利用三维加速度点质量模型法监测2010年中国西南干旱

在附有空间约束的三维加速度点质量模型法的基础上引入水文模型进行约束,利用水文模型计算地理点之间的相关性,采用L曲线法确定最优正则化参数。计算结果表明,引入水文模型的三维加速度点质量模型法相比零阶Tikhonov约束的三维加速度点质量模型法信噪比大于0的比例更高。采用该方法对2010年中国西南地区干旱情况进行监测;同时,在剔除季节性信号后,利用主成分分析法对水储量异常进行分析。结果表明,西南地区在2009年秋至2010年春存在明显的水储量负异常特征。

中国西南干旱河谷植物群落的数量分类和排序分析

中国西南干旱河谷植被是我国西南横断山区特有的植被类型,目前关于西南干旱河谷植被还没有整体性的群落类型划分研究。根据对甘肃、四川、云南三省九条主要河流的干旱河谷段野外调查和文献来源的1,339个植物群落样方数据,采用自适应仿射传播聚类方法,对我国西南干旱河谷的植物群落进行数量分类,并采用典范对应分析方法进行排序分析。结果表明:(1)调查样方的植物群落分为7个植被型(稀树草原、肉质灌丛、常绿阔叶灌丛、暖性落叶阔叶灌丛、常绿硬叶林、落叶阔叶林和暖性针叶林),24个群系,31个群丛类型。暖性落叶阔叶灌丛是本植被区的代表性植被类型;分布最广的群系为鞍叶羊蹄甲灌丛(Form.Bauhinia brachycarpa,样方比例50.9%)、黄茅灌草丛(Form.Heteropogon contortus,样方比例11.9%)、孔颖草灌草丛(Form.Bothriochloa pertusa,样方比例5.6%)、黄荆灌丛(Form.Vitex negundo,样方比例4.2%)、知风草灌草丛(Form.Eragrostis ferruginea,样方比例3.8%)、车桑子灌丛(Form.Dodonaea viscosa,样方比例3.4%)、云南松疏林(Form.Pinus yunnanensis,样方比例3.3%)。(2)冬季低温和降水的季节性是限制干旱河谷植物群落分布的主要气候因子。稀树草原、肉质灌丛是典型的干热河谷植被类型;暖性落叶阔叶灌丛、常绿硬叶林、常绿阔叶灌丛是干暖河谷植被的优势类型;暖性针叶林、落叶阔叶林则主要在干温河谷环境占优势。

中国西南干旱河谷植被的区系地理成分与空间分异

根据对云南、四川、甘肃三省九条主要河流干旱河谷的植物群落调查数据,对我国西南干旱河谷维管束植物区系的科、属分布区类型进行划分,并分析其地理分布格局。结果表明:(1)西南干旱河谷区的植物区系地理成分复杂,联系广泛,共包含11个科级和15个属级分布区类型;总体上,科、属两级热带/温带成分比例分别为3.06和1.77,显示了强烈的热带区系亲缘及温带区系的后期影响;与地中海–西亚至中亚植物区系存在一定联系;其东亚成分和中国特有成分比例低于亚热带区系平均水平,且中国–喜马拉雅成分比例高于中国–日本成分。(2)从西南向东北方向,植物区系的热带性质逐渐减弱,温带性质逐渐增强;科、属水平区系成分与古地中海–中亚区系的相似性逐渐增强;东亚和中国特有成分比例增加;南盘江与元江的干旱河谷植物区系之间存在中国–日本和中国–喜马拉雅成分的分界线。(3)根据干旱河谷植物属区系成分的比例构成将怒江、澜沧江和元江与其他流域分开,显示了长江溯源侵蚀和水系合并对西南诸河流植物区系发育的影响。

中国西南地区干旱Copula函数模型对样本量的敏感性分析

基于中国西南地区(四川省、云南省、贵州省和重庆市)89个站点1961—2010年的逐月标准化降水指数序列,利用游程理论和Copula函数建立干旱历时和干旱强度的概率模型,基于该模型讨论了干旱事件样本量对分布参数、干旱类型的出现概率及联合重现期的影响.结果表明:分布参数稳定对样本量的要求较大,部分区域样本量要求大于50,并且各参数对样本量的要求不一致,又以干旱强度分布的参数对样本量的要求最大;干旱事件样本量为10个左右求得的干旱类型出现概率和联合重现期与样本量为40求得的结果已无明显差异,以计算结果作为标准可大幅降低统计模型建立对样本量的要求,进而表明起止时间不一致和具有缺测数据的站点仍可建立干旱历时和干旱强度的分布函数;气候变暖对模型建立所需的最少样本量影响不大,样本量波动在±5之间,即统计模型具有一定的稳定性,同时气候态的划分降低了分布检验对样本量的需求,易于模型的建立.

Drought over China in the 21st Century: Results of RegCM3

Based on 150-year simulations of a regional climate model, RegCM3, under the Special Report on Emissions Scenarios (SRES) A1B scenario, the effective drought index (EDI) is used to project the future drought change in China. During the baseline period 1986-2005, RegCM3 was found to reliably simulate the spatial pattern of drought over the country. Over the 21st century, the regionally averaged EDI should increase, corresponding to a decrease of drought, while the probability of extreme drought events should increase. Geographically, drought should clearly increase in Northeast China, the middle and lower reaches of the Yangtze River valley, Southwest China, and southern Tibet but decrease in most parts of the rest of the country.

Evaluation of the WRF Model with Different Land Surface Schemes: A Drought Event Simulation in Southwest China during 2009–10

The authors examined the performance of version 3.4.1 of the Weather Research and Forecasting Model(WRF) with various land surface schemes in simulating a severe drought event in Southwest China. Five numerical experiments were completed using the Noah land surface scheme, the Pleim-Xiu land surface scheme, the Noah-MP land surface schemes, the Noah- MP scheme with dynamic vegetation, and the Noah-MP scheme with dynamic vegetation and groundwater processes. In general, all the simulations reasonably reproduced the spatial and temporal variations in precipitation, but significant bias was also found, especially for the spatial pattern of simulated precipitation. The WRF simulations with the Noah-MP series land surface schemes performed slightly better than the WRF simulation with the Noah and Pleim-Xiu land surface schemes in reproducing the severe drought events in Southwest China. The leaf area index(LAI) simulated by the different land surface schemes showed significant deviations in Southwest China. The Pleim-Xiu scheme overestimated the value of LAI by a factor of two. The Noah-MP scheme with dynamical vegetation overestimated the magnitude of the annual cycle of the LAI, although the annual mean LAI was close to observations. The simulated LAI showed a long-term lower value from autumn 2009 to spring 2010 relative to normal years. This indicates that the LAI is a potential indictor to monitor drought events.

Daily SPEI Reveals Long-term Change in Drought Characteristics in Southwest China

Drought is the most widespread and insidious natural hazard, presenting serious challenges to ecosystems and human society. The daily Standardized Precipitation Evapotranspiration Index(SPEI) has been developed to identify the regional spatiotemporal characteristics of drought conditions from 1960 to 2016, revealing the variability in drought characteristics across Southwest China. Daily data from142 meteorological stations across the region were used to calculate the daily SPEI at the annual and seasonal time scale. The Mann-Kendall test and the trend statistics were then applied to quantify the significance of drought trends, with the following results. 1) The regionally averaged intensity and duration of all-drought and severe drought showed increasing trends, while the intensity and duration of extreme drought exhibited decreasing trends. 2) Mixed(increasing/decreasing) trends were detected, in terms of intensity and duration, in the three types of drought events. In general, no evidence of significant trends(P < 0.05) was detected in the drought intensity and duration over the last 55 years at the annual timescale. Seasonally, spring was characterized by a severe drought trend for all drought and severe drought conditions, while extreme drought events in spring and summer were very severe. All drought intensities and durations showed an increasing trend across most regions, except in the northwestern parts of Sichuan Province. However, the areal extent of regions suffering increasing trends in severe and extreme drought became relatively smaller. 3) We identified the following drought hotspots: Guangxi Zhuang Autonomous Region from the 1960 s to the 1990 s, respectively. Guangxi Zhuang Autonomous Region and Guizhou Province in the 1970 s and 1980 s, and Yunnan Province in the 2000 s. Finally, this paper can benefit operational drought characterization with a day-to-day drought monitoring index, enabling a more risk-based drought management strategy in the context of global warming.

Detecting Effects of the Recent Drought on Vegetation in Southwestern China

The severest drought on record occurred in southwestern China from September 2009 until March 2010. In order to measure the impact the drought imposed on vegetation, we developed an evaluation indicator called the Vegetation Index Anomaly （VIA） based on MODIS/EVI. The tempo- spatial pattern of this impact was analyzed. Given that this impact may be modulated by many factors, the responses of different vegetation types （woodland, grassland and cropland）, and the spatial pattern of meteorological drought were also analyzed. Results show that more than 50% of vegetation suffered because of this drought event, but there was significant tempo-spatial variability in the range and intensity of impact. This variability may be caused by many factors. Of the three major vegetation types, cropland was the most sensitive to drought, followed by grassland and then woodland. In addition, meteorological factors （precipitation and air temperature） also played a role; however, obvious differences exist between the spatial distribution pattern of drought-stricken vegetation and that of meteorological drought, which further demonstrates the intervention of other factors besides meteorological factors. So compared to meteorological drought, the vegetation index may be more useful for measuring the actual intensity, duration and impact of drought events. The limitations of vegetation indices are also considered.