TOWARDS CHARACTERIZING AND PLANNING FOR DROUGHT IN VERMONT‐PART I: A CLIMATOLOGICAL PERSPECTWE1

ABSTRACT: In the Green Mountain state of Vermont, droughts of one form or another and of varying intensities, seventies, and areal extent are not uncommon occurrences. The 1990s were marked by at least three drought events of which the 1998 to 1999 was the most recent. In spite of this recurrence, ongoing drought monitoring and mitigative planning efforts are not as advanced as they could be and no official drought plan exists for the state. This article is the first of two in this volume. It summarizes the cascade of drought types that impacted the state during the 1998 to 1999 episode. From a number of precipitation statistics and drought indices, fine spatial scales (county or better) were found to best capture the character of drought impacts, while the weekly time step is recommended as the temporal unit around which to base planning and monitoring efforts. The companion article outlines a possible framework for drought planning efforts and highlights key constituencies to be included in the process.     

DOWNSCALED CLIMATE AND STREAMFLOW STUDY OF THE SOUTHWESTERN UNITED STATES1

ABSTRACT: Downscaling coarse resolution climate data to scales that are useful for impact assessment studies is receiving increased attention. Basin-scale hydrologic processes and other local climate impacts related to water resources such as reservoir management, crop and forest productivity, and ecosystem response require climate information at scales that are much finer than current and future GCM resolutions. The Regional Climate System Model (RCSM) is a dynamic downscaling system that has been used since 1994 for short-term precipitation and streamflow predictions and seasonal hindcast analysis with good skill. During the 1997–1998 winter, experimental seasonal forecasts were made in collaboration with the NOAA Climate Prediction Center and UCLA with promising results. Preliminary studies of a control and 2°CO₂ perturbation for the southwestern U.S. have been performed.     

MODELED REGIONAL CLIMATE CHANGE IN THE HYDROLOGIC REGIONS OF CALIFORNIA: A CO2 SENSITIVITY STUDY1

ABSTRACT: Using a regional climate model (RegCM2.5), the potential impacts on the climate of California of increasing atmospheric CO₂ concentrations were explored from the perspective of the state's 10 hydrologic regions. Relative to preindustrial CO₂ conditions (280 ppm), doubled preindustrial CO₂ conditions (560 ppm) produced increased temperatures of up to 4°C on an annual average basis and of up to 5°C on a monthly basis. Temperature increases were greatest in the central and northern regions. On a monthly basis, the temperature response was greatest in February, March, and May for nearly all regions. Snow accumulation was significantly decreased in all months and regions, with the greatest reduction occurring in the Sacramento River region. Precipitation results indicate drier winters for all regions, with a large reduction in precipitation from December to April and a smaller decrease from May to November. The result is a wet season that is slightly reduced in length. Findings suggest that the total amount of water in the state will decrease, water needs will increase, and the timing of water availability will be greatly perturbed.     

SUMMER FLOODING AT CHICAGO AND POSSIBLE RELATIONSHIPS TO URBAN-INCREASED HEAVY RAINFALL1

ABSTRACT: : Studies of two measures of flooding in the Chicago metropolitan area reveal a wide range of floods with the magnitude related to recurrence interval expressions of rain intensity. Minor type floods (in basements and underpasses) usually result from localized heavy rains (≤ 3-hour duration) with return intervals of 1 to 2 years, and more major floods result from rains with return intervals of 2 to 5 years (or more). Urban-factors help lead to increases in warm season rain events in Chicago with 1- to 4-year return intervals. These apparently help lead to 10 to 100 percent more flooding events in Chicago than expected. The range of increase varies depending on locale and type of flood, but the increases in storms should be accounted for in drainage designs.     

STREAM TEMPERATURE CORRELATIONS WITH AIR TEMPERATURES IN MINNESOTA: IMPLICATIONS FOR CLIMATE WARMING1

ABSTRACT: Air temperatures are sometimes used as easy substitutes for stream temperatures. To examine the errors associated with this substitution, linear relationships between 39 Minnesota stream water temperature records and associated air temperature records were analyzed. From the lumped data set (38,082 daily data pairs), equations were derived for daily, weekly, monthly, and annual mean temperatures. Standard deviations between all measured and predicted water temperatures were 3.5°C (daily), 2.6°C (weekly), 1.9°C (monthly), and 1.3°C (annual). Separate analyses for each stream gaging station gave substantially lower standard deviations. Weather monitoring stations were, on average, 37.5 km from the stream. The measured water temperatures follow the annual air temperature cycle closely. No time lags were taken into account, and periods of ice cover were excluded from the analysis. If atmospheric CO₂ doubles in the future, air temperatures in Minnesota are projected (CCC GCM) to rise by 4.3°C in the warm season (April-October). This would translate into an average 4.1°C stream temperature rise, provided that stream shading would remain unaltered.     

近10年中国大陆MODlS遥感气溶胶光学厚度特征

应用2001-2010年MODIS大气气溶胶光学厚度（AOD）资料,分析中国550nmAOD年和季节平均分布。还选取了10个代表性区域,分析AOD变化特征。这些分析建立起了近10年来中国气溶胶光学厚度的气候学特征：中国年平均AOD空间区域分布中心大体呈现两低两高。两低中心位于植被覆盖度高和人烟稀少的（1）黑龙江和内蒙古东北高纬度地区（－0．2）;（2）川、滇与青藏高原交界的西南高海拔地区（0．1-0．2）。一个AOD低值带（0．2－0．3）连接这两个低中心,呈东北西南走向跨过中国大陆。在此低值带两侧,各有一片AOD高值中心（－0．8）：（1）人口密集和工业化发展带来的大量人为气溶胶形成了一个覆盖了华北、长江流域（从四川盆地,两湖地区到长三角）到华南珠江三角洲相联的大片高AOD中心区域;（2）以沙尘为主的自然气气溶胶造就了西北塔克拉玛干沙漠及周边高AOD区。中国AOD这一两低两高区域分布特征基本保持四季不变,但其中心强度呈现各自区域性季节变化。中国春季AOD高值区的面积最大,其次是夏季,然后是秋季,面积最小的是冬季。南方AOD月变化规律多为双峰型,即3－5和8－9月出现2次高峰,5－7月从南向北先后出现波谷,变化规律与季风响应。北方为单峰型,6－7月为高峰,11到来年2月为低谷。用弱季风年（2002）和强季风年（2003）季风影响区域气象条件和气溶胶数据对比分析表明,大陆AOD的月空间分布和变化与季风气候,以及风速、风向、降水、温度和湿度等的变化有关。     

一次暴雨空报和预警失误分析

通过分析2009年5月17到20日的天气背景、对比分析清远本站和郴州站的探空资料,以及清远本站的湿度、风等要素,找出北部地区和南部地区在同一环流背景下,所产生量级差异较大的降水原因。得出郴州站对北部地区的强降水指示意义在一定程度上大于清远本站;而清远本站的单站资料对清远本站强降雨指示意义明显。精细分析天气系统位置,可提高强天气在同一地区内的精细落区预报。雷达资料对本站的强天气预警信号发布具有重要指示意义。     

南极长城站夏季海雾预报的初步研究

基于南极长城站的气象观测(1985-2006年)和NCEP(National Centers for Environmental Prediction)的再分析数据,分析了该地区海雾的天气气候特征、海雾与气象要素的关系以及有利于海雾发生的3种典型天气形势,并据此初步建立了长城站夏季海雾预报系统。后报试验表明,该系统对长城站夏季海雾的预报效果较好。     

近50 a来广西各级降水气候变化特征分析

利用1961-2012 年广西80 个地面气象观测站的降水资料,分析广西各级降水的气候趋势特征,结果得到：春季大雨和中雨降水占总雨量百分率最大;夏季暴雨百分率最大,其次为大雨和中雨,最小为小雨;秋季中雨百分率最大,其次为小雨和大雨,最小为暴雨;冬季小雨百分率最大,其次为中雨和大雨,最小为暴雨。小雨雨量占总雨量的百分率在春夏季广西大部地区呈减小趋势;中雨雨量百分率在春夏季有减小的变化趋势,秋冬季变化趋势不明显;大雨雨量百分率在春夏秋季变化趋势不明显,冬季有增大的趋势;广西大部分地区暴雨雨量百分率在一年四季里均有增多的趋势,尤其在夏季增多趋势最明显。总的来看,广西的降水结构有向极端强降水转移的发展趋势。     

天气形势对四川盆地区域性臭氧污染的影响

本研究结合地面观测资料,ERA5再分析数据和PCT客观分型法,分析了2014~2019年四川盆地区域性O₃污染特征以及天气形势与O₃污染的关系.结果表明,2014~2019年四川盆地O₃区域污染发生频数呈单峰型分布,于2016年达到峰值,且发生区域主要集中在成都平原城市群.在6种典型天气类型中,类型1、2、6为污染型,其海平面气压呈西高东低,四川盆地受低压系统控制.类型3、4为清洁型,其中类型3呈北高南低,且在四川盆地东部存在1个低值中心;类型4呈东高西低,在青藏高原区域有一些小范围的高压中心.在污染型天气形势下,四川盆地的气象条件为温度高、云量低、地面接收到的紫外辐射强、相对湿度低,加速了O₃的生成,再叠加类型1的静风条件不利于污染物扩散;类型2、6盛行的东南气流对O₃及其前体物的输送,造成污染型天气类型发生区域性O₃污染比例明显高于其他几种类型.此外,基于环流分型的预测结果表明环流形势对四川盆地各城市群区域O₃污染影响可以达到其年变化的2倍以上,对整个四川盆地O₃浓度变化的贡献率为34.8%~66.3%.