Recent Changes in Precipitation Extremes in the Heihe River Basin,Northwest China

Changes in rainfall extremes pose a serious and additional threat to water resources planning and management, natural and artificial oasis stability, and sustainable development in the fragile ecosystems of arid inland river basins. In this study, the trend and temporal variation of extreme precipitation are analyzed using daily precipitation datasets at 11 stations over the arid inland Heihe River basin in Northwest China from 1960 to 2011. Eight indices of extreme precipitation are studied. The results show statistically significant and large-magnitude increasing and decreasing trends for most indices, primarily in the Qilian Mountains and eastern Hexi Corridor. More frequent and intense rainfall extremes have occurred in the southern part of the desert area than in the northern portion. In general, the temporal variation in precipitation extremes has changed throughout the basin. Wet day precipitation and heavy precipitation days show statistically significant linear increasing trends and step changes in the Qilian Mountains and Hexi Corridor. Consecutive dry days have decreased obviously in the region in most years after approximately the late 1980s, but meanwhile very long dry spells have increased, especially in the Hexi Corridor. The probability density function indicates that very long wet spells have increased in the Qilian Mountains. The East Asian summer monsoon index and western Pacific subtropical high intensity index possess strong and significant negative and positive correlations with rainfall extremes, respectively. Changes in land surface characteristics and the increase in water vapor in the wet season have also contributed to the changes in precipitation extremes over the river basin.

气候变化对黄河径流的影响

讨论了自然气候变化和人类活动产生的未来气候变化对黄河区域水情的影响。通过比较不同区域气候模式如厄尔尼诺（其概念采用Trenberth的定义，即“在Nino3和4区域海平面气温在6个月或更长时间内的5个月的滑动平均异常升高值为0．4℃”）、拉尼娜（热带太平洋海域变冷，是厄尔尼诺的对立事件）及南方涛动等来研究自然气候变化对径流的影响；通过观测数据和Arc GIS地理统计分析工具获得的径流、降水和温度的关系，评估未来气候变化对区域水情的影响。结果显示：①人类活动是导致过去50年中黄河流域水资源危机的首要因子；②除了人类活动，气候变化也是黄河流域径流减少的主要因子；③黄河流域的降水和径流显示了与厄尔尼诺或拉尼娜气候变化的有显著的响应，同时该响应也具有空间上的差异；④运用41年的观测资料建立了降水-径流-气温的关系，结果显示径流对降水和气温同样具有敏感性；⑤在研究基于观测资料的气候变化对区域水情的影响中，ArcGIS地理统计分析软件是一个有用的工具。

Isotopic evidence for soil water sources and reciprocal movement in a semi-arid degraded wetland:Implications for wetland restoration

Understanding water dynamics is a prerequisite for the restoration of degraded ecosystems in arid and semiarid regions.In this study,we carried out δD and δ^(18)O analyses of precipitation,unsaturated soil water,overland flow,surface runoff,and groundwater samples from a seasonally flooded wetland in the Momoge National Nature Reserve of the Songnen Plain,Northeast China,to identify the water sources and understand the mechanisms of unsaturated soil water movement.Unsaturated soil water content(W/W%)at every 20 cm along with a soil profile(0–100 cm)was collected during the growing season,and the HYDRUS-1D model was used to simulate temporal-spatial variations.The results showed that the local meteoric water line(δD=5.90δ18O-7.34,R2=0.95)had a smaller slope and intercept than the global meteoric water line because of strong evaporation at our study site under semi-arid climate.The groundwater was partly recharged by local precipitation via overland flow and unsaturated soil water infiltration.Unsaturated soil water was sourced from both precipitation and groundwater with variations at different depths.The upper soil layer at 0–15 cm was mainly sourced from limited precipitation,while the groundwater could move up to a 25 cm layer during the dry period.The unsaturated soil water content increased with soil depth in the top 40 cm,decreased at depths of 40 to 80 cm,and increased again at depths of 80 to 100 cm.The HYDRUS-1D model could simulate the unsaturated soil water dynamics well in the upper(0–40 cm)and lower(80–100 cm)sections,but poorly for depths of 40–80 cm due to the upward and downward flow.The bidirectional unsaturated soil water movement highlights the importance of capillary groundwater for wetland plants with similar climatic or hydrogeological conditions.

Vegetation dynamics induced by groundwater fluctuations in the lower Heihe River Basin,northwestern China

Aims Since 2000,the environmental flow controls project has been implemented in the lower Heihe River Basin,a typical arid inland river basin in northwest China,to restore the deteriorated ecological environment in this region.The aim of this study was to explore the impacts of groundwater fluctuations on vegetation dynamics.Our results can be used as a reference for water resources planning and management to maintain proper environmental flows in arid areas.Methods The location(by Global Positioning System)and depth of the monitoring wells,as well as groundwater table depth and salinity were measured in situ at each site from July to August 2009.Based on the measurements of the groundwater table depth and salinity following the implementation of environmental flow controls project(EFCP)in the lower Heihe River Basin,the groundwater fluctuations during the period from 2001 to 2009 were analyzed.Descriptive statistics and Pearson’s correlation were used to analyze the relationship between vegetation changes and groundwater table fluctuations.Additionally,the spatial distributions of the groundwater table depth and salinity were interpolated using the simple kriging method.Trend analysis was applied to the time series of integrated Moderate Resolution Imaging Spectroradiometer normalized difference vegetation index data to identify interannual vegetation dynamics.The relationship between vegetation status and groundwater environment was investigated at different spatial scales by analyzing and comparing the time series and trends.Important Findings(i)The groundwater table and salinity increased significantly in most of the study area with spatial heterogeneity.On average,the groundwater table rose;0.5 and 1.5 m in the upper and lower Ejina Basin,respectively,and the groundwater salinity increased across the study area by 0–4%.(ii)A notable correlation between the vegetation status and the groundwater table was revealed when the groundwater table depth fluctuated between 1.8 and 3.5 m,whereas the vegetation did not show an obvious response to groundwater table changes when the groundwater table depth was more than 5–6 m.(iii)Vegetation restoration mainly occurred in riparian areas within 500–1000 m of from natural rivers,where the groundwater table depth varied from 2 to 4 m,and salinity was<5%,whereas vegetation degradation appeared at some locations where groundwater environment had deteriorated.

Operational Reliability Model of Hybrid MMC Considering Multiple Time Scales and Multi-state Submodule

Environmental and electrical factors such as wind speed,air temperature and switching frequency have significant influences on the operational reliability of hybrid modular multilevel converter(MMC),which is commonly used for the wind power transmission.However,the existing reliability model of hybrid MMC based on statistics cannot accurately reflect the impact of these factors.In this paper,a new operational reliability model of hybrid MMC is presented.The reliability index of the hybrid MMC is coupled with its operation characteristics by calculating multi-term thermal cycling.In addition,an operation strategy of hybrid MMC is proposed to improve its reliability.The multi-state submodule(SM)is developed,which is capable of bypassing specific faulty power modules instead of the whole SM.Case studies show that the proposed operational reliability model could describe the impact of environmental and electrical factors.Also,the proposed operation strategy can improve the reliability of hybrid IMMC by extending the operation time of SMs.

Opportunities and challenges of immune checkpoint inhibitors for extensive-stage small-cell lung cancer

Small-cell lung cancer(SCLC)accounts for 15%–20%of primary lung cancers,and it is characterized by low differentiation,rapid proliferation,and early metastasis.At least two-thirds of SCLC patients present with the extensive stage(ES)at the time of initial clinical diagnosis.Over the last 2 decades,platinum-based combination chemotherapy has remained the standard first-line treatment for SCLC.With the introduction of the immunotherapy era,immunotherapy plus chemotherapy has replaced conventional chemotherapy as the first-line treatment option for ES-SCLC and is recommended by National Comprehensive Cancer Network clinical guidelines.Therefore,in this review,we present the latest research advances in SCLC treatment,predictive biomarkers,and other topics of high interest to provide options for patients with SCLC.