scholarly journals The impact of initial conditions on convection-permitting simulations of a flood event over complex mountainous terrain

2020 ◽  
Vol 24 (2) ◽  
pp. 771-791 ◽  
Author(s):  
Lu Li ◽  
Marie Pontoppidan ◽  
Stefan Sobolowski ◽  
Alfonso Senatore
Keyword(s):  
Snow Depth ◽  
Peak Flow ◽  
Initial Conditions ◽  
Flood Event ◽  
Precipitation Pattern ◽  
Mountainous Terrain ◽  
Western Norway ◽  
Snow Conditions ◽  
The Impact ◽  
Hbv Model

Abstract. Western Norway suffered major flooding after 4 d of intense rainfall during the last week of October 2014. While events like this are expected to become more frequent and severe under a warming climate, convection-permitting scale models are showing their skill with respect to capturing their dynamics. Nevertheless, several sources of uncertainty need to be taken into account, including the impact of initial conditions on the precipitation pattern and discharge, especially over complex, mountainous terrain. In this paper, the Weather Research and Forecasting Model Hydrological modelling system (WRF-Hydro) is applied at a convection-permitting scale, and its performance is assessed in western Norway for the aforementioned flood event. The model is calibrated and evaluated using observations and benchmarks obtained from the Hydrologiska Byråns Vattenbalansavdelning (HBV) model. The calibrated WRF-Hydro model performs better than the simpler conceptual HBV model, especially in areas with complex terrain and poor observational coverage. The sensitivity of the precipitation pattern and discharge to poorly constrained elements such as spin-up time and snow conditions is then examined. The results show the following: (1) the convection-permitting WRF-Hydro simulation generally captures the precipitation pattern/amount, the peak flow volume and the timing of the flood event; (2) precipitation is not overly sensitive to spin-up time, whereas discharge is slightly more sensitive due to the influence of soil moisture, especially during the pre-peak phase; and (3) the idealized snow depth experiments show that a maximum of 0.5 m of snow is converted to runoff irrespective of the initial snow depth and that this snowmelt contributes to discharge mostly during the rainy and the peak flow periods. Although further targeted experiments are needed, this study suggests that snow cover intensifies the extreme discharge instead of acting as a sponge, which implies that future rain-on-snow events may contribute to a higher flood risk.

scholarly journals The impact of initial conditions on convection-permitting simulations of flood events

2019 ◽  
Author(s):  
Lu Li ◽  
Marie Pontoppidan ◽  
Stefan Sobolowski ◽  
Alfonso Senatore
Keyword(s):  
Snow Depth ◽  
Peak Flow ◽  
Initial Conditions ◽  
Coarse Grained ◽  
Flood Event ◽  
Precipitation Pattern ◽  
Western Norway ◽  
Earth’S Climate ◽  
The Impact ◽  
Modelling System

Abstract. Western Norway suffered major flooding after 4 days of intense rainfall during the last week of October 2014, resulting in damages totalling hundreds of millions Norwegian kroner. These types of events are expected to become more frequent and severe as Norwegian (and the earth's) climate continues to warm. However, due to the strong effects that local features and conditions can have on these kinds of events, coarse-grained global or regional models are unable to capture their characteristics. Very high resolution models run at so-called convection-permitting scales have shown some promise for reliably capturing such events. Doing so in a robust manner is, as a matter of course, of high interest to both scientists and stakeholders in both climate prediction and projection contexts. Despite this promise, the impacts of initial conditions on convection-permitting simulations, i.e., precipitation pattern and discharge, are uncertain, especially over complex, mountainous terrain. Complicating matters, these areas also usually lack dense measurement networks. In this paper, we apply a distributed dynamic regional atmosphere-hydrological modelling system (WRF-Hydro) at convection-permitting scale and assess its performance over four catchments in western Norway for the aforementioned flood event. The model is calibrated and then evaluated using observations and benchmarks obtained from the HBV light model. Interestingly, the calibrated WRF-Hydro model with NSE value of 0.86 exceeds the upper benchmark obtained from the conceptual HBV model with NSE value of 0.80 suggesting that the former performs as well or better than the simpler conceptual model, especially in areas with complex terrain and poor observational coverage. Confident in the capabilities of the modelling system we then examined the sensitivity of precipitation pattern and discharge, especially peak flow, to poorly constrained elements such as spinup time and snow conditions. The results show that: (1) overall the convection-permitting WRF-Hydro simulation captures the precipitation pattern/amount, the peak flow volume and the timing of the flood event; (2) precipitation is not overly sensitive to spinup time, while discharge is slightly more sensitive due to the influence of soil moisture, especially during the pre-peak phase; (3) the idealized snow depth experiments show that a maximum of 0.5 m of snow is converted to runoff irrespective of the initial snow depth and that this snowmelt contributes to discharge mostly during the rainy and the peak flow periods. This suggests that snow-cover, in these experiment at least, intensifies the extreme discharge instead of acting as sponge, which further implies that future rain-on-snow events may contribute to higher flood risk. While targeted experiments on the changing characteristics of projected future rain-on-snow events are needed to confirm this study suggests that WRF-Hydro is an ideally formulated tool to investigate these questions.

Quantifying the impact of climate change on floods by using both continuous and event-based hydrological modelling

2020 ◽  
Author(s):  
Enrique Soriano Martín ◽  
Luis Mediero Orduña ◽  
Carlos Garijo Sarria
Keyword(s):  
Climate Change ◽  
Moisture Content ◽  
Soil Moisture Content ◽  
Peak Flow ◽  
Control Period ◽  
The Future ◽  
Event Model ◽  
Flood Response ◽  
The Impact ◽  
Hbv Model

<p>Climate change will modify magnitude and timing of floods in the future. Consequently, new methodologies to quantify the impact of climate change on floods at the catchment scale are required. This study aims to quantify the changes in peak flow quantiles expected in the future, by using the climate change projections of the Fifth Report (AR5) of the IPCC, supplied by the EURO-CORDEX programme. Four catchments located in the Duero River Basin in northwestern Spain are considered as case studies.</p><p> </p><p>First, biases in precipitation and temperature climate projections have been corrected by using the available observations in the control period (1971-2004) in the four catchments. Second, the hydrological response in the four catchments has been simulated with the continuous simulation model HBV. The model has been calibrated in the four catchments. Time series of soil moisture content in the catchment were obtained, identifying the initial moisture content in the day of occurrence of the annual maximum rainfalls. Third, an event model has been used to simulate flood response to the annual maximum rainfalls, considering the initial soil moisture content supplied by the HVB model. The results of the event model provides a better characterization of the catchment flood response than the continuous HBV model.</p><p> </p><p>The methodology has been applied in the control period (1971-2004), for validation purposes. Then, the methodology has been applied to the future period (2011-2095), to obtain the expected changes in peak flow quantiles, as a consequence of climate change. The combined use of the results of the continuous hydrological simulation with the HBV model with the event model improves the results provided by either the HBV model or the event model independently. The proposed methodology allows a better characterisation of the catchment flood response to a given precipitation event, while also considering the expected variation in the antecedent moisture content in the catchment in the future, as a consequence of expected changes in temperature and precipitation regimes. The application of the proposed methodology to the case studies has shown that climate change will increase peak flow quantiles in the future, in three of the four catchments.</p>

The declining dependence of ski lift operators on natural snow conditions

2018 ◽  
Vol 24 (6) ◽  
pp. 662-676 ◽  
Author(s):  
Martin Falk ◽  
Xiang Lin
Keyword(s):  
Snow Depth ◽  
Time Series Data ◽  
Series Data ◽  
Adaptation Measures ◽  
Ticket Sales ◽  
Distributed Lag ◽  
Natural Snow ◽  
Snow Conditions ◽  
The Impact ◽  
Rolling Windows

This study tests for a structural shift in the relationship between revenues of ski lift operators and natural snow conditions. The analysis is based on time series data for the Swedish ski lift industry spanning from 1980 to 2017. Since 1970, snow depth in winter sport destinations has decreased markedly by about 5 cm per decade. Estimations based on the autoregressive distributed lag (ARDL) model show that revenues (in constant prices) of ski lift operators are significantly positively related to natural snow conditions, given the impact of relative prices and real GDP. However, ARDL estimations with rolling windows reveal that the sensitivity of revenues from ski lift ticket sales to variations in snow depth is declining over time. For the subsamples starting at the end of 1980s onward, revenues no longer significantly depend on natural snow depth. This is likely due to the implementation of adaptation measures such as investments in snowmaking facilities.

scholarly journals Investigating 3D and 4D Variational Rapid-Update-Cycling Assimilation of Weather Radar Reflectivity for a Flash Flood Event in Central Italy

2021 ◽  
Author(s):  
Vincenzo Mazzarella ◽  
Rossella Ferretti ◽  
Errico Picciotti ◽  
Frank S. Marzano
Keyword(s):  
Data Assimilation ◽  
Roc Curve ◽  
Initial Conditions ◽  
Flash Flood ◽  
Central Italy ◽  
Wrf Model ◽  
Radar Reflectivity ◽  
Precipitation Forecast ◽  
Precipitation Pattern ◽  
The Impact

Abstract. The precipitation forecast over the Mediterranean basin is still a challenge because of the complex orographic region which amplifies the need for local observation to correctly initialize the forecast. In this context the data assimilation techniques play a key role in improving the initial conditions and consequently the timing and position of precipitation pattern. For the first time, the ability of a cycling 4D-Var to reproduce a severe weather event in central Italy, as well as to provide a comparison with the largely used cycling 3D-Var, is evaluated in this study. The radar reflectivity measured by the Italian ground radar network is assimilated in the WRF model to simulate an event occurred on May 3, 2018 in central Italy. In order to evaluate the impact of data assimilation, several simulations are objectively compared by means of a Fraction Skill Score (FSS), which is calculated for several threshold values, and a Receiver Operating Characteristic (ROC) curve. The results suggest that both assimilation methods in cycling mode improve the 1, 3 and 6-hourly quantitative precipitation estimation. More specifically, the cycling 4D-Var with a warm start initialization shows the highest FSS values in the first hours of simulation both with light and heavy precipitation. Finally, the ROC curve confirms the benefit of 4D-Var: the area under the curve is 0.91 compared to the 0.88 of control experiment without data assimilation.

scholarly journals On Kaufmann's theory of the impact of the pianoforte hammer

1920 ◽  
Vol 97 (682) ◽  
pp. 99-110 ◽  
Keyword(s):  
Initial Conditions ◽  
Practical Importance ◽  
Prima Facie ◽  
Point Of View ◽  
Infinite Length ◽  
Modes Of Vibration ◽  
Rigorous Treatment ◽  
The Subject ◽  
Set Up ◽  
The Impact

The theory of the vibrations of the pianoforte string put forward by Kaufmann in a well-known paper has figured prominently in recent discussions on the acoustics of this instrument. It proceeds on lines radically different from those adopted by Helmholtz in his classical treatment of the subject. While recognising that the elasticity of the pianoforte hammer is not a negligible factor, Kaufmann set out to simplify the mathematical analysis by ignoring its effect altogether, and treating the hammer as a particle possessing only inertia without spring. The motion of the string following the impact of the hammer is found from the initial conditions and from the functional solutions of the equation of wave-propagation on the string. On this basis he gave a rigorous treatment of two cases: (1) a particle impinging on a stretched string of infinite length, and (2) a particle impinging on the centre of a finite string, neither of which cases is of much interest from an acoustical point of view. The case of practical importance treated by him is that in which a particle impinges on the string near one end. For this case, he gave only an approximate theory from which the duration of contact, the motion of the point struck, and the form of the vibration-curves for various points of the string could be found. There can be no doubt of the importance of Kaufmann’s work, and it naturally becomes necessary to extend and revise his theory in various directions. In several respects, the theory awaits fuller development, especially as regards the harmonic analysis of the modes of vibration set up by impact, and the detailed discussion of the influence of the elasticity of the hammer and of varying velocities of impact. Apart from these points, the question arises whether the approximate method used by Kaufmann is sufficiently accurate for practical purposes, and whether it may be regarded as applicable when, as in the pianoforte, the point struck is distant one-eighth or one-ninth of the length of the string from one end. Kaufmann’s treatment is practically based on the assumption that the part of the string between the end and the point struck remains straight as long as the hammer and string remain in contact. Primâ facie , it is clear that this assumption would introduce error when the part of the string under reference is an appreciable fraction of the whole. For the effect of the impact would obviously be to excite the vibrations of this portion of the string, which continue so long as the hammer is in contact, and would also influence the mode of vibration of the string as a whole when the hammer loses contact. A mathematical theory which is not subject to this error, and which is applicable for any position of the striking point, thus seems called for.

scholarly journals A Rational Numerical Method for Simulation of Drop-Impact Dynamics of Oleo-Pneumatic Landing Gear

2021 ◽  
Vol 11 (9) ◽  
pp. 4136
Author(s):  
Rosario Pecora
Keyword(s):  
Numerical Method ◽  
Initial Conditions ◽  
Impact Load ◽  
Numerical Models ◽  
Landing Gear ◽  
Design Stage ◽  
Impact Dynamics ◽  
State Variables ◽  
Adopted Model ◽  
The Impact

Oleo-pneumatic landing gear is a complex mechanical system conceived to efficiently absorb and dissipate an aircraft’s kinetic energy at touchdown, thus reducing the impact load and acceleration transmitted to the airframe. Due to its significant influence on ground loads, this system is generally designed in parallel with the main structural components of the aircraft, such as the fuselage and wings. Robust numerical models for simulating landing gear impact dynamics are essential from the preliminary design stage in order to properly assess aircraft configuration and structural arrangements. Finite element (FE) analysis is a viable solution for supporting the design. However, regarding the oleo-pneumatic struts, FE-based simulation may become unpractical, since detailed models are required to obtain reliable results. Moreover, FE models could not be very versatile for accommodating the many design updates that usually occur at the beginning of the landing gear project or during the layout optimization process. In this work, a numerical method for simulating oleo-pneumatic landing gear drop dynamics is presented. To effectively support both the preliminary and advanced design of landing gear units, the proposed simulation approach rationally balances the level of sophistication of the adopted model with the need for accurate results. Although based on a formulation assuming only four state variables for the description of landing gear dynamics, the approach successfully accounts for all the relevant forces that arise during the drop and their influence on landing gear motion. A set of intercommunicating routines was implemented in MATLAB® environment to integrate the dynamic impact equations, starting from user-defined initial conditions and general parameters related to the geometric and structural configuration of the landing gear. The tool was then used to simulate a drop test of a reference landing gear, and the obtained results were successfully validated against available experimental data.

scholarly journals Variation in human mobility and its impact on the risk of future COVID-19 outbreaks in Taiwan

2021 ◽  
Vol 21 (1) ◽  
Author(s):  
Meng-Chun Chang ◽  
Rebecca Kahn ◽  
Yu-An Li ◽  
Cheng-Sheng Lee ◽  
Caroline O. Buckee ◽  
...  
Keyword(s):  
Disease Surveillance ◽  
Initial Conditions ◽  
Human Mobility ◽  
Human Movement ◽  
Disease Spread ◽  
Spatial Spread ◽  
Movement Data ◽  
Intercity Travel ◽  
Travel Restrictions ◽  
The Impact

Abstract Background As COVID-19 continues to spread around the world, understanding how patterns of human mobility and connectivity affect outbreak dynamics, especially before outbreaks establish locally, is critical for informing response efforts. In Taiwan, most cases to date were imported or linked to imported cases. Methods In collaboration with Facebook Data for Good, we characterized changes in movement patterns in Taiwan since February 2020, and built metapopulation models that incorporate human movement data to identify the high risk areas of disease spread and assess the potential effects of local travel restrictions in Taiwan. Results We found that mobility changed with the number of local cases in Taiwan in the past few months. For each city, we identified the most highly connected areas that may serve as sources of importation during an outbreak. We showed that the risk of an outbreak in Taiwan is enhanced if initial infections occur around holidays. Intracity travel reductions have a higher impact on the risk of an outbreak than intercity travel reductions, while intercity travel reductions can narrow the scope of the outbreak and help target resources. The timing, duration, and level of travel reduction together determine the impact of travel reductions on the number of infections, and multiple combinations of these can result in similar impact. Conclusions To prepare for the potential spread within Taiwan, we utilized Facebook’s aggregated and anonymized movement and colocation data to identify cities with higher risk of infection and regional importation. We developed an interactive application that allows users to vary inputs and assumptions and shows the spatial spread of the disease and the impact of intercity and intracity travel reduction under different initial conditions. Our results can be used readily if local transmission occurs in Taiwan after relaxation of border control, providing important insights into future disease surveillance and policies for travel restrictions.

scholarly journals Spatio-Temporal Variation Characteristics of Snow Depth and Snow Cover Days over the Tibetan Plateau

Water ◽  
2021 ◽  
Vol 13 (3) ◽  
pp. 307
Author(s):  
Chi Zhang ◽  
Naixia Mou ◽  
Jiqiang Niu ◽  
Lingxian Zhang ◽  
Feng Liu
Keyword(s):  
Tibetan Plateau ◽  
Snow Cover ◽  
Snow Depth ◽  
Feedback Effect ◽  
Effect Of Temperature ◽  
The Tibetan Plateau ◽  
Reanalysis Dataset ◽  
Spatio Temporal ◽  
The Impact ◽  
Main Factor

Changes in snow cover over the Tibetan Plateau (TP) have a significant impact on agriculture, hydrology, and ecological environment of surrounding areas. This study investigates the spatio-temporal pattern of snow depth (SD) and snow cover days (SCD), as well as the impact of temperature and precipitation on snow cover over TP from 1979 to 2018 by using the ERA5 reanalysis dataset, and uses the Mann–Kendall test for significance. The results indicate that (1) the average annual SD and SCD in the southern and western edge areas of TP are relatively high, reaching 10 cm and 120 d or more, respectively. (2) In the past 40 years, SD (s = 0.04 cm decade−1, p = 0.81) and SCD (s = −2.3 d decade−1, p = 0.10) over TP did not change significantly. (3) The positive feedback effect of precipitation is the main factor affecting SD, while the negative feedback effect of temperature is the main factor affecting SCD. This study improves the understanding of snow cover change and is conducive to the further study of climate change on TP.

scholarly journals The Impact of Initial Conditions in N-Body Simulations of Debris Discs

2015 ◽  
Vol 32 ◽  
Author(s):  
E. Thilliez ◽  
S. T. Maddison
Keyword(s):  
Numerical Simulations ◽  
Initial Conditions ◽  
Parent Body ◽  
Dust Trapping ◽  
Physical Context ◽  
Disc Width ◽  
Wide Range ◽  
Belt Width ◽  
New Generation ◽  
The Impact

AbstractNumerical simulations are a crucial tool to understand the relationship between debris discs and planetary companions. As debris disc observations are now reaching unprecedented levels of precision over a wide range of wavelengths, an appropriate level of accuracy and consistency is required in numerical simulations to confidently interpret this new generation of observations. However, simulations throughout the literature have been conducted with various initial conditions often with little or no justification. In this paper, we aim to study the dependence on the initial conditions of N-body simulations modelling the interaction between a massive and eccentric planet on an exterior debris disc. To achieve this, we first classify three broad approaches used in the literature and provide some physical context for when each category should be used. We then run a series of N-body simulations, that include radiation forces acting on small grains, with varying initial conditions across the three categories. We test the influence of the initial parent body belt width, eccentricity, and alignment with the planet on the resulting debris disc structure and compare the final peak emission location, disc width and offset of synthetic disc images produced with a radiative transfer code. We also track the evolution of the forced eccentricity of the dust grains induced by the planet, as well as resonance dust trapping. We find that an initially broad parent body belt always results in a broader debris disc than an initially narrow parent body belt. While simulations with a parent body belt with low initial eccentricity (e ~ 0) and high initial eccentricity (0 < e < 0.3) resulted in similar broad discs, we find that purely secular forced initial conditions, where the initial disc eccentricity is set to the forced value and the disc is aligned with the planet, always result in a narrower disc. We conclude that broad debris discs can be modelled by using either a dynamically cold or dynamically warm parent belt, while in contrast eccentric narrow debris rings are reproduced using a secularly forced parent body belt.

Risk assessment in mission planning of uninhabited aerial vehicles

2019 ◽  
Vol 233 (10) ◽  
pp. 3499-3518 ◽  
Author(s):  
Giulio Avanzini ◽  
David S Martínez
Keyword(s):  
Initial Conditions ◽  
Mission Planning ◽  
Unmanned Aerial Systems ◽  
Steady State Condition ◽  
Motion Primitives ◽  
Uninhabited Aerial Vehicles ◽  
Aerial Systems ◽  
The Impact ◽  
Navigation Errors ◽  
Time Of Failure

A procedure for evaluating the risk related to the use of unmanned aerial systems over populated areas is proposed. A nominal trajectory, planned for performing a given mission, is represented by means of motion primitives, that is segments and arcs flown in a steady-state condition. The risk of hitting a person on the ground after catastrophic failure is evaluated as a function of vehicle reliability and population density (assumed known), and position of the impact point (which depends on initial conditions at the time of failure and trajectory flown afterwards). In the deterministic case, a lethal area is introduced and the risk at each point on the ground is proportional to the amount of time spent by the point inside the lethal area. Under the assumptions of a ballistic fall, the position of the lethal area with respect to the nominal trajectory depends only on altitude and velocity at the time of failure. When the effect of navigation errors is introduced, impact points are described by a statistical impact footprint, assuming that position and velocity errors at time of failure are normally distributed with known standard deviations. The two approaches are compared for a fictitious, yet realistic, mission scenario.

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