The spatial distribution of valley setting （laterally-unconfined, partly-confined, or confined） and fluvial morphology in the source region of the Yangtze and Yellow Rivers is contrasted and analyzed. The source reg...The spatial distribution of valley setting （laterally-unconfined, partly-confined, or confined） and fluvial morphology in the source region of the Yangtze and Yellow Rivers is contrasted and analyzed. The source region of the Yangtze River is divided into 3 broad sections （I, II and III） based on valley setting and channel gradient, with the upstream and downstream sections being characterized by confined （some reaches partly-confined） valleys while the middle section is characterized with wide and shallow, laterally-unconfined valleys. Gorges are prominent in sections I and III, while braided channel patterns dominate section II. By contrast, the source region of the Yellow River is divided into 5 broad sections （sections I-V） based on valley characteristics and channel gradient. Sections I, II and IV are alluvial reaches with mainly laterally-unconfined （some short reaches partly-confined） valleys. Sections III and V are mainly confined or partly-confined. Greater morphological diversity is evident in the source region of the Yellow River relative to the upper Yangtze River. This includes braided, anabranching, anastomosing, meandering and straight alluvial patterns, with gorges in confined reaches. The macro-relief （elevation, gradient, aspect, valley alignment and confinement） of the region, linked directly to tectonic movement of the Qinghai-Tibet Plateau, tied to climatic, hydrologic and biotic considerations, are primary controls upon the patterns of river diversity in the region.展开更多
Previous study comes to the conclusion： based on the anomalies of the South Asian high （SAH）, 100-hPa geopotential height, and 100-hPa circulation over tropical and subtropical regions, we can predict precipitation...Previous study comes to the conclusion： based on the anomalies of the South Asian high （SAH）, 100-hPa geopotential height, and 100-hPa circulation over tropical and subtropical regions, we can predict precipitation anomaly in the Yangtze River Valley and North China. To test its validity, a series of experiments have been designed and operated, which include controlled experiment, sensitivity experiment （which has added anomalies into 100-hPa geopotential height and wind field）, and four-composite experiments. Experiments based on the composed initial field such as EPR-CF, EPR-CD, EPR-HF, and EPR-HD, can reproduce the floods or droughts in the Yangtze River Valley and North China. It suggests that anomalies of the SAH, 100- hPa geopotential height, and circulation over tropical and subtropical regions may probably imply summer precipitation anomalies in the two regions. Sensitivity experiment results show that anomalies of the SAH, 100-hPa geopotential height, and southwest flow in the previous period is a signal of droughts or floods for the following summer in the Yangtze River Valley and North China. And it is also one of the factors that have impact on summer precipitation anomaly in the two regions. Positive anomaly of 100-hPa geopotential height and the anomalous intensifying of the SAH and southwest flow will induce floods in the Yangtze River Valley and droughts in North China; while negative anomaly of 100-hPa geopotential height and anomalous weakening of the SAH and southwest flow will induce droughts in the Yangtze River Valley and floods in North China.展开更多
A novel species of Rhamnaceae,Colubrina zhaoguangii,is discovered in Sichuan,China,during the biodiversity investigations of the Second Tibetan Plateau Scientific Expedition and Research.Detailed descriptions and illu...A novel species of Rhamnaceae,Colubrina zhaoguangii,is discovered in Sichuan,China,during the biodiversity investigations of the Second Tibetan Plateau Scientific Expedition and Research.Detailed descriptions and illustrations of the new species are presented herein.To date,the new species is only found in dry-warm river valleys of the Jinsha River basin in the Hengduan Mountains region(HDM).Compared with the other two known Chinese Colubrina species,C.zhaoguangii features by the habit of twisted shrub and tiny leaves with emarginate apex.In morphology,the new species highly resembles C.alluaudii endemic in Madagascar and C.viridis in northwestern Mexico,whereas it is distinguished from these two relatives by its minutely white scales on the leaf blades.The discovery of C.zhaoguangii reminds us again that the bottom region is also important for biodiversity conservation in HDM and should be a flora survey priority.展开更多
基金National Natural Science Foundation of China, No.41001008 No.51209010+1 种基金 International Science ＆ Technology Cooperation Program of China, No.2011DFA20820 No.2011DFG93160Acknowledgements Gary Brierley gratefully acknowledges support from a Visiting Professorship awarded by the Chinese Academy of Sciences.
文摘The spatial distribution of valley setting （laterally-unconfined, partly-confined, or confined） and fluvial morphology in the source region of the Yangtze and Yellow Rivers is contrasted and analyzed. The source region of the Yangtze River is divided into 3 broad sections （I, II and III） based on valley setting and channel gradient, with the upstream and downstream sections being characterized by confined （some reaches partly-confined） valleys while the middle section is characterized with wide and shallow, laterally-unconfined valleys. Gorges are prominent in sections I and III, while braided channel patterns dominate section II. By contrast, the source region of the Yellow River is divided into 5 broad sections （sections I-V） based on valley characteristics and channel gradient. Sections I, II and IV are alluvial reaches with mainly laterally-unconfined （some short reaches partly-confined） valleys. Sections III and V are mainly confined or partly-confined. Greater morphological diversity is evident in the source region of the Yellow River relative to the upper Yangtze River. This includes braided, anabranching, anastomosing, meandering and straight alluvial patterns, with gorges in confined reaches. The macro-relief （elevation, gradient, aspect, valley alignment and confinement） of the region, linked directly to tectonic movement of the Qinghai-Tibet Plateau, tied to climatic, hydrologic and biotic considerations, are primary controls upon the patterns of river diversity in the region.
基金Supported by the National Key Developing Programme for Basic Science Project under No.1998040900 amd the Key Project of National Natural Science Foundation of China under No.40175021.
文摘Previous study comes to the conclusion： based on the anomalies of the South Asian high （SAH）, 100-hPa geopotential height, and 100-hPa circulation over tropical and subtropical regions, we can predict precipitation anomaly in the Yangtze River Valley and North China. To test its validity, a series of experiments have been designed and operated, which include controlled experiment, sensitivity experiment （which has added anomalies into 100-hPa geopotential height and wind field）, and four-composite experiments. Experiments based on the composed initial field such as EPR-CF, EPR-CD, EPR-HF, and EPR-HD, can reproduce the floods or droughts in the Yangtze River Valley and North China. It suggests that anomalies of the SAH, 100- hPa geopotential height, and circulation over tropical and subtropical regions may probably imply summer precipitation anomalies in the two regions. Sensitivity experiment results show that anomalies of the SAH, 100-hPa geopotential height, and southwest flow in the previous period is a signal of droughts or floods for the following summer in the Yangtze River Valley and North China. And it is also one of the factors that have impact on summer precipitation anomaly in the two regions. Positive anomaly of 100-hPa geopotential height and the anomalous intensifying of the SAH and southwest flow will induce floods in the Yangtze River Valley and droughts in North China; while negative anomaly of 100-hPa geopotential height and anomalous weakening of the SAH and southwest flow will induce droughts in the Yangtze River Valley and floods in North China.
基金This study was supported by the Second Tibetan Plateau Scientific Expedition and Research(STEP)program(2019QZKK0301)National Natural Science Foundation of China(31860167 and 32101234)Wild Plants Sharing and Service Platform of Sichuan Province.
文摘A novel species of Rhamnaceae,Colubrina zhaoguangii,is discovered in Sichuan,China,during the biodiversity investigations of the Second Tibetan Plateau Scientific Expedition and Research.Detailed descriptions and illustrations of the new species are presented herein.To date,the new species is only found in dry-warm river valleys of the Jinsha River basin in the Hengduan Mountains region(HDM).Compared with the other two known Chinese Colubrina species,C.zhaoguangii features by the habit of twisted shrub and tiny leaves with emarginate apex.In morphology,the new species highly resembles C.alluaudii endemic in Madagascar and C.viridis in northwestern Mexico,whereas it is distinguished from these two relatives by its minutely white scales on the leaf blades.The discovery of C.zhaoguangii reminds us again that the bottom region is also important for biodiversity conservation in HDM and should be a flora survey priority.
