The Variability of the Snow and Ice Melt in Alpine Rivers in Northwestern China

The study of snow and ice melt （SIM） is important in water-scarce arid regions for the assessment of water supply and quality. These studies involve unique difficulties, especially in the calibration of hydro-models because there is no direct way to continuously measure the SIM at hydrostations. The recursive digital filter （RDF） and the isotopic hydro-geochemical method （IHM） were coupled to separate the SIM from eight observed series of alpine streamflows in northwestern China. Validation of the calibrated methods suggested a good capture of the SIM characteristics with fair accuracy in both space and time. Applications of the coupled methods in the upper reaches of the Hei River Basin （HRB） suggested a double peak curve of the SIM fraction to streamflow for the multi-component recharged （MCR） rivers, while a single peak curve was suggested for the rainfall-dominant recharged （RDR） rivers. Given inter-annual statistics of the separation, both types of the alpine rivers have experienced an obvious decrease of SIM since 196os. In the past 10 years, the SIM in the two types of rivers has risen to the levels of the 1970s, but has remained lower than the level of the 1960s. The study provided a considerable evidence to quantify the alpine SIMbased on the separation of observed data series at gauge stations. Application of the coupled method could be helpful in the calibration and validation of SIM-related hydro-models in alpine regions.

Human settlement and changes in the distribution of river systems in the Minqin Basin over the past 2000 years in Northwest China

Introduction:Arid area is an important base for human settlement,however,long and drastic human activities have altered the drainage patterns in the arid watersheds significantly,causing serious ecological consequences.This study,through a case study of the Minqin Basin,a microcosm of the artificial oases in the arid northwest China,used the multitypes of data to recover the spatial distribution of human settlement and drainage patterns during historical period and analyze the relationship between them over the past 2000 years.Outcomes:Before the Han Dynasty(121 BC),the utilization of water resources in the Minqin Basin was in the primitive stage and the drainage pattern maintained the natural state.From the Han(121 BC-220)to the Wei-Jin Dynasties(220-316),the utilization of water resources intensified unprecedentedly,but the natural shape of the river systems was still maintained.In the following 1,000 years or so,the drainage pattern was in the state of“following its own course”due to the small human population.In the Ming Dynasty(1368-1644),with the alteration of the main rivers,the water resource utilization increased obviously,but the human reclamations were mainly confined to the southern part of the basin.In the Qing Dynasty(1644-1911),the reclamation of the Liulin Lake area significantly changed the drainage patterns,resulted in the drastically northward expansion of human settlement.Since the foundation of the People’s Republic of China(PRC)in 1949,the artificial water system completely replaced the natural water system and intensified the ecological problems in the basin.Discussion:The changes over the past 2000 years show the drastic impacts of human activities on the alterations of the drainage patterns and related ecological problems in the arid Northwest China.Conclusion:Rehabilitation of such ecological impairments requires both ecological restoration projects and changes in human paradigm and behavior over multiple temporal and spatial scales.

Understanding the attributes of the dual oasis effect in an arid region using remote sensing and observational data

Investigating the attributes of the dual oasis effect and oasis–desert interactions is crucial for understanding the climatic and ecological effects of oases.In this study,oasis effect intensity(OEI)was used as an indicator to investigate the factors that contribute to the dual oasis effect.The oasis effect has two attributes:the surface oasis heating effect(OHE)occurred in winter,while the oasis cooling effect(OCE)occurred in the other three seasons,especially in summer.During the day,the OEI of the whole oasis was−12.8℃,−5.2℃,and−4.5℃ in summer,spring,and autumn,respectively,which indicated a strong OCE;and OEI was 0.5℃ in winter,which indicated a weaker OHE.In arid regions,the OCE dominated most of the time,but the OHE occurred in winter and cannot be ignored.In addition,through statistical analysis and energy balance analysis,high evapotranspiration of the oasis was the main factor leading to the occurrence of OCE in the summer,while low albedo to the occurrence of OHE in winter.