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Spatial and temporal variability of temperature,precipitation, and streamflow in upper Sang‐kan basin,China 
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下载免费PDF全文 Temporal streamflow variability in an inland hydrologic station and temporal trends and frequency changes at three weather stations in a semiarid river basin located in Loess Plateau, China, were detected by using linear regression, Mann–Kendall analysis, and wavelet transform methods. Double cumulative curve and ordered clustering were used to identify the hydrological periods of upper Sang‐kan (USK) basin between 1957 and 2012. The results indicate that (1) precipitation in the USK basin over the study period did not show any trend, while the temperature showed a significant increase; (2) streamflow flowing out of the USK basin indicated a significant decrease; (3) two distinct hydrological periods – the ‘natural period’ from 1957 to 1984 and the ‘human impact period’ from 1985 to 2012 – were present; and (4) the contributions of climate change and human activities to reduce the streamflow were 36.9% and 63.1% respectively. The results indicate that human activities may be contributing to a decrease in streamflow in the USK basin. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
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Leif Kullman 《Geografiska Annaler: Series A, Physical Geography》1997,79(3):139-165
The paper reviews various kinds of geoecological change in the tree-limit ecotone of the Scandes Mountains during the period 1970–95. The focus of the study is a part of a regional network of sites intended for long-term tree-limit monitoring, with special stress on effects of climatic variability. The elevational tree-limits of Betula pubescens sp. Sortuosa, Picea abies and Pinus sylvestris, which rose in response to the climatic amelioration earlier this century, now show clear symptoms of increasing climatic stress and disturbance. This manifests as defoliation, growth recession and reproductive failure, locally leading to some initial elevational tree-limit retraction (unbalanced mortality). Defoliation was preceded by decades of weak summer cooling and an increasingly maritime climate, but recently it correlates significantly with low winter soil temperatures, causing death of needles, shoots and buds. In some habitats, Betula pubescens has suffered from mechanical stress and disturbance by increased snow accumulation. Tree-limit decline is paralleled by analogous responses of high-elevation boreal forests as well as the ground cover, encompassing elevational range-limit retraction of certain plant species, deterioration of alpine/subalpine dwarf-shrub heaths and terricolous lichen mats. These processes coincide with indications of enhanced periglacial activity, chiefly wind deflation of frost-heaved top-soils at exposed sites. Presumably, reindeer trampling and grazing play a certain role in the latter context, although this disturbance interacts with climate cooling and increased storminess. Short-term extreme events, particularly concerning winter climate (e.g. ground frost), represent previously underrated disturbance mechanisms in cold-stressed, high-altitude boreal forest. The results suggest mechanisms of tree-layer regression, which lag behind the most severe stresses and disturbances by decades and make cold-marginal trees increasingly sensitive to climatic extremes and, in addition, unable to respond progressively to later positive weather anomalies, due to major defoliation and hypothetical xylem cavitation. The recorded changes are logical in consequence of the irregular climatic cooling and a more maritime climate since the late 1930s. In a wider perspective, the results fit a current pattern of natural geoecological destabilization and rapid vegetation change in the North Atlantic region. In addition, the results are discussed in the perspective of global climate change and biogeographical records over the past few decades. 相似文献
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