Steady Rainfall Research Articles

Assessment of wind-driven rain (WDR) on buildings in an urban area: comparison of different CFD frameworks

The study of Wind-Driven Rain (WDR) loading on building facades is essential to design more sustainable and climate-resilient buildings, as well as to prevent further damage to old and historical buildings. Both WDR loading on buildings and façade responses to impinging raindrops have been studied previously but results for such a multi-parameter problem are not generally conclusive. Thus, the relevant provisions of ISO semi-empirical model cannot be applied with confidence for complex building configurations, such as those in urban areas since the WDR prediction can be more than twice that of the experimental data. In this paper, the Eulerian Multiphase (ME) technique is coupled with the RANS model to simulate the WDR loading on a six-story building under steady rainfall event conditions. Wind and WDR results are compared with the available wind-tunnel and on-site field measurement results, respectively. The field measurements were carried out on a six-story mid-rise residential building, located in Vancouver, Canada. The results show that the Euler-Euler framework (RANS-EM) predicts wind and WDR in such an urban area configuration more rapidly and accurately compared to the more traditional Euler-Lagrange framework (RANS-LPT) for both stand-alone and urban area configurations.

Value of Spatially Distributed Rainfall Design Events—Creating Basin-Scale Stochastic Design Storm Ensembles

Current design storms used in hydrological modeling, urban planning, and dimensioning of structures are typically point-scale rainfall events with a steady rainfall intensity or a simple temporal intensity pattern. This can lead to oversimplified results because real rainfall events have more complex patterns than simple design series. In addition, the interest of hydrologists is usually in areal estimates rather than point values, most commonly in river-basin-wide areal mean rainfall estimates. By utilizing weather radar data and the short-term ensemble prediction system pySTEPS, which has so far been used for precipitation nowcasting, ensembles of high-resolution stochastic design storms with desired statistical properties and spatial structure evolving in time are generated. pySTEPS is complemented by adding time-series models for areal average rainfall over the simulation domain and field advection vectors. The selected study area is the Kokemäenjoki river basin located in Western Finland, and the model parametrization is carried out utilizing the Finnish Meteorological Institute’s weather radar data from the years 2013 to 2016. The results demonstrate how simulated events with similar large-scale mean areal rainfall can produce drastically different total event rainfalls in smaller scales. The sampling method, areal vs. gauge estimate, is also shown to have a prominent effect on total event rainfall across different spatial scales. The outlined method paves the way towards a more thorough and wide-spread assessment of the hydrological impacts of spatiotemporal rainfall characteristics.

Winter Climate of Northeastern Dominican Republic and Cash Crop Production

The winter climate of the northeastern Dominican Republic features steady rainfall, which sustains cash crop production. Using a representative season, December 2016–February 2017, the mesoscale climate is characterized by high-resolution reanalysis, satellite measurements and local observations, and statistical analyses of time series from an index area of 18.8–19.6° N, 70.4–69.6° W in the Cibao Valley, where cacao and coffee are grown. Winter rainfall depends on strong trade winds that push shallow stratiform convections over 100 km inland, where nocturnal drainage flows induce orographic uplift. Interannual climate variability is studied in the context of cacao and coffee production in the years 1976–2019. Lag correlations demonstrate that higher yields follow a wet autumn, a windy winter with cool sea temperatures, and a dry spring. Changes in high-value agricultural production in the northeastern Dominican Republic may be anticipated by the climatic determinants uncovered here.

Impact of a white noise app on sleep quality among critically ill patients.

Sleep disturbance negatively affects recovery and survival of patients in intensive care units (ICUs). This study aimed to measure the noise levels and evaluate the impact of a white noise app on the sleep quality of critically ill patients. A quasi-experimental time series pre-test-post-test control group design with repeated measures was adopted. The study was conducted in the high dependency unit (HDU) of a selected tertiary care hospital in Mangalore, Karnataka State, India. Conscious oriented patients with systolic blood pressure ranging from 100/70 to 140/90 mm Hg and hearing acuity of at most 20 dB in both ears were included in the study. Noise levels in the HDU were measured using calibrated sound level meter on weekdays/weekends in three different shifts and an average of 24 readings was obtained per shift. A 4-point Likert scale was used to assess the sleep quality. The intervention included administration of white noise app twice a day, for three consecutive days by using different masking sounds such as white noise on day 1 which resembles to a humming AC conditioner, pink noise on day 2 which resembles to the sound of ocean waves and brown noise on day 3 which resembles a steady rainfall. The app was used with the help of JBL earphones C10SI an excellent noise cancellation and noise isolating earphone. Among the 54 subjects, the mean age of the patients was 40.28 years, majority 34 (63%) were males. The noise level in the ICU was more than 60 dB. There was a significant difference in the sleep quality after the application of the white noise app in the experimental group on Day 1 (Z=-3.996; P= .001), Day 2 (Z=-3.302; P= .001), and Day 3 (-2.822; P= .005) compared to the control group. Adoption of technology driven noise reduction applications would enhance the quality of sleep among the ICU patients. The use of a technology-driven application helps control noise levels which promotes improved sleep quality among critically ill patients in the intensive care units.

Soil moisture migration model based on flux-concentration relation under steady rainfall

Abstract Moisture content distribution in soil is of great importance for understanding rainfall-induced slope failure and roadbed settlement. This study aims to develop a moisture migration model that improves the quantification of moisture content at an arbitrary point of the soil at any time for the whole process of infiltration under steady rainfall. The model was derived from the Richards equation using the flux-concentration relation, which was validated by numerical solutions calculated by Hydrus-1D software to evaluate the performance of the model. Results showed good accuracy and high adaptability for the moisture migration simulation of a wide range of soil types, and is applicable for short-duration and long-duration steady rainfall. Moreover, it can also reflect the stratification phenomenon for soil profile wetting by infiltration. Our analysis indicates that the flux and surface volumetric moisture content together can bound the boundary conditions of rainfall infiltration, which presents a shift from constant-flux to constant-concentration during long-duration steady rainfall. The migration rate of the wetting front in the later stage of infiltration positively correlates with rainfall intensity under the constant-flux condition, while it finally stabilizes at Ks/(θs − θi) under the constant-concentration condition (i.e., Ks – saturated hydraulic conductivity, θs – saturated volumetric moisture content, θi – initial volumetric moisture content).

Modeling slope rainfall-infiltration-runoff process with shallow water table during complex rainfall patterns

Limitations in current infiltration modeling approaches hamper the evaluation of the effects of complex rainfall pattern and slope gradient on soil infiltration and runoff in presence of a water table (WT), although they can markedly alter the hydrologic processes. To fill the gap, the Smith et al. (1993)’s infiltration model was modified, and a modeling framework was then developed to simulate the rainfall-infiltration-runoff process in presence of a WT. The model was tested against experimental infiltration and runoff data at two different constant inflow rates and WT depths. Good agreements between the modeled and observed results were found in infiltration and runoff rates for two cases. The model was evaluated under complex rainfall patterns and the results showed that the model performs well in the infiltration rate and the soil water redistribution predictions. With an increasing of slope gradient, the decrease of runoff rate tends to become more prominent under steady rainfall pattern, but the trend becomes more complicated under complex rainfall patterns. The model was compared with Hydrus-1D and Shallow Water table Infiltration Algorithm (SWINGO) and found that both the model and Hydrus-1D can well predict the soil infiltration rate and soil water redistribution in presence of a shallow WT for the silt loam, sandy loam, and clay. SWINGO is likely to overestimate the ponding time and the infiltration rate but underestimate the time to column saturation for clayey soils with a shallow WT. The model is expected to produce a more realistic and accurate approach for infiltration and runoff prediction in presence of a WT.

A physics-based routing model for modular green roof systems

The ability of green roof systems to impact stormwater runoff from buildings has been covered in many research studies. However, a lot of these studies looked at long-term retention, with much less work focused on how to model a green roof's response to larger design storms. Work that has examined flow routing for individual rainfall events has focused on empirical routing models that are tuned to the specific roof being modelled. This paper presents a new physics-based model for flow routing based on the green roof module geometry and soil properties, which requires only a single discharge coefficient to be measured. The results of this model were compared with the results of a series of experiments to quantify a modular green roof system's hydraulic response to drawdown and steady rainfall.

Time of concentration based infiltration under different soil density, water content, and slope during a steady rainfall

Abstract Time of concentration, Tc, is defined as time elapsed from the beginning of rainfall infiltrated into soil layer until it reaches a constant infiltration rate (fc) which is indicated an equilibrium subsurface flow rate. In hydrological view, time of concentration plays a significant role in elaboration of transformation of rainfall into runoff in a watershed. The aims of this research are to define influence of soil density and soil water content in determining time of concentration using infiltration concept based on water balance theory, and to find out the effect of land slope this time. Watershed laboratory experiment using rainfall simulator was employed to examine time of concentration associated with infiltration process under different slope, soil density and soil water content based on water balance concept. The steady rainfall intensity was simulated using sprinklers which produced 2 dm3∙min−1. Rainfall, runoff and infiltration analysis were carried out at laboratory experiment on soil media with varied of soil density (d) and soil water content (w), where variation of land slopes (s) were designed in three land slopes 2, 3 and 4%. The results show that relationship between soil density and land slope to time of concentration showed a quadratic positive relationship where the higher the soil density address to the longer time of concentration. Moreover, time of concentration had an inverse relationship with soil water content and land slope that means time of concentration decreased when the soil water content increased.

Who are most likely to adapt their travel behaviour to changes in weather conditions? A study of weather tolerance and travel behaviour in Norway

This study, based on two questionnaire surveys from two cities in Norway with different climate conditions, explores to which extent weather tolerance in terms of travel behaviour – here defined as using a non-motorized vehicle despite poor weather conditions (precipitation and/or cold weather) – is related to socio-demographic factors, environmental attitudes, transport habits as well as the climate conditions (coastal/inland) of where people live. Three indicators are used to measure ‘weather tolerance’: a) Disagreement to the statement “I always drive when it rains”; b) Willingness to walk 2-3 kilometers in minus 10 degrees Celsius or more in steady snowfall (yes/no), and c) Willingness to walk 2-3 kilometer in +20 degrees Celsius or more in steady rainfall” (yes/no). The study finds that environmental attitudes and travel habits (as perceived by the respondents) are the factors most strongly related to weather tolerance, independent on how it is measured, when other factors are controlled for. The findings suggest that policy measures to change attitudes/ increase environmental awareness as well as promoting outdoor activity in general can be effective in terms of making people choose active transportation even in poor weather conditions. This might be important steps to reduce the likelihood of car use in the future, when extreme weathers are to become more likely. Keywords: travel behaviour, environmental attitudes, weather tolerance, climate change, sustainable travel behaviour

Numerical Investigation on Infiltration and Runoff in Unsaturated Soils with Unsteady Rainfall Intensity

Modeling infiltration into soil and runoff quantitative evaluations is very significant for hydrological applications. In this paper, a flow model of unsaturated soils was established. A computational process of soil water content and runoff prediction was presented that combines an analytical solution with numerical approaches. The solutions have good agreements with the experimental results and other infiltration solutions (Richards numerical solution and classical Green–Ampt solution). We analyzed the effects on cumulative infiltration and runoff under three conditions of rainfall intensity with same average magnitude. These rainfall conditions were (Case 1) decreasing rainfall, (Case 2) steady rainfall, and (Case 3) increasing rainfall, respectively. The results show that the cumulative infiltration in Case 1 is the highest among the three cases. The cumulative runoff under condition of Case 3 is smaller than that of decreasing rainfall at the initial stage, which then becomes larger at the later stage. The time of runoff under the conditions of Case 1 is earliest among the three rainfall conditions, which is about 50% earlier than Case 3. Therefore, project construction for urban flood control should pay more attention to urban flood defense in increasing rainfall weather than other rainfall intensities under the same average magnitude. The approaches presented can be utilized to easily and effectively evaluate infiltration and runoff as a theoretical foundation.

Coupled infiltration model of unsaturated porous media for steady rainfall

Unsaturated soil slopes introduce complex hydro-mechanical coupled processes which greatly alter matric suction distribution of an unsaturated soil during rainfall. In order to investigate matric suction and volume change of unsaturated soils, a two-dimensional hydro-mechanical coupled infiltration model (YS-Slope) is developed by incorporating the hydraulic and mechanical characteristics of unsaturated soils, such as the soil-water characteristic curve, permeability function, shear strength, and porosity. Special attention is given to the porosity-dependent permeability function of unsaturated soils. In addition, in order to highlight effectiveness of YS-Slope and coupling effects of hydro-mechanical processes on the infiltration behavior of unsaturated soils, a series of infiltration analyses for a soil column under various soil properties is conducted and their results are compared with those of commercial software, GEO-SLOPE (2012). The results of the numerical analyses show good agreement with data from the analytical solution and laboratory tests, which indicates that the proposed model is appropriate for use in the simulatfion o the infiltration of rainwater into deformable soils. The transient seepage and rainwater flow in deformable soils are influenced by the volume change of the soil. The change in matric suction on a slope due to rainfall infiltration influences change in effective stress while the effective stress alters seepage processes according to hydraulic properties. The results indicate that hydro-mechanical coupled behavior of soils has a positive effect on the stability of unsaturated soil slops during rainfall.

Study of Horizontal Drain Effect on Slope Stability

Abstract Slope failure usually occurs when soil particles are unable to build a strong bond with each other and become loose because of the presence of water. Water pressure weakens the ties between the particles and they tend to slip. Therefore, this study focused on the use of horizontal drains to reduce water entry and control the ground water level as a method of slope stabilization. Several previous studies have shown that the use of horizontal drains to lower the water level in soil is one of the fastest and cheapest slope stabilization methods. The main objective of this study is to analyze the effect of horizontal drains on slope stability. Information on slope condition during the landslides which happened at Precinct 9, Putrajaya, Malaysia was used for analytical simulation. Seep/W and Slope/W analyses were carried out with GeoStudio version 2007 software. Slopes with and without horizontal drains were then compared in terms of groundwater level and factor of safety (FOS) values. Scenarios were created for seven types of soil namely: residual, clay, silt, loam, sandy loam, sandy clay loam, and silt clay loam for a case wise analysis. The effect of daily steady rainfall and real-condition rainfall was studied. These cases were studied to find the effectiveness of horizontal drains as a slope stabilization tool. The results revealed that when a drain was installed on a slope, the groundwater level dropped immediately and the safety factor of the slope increased. Sandy loam (sL) soil was identified as the best candidate for a horizontal drain. Its highly saturated hydraulic conductivity Ks facilitated groundwater drain through the horizontal drain effectively. Silt clay loam (scL) soil was identified as the least effective candidate.

The environmental magnetic record of palaeoenvironmental variations during the past 3100 years: A possible solar influence?

Sediments from Pookot Lake (PK) in southern India have provided a record of local environmental changes and catchment processes during the past 3100cal.yearsB.P. Variations in the rock magnetic parameters (χlf, χfd, χARM and IRM's at different field strengths) of sediments from two AMS 14C-dated cores reflect climate-induced changes in the catchment of Pookot Lake. Assuming that rainfall is most likely the dominant driving mechanism behind the rock magnetic variations of PK sediments, the environmental history of the site has been reconstructed. Rock magnetic parameters exhibit significant variations during the past 3100years. The palaeoenvironmental history of the Pookot Lake region may be divided into three phases. During the first phase (~3100 to 2500cal.yearsB.P.), catchment erosion and detrital influx were high, indicating a strong monsoon. The second phase, which lasted from 2500 to 1000cal.yearsB.P., was characterised by low and steady rainfall, resulting in a low and uniform catchment erosion and detrital influx. Phase 2 was interspersed with brief intervals of strong monsoon and characterised by frequent drying up of the lake. During Phase 3 (~1000cal.yearsB.P. to the present), catchment erosion was high, indicating a shift to strong monsoonal conditions. It appears that monsoonal rainfall in the region is influenced by solar activity, with periods of high total solar irradiance being characterised by high rainfall and vice versa; it was relatively low during the Little Ice Age and high during the Medieval Warm Period. The magnetic susceptibility (χlf) data exhibit a number of periodicities which might have a solar origin. The χlf record exhibits similarities with other continental and marine palaeoclimatic records from the region, indicating that regional trends in the monsoon during the Late Holocene are broadly similar.

Discussion of “Modified Green-Ampt Infiltration Model for Steady Rainfall” by J. Almedeij and I. I. Esen

The discusser would like to thank the authors of the original paper for modifying the classical Green-Ampt equation by incorporating the ponding time. The authors of the original paper have developed two elegant equations for the cumulative infiltration and infiltration rate using the asymptotic matching technique. Proposed unified equations are valid for both cases of steady rainfall greater or less than the infiltration capacity. The work by the authors of the original paper is really appreciated. The discusser, however, would like to add some points. Given the initial condition of F 1⁄4 0 at t 1⁄4 0, the implicit relation for the cumulative infiltration can be written as

Closure to “Modified Green-Ampt Infiltration Model for Steady Rainfall” by J. Almedeij and I. I. Esen

The writers thank the discusser for the interest shown in the original paper. The writers would like to point out that Eq. (14), which was proposed to improve the performance of the explicit approximation of Li et al. (1976), has sufficient accuracy for a range of dimensionless infiltration times for most of the conditions encountered in practice. For example, the dimensionless cumulative infiltration F values determined by the exact relationship given by Eq. (5) and by the approximate Eq. (14) are almost identical for dimensionless times t ≤ 2. For the silt loam discussed in the original paper, this corresponds to about 17.5 h of continuous rainfall of constant intensity. For t < 5, the maximum difference in the F values would be less than 3%. This is much less than the probable error in selecting appropriate values for the hydraulic conductivity, capillary suction head, and the available porosity. Fig. 1 of the closure presents a comparison between Eq. (4) of the discussion and Eq. (14) of the original paper. Eq. (14) can be considered more accurate for t ≤ 1, which corresponds to about 8.7 h for the case study of silt loam. However, for considerably higher t values, Eq. (4) is more accurate than Eq. (14). The writers agree that to satisfy the wide range of t , improvement in accuracy can be obtained by changing the entire form of the original model of Li et al. (1976).

Kinetics of gravity-driven water channels under steady rainfall.

We investigate the formation of fingered flow in dry granular media under simulated rainfall using a quasi-two-dimensional experimental setup composed of a random close packing of monodisperse glass beads. Using controlled experiments, we analyze the finger instabilities that develop from the wetting front as a function of fundamental granular (particle size) and fluid properties (rainfall, viscosity). These finger instabilities act as precursors for water channels, which serve as outlets for water drainage. We look into the characteristics of the homogeneous wetting front and channel size as well as estimate relevant time scales involved in the instability formation and the velocity of the channel fingertip. We compare our experimental results with that of the well-known prediction developed by Parlange and Hill [D. E. Hill and J. Y. Parlange, Soil Sci. Soc. Am. Proc. 36, 697 (1972)]. This model is based on linear stability analysis of the growth of perturbations arising at the interface between two immiscible fluids. Results show that, in terms of morphology, experiments agree with the proposed model. However, in terms of kinetics we nevertheless account for another term that describes the homogenization of the wetting front. This result shows that the manner we introduce the fluid to a porous medium can also influence the formation of finger instabilities. The results also help us to calculate the ideal flow rate needed for homogeneous distribution of water in the soil and minimization of runoff, given the grain size, fluid density, and fluid viscosity. This could have applications in optimizing use of irrigation water.

Modeling infiltration rates in a saturated/unsaturated soil under the free draining condition

We propose a model to simulate infiltration into heterogeneous soils, with arbitrary initial water content distributions, subject to unsteady rainfall, and under the free draining condition. It is a mass conservative theoretical approach based on the numerical resolution of the one-dimensional Richards equation. The model tracks the movement of the wetting front along the soil profile, checks the ponding status, and handles the shift between ponding and non-ponding conditions in the course of the simulation. It partitions the rainfall input into infiltration and surface runoff whenever the upper soil layer is saturated. We validate our theoretical approach by comparing the results for a homogeneous soil under steady rainfall with those calculated with Chemflo-2000. The differences between our approach and the modified Green-Ampt model are showed by considering the infiltration under unsteady rainfall conditions. Finally, we illustrate the model capabilities by examining the water flow and surface runoff for both homogeneous and stratified soils under intense rainfall events.

Modified Green-Ampt Infiltration Model for Steady Rainfall

AbstractThe Green-Ampt equation describing the infiltration of water into soil requires that the rainfall intensity is greater than the infiltration capacity of the soil at all times. The well-known Mein-Larson model modifies the Green-Ampt equation and attempts to avoid this restriction for infiltration of water into a homogeneous soil under rainfall of constant intensity. The rainfall intensity is considered to be less than the infiltration capacity of the soil in the initial phases of a storm. The Mein-Larson model assumes that until the time to ponding of water over the soil surface, the infiltration rate is constant and equals the rainfall intensity. This study shows that the Mein-Larson model underestimates the ponding time and that the cumulative infiltration predicted by the model is always less than the cumulative infiltration potential of the soil. To avoid these drawbacks, an alternative modification of the Green-Ampt equation is presented. In the proposed modification, the ponding time is cons...

Effect of the Capillary Fringe on Steady-State Water Tables in Drained Lands. II: Effect of an Underlying Impermeable Bed

AbstractA tension-saturated capillary fringe above the water table in drained lands gives rise to lower water tables than would occur in its absence. Results of a conformal mapping solution for the flow from uniform steady rainfall rates on the soil surface to deep drains installed above an impermeable bed when the soil above the drains is wholly tension-saturated show that the effect on the water table is greater the nearer the drain is to the impermeable floor. The effect becomes less with increasing rainfall rate. For the very deep tension-saturated soils assumed in the analysis (that implies a very large negative value for the air-entry pressure for the soil), the results obtained give lower bounds for the water-table heights in real soils with finite air-entry values that lie between the calculated ones and those obtained by theory neglecting a capillary fringe.

Drop Shapes and Axis Ratio Distributions: Comparison between 2D Video Disdrometer and Wind-Tunnel Measurements

Abstract Comparisons of drop shapes between measurements made using 2D video disdrometer (2DVD) and wind-tunnel experiments are presented. Comparisons are made in terms of the mean drop shapes and the axis ratio distributions. Very close agreement of the mean shapes is seen between the two sets of measurements; the same applies to the mean axis ratio versus drop diameter. Also, in both sets of measurements, an increase in the oscillation amplitudes with increasing drop diameter is observed. In the case of the 2DVD, a small increase in the skewness was also detected. Given that the two sets of measurements were conducted in very different conditions, the agreement between the two sets of data implies a certain “robustness” in the mean shape of oscillating drops that may be extended to natural raindrop oscillations, at least in steady rainfall and above the surface layer.