Tag Archives: modelling

最近几个工作进展

  • Yin Z, Nan Z*, Cao Z, Zhang G. Evaluating the applicability of a quantile-quantile adjustment approach for downscaling monthly GCM projections to site scale over the Qinghai-Tibet Plateau. Atmosphere. 2021, 12(9): 1170. (链接

这是一个本科生的工作,在青藏高原上验证了一个降尺度方法的适用性。我们其实在里面提出来了我们的改进方案,但不想开展后续工作了,感觉只是技术细节。这位本科生保送了北京大学直博。

  • Hu J, Nan Z*, Ji H. Spatiotemporal characteristics of NPP changes in frozen ground areas of the Three-River Headwaters Region, China: a regional modeling perspective. Frontier in Environmental Sciences. 2022, 10. doi:10.3389/feart.2022.838558.

我们关于三江源不同冻土类型对NPP影响的一个初步工作,大概结论是多年冻土区比季节冻土区NPP更小,但有更大的NPP变化速率。第一作者正延着此方向工作,后续会有新的进展。

  • Ji H, Nan Z*, Hu J, Zhao Y, Zhang Y. On the spin-up strategy for spatially modeling permafrost dynamics: A case study on the Qinghai-Tibet Plateau. Journal of Advances in Modeling Earth Systems. 2022, 14(3). doi:10.1029/2021MS002750.

这是我硕士生的工作。我发几个帖子描述关于这个论文的审稿过程,感触颇多。我们通过很全面的试验,说明了利用陆面过程模型模拟区域冻土水热状况变化/退化,一定要合适选择预热策略。不合适的模型预热策略会导致模拟结果的很大偏差,这个偏差会大到使得模拟退化速率无效。我们推荐至少500年的预热长度和多年循环的预热驱动方案(当然这个推荐可能不同模型不一样)。这些发现应该对我们的冻土区域模拟工作会有所启示。

  • Zhao Y, Nan Z*, Ji H, Zhao L. Convective heat transfer of spring meltwater accelerates active layer phase change in Tibet permafrost areas. The Cryosphere. 2022, 16: 825-849. doi:10.5194/tc-16-825-2022.

Cryosphere应该算是冰冻圈领域最好的专业期刊了吧,就是审稿太慢,前后花了1年时间。这个工作通过SHAW模型代码层面的修改对比分析了对流传热对冻土活动层水热过程的影响。亮点在于我们发现夏季融雪的对流传流起到加带活动层相变的作用。

我们利用数值模拟方法研究季节变暖和温湿变化对青藏高原冻土热响应的系列工作

背景是青藏高原在近几十年有明显的气候变化,气温在升高,降水在2000年后也有较大增加。而气温的升高具有季节性,冷季的升温比暖季更大。而青藏高原土壤里有大量的冻土存在,这些气候要素的变化影响到了下伏冻土的热状况。所谓冻土是土壤里有冰,冰融化变成水就流出来,青藏高原三江源是重要河流的源头(长江、黄河、澜沧江)。同时冻土的变化也会反馈到气候,冻土融化也可能释放出有机碳等温室气体。

因此,我们针对的科学问题便很有意思,a 冬季和夏季气温升高如何改变冻土热状况?b 从定量角度,冬季气温升高对冻土热指标的贡献是多少?c 在气温、降水同时变化的情况下,升温和增温对冻土热状况的影响分别是多少。

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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。

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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

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;

一个洪水预报论文

强德霞,赵彦博,南卓铜*,吴小波. 基于参数实时优化的洪水预报系统研究:以黑河干流洪水为例. 水利水电技术. 2017, 48(4): 13-17.

另:对于里面使用不同模型进行不同场次洪水预报我有不同意见,因为我们无法知道下一场次洪水到底适合何种模型,从而不能实际用起来。但使用实测数据,对给定模型参数进行实时率定,从而优化使用该模型的洪水预报精度,是本文主要想传达的。

Full text available upon request.

A paper on evaluation of some simple permafrost models on QTP

Zhao S, Nan Z*, Huang Y, Zhao L. The application and evaluation of simple permafrost distribution models on the Qinghai-Tibet Plateau. Permafrost and Periglacial Processes. 2017, 28(2): 391-404. DOI:10.1002/ppp.1939.

ABSTRACT

The performance of simple permafrost distribution models widely used on the Qinghai–Tibet Plateau (QTP) has not been fully evaluated. In this study, two empirical models (the elevation model and mean annual ground temperature model) and three semi-physical models (the surface frost number model, the temperature at the top of permafrost model and the Kudryavtsev model) were investigated. The simulation results from the models were compared to each other and validated against existing permafrost maps of the entire QTP and in three representative areas investigated in the field. The models generally overestimated permafrost distribution in the investigated areas, but they captured the broad characteristics of permafrost distribution on the entire QTP, and performed best in areas with colder, continuous permafrost. Large variations in performance occurred at elevations of 3800–4500 m asl and in areas with thermally unstable permafrost. The two empirical models performed best in areas where permafrost is strongly controlled by elevation, such as eastern QTP. In contrast, the three semi-physical models were better in southern island permafrost areas with relatively flat terrain, where local factors considerably impact the distribution of permafrost. Model performance could be enhanced by explicitly considering the effects of elevation zones and regional conditions.

Links: Baidu;