reduce the overland flow component of streamflow and increase groundwater release. An expansion in grassland will decrease actual ET, increase annual streamflow and groundwater release, while decreasing overland flow. Urbanization will result in increases in streamflow and overland flow and reductions in groundwater release and actual ET. Land‐cover change dominated over effects on streamflow of climate change in the short and middle terms. The predicted changes in buffer indicator for land‐use plus climate‐change scenarios reach up to 50% of the current (and future) range of inter‐annual variability. Copyright © 2010 John Wiley & Sons, Ltd.     

Integrating downscaled CMIP5 data with a physically based hydrologic model to estimate potential climate change impacts on streamflow processes in a mixed‐use watershed

Climatic changes have altered surface water regimes worldwide, and climate projections suggest that such alterations will continue. To inform management decisions, climate projections must be paired with hydrologic models to develop quantitative estimates of watershed scale water regime changes. Such modeling approaches often involve downscaling climate model outputs, which are generally presented at coarse spatial scales. In this study, Coupled Model Intercomparison Project Phase 5 climate model projections were analyzed to determine models representing severe and conservative climate scenarios for the study watershed. Based on temperature and precipitation projections, output from GFDL‐ESM2G (representative concentration pathway 2.6) and MIROC‐ESM (representative concentration pathway 8.5) were selected to represent conservative (Δ_C) and severe (Δ_S) change scenarios, respectively. Climate data were used as forcing for the soil and water assessment tool to analyze the potential effects of climate change on hydrologic processes in a mixed‐use watershed in central Missouri, USA. Results showed annual streamflow decreases ranging from ?5.9% to ?26.8% and evapotranspiration (ET) increases ranging from +7.2% to +19.4%. During the mid‐21st century, sizeable decreases to summer streamflow were observed under both scenarios, along with large increases of fall, spring, and summer ET under Δ_S. During the late 21st century period, large decreases of summer streamflow under both scenarios, and large increases to spring (Δ_S), fall (Δ_S) and summer (Δ_C) ET were observed. This study demonstrated the sensitivity of a Midwestern watershed to future climatic changes utilizing projections from Coupled Model Intercomparison Project Phase 5 models and presented an approach that used multiple climate model outputs to characterize potential watershed scale climate impacts.