东北高空湿度变化特征及其与地面气温和降水的关系

利用1971-2005年探空和地面观测资料，详细分析了东北地区高空比湿和相对湿度的时空变化特征，并探讨了比湿和相对湿度与地面气温、降水量的关系。结果表明：东北地区比湿空间分布主要受到水汽来源的影响，地面由东南向西北递减，高空由南向北递减；相对湿度受水汽、海拔高度和纬度的共同影响，地面和对流层下层由南向北先减后增，对流层中层由南向北递增，赤峰向通辽延伸的西南一东北向干舌地面最明显，随高度增加逐渐减弱。1971～2005年，东北地区比湿从地面到高空均为增加趋势，对流层中下层的增加趋势更加显著；相对湿度在地面呈显著减小趋势，对流层中层呈显著增加趋势。大气比湿与地面气温在年、季尺度上存在一致的显著正相关关系，大气相对湿度与地面气温在季节尺度上存在显著负相关关系；对流层中下层相对湿度与降水量相关最显著；地面气温升高对东北气候趋于干旱化起了重要作用，高空相对湿度增加有利于降水增加，气温与比湿的相互消长，影响了气候的干、湿变化。

1960-2012年山东省近地面和高空相对湿度时空变化特征

[目的]探讨近地面和高空相对湿度的时空变化特征及其与气温和降水的关系,为研究山东省气候波动过程提供依据。[方法]基于山东省1960—2012年探空和地面观测资料,采用回归分析、IDW空间插值、Mann-Kendall单调趋势检验法以及敏感性分析等方法研究了相对湿度变化特征。[结果]1960—2012年,山东省近地面年均相对湿度呈下降趋势,变化速率为-0.23%/10a(p>0.05)。其中,春季、秋季和夏季相对湿度下降速率大小依次为-0.45%/10a,-0.42%/10a和-0.18%/10a,而冬季相对湿度却呈增加趋势(0.10%/10a)。空间上,近地面相对湿度从东部沿海向西部内陆递减,而下降趋势呈现"东快西慢"的特点。高空相对湿度也呈下降趋势,而且对流层中下层的变化趋势比上层明显。近地面相对湿度季节变化对年变化的贡献率由大到小依次为:秋季>春季>冬季>夏季,对流层中下层各季的贡献率大小依次为:秋季>冬季>春季>夏季,而对流层上层各季贡献率由大到小为:夏季>秋季>冬季>春季。[结论]敏感性分析表明,干旱指数变化1%,将引起近地面和高空相对湿度分别变化-1.55%和-1.95%,而气温或降水变化1%,将导致相对湿度变化在-0.15%~0.09%。

Drought Forecasting in a Semi-arid Watershed Using Climate Signals:a Neuro-fuzzy Modeling Approach

Large-scale annual climate indices were used to forecast annual drought conditions in the Maharlu-Bakhtegan watershed,located in Iran,using a neuro-fuzzy model.The Standardized Precipitation Index(SPI) was used as a proxy for drought conditions.Among the 45 climate indices considered,eight identified as most relevant were the Atlantic Multidecadal Oscillation(AMO),Atlantic Meridional Mode(AMM),the Bivariate ENSO Time series(BEST),the East Central Tropical Pacific Surface Temperature(NINO 3.4),the Central Tropical Pacific Surface Temperature(NINO 4),the North Tropical Atlantic Index(NTA),the Southern Oscillation Index(SOI),and the Tropical Northern Atlantic Index(TNA).These indices accounted for 81% of the variance in the Principal Components Analysis(PCA) method.The Atlantic surface temperature(SST:Atlantic) had an inverse relationship with SPI,and the AMM index had the highest correlation.Drought forecasts of neuro-fuzzy model demonstrate better prediction at a two-year lag compared to a stepwise regression model.

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.

The influence of anthropogenic climate change on wet and dry summers in Europe

Understanding the role of anthropogenic forcings in regional hydrological changes can help communities plan their adaptation in an informed manner.Here we apply attribution research methods to investigate the effect of human influence on historical trends in wet and dry summers and changes in the likelihood of extreme events in Europe.We employ an ensemble of new climate models and compare experiments with and without the effect of human influence to assess the anthropogenic contribution.Future changes are also analysed with projections to year 2100.We employ two drought indices defined relative to the pre-industrial climate:one driven by changes in rainfall only and one that also includes the effect of temperature via changes in potential evapotranspiration.Both indices suggest significant changes in European summers have already emerged above variability and are expected to intensify in the future,leading to widespread dryer conditions which are more extreme in the south.When only the effect of rainfall is considered,there is a distinct contrast between a shift towards wetter conditions in the north and dryer in the south of the continent,as well as an overall increase in variability.However,when the effect of warming is also included,it largely masks the wet trends in the north,resulting in increasingly drier summers across most of the continent.Historical index trends are already detected in the observations,while models suggest that what were extremely dry conditions in the pre-industrial climate will become normal in the south by the end of the century.

Are regional precipitation-productivity relationships robust to decadal-scale dry period?

Precipitation(PPT)is the primary climatic determinant of plant growth and aboveground net primary productivity(ANPP)for many of the world’s major terrestrial ecosystems.Thus,relationships between PPT and productivity can provide insight into how changes in climate may alter ecosystem functions globally.Spatial PPT–ANPP relationships for grasslands are found remarkably similar around the world,but whether and how they change during periods of extended climatic anomalies remain unknown.Here,we quantifed how regional-scale PPTANPP relationships vary between an extended wet and a dry period by taking advantage of a 35-year record of PPT and NDVI(as a surrogate for ANPP)at 1700 sites in the temperate grasslands of northern China.We found a sharp decrease in the strength of the spatial PPT–ANPP relationship during an 11-year period of below average PPT.We attributed the collapse of this relationship to asynchrony in the responses of different grassland types to this decadal period of increased aridity.Our results challenge the robustness of regional PPT–productivity if aridity in grasslands is increased globally by climate change.