Snow and climate trends and their impact on seasonal runoff and hydrological drought types in selected mountain catchments in Central Europe     

Andrea Blahušiaková  Milada Matoušková  Michal Jenicek  Ondřej Ledvinka  Zdeněk Kliment  Jana Podolinská 《水文科学杂志》2020,65(12):2083-2096

ABSTRACT

This study investigates changes in seasonal runoff and low flows related to changes in snow and climate variables in mountainous catchments in Central Europe. The period 1966–2012 was used to assess trends in climate and streamflow characteristics using a modified Mann–Kendall test. Droughts were classified into nine classes according to key snow and climate drivers. The results showed an increase in air temperature, decrease in snowfall fraction and snow depth, and changes in precipitation. This resulted in increased winter runoff and decreased late spring runoff due to earlier snowmelt, especially at elevations from 1000 to 1500 m a.s.l. Most of the hydrological droughts were connected to either low air temperatures and precipitation during winter or high winter air temperatures which caused below-average snow storages. Our findings show that, besides precipitation and air temperature, snow plays an important role in summer streamflow and drought occurrence in selected mountainous catchments.  相似文献   

A first-order approximation to stochastic optimal control of reservoirs     

P. K. Kitanidis 《Stochastic Environmental Research and Risk Assessment (SERRA)》1987,1(3):169-184

A new approximate method of solution for stochastic optimal control problems with many state and control variables is introduced. The method is based on the expansion of the optimal control into the deterministic feedback control plus a caution term. The analytic, small-perturbation calculation of the caution term is at the heart of the new method. The developed approximation depends only on the first two statistical moments of the random inputs and up to the third derivatives of the cost functions. Its computational requirements do not exhibit the exponential growth exhibited by discrete stochastic DP and can be used as a suboptimal solution to problems for which application of stochastic DP is not feasible. The method is accurate when the cost-to-go functions are approximately cubic in a neighbourhood around the deterministic trajectory whose size depends on forecasting uncertainty. Furthermore, the method elucidates the stochastic optimization problem yielding insights which cannot be easily obtained from the numerical application of discrete DP.  相似文献   

Stochastic partial differential equations in groundwater hydrology     

T. E. Unny 《Stochastic Environmental Research and Risk Assessment (SERRA)》1989,3(2):135-153

Many problems in hydraulics and hydrology are described by linear, time dependent partial differential equations, linearity being, of course, an assumption based on necessity.Solutions to such equations have been obtained in the past based purely on deterministic consideration. The derivation of such a solution requires that the initial conditions, the boundary conditions, and the parameters contained within the equations be stipulated in exact terms. It is obvious that the solution so derived is a function of these specified, values.There are at least four ways in which randomness enters the problem. i) the random initial value problem; ii) the random boundary value problem; iii) the random forcing problem when the non-homogeneous part becomes random and iv) the random parameter problem.Such randomness is inherent in the environment surrounding the system, the environment being endowed with a large number of degrees of freedom.This paper considers the problem of groundwater flow in a phreatic aquifer fed by rainfall. The goveming equations are linear second order partial differential equations. Explicit form solutions to this randomly forced equation have been derived in well defined regular boundaries. The paper also provides a derivation of low order moment equations. It contains a discussion on the parameter estimation problem for stochastic partial differential equations.  相似文献   

Some results comparing Monte Carlo simulation and first order Taylor series approximation for steady groundwater flow     

L. Jones 《Stochastic Environmental Research and Risk Assessment (SERRA)》1989,3(3):179-190

The expected head and standard deviation of the head from the first order Taylor series approximation is compared to Monte Carlo simulation, for steady flow in a confined aquifer with transmissivity as a random variable. Emphasis is on the effect of changes in the covariance structure of the transmissivity, and pumping rates, on the errors in the first order Taylor series approximation. The accuracy of the first order Taylor series approximation is found to be particularly sensitive to pumping rates. With significant pumping the approximation is found to under estimate both the expected drawdown and head variance, and the error increases as the pumping rate increases. This can lead to large errors in probability constraints based on moments from the first order Taylor series approximation.  相似文献   

The fractal geometry of interfaces and the multifractal distribution of dissipation in fully turbulent flows     

K. R. Sreenivasan  R. R. Prasad  C. meneveau  R. Ramshankar 《Pure and Applied Geophysics》1989,131(1-2):43-60

We describe scalar interfaces in turbulent flowsvia elementary notions from fractal geometry. It is shown by measurement that these interfaces possess a fractal dimension of 2.35±0.05 in a variety of flows, and it is demonstrated that the uniqueness of this number is a consequence of the physical principle of Reynolds number similarity. Also, the spatial distribution of scalar and energy dissipation in physical space is shown to be multifractal. We compare thef() curves obtained from one- and two-dimensional cuts in several flows, and examine their value in describing features of turbulence in the three-dimensional physical space.  相似文献   

Research Progress and Challenges of Submarine Cyclic Steps     

Dawei Wang  Yue Sun  Shaowen Si  Shiguo Wu 《地球科学进展》1986,35(9):890-901

Cyclic steps structure derived from the supercritical flows is one of the common bedforms， which is commonly found in sedimentary systems such as delta systems， deep-water canyon-channel systems， and carbonate platforms. In this paper， the research progresses of cyclic steps were introduced from the aspects of sedimentary environment， the features of bedforms， sedimentary structure， formation mechanism， and numerical simulation. The Research scale differences associated with the survey techniques or study methods， such as the ship survey and AUV-based multi-beams， sub-bottom profiles， multichannel seismic， the field outcrop， and numerical simulation were discussed. Finally， the breakthrough directions of the cyclic steps research were given. The combining method of ground penetrating radar， multichannel seismic， drilling and well logging were used to accurately detect the location of field outcrop thalweg. Within the area with water depth greater than 500 meters， the blending of multi-data for the cyclic steps research involved the AUV-based and the ship multi-beams， sub-bottom profiles， and multichannel seismic data. With the in situ samples and observation data obtained by human occupied vehicles， three-dimensional numerical simulation was developed to establish a set of dynamic simulation equations suitable for the real cyclic steps. Therefore， the high resolution three dimensional mode of the deep-water cyclic steps could be obtained more accurately.  相似文献   

洪水混沌特性初步研究   总被引：27，自引：4，他引：27       下载免费PDF全文

傅军  丁晶 《水科学进展》1996,7(3):226-230

混沌与随机是本质上不同的两种特性。区分产生洪水过程系统的混沌性和随机性是进行洪水模拟和预测的基础。从洪水时间序列出发,通过非线性动力系统重构和信息提取识别其基本特征。初步结果表明,洪水时间序列具有混沌动力系统的一些特征,即存在具有较低分维值、正的Lyapunov指数和Kolomogolov熵的奇怪吸引子,从而表明看起来异常复杂的洪水现象可能是由内在的非线性动力系统演化的结果。  相似文献   

Deformation patterns in a high-viscosity lava flow inferred from the crystal preferred orientation and imbrication structures: an example from Salina (Aeolian Islands,southern Tyrrhenian Sea,Italy)     

G. Ventura  R. De Rosa  E. Colletta  R. Mazzuoli 《Bulletin of Volcanology》1996,57(7):555-562

Shape-preferred orientation and imbrication structures of crystals have been measured on samples representative of the base, centre and top of a highly viscous lava flow on Salina (Aeolian Islands, southern Tyrrhenian Sea). The data allow zones with different deformation patterns to be identified. In the base and top of the flow, deformation leads to the development of discrete preferred orientation and imbrication of the elongate crystals. The sense of shear is right-lateral at the base and left-lateral at the top of the flow. Shear strain can be estimated by the analysis of crystal preferred orientation. Deformation increases from the flow centre to the outer, more viscous boundary layers. Random orientation of crystals in the inner zone supports the presence of plug flow in a pseudoplastic lava. The textural features of the studied lava may be related to different mechanisms (i.e. lateral expansion). We conclude that the observed crystal alignments and imbrication structures may be related to a plug flow moving between two non-deforming walls. The walls are represented by the solidified, broken upper and basal crust of the flow. The low shear strain values calculated in the outer margins of the flow are indicative of the last deformation event. Crystal preferred orientation and imbrication structures may be related to the occurrence of velocity gradients existing between the inner zone of the flow and its solidus or near-solidus outer margins.  相似文献   

TRACING FLOOD FLOWS USING SEDIMENTARY INDICATORS     

Carmen DE JONG Habilitation fellow of the Deutsche Bundesstiftung Umwelt  B.E.R.G. 《国际泥沙研究》1997,(3)

LinTRODUCTIONANDAIMSTheaimsofthisStUdyaretointroducenewtechniquesforanalysingfloodflowsfromsedimentarrangementmsapproachincorporatestheeffectsofflotvonthedevelopmentofrouglmessontheriverbed,andnot,asismostlythecase,theeffectsofbedroughnessonflow.Differentacsofflows,includingthemaalmumfloodflowarereconsmictedfromfloworientahonsofparticlesoveranentiregravCIbar.DuetOtheddricultiesinvolvedinobtaininglargeparticlesamples,studiesonpAncleOrientationsintheliteratUrearerare.WhilstmoStanalyse…  相似文献   

Erosion by pyroclastic flows on Lascar Volcano, Chile     

R. S. J. Sparks  M. C. Gardeweg  E. S. Calder  S. J. Matthews 《Bulletin of Volcanology》1997,58(7):557-565

 Pyroclastic flows generated in the 19–20 April 1993 eruption of Lascar Volcano, Chile, produced spectacular erosion features. Scree and talus were stripped from the channels and steep slopes on the flanks of the volcano. Exposed bedrock and boulders suffered severe abrasion, producing smoothed surfaces on coarse breccias and striations and percussion marks on bedrock and large boulders. Erosional furrows developed with wavelengths of 0.5–2 m and depths of 0.1–0.3 m. Furrows commonly nucleated downstream of large boulders or blocks, which are striated on the upstream side, and thereby produced crag-and-tail structures. Erosive features were produced where flows accelerated through topographic restrictions or where they moved over steep slopes. The pyroclastic flows are inferred to have segregated during movement into lithic-rich and pumice-rich parts. Lithic-rich deposits occur on slopes up to 14°, whereas pumice-rich deposits occur only on slopes less than 4°, and mainly at the margins and distal parts of the 1993 fan. The lithic-rich deposits contain large (up to 1 m) lithic clasts eroded from the substrate and transported from the vent, whereas pumice-rich deposits contain only small (typically <2 cm) lithic clasts. These observations suggest that lithic clasts segregated to the base of the flows and were responsible for much of the erosive phenomena. The erosive features, distribution of lithic clasts and deposit morphology indicate that the 1993 flows were highly concentrated avalanches dominated by particle interactions. In some places the flows slid over the bedrock causing abrasion and long striations which imply that large blocks were locked in fixed positions for periods of about 1 s. However, shorter striae at different angles, impact marks, segregation of the deposits into pumice- and lithic-rich parts, and mixing of bedrock-derived lithic clasts throughout the deposits indicate that clasts often had some freedom of movement and that jostling of particles allowed internal mixing and density segregation to occur within the flows. Received: 15 July 1996 / Accepted: 15 January 1997  相似文献