Statistical downscaling of extremes of precipitation and temperature and construction of their future scenarios in an elevated and cold zone

Reliable projections of extremes at finer spatial scales are important in assessing the potential impacts of climate change on societal and natural systems, particularly for elevated and cold regions in the Tibetan Plateau. This paper presents future projections of extremes of daily precipitation and temperature, under different future scenarios in the headwater catchment of Yellow River basin over the 21st century, using the statistical downscaling model (SDSM). The results indicate that: (1) although the mean temperature was simulated perfectly, followed by monthly pan evaporation, the skill scores in simulating extreme indices of precipitation are inadequate; (2) The inter-annual variabilities for most extreme indices were underestimated, although the model could reproduce the extreme temperatures well. In fact, the simulation of extreme indices for precipitation and evaporation were not satisfactory in many cases. (3) In future period from 2011 to 2100, increases in the temperature and evaporation indices are projected under a range of climate scenarios, although decreasing mean and maximum precipitation are found in summer during 2020s. The findings of this work will contribute toward a better understanding of future climate changes for this unique region.     

万全断裂的几何结构和活动特征

本文根据实地调查和探测资料对万全断裂的几何结构和构造活动进行分析与研究,结果表明：该断裂是洋河盆地北缘断裂带的组成断裂之一,由南、北两段斜列组成,呈北东-北北东走向展布,为正断层,长约15km;断裂在第四纪期间持续活动,控制着附近地区的构造演化和地貌发育：西北侧中生代地层抬升,形成低山丘陵;东南侧地块下降,接受第四纪堆积,构成山间盆地;晚更新世以来单条断层的平均垂直活动速率大于0.03—0.3mm/a。     

The Runoff Declining Process and Water Quality in Songhuajiang River Catchment,China under Global Climatic Change

The runoff in Songhuajiang River catchment has experienced a decreasing trend during the second half of the 20th century. Serially complete daily rainfall data of 42 rainfall stations from 1959 to 2002 and daily runoff data of five meteorological stations from 1953 to 2005 were obtained. The Mann–Kendall trend test and the sequential version of Mann–Kendall test were employed in this study to test the monthly and annual trends for both rainfall and runoff, to determine the start point of abrupt runoff declining, and to identify the main driving factors of runoff decline. The results showed an insignificant increasing trend in rainfall but a significant decreasing trend in runoff in the catchment. For the five meteorological stations, abrupt runoff decline occurred during 1957–1963 and the middle 1990s. Through Mann–Kendall comparisons for the area‐rainfall and runoff for the two decreasing periods, human activity, rather than climatic change, is identified as the main driving factor of runoff decline. Analysis of land use/cover shows that farmland is most related with runoff decline among all the land use/cover change in Nenjiang catchment. From 1986 to 1995, the area of farmland increased rapidly from 6.99 to 7.61 million hm². Hydraulic engineering has a significant influence on the runoff decline in the second Songhuajiang catchment. Many large‐scale reservoirs and hydropower stations have been built in the upstream of the Second Songhuajiang and lead to the runoff decline. Nenjiang and the Second Songhuajiang are the two sources of mainstream of Songhuajiang. Decreased runoff in these two sub‐catchments then results in runoff decrease in mainstream of Songhuajiang catchment. It is, therefore, concluded that high percent agricultural land and hydraulic engineering are the most probable driving factors of runoff decline in Songhuajiang River catchment, China.     

A hybrid stochastic-weather-generation method for temporal disaggregation of precipitation with consideration of seasonality and within-month variations

Linking atmospheric and hydrological models is challenging because of a mismatch of spatial and temporal resolutions in which the models operate: dynamic hydrological models need input at relatively fine temporal (daily) scale, but the outputs from general circulation models are usually not realistic at the same scale, even though fine scale outputs are available. Temporal dimension downscaling methods called disaggregation are designed to produce finer temporal-scale data from reliable larger temporal-scale data. Here, we investigate a hybrid stochastic weather-generation method to simulate a high-frequency (daily) precipitation sequence based on lower frequency (monthly) amounts. To deal with many small precipitation amounts and capture large amounts, we divide the precipitation amounts on rainy days (with non-zero precipitation amounts) into two states (named moist and wet states, respectively) by a pre-defined threshold and propose a multi-state Markov chain model for the occurrences of different states (also including non-rain days called dry state). The truncated Gamma and censored extended Burr XII distributions are then employed to model the precipitation amounts in the moist and wet states, respectively. This approach avoids the need to deal with discontinuity in the distribution, and ensures that the states (dry, moist and wet) and corresponding amounts in rainy days are well matched. The method also considers seasonality by constructing individual models for different months, and monthly variation by incorporating the low-frequency amounts as a model predictor. The proposed method is compared with existing models using typical catchment data in Australia with different climate conditions (non-seasonal rainfall, summer rainfall and winter rainfall patterns) and demonstrates better performances under several evaluation criteria which are important in hydrological studies.     

阿尔金南缘断裂东段晚第四纪活动特征

阿尔金断裂的几何学和运动学特征对研究青藏高原构造演化和陆内地震机理非常重要。为定量科学研究较为薄弱的阿尔金南缘断裂东段的运动学参数,我们采用航卫片的解译、野外调查、地形测绘和年代学样品测试等多种方法对该段进行了初步研究。结果显示该段断裂主要以左旋走滑运动为主,且沿线存在较多的小位移,其位移空间分布的3个明显峰值分别为4.5m、8m和13m。根据河流阶地的左旋位移和相应的地貌面沉积年龄,得到晚第四纪以来阿尔金断裂东段的走滑速率约为2.7±0.9mm/a。基于所获得的定量参数,认为该段断裂向东以应变分解的形式将其应变量传递到相邻的逆冲断裂上。     

沙漠细沙筛分时间和投加量对干筛分析结果的影响

筛分时间和投加量对沙漠沙干筛分析结果有着直接的影响,但目前对此鲜有报导。本文研究筛分时间（1~17 min）和投加量（20~100 g）对沙漠细沙筛分效果的影响。结果表明：在干筛分析过程中,20 g投加量时筛分效果在3 min达到稳定,而投加量在30~100 g时约在9 min达到稳定,意味着沙漠样品筛分需要的最短筛分时间与样品投加量有关。光学显微镜检测表明,干筛筛分的沙粒样品仍有11%~30%粗颗粒和1%~4%的细颗粒存在,此混杂比例具体因沙粒粒级而异。颗粒形状等因素造成了干筛筛分法与光学显微镜分析法的差异。     

塔里木盆地北缘奥陶系古溶洞和古岩溶沉积中包壳砾石和包壳砾岩的发现及特征*

塔里木盆地北缘奥陶系发育典型的古岩溶,笔者在其中发现了一种非常特殊的沉积物或沉积构造:包壳砾石和包壳砾岩,且这种包壳砾岩之前从未见报道。该包壳砾石和包壳砾岩的结构类似鲕粒或核形石,可分为核心和包壳2部分,大部分呈近圆形或扁圆形,少数形态不规则,直径为数厘米到数十厘米。核心可分为4种,分别是:(1)与溶洞围岩相同的灰岩砾石;(2)由砂岩形成的核心;(3)由砾岩构成的复合核心;(4)由古钙华碎块形成的核心。包壳也可分为4种类型,分别是:(1)具有圈层的包壳;(2)颗粒状包壳;(3)均质包壳;(4)由颗粒状包壳和圈层状包壳组合形成的复合包壳。包壳砾石和包壳砾岩是溶洞和岩溶沉积中的典型产物,其不仅可以作为识别溶洞和岩溶的标志之一,而且具有一定的储集能力,是一种有效的油气储集体。     

闸坝的水文水环境效应及其量化方法探讨

如何正确处理流域开发与生态环境保护的关系,客观评价闸坝对生态环境的影响,是我国流域管理中亟待解决的科学问题之一。本文从河流的自然特性入手,剖析了闸坝修建和调控引起的水文水环境效应,探讨了闸坝对河流水量水质影响评价的理论基础、关键内容和技术手段等,提出了基于流域水循环过程认识和模拟的闸坝效应量化体系和分析方法;并以我国水利工程最密集、污染最严重的淮河流域为例,初步探索了流域闸坝的水文水环境效应。研究可为多闸坝调控流域水资源开发利用和水污染治理提供理论支持,为实现流域综合管理及社会经济可持续发展作出贡献。     

有关地理学研究中几个学术问题的研讨——学习黄秉维院士严谨治学的精神

黄秉维院士是我国地学、资源、环境领域的伟大思想家与设计大师。作为新中国地理学奠基人, 他为我国地理科学的发展做出了巨大贡献。值黄秉维院士诞辰百年之际, 作者回顾了黄秉维院士提出的四个学术问题:“生态环境”、“水热平衡在地理学研究中的作用”、“确切地估计森林的作用”和“钝端科学”, 并结合作者的相关研究工作阐述了对这四个问题的认识与体会, 以印证他的学术思想对后学者研究工作的重要引领与指导作用。