Influence of late Holocene hillslope processes and landforms on modern channel dynamics in upland watersheds of central Nevada

Stratigraphic, geomorphic, and paleoecological data were collected from upland watersheds in the Great Basin of central Nevada to assess the relationships between late Holocene climate change, hillslope processes and landforms, and modern channel dynamics. These data indicate that a shift to drier, warmer climatic conditions from approximately 2500 to 1300 YPB led to a complex set of geomorphic responses. The initial response was massive hillslope erosion and the simultaneous aggradation of both side-valley alluvial fans and the axial valley system. The final response was fan stabilization and axial channel incision as fine-grained sediments were winnowed from the hillslope sediment reservoirs, and sediment yield and runoff processes were altered. The primary geomorphic response to disturbance for approximately the past 1900 years has been channel entrenchment, suggesting that the evolutionary history of hillslopes has produced watersheds that are prone to incision. The magnitude of the most recent phase of channel entrenchment varies along the valley floor as a function of geomorphic position relative to side-valley alluvial fans. Radial fan profiles suggest that during fan building, fan deposits temporarily blocked the flow of sediment down the main stem of the valley, commonly creating a stepped longitudinal valley profile. Stream reaches located immediately upvalley of these fans are characterized by low gradients and alternating episodes of erosion and deposition. In contrast, reaches coincident with or immediately downstream of the fans exhibit higher gradients and limited valley floor deposition. Thus, modern channel dynamics and associated riparian ecosystems are strongly influenced by landforms created by depositional events that occurred approximately 2000 years ago.     

气候变化对青海生态环境的影响及对策研究

通过分析和总结青海的气候变化及其对生态环境的影响，从气候的角度提出了治理和保护生态环境的措施。     

华山松树木年轮对气候响应的模拟分析

采用树木年轮生长模型，从细胞尺度对华山松在不同时期的树木生长状况，包括早材和晚材的细胞大小等年轮结构变化进行了模拟。所建立的细胞大小年表对气候的响应函数结果，揭示出华山松的生长主要受生长季中4～7月份以及滞后一年降水的影响，而温度只是在生长季节开始的4月份起限制作用。利用气候资料对华山松的细胞大小及变化趋势的模拟结果表明，它与实测值十分接近。     

末次冰期东亚季风气候的数值模拟研究

利用一个Ｔ４２全球大气环流谱模式模拟了现代及末次冰期极盛时期边界条件下的东亚季风气候，并与中国区域内古气候变化的地质证据了对比，综合分析表明，末次末期时东亚冬季风强盛，夏季风衰退，气候大陆度增加。年平均气温普遍下降，我国华南，西北东部至华北，东北地区分别比现代降温２－４℃、８－１０℃及１０℃以上；季风多降水明显减少，与现代相比，东南沿海，江淮至华北，东北地区年降水量分别减少７０－８０％，６０－７０     

“94·7"北京大暴雨的湿位势倾向诊断

利用湿位势倾向方程，对１９９４年７月１２－１３日的７００ｈＰａ位势高度场进行了诊断分析。结果表明，湿位势倾向方程中的差动潜热能平流项，对产生北京地区本次大暴雨天气的台风低压系统发展和移动，起到不可忽视的作用；而相对涡度平流项，在该次过程中作用不大。     

Potential impacts of global warming on the frequency and magnitude of heavy precipitation

It is now widely recognised that the most significant impacts of global warming are likely to be experienced through changes in the frequency of extreme events, including flooding. This paper reviews physical and empirical arguments which suggest that global warming may result in a more intense hydrological cycle, with an associated increase in the frequency and/or magnitude of heavy precipitation. Results derived from enhanced-greenhouse experiments using global climate models (GCMs) are shown to be consistent with these physical and empirical arguments. Detailed analysis of output from three GCMs indicates the possibility of substantial increases in the frequency and magnitude of extreme daily precipitation, with amplification of the effect as the return period increases. Moreover, return period analyses for locations in Australia, Europe, India, China and the USA indicate that the results are global in scope. Subsequent discussion of the limitations of GCMs for this sort of analysis highlights the need for caution when interpreting the precipitation results presented here. However, the consistency between physically-based expectations, empirical observations, and GCM results is considered sufficient for the GCM results to be taken seriously, at least in a qualitative sense, especially considering that the alternative seems to be reliance by planners on the fundamentally flawed concept of a stationary climate.     

人口压力、气候变化与太平天国运动

通过大量史料分析,本文认为:人地矛盾的激化,及在此基础上气候异常造成全国农业大范围连年歉收,对中国历史上着名的太平天国运动(1851-1864年)的爆发,起着特别地激发作用.     

采用条件分位数调整法合并二类气候代用资料的初步分析*

本文采用条件分位数调整法,对二类气候代用资料,华山树木年轮年表和西安旱涝等级序列进行合并尝试,既最大限度地利用在年轮资料中的连续变化信息,又能使历史文献资料可以与其相互补充、校准,从而使得合并出来的序列更有助于对过去气候的重建。     

Multi-source spatial data-based invasion risk modeling of Striga (Striga asiatica) in Zimbabwe

ABSTRACT

Monitoring of destructive invasive weeds such as those from the genus Striga requires accurate, near real-time predictions and integrated assessment techniques to enable better surveillance and consistent assessment initiatives. Thus, in this study, we predicted the potential ecological niche of Striga (Striga asiatica) weed in Zimbabwe, to identify and understand its propagation and map potentially vulnerable cropping areas. Vegetation phenology from remote sensing, bioclimatic and other environmental variables (i.e. cropping system, edaphic, land surface temperature, and terrain) were used as predictors. Six machine learning modeling techniques and the ensemble model were evaluated on their suitability to predict current and future Striga weed distributional patterns. The mentioned predictors (n = 40) were integrated into six models with “presence-only” training and evaluation data, collected in Zimbabwe over the period between the 12^th and 28^th of March 2018. The area under the curve (AUC) and true skill statistic (TSS) were used to measure the performance of the Striga modeling framework. The results showed that the ensemble model had the strongest Striga occurrence predictive power (AUC = 0.98; TSS = 0.93) when compared to the other modeling algorithms. Temperature seasonality (Bio4), the maximum temperature of the warmest month (Bio5) and precipitation seasonality (Bio15) were determined to be the most dominant bioclimatic variables influencing Striga occurrence. “Start of the season” and “season minimum value” of the “Enhanced Vegetation Index base value” were the most relevant remote sensing-based variables. Based on projected climate change scenarios, the study showed that up to 2050, the suitable area for Striga propagation will increase by ~ 0.73% in Zimbabwe. The present work demonstrated the importance of integrating multi-source data in predicting possible crop production restraints due to weed propagation. The results can enhance national preparedness and management strategies, specifically, if the current and future risk areas can be identified for early intervention and containment     

气候的多平衡态及其转换

本文利用一个简单的气候模式,求得三个平衡态的全球半均温度值分别为:T_1=248.5K,T_2=271.9K和T_3=288.1K,其中对应于温暖时期和寒冷时期的T_3和T_1是稳定的.若要使现代温暖气候转变为寒冷气候,太阳常数约需比现代值减少3％:若从寒冷气候转变成温暖气候,太阳常数需增加约6.3％.这表明寒冷气候的状态要比温暖气候的状态相对稳定些.然后讨论了随机扰动对气候半衡态之间转换的作用.结果表明:仅通过天气随机扰动的涨落效应不可能使气候系统实现冰期-间冰期之间10~5年周期尺度的转换.