Tag Archives: paper

近期两个工作

  • Zhang G, Nan Z*, Zhao L, Liang Y, Cheng G. Qinghai-Tibet Plateau wetting reduces  permafrost thermal responses to climate warming. Earth and Planetary Science Letters.  2021, 562: 116858. https://doi.org/10.1016/j.epsl.2021.116858

我们在这个工作利用数值模拟研究了同时增温与增湿情况下的冻土热效应。我们有一些有意思的发现:1 夏季降水增多有助于保存冻土 (活动层土壤降温),气温升高会导致退化,因此增湿能起到缓冲、抵消增温对冻土的影响。2 增湿的这种效应具有空间性,在干旱区、半干旱区有显著作用,在半湿润与湿润区则作用不明显。3 在半干旱区发现增湿的双重作用,对活动层起到降温效果,对下伏多年冻土层则起到升温作用。详细介绍及论文原文请见我们的小组官网

此工作是我们此前一个关于冬季变暖对多年冻土影响的工作的后续工作。

  • Cao Z, Gao H, Nan Z*, Yin Z, Zhao Y. A semi-physical approach for downscaling soil  moisture data in a typical cold alpine area, Northwest China. Remote Sensing. 2021,  13(3): 509. https://doi.org/10.3390/rs13030509.

这是我两位硕士的工作。他们改进了一个前人工作,利用表观热惯性(ATI)作为代理变量,考虑土壤异质性,实现卫星土壤水产品的降尺度。区别于直接利用ATI 与土壤水的关系,该工作利用一个物理方法估算土壤质地方差以表征粗网格内部的土壤异质性。效果不错,但实用性一般,主要是因为他们是利用MODIS 产品计算ATI,而MODIS产品存在严重数据缺失,因此导致该方法在数据缺失的时候也不能用。但应该会有其他合适的变量。更详细介绍及论文见这里

最近的两个论文

  • Hu J#, Zhao S#, Nan Z*, Wu X, Sun X. A novel approach for mapping permafrost in a large  area using subregion maps and satellite data. Permafrost and Periglacial Processes. 2020,  31(4): 548-560. 

我们发展了一个利用区域调查图来制作大区域冻土分布图的方法,输入包括遥感地表温度、土壤类型等数据。详细介绍见:https://permalab.science/frostnum-cop-permafrost-mapping-method.html

  • Chen Y, Nan Z*, Zhao S, Xu Y. A Bayesian approach for interpolating clear-sky MODIS  land surface temperatures on areas with extensive missing data. IEEE Journal of Selected  Topics in Applied Earth Observations and Remote Sensing. 2020, 14: 515-528.  

我们在Yu et al. 2015的基础上,发展了一种利用时序上邻近的多个影像对缺失的地表温度进行晴空等效地表温度插值的方法。详细介绍见:https://permalab.science/modis-jstars-2020.html

GRL: 青藏高原冬季变暖对多年冻土的影响研究

被誉为世界“第三极”的青藏高原是全球中低纬度地区海拔最高、面积最大的多年冻土区,被称为全球变化的“驱动机”和“放大器”。过去50年青藏高原变暖趋势明显,导致多年冻土发生显著退化,进而严重影响到区域水文、生态乃至全球气候系统。近30年高原变暖速率显著增加,且冬季变暖速率快于夏季变暖。这就引发了一个重要的科学问题,即冬季变暖如何影响整个高原多年冻土的变化。然而,迄今为止,尚未有研究评估多年冻土对冬季变暖的响应。

针对上述科学问题,我们以数值实验为手段,首次研究了青藏高原冬季变暖对多年冻土的影响,结果表明:

  • 1980−2009年,青藏高原冬季气温以0.66 °C/10a的速度升高,是夏季增温0.27 °C/10a的两倍多。在2000s,夏季变暖有所减缓而冬季变暖不断增强。
  • 多年冻土的活动层厚度主要受夏季变暖的影响,而季节性冻土的最大冻结深度主要受冬季变暖的影响。即使气候持续变暖,多年冻土的活动层厚度却呈轻微下降趋势,为0.07 m/10a。虽然多年冻土的面积总体上保持相对稳定,但过去30年,多年冻土的年平均低温以0.13 °C/10a的速度升高。
  • 2000年以前,夏季变暖主导着多年冻土热状况的变化,之后,冬季变暖对多年冻土热状况的影响逐渐增大并超过了夏季变暖,冬季变暖加剧了多年冻土的热退化。由于2000年以来冬季快速变暖,青藏高原北部羌塘高原的高寒连续多年冻土发生了显著的区域性变暖。这是先前研究从未报道过的一个新的发现。

该研究通过假设数值实验首次研究了冬季变暖对多年冻土变化的影响,为理解青藏高原多年冻土对季节性变暖的响应提供了一个新的视角。

Continue reading

教学论文:“GIS算法基础”课程教学研究

摘要:“ GIS 算法基础”课程是高校GIS 专业主干课该课程具有理论性强、内容碎片化、前沿性和知识面广的特点,对数学和计算机的能力要求高,学生学习和教师授课都有较大难度。文章总结了南京师范大学GIS 专业开展该课程的教学经验提出注重基础、兼顾前沿、旨在启迪的原则和问题求解导向、整体把握、翻转课堂、同伴教学等针对性措施此外还应通过大量实验课程来巩固教学效果和驱动学生主动学习。

南卓铜,张宏,潘雪莹,高红侠,赵淑萍. “GIS算法基础”课程教学研究. 高等理科教育. 2019(3): 114-120.

一篇关于冻土区调参的论文

Zhao Y, Nan Z*, Yu W, Zhang L. Calibrating a hydrological model by stratifying frozen ground types and seasons in a cold alpine basin. Water. 2019, 11(5): 985. DOI:10.3390/w11050985.

Abstract: Frozen ground and precipitation seasonality may strongly affect hydrological processes in a cold alpine basin, but the calibration of a hydrological model rarely considers their impacts on model parameters, likely leading to considerable simulation biases. In this study, we conducted a case study in a typical alpine catchment, the Babao River basin, in Northwest China, using the distributed hydrology–soil–vegetation model (DHSVM), to investigate the impacts of frozen ground type and precipitation seasonality on model parameters. The sensitivity analysis identified seven sensitive parameters in the DHSVM, amid which soil model parameters are found sensitive to the frozen ground type and land cover/vegetation parameters sensitive to dry and wet seasons. A stratified calibration approach that considers the impacts on model parameters of frozen soil types and seasons was then proposed and implemented by the particle swarm optimization method. The results show that the proposed calibration approach can obviously improve simulation accuracy in modeling streamflow in the study basin. The seasonally stratified calibration has an advantage in controlling evapotranspiration and surface flow in rainy periods, while the spatially stratified calibration considering frozen soil type enhances the simulation of base flow. In a typical cold alpine area without sufficient measured parametric values, this approach can outperform conventional calibration approaches in providing more robust parameter values. The underestimation in the April streamflow also highlights the importance of improved physics in a hydrological model, without which the model calibration cannot fully compensate the gap.

Keywords: parameter calibration; cold alpine basin; frozen ground; precipitation seasonality; sensitivity analysis; distributed hydrology–soil–vegetation model

官方下载链接:Link

一篇冰川冻土中文论文

赵奕,南卓铜*,李祥飞,徐毅,张凌. 分布式水文模型DHSVM在西北高寒山区流域的适用性研究. 冰川冻土. 2019, 41(1): 147-157.

分布式水文-土壤-植被模型(Distributed Hydrology Soil Vegetation Model, DHSVM)是基于栅格离散的分布式水文模型,对地表水热循环的各个过程能进行很精细地刻画,被广泛应用于世界各地很多类型的流域的高时空分辨率的水文模拟,然而它在高寒山区的适用性并不清楚。基于300m数字高程模型,应用DHSVM 模型对典型的高寒山区流域八宝河流域2001-2009年的水文过程展开模拟,并采用流域出口祁连站的水文实测数据对模型进行了精度评价。参数敏感性分析表明,土壤横向导水率、田间持水量和植被反照率等是该区域主要的敏感性参数。模型默认参数会高估高寒山区流域的潜在蒸散发量,导致夏季径流量远小于观测值。通过参数率定,模型校准期(2001-2004)的模拟日径流和月径流Nash 效率系数分别达到0.72 和0.87;而模型验证期(2005-2009)分别为0.60 和0.74 。结果表明,DHSVM 模型基本具备了模拟高寒山区流域降水-径流过程的能力。然而,由于DHSVM 模型缺少对高寒山区流域土壤的冻融过程的刻画,春季径流的模拟精度明显受到影响,需要在将来重点改进。

下载 (pdf, ~1.86 MB):

期刊官网:Link

A paper published online on 水文过程

Zhang L, Nan Z, Wang W, Ren D, Zhao Y, Wu X. Separating climate change and human contributions to variations in streamflow and its components using eight time-trend methods. Hydrological Processes. 2018, Online. DOI:10.1002/hyp.13331.

使用了八种时间趋势法调查了气候变化和人类活动对河川径流及成份变化的贡献,均表明在西北典型流域——黑河流域气候变化和人类活动导致河川径流及组分的增加,但不同方法得到明显不同的增幅。其中,不同方法模拟的人类活动对基流变化的贡献可能占到24-92%,气候变化的贡献则占到8-76%。但对于地表径流变化,人类活动的贡献(21-49%)均小于气候变化。我们也对比了时间趋势法与两种Budyko方法在结果上异同,并且分析和讨论了可能存在的问题、不确定性以及未来工作。

Continue reading

一篇冰川冻土中文论文

植被和土壤参数会较大影响到陆面过程模型的模拟结果,但在青藏高原的相关模拟中,通常并没有对这些参数进行专门的考虑,而相对地其他区域,青藏高原具有植被稀疏和土壤粗颗粒含量高等显著特征,那么这些特点会对多年冻土的模拟结果会有产生多大的影响?我们的研究表明,青藏高原植被土壤特性对Noah模拟结果较大影响。该成果发表在2018年第2期《冰川冻土》。

引用:吴小波,南卓铜*,王维真,赵林. 基于Noah陆面过程模型模拟青藏高原植被和土壤特征对多年冻土影响的模拟. 冰川冻土. 2018, 40(2): 279-287.

下载:官网; Baidu;

A paper on an application of GRACE gravity data

Cao Y, Nan Z, Cheng G, Zhang L. Hydrological variability in the arid lands of northwest China during 2002-2013. Advances in Meteorology. 2018, 2018(1502472): 1-13. DOI:10.1155/2018/1502472.

Abstract:

The arid region of Northwest China (ANC) has a distinct and fragile inland water cycle. This study examined the hydrological variations in ANC and its three subregions from August 2002 to December 2013 by integrating terrestrial water storage (TWS) anomaly data derived from the Gravity Recovery and Climate Experiment (GRACE) satellite, soil moisture data modeled by the Global Land Data Assimilation System, and passive microwave snow water equivalent data. The results show that the TWS in ANC increased at a rate of 1.7mm/a over the past decade, which consisted of an increasing trend of precipitation (0.12mm/a). Spatially, in the northern ANC, TWS exhibited a significant decreasing trend of −3.64 mm/a ( < 0.05) as a result of reduced rainfall, increased glacial meltwater draining away from the mountains, and intensified human activities. The TWS in southern and eastern ANC increased at a rate of 2.14 ( = 0.10) and 1.63 ( < 0.01)mm/a, respectively. In addition to increasing precipitation and temperature, decreasing potential evapotranspiration in Southern Xinjiang and expanding human activities in Hexi-Alashan together led to an overall increase in TWS. Increased glacier meltwater and permafrost degradation in response to climate warming may also affect the regional TWS balance. The variations in soil moisture, groundwater, and surface water accounted for the majority of the TWS anomalies in southern and easternANC.The proposed remote sensing approach combiningmultiple data sources proved applicable and useful to understand the spatiotemporal characteristics of hydrological variability in a large area of arid land without the need for field observations.

Links: Baidu, Official,

A JoH paper on routing

Zhang L, Nan Z*, Liang X*, Xu Y, Hernandez F, Li L. Application of the MacCormack Scheme to Overland Flow Routing for High-spatial Resolution Distributed Hydrological Model. Journal of Hydrology. 2018, 558: 421-431.

Abstract:

Although process-based distributed hydrological models (PDHMs) are evolving rapidly over the last few decades, their extensive applications are still challenged by the computational expenses. This study attempted, for the first time, to apply the numerically efficient MacCormack algorithm to overland flow routing in a representative high-spatial resolution PDHM, i.e., distributed hydrology-soil-vegetation model (DHSVM), in order to improve its computational efficiency. The analytical verification indicates that both the semi and full versions of the MacCormack schemes exhibit robust numerical stability and are more computationally efficient than the conventional explicit linear scheme. The full-version outperforms the semi-version in terms of simulation accuracy when a same time step is adopted. The semi-MacCormack scheme was implemented into DHSVM (version 3.1.2) to solve the kinematic wave equations for overland flow routing. The performance and practicality of the enhanced DHSVM-MacCormack model were assessed by performing two groups of modeling experiments in the Mercer Creek watershed, a small urban catchment near Bellevue, Washington. The experiments show that DHSVM-MacCormack can considerably improve the computational efficiency without compromising the simulation accuracy of the original DHSVM model. More specifically, with the same computational environment and model settings, the computational time required by DHSVM-MacCormack can be reduced to several dozen minutes for a simulation period of three months (in contrast with one day and a half by the original DHSVM model) without noticeable sacrifice of the accuracy. The MacCormack scheme proves to be applicable to overland flow routing in DHSVM, which implies that it can be coupled into other PHDMs for watershed routing to either significantly improve their computational efficiency or to make the kinematic wave routing for high resolution modeling computational feasible.

Keywords: MacCormack Scheme; Overland Flow Routing; DHSVM; Kinematic Wave; Computational Efficiency

Links: Link1 (Elesvier, 50day’s free access since Feb 4, 2018) ; Baidu;