冬季热带印度洋季节内振荡的物理结构

利用最新的卫星遥感资料、现场观测资料以及海-气通量再分析资料,采用延时相关分析和合成分析方法,分析了冬季热带印度洋季节内振荡的物理结构.结果表明,季节内振荡的结构与原有认识不同,大气深对流中心(短波辐射极小值)和纬向西风极大值(潜热通量极大值)同位相,这种结构有利于海表温度对季节内振荡强迫产生显著的响应,与观测到的热带印度洋海表温度的强季节内变化信号一致,也预示着海-气耦合对于热带印度洋季节内振荡具有重要影响.     

江苏近岸高、低潮位变化规律探讨

利用MForeman改进的G·Godin潮汐调和分析及预报程序对江苏省辐射沙洲海域的16个验潮站潮位资料进行了调和分析和潮汐预报。根据各测潮站高、低潮位预报结果,对各站高低潮潮时差、低潮每日延迟时间、高潮每日延迟时间进行了统计计算,并对辐射沙洲海域高低潮潮时差特征值的分布进行了分析。利用潮汐表预报结果探讨了江苏沿岸6站的高潮位、低潮位、高低潮潮时差、高潮每日延迟时间、低潮每日延迟时间之间的对应关系,并分析给出了各量的变化周期。     

基于Geoda 095i区域经济增长率的空间统计分析研究

空间统计分析的核心是认识与地理位置相关的数据间的空间依赖、空间关联或空间自相关,通过空间位置建立数据间的统计关系。本文利用空间分析的相关知识,通过对河南省各辖市2006年第一季度GDP增长速度及其相关因素的分析,发现该时期内河南省各辖市GDP增长率水平的空间分布并非表现出完全随机性,而是表现出空间相似值之间的空间聚集。基于对Moran散点图的分析和空间滞后回归模型的回归分析,得出空间统计分析对于分析区域经济发展的空间结构形态以及政策制定具有参考价值。     

Spatio‐temporal variability of piezometric response on two steep alpine hillslopes

Information on the main drivers of subsurface flow generation on hillslopes of alpine headwater catchments is still missing. Therefore, the dominant factors controlling the water table response to precipitation at the hillslope scale in the alpine Bridge Creek Catchment, Northern Italy, were investigated. Two steep hillslopes of similar size, soil properties and vegetation cover but contrasting topography were instrumented with 24 piezometric wells. Sixty‐three (63) rainfall‐runoff events were selected over three years in the snow‐free months to analyse the influence of rainfall depth, antecedent moisture conditions, hillslope topographic characteristics and soil depth on shallow water table dynamics. Piezometric response, expressed as percentage of well activation and water peak magnitude, was strongly correlated with soil moisture status, as described by an index combining antecedent soil moisture and rainfall depth. Hillslope topography was found to be a dominant control only for the convex‐divergent hillslope and during wet conditions. Timing of water table response depended primarily on soil depth and topographic position, with piezometric peak response occurring later and showing a greater temporal variability at the hillslope bottom, characterized by thicker soil. The relationship between mean hillslope water table level and standard deviation for all wells reflected the timing of the water table response at the different locations along the hillslopes. The outcomes of this research contribute to a better understanding of the controls on piezometric response at the hillslope scale in steep terrain and its role on the hydrological functioning of the study catchment and of other sites with similar physiographic characteristics. Copyright © 2014 John Wiley & Sons, Ltd.     

THE RELATIONSHIPS BETWEEN SNOW COVER AND CYCLONES IN THE EASTERN UNITED STATES

Snow cover extent is correlated with the latitude, pressure, and frequency of cyclones at every five degrees of longitude from 70° to 100° West, for the winter seasons 1971 to 1980. Each cyclone parameter is also lag correlated with snow cover extent to test relationships between snow cover extent of one week and cyclone variables of successive weeks. More extensive snow cover is related to cyclones traveling farther south, having higher central pressure, and becoming less frequent.     

Impact of Meteorological Drought on Streamflow Drought in Jinghe River Basin of China

Under global climate change, drought has become one of the most serious natural hazards, affecting the ecological environ- ment and human life. Drought can be categorized as meteorological, agricultural, hydrological or socio-economic drought. Among the different categories of drought, hydrological drought, especially streamflow drought, has been given more attention by local govern- ments, researchers and the public in recent years. Identifying the occurrence of streamflow drought and issuing early warning can pro- vide timely information for effective water resources management. In this study, streamflow drought is detected by using the Standard- ized Runoff Index, whereas meteorological drought is detected by the Standardized Precipitation Index. Comparative analyses of fre- quency, magnitude, onset and duration are conducted to identify the impact of meteorological drought on streamflow drought. This study focuses on the Jinghe River Basin in Northwest China, mainly providing the following findings. 1） Eleven meteorological droughts and six streamflow droughts were indicated during 1970 and 1990 after pooling using Inter-event time and volume Criterion method. 2） Streamflow drought in the Jinghe River Basin lagged meteorological drought for about 127 days. 3） The frequency of streamflow drought in Jinghe River Basin was less than meteorological drought. However, the average duration of streamflow drought is longer. 4） The magnitude of streamflow drought is greater than meteorological drought. These results not only play an important theo- retical role in understanding relationships between different drought categories, but also have practical implications for streamflow drought mitigation and regional water resources management.     

Grassland coverage inter-annual variation and its coupling relation with hydrothermal factors in China during 1982-2010

GIMMS (Global Inventory Modeling and Mapping Studies) NDVI (Normalised Difference Vegetation Index) from 1982 to 2006 and MODIS (Moderate Resolution Imaging Spectroradiometer) NDVI from 2001 to 2010 were blended to extract the grass coverage and analyze its spatial pattern. The response of grass coverage to climatic variations at annual and monthly time scales was analyzed. Grass coverage distribution had increased from northwest to southeast across China. During 1982-2010, the mean nationwide grass coverage was 34% but exhibited apparent spatial heterogeneity, being the highest (61.4%) in slope grasslands and the lowest (17.1%) in desert grasslands. There was a slight increase of the grass coverage with a rate of 0.17% per year. Increase in slope grasslands coverage was as high as 0.27% per year, while in the plain grasslands and meadows the grass coverage increase was the lowest (being 0.11% per year and 0.1% per year, respectively). Across China, the grass coverage with extremely significant increase (P<0.01) and significant increase (P<0.05) accounted for 46.03% and 11% of the total grassland area, respectively, while those with extremely significant and significant decrease accounted for only 4.1% and 3.24%, respectively. At the annual time scale, there are no significant correlations between grass coverage and annual mean temperature and precipitation. However, the grass coverage was somewhat affected by temperature in alpine and sub-alpine grassland, alpine and sub-alpine meadow, slope grassland and meadow, while grass coverage in desert grassland and plain grassland was more affected by precipitation. At the monthly time-scale, there are significant correlations between grass coverage with both temperature and precipitation, indicating that the grass coverage is more affected by seasonal fluctuations of hydrothermal conditions. Additionally, there is one-month time lag-effect between grass coverage and climate factors for each grassland types.     

三江源区植被 NDVI 对区域气候的时滞效应分析

以三江源区为研究区,主要利用一元线性趋势法和简单相关分析法分析了源区1982～2004年生长季累积NDVI的时间序列变化特征及其与气温、降雨、光照时间、风速、地表温度这些气候因子之间的相关性,从月尺度上研究了三江源区植被NDVI对气候因子响应的滞后性特征。最后表明,生长季累积NDVI对气温的滞后期为1个月,对风速的滞后期为2个月,对地表温度的滞后期为4个月,而对降雨量和日照时数不存在滞后响应或者滞后期小于1个月。     

Analyses of suspended sediment loads in Slovenian rivers

ABSTRACT

Suspended solids are present in every river, but high quantities can worsen the ecological conditions of streams; therefore, effective monitoring and analysis of this hydrological variable are necessary. Frequency, seasonality, inter-correlation, extreme events, trends and lag analyses were carried out for peaks of suspended sediment concentration (SSC) and discharge (Q) data from Slovenian streams using officially monitored data from 1955 to 2006 that were made available by the Slovenian Environment Agency. In total more than 500 station-years of daily Q and SSC data were used. No uniform (positive or negative) trend was found in the SSC series; however, all the statistically significant trends were decreasing. No generalization is possible for the best fit distribution function. A seasonality analysis showed that most of the SSC peaks occurred in the summer (short-term intense convective precipitation produced by thunderstorms) and in the autumn (prolonged frontal precipitation). Correlations between Q and SSC values were generally relatively small (Pearson correlation coefficient values from 0.05 to 0.59), which means that the often applied Q–SSC curves should be used with caution when estimating annual suspended sediment loads. On average, flood peak Q occurred after the corresponding SSC peak (clockwise-positive hysteresis loops), but the average lag time was rather small (less than 1 day).

Editor M.C. Acreman; Associate editor Y. Gyasi-Agyei     

Temporal and spatial response of vegetation NDVI to temperature and precipitation in eastern China

Temporal and spatial response characteristics of vegetation NDVI to the variation of temperature and precipitation in the whole year, spring, summer and autumn was analyzed from April 1998 to March 2008 based on the SPOT VGT–NDVI data and daily temperature and precipitation data from 205 meteorological stations in eastern China. The results indicate that as a whole, the response of vegetation NDVI to the variation of temperature is more pronounced than that of precipitation in eastern China. Vegetation NDVI maximally responds to the variation of temperature with a lag of about 10 days, and it maximally responds to the variation of precipitation with a lag of about 30 days. The response of vegetation NDVI to temperature and precipitation is most pronounced in autumn, and has the longest lag in summer. Spatially, the maximum response of vegetation NDVI to the variation of temperature is more pronounced in the northern and middle parts than in the southern part of eastern China. The maximum response of vegetation NDVI to the variation of precipitation is more pronounced in the northern part than in the middle and southern parts of eastern China. The response of vegetation NDVI to the variation of temperature has longer lag in the northern and southern parts than in the middle part of eastern China. The response of vegetation NDVI to the variation of precipitation has the longest lag in the southern part, and the shortest lag in the northern part of eastern China. The response of vegetation NDVI to the variation of temperature and precipitation in eastern China is mainly consistent with other results, but the lag time of vegetation NDVI to the variation of temperature and precipitation has some differences with those results of the monsoon region of eastern China.