Initial Rainfall Research Articles

Physical Initialization and Hurricane Ensemble Forecasts

Ensemble forecasting of hurricane tracks is an emerging area in numerical weather prediction. In this paper, the spread of the ensemble of forecast tracks from a family of different First Global GARP (Global Atmospheric Research Program) Experiment analyses is illustrated. All forecasts start at the same date and use the same global prediction model. The authors have examined ensemble forecasts for three different hurricanes/typhoons of the year 1979. The authors have used eight different initial analyses to examine the spread of ensemble forecasts through 6 days from the initial state. A total of 16 forecasts were made, of which 8 of them invoked physical initialization. Physical initialization is a procedure for improving the initial rainfall rates consistent with satellite/rain gauge based measures of rainfall. The main results of this study are that useful track forecasts are obtained from physical initialization, which is shown to suppress the spread of the ensemble of track forecasts. The spread of the tracks is quite large if the rain rates are not initialized. The major issue here is how one could make use of this information on ensemble forecasts for providing guidance. Toward that end, a statistical framework that makes use of the spread of forecast tracks to provide such guidance is presented.

Effects of Stormwater Nutrient Discharges on Eutrophication Processes in Nearshore Waters of the Florida Keys

Rainfall events cause episodic discharges of groundwaters contaminated with septic tank effluent into nearshore waters of the Florida keys, enhancing eutrophication in sensitive coral reef communities. Our study characterized the effects of stormwater discharges by continuously (30-min intervals) measuring salinity, temperature, tidal stage, and dissolved oxygen (DO) along an offshore eutrophication gradient prior to and following heavy rainfall at the beginning of the 1992 rainy season. The gradient included stations at a developed canal system (PP) on Big Pine Key, a seagrass meadow in a tidal channel (PC), a nearshore patch reef (PR), a bank reef at Looe Key National Marine Sanctuary (LK), and a blue water station (BW) approximately 9 km off of Big PIne Key. Water samples were collected at weekly intervals during this period to determine concentrations of total nitrogen (TN), ammonium (NH4 +), nitrate plus nitrite NO3 − plus NO2 −), total phosphorus (TP), total dissolved phosphorus (TDP), soluble reactive phosphorus (SRP), and chlorophyll a (chl a). Decreased salinity immediately followed the first major rainfall at Big Pine Key, which was followed by anoxia (DO <0.1 mg I−1), high concentrations of NH4 + (≈24 μM), TDP (≈1.5 μM), and chl a (≈20 μg I−1). Maximum concentration of TDP (≈0.30 μM) also followed the initial rainfall at the PC, PR, and LK stations. In contrast, NH4 + (≈4.0 μM) and chl a (0.45 μg I−1) lagged the rain event by 1–3 wk, depending on distance from shore. The highest and most variable concentrations of NH4 +, TDP, and chl a occurred at PP, and all nutrient parameters correlated positively with rainfall. DO at all stations was positively correlated with tide and salinity and the lowest values occurred during low tide and low salinity (high rainfall) periods. Hypoxia (DO <2.5 mg I−1) was observed at all stations follwing the stormwater discharges, including the offshore bank reef station LK. Our study demonstrated that high frequency (daily) sampling is necessary to track the effects of episodic rainfall events on water quality and that such effects can be detected at considerable distances (12 km) from shore. The low levels of DO and high levels of nutrients and chl a in coastal waters of the Florida Keys demand that special precautions be exercised in the treatment and discharge of wastewaters and land-based runoff in order to preserve sensitive coral reef communities.

有害物質・障害生物の水環境への影響と制御 都市域における降雨初期雨水排水中のベンゾ（ａ）ピレンの挙動

The early phase rain fall current of the time appearance characteristic of benzo (a) pyrene contained in combined sewerage overflow, separate sewerage rain-water drainage, and road runoff was investigated. Analytical conditioning method of benzo (a) pyrene was also examined. Benzo (a) pyrene is one of polynuclear aromatic hydrocarbons which are carcinogenic agents contained in auto exhaust, and it is carried in rivers and sea by initial rain fall. As for benzo (a) pyrene accumulated with bottommud, that influence to ecosystem is pointed out.Benzo (a) pyrene didn't exist in the filtrate of rain water samples, but absorbed with the suspended solid almost. Benzo (a) pyrene was detected with high concentration in road runoff and combined sewerage overflow. It was suggested that sediment in the sewerage pipe and road sediment coexisted in the combined sewerage overflow, and that the road sediment contaminated with benzo (a) pyrene was still drained after the sediment in the pipe which was easy to be transferred.

FLUOMETURON BEHAVIOR IN LONG-TERM TILLAGE PLOTS

Fluometuron (N, N-dimethyl-N'-[3-(trifluoromethyl) phenyl] urea) is a preemergence herbicide used widely for weed control in cotton (Gossypium hirsutum L.). Field research results suggest that many herbicides, including fluometuron, may be subject to preferential transport and leaching through the soil profile. The objectives of this study were to evaluate the distribution and leaching of fluometuron in a Lexington silt loam (Typic Paleudalf) through 3 years of study by analyzing depth incremented soil samples and tension-free pan lysimeter leachates collected at a soil depth of 90 cm under no-till (NT) and conventional tillage (CT, disc 2x - roller harrowed) management. Fluometuron depth distribution following application and subsequent rainfall was related to soil organic carbon content, with tillage effects restricted to the surface 2-cm. The amount of herbicide remaining in the soil profile after application decreased with increasing rainfall amounts. On average, 11% of applied herbicide in NT and 6% in CT remained in the surface 15 cm after 1 year. Fluometuron was detected in all lysimeter leachates during the 3-year period. Peak herbicide leachate concentrations ranged from 68 mg L -1 to 1700 mg L -1 , depending on herbicide application in relation to rainfall timing. Annual leaching losses ranged from 5 to 53% of applied fluometuron during the study. Of the amounts lost to leaching, 68 to 100% (averaging 87% of the total lost to leaching) were lost during the first two or three significant rainfall events after treatment. Rainfall timing in relation to herbicide application was the dominant effect in herbicide mobilization through the soil profile. Antecedent soil moisture content (predicted from rainfall amounts prior to fluometuron application) also influenced the appearance of leachate and herbicide in the lysimeters, with lower soil moisture conditions at application producing lower preferential flow. Depth-incremented soil sampling after initial rainfall events was a poor mechanism for detecting fluometuron mobility through the soil profile. The rapidity at which fluometuron was detected in the lysimeter leachates, the exceedingly high fluometuron concentrations, and the variability in leachate collection by the lysimeters, illustrated the significance of preferential flow. The influence of tillage practice on the volume of drainage collected by the lysimeters and on fluometuron leaching was of little significance when compared with the influence of natural infiltration heterogeneity.

Mesoscale Signatures within the Tropics Generated by Physical Initialization

Abstract This paper presents some recent results on physical initialization from the use of a very high resolution global model. Fundamentally this procedure improves the model-based initial rainfall, surface fluxes, and diagnostic cloud amount. Physical initialization is a useful procedure for the nowcasting of rainfall. Correlation between model-based initialized rain and satellite/rain gauge-based rain over the Tropics (for 6-h averages and averaged over transform grid squares) is of the order 0.85. This compares with a correlation of around 0.3 for models that do not include physical initialization. The day 1 tropical rainfall forecast skill is also relatively high for the physically initialized experiments; the correlation is of the order 0.55. It should be noted that the lifetime of mesoconvective systems is approximately 1 day, whereas more organized tropical disturbances may last substantially longer. A major portion of the tropical rainfall is associated with these short-lived systems, hence the ...

Azinphosmethyl and fenvalerate washoff from cotton plants as a function of time between application and initial rainfall

Understanding pesticide foliar washoff is important in pest management, in development of integrated management systems, and in environmental modeling. This study was conducted to determine the effect of elapsed time between spray application and initial rainfall on insecticide washoff from foliage. Azinphosmethyl and fenvalerate were applied to mature cotton plants as tank-mixed emulsifiable concentrates with a water carrier. DT50s (50% disappearance time) for azinphosmethyl and fenvalerate were 3.9 and 237 h, respectively. Simulated rain (51 mm in 1 h) was applied to the cotton plants at times ranging from 2 to 146 h after insecticide application to determine washoff characteristics for both compounds. Residues of both insecticides became increasingly resistant to wash-off with increasing time interval between insecticide application and initial rainfall, e.g., about 95% of the plant Xload washed off 2 h after application, whereas at 146 h <50% washed off. The mean amounts of both insecticides washed from the plants decreased with time and were related to the mean plant loads. The results of this study show that foliar pesticide application should be delayed when rain is imminent.

Permethrin and Sulprofos Washoff from Cotton Plants as a Function of Time between Application and Initial Rainfall

AbstractUnderstanding pesticide foliar washoff is important in environmental modeling, pest management, and development of integrated management systems. This study was conducted to determine the effect of elapsed time between spray application and initial rainfall on insecticide washoff from foliage. Permethrin [(3‐phenoxyphenyl)‐methyl(1K,S)‐cis,trans‐3‐(2,2‐dichloroethenyl)2,2‐dimethylcyclopropanecarboxylate] and sulprofos [O‐ethyl O‐(4‐methylthiophenyl)‐S‐propyl phosphorodithioate] were applied to mature cotton (Gossypium hirsutum L.) plants as tank‐mixed emulsifiable concentrates with a water carrier. Simulated rain (51 mm in 1 h) was applied to the cotton plants at different times after insecticide application to determine washoff characteristics for both compounds. Residues of both insecticides became increasingly resistant to washoff with increasing time interval between insecticide application and initial rainfall. The mean amounts of both insecticides washed from the plants were related to the mean insecticide loads on the plants and decreased with time. On the average, the first 2 to 3 mm of rain removed 50% of the total amounts of insecticide washed from the plants by the 51‐mm storm.

Effects of N and P rates and proportional timing of N application on rainfed wheat in Zambia

A study was carried out to establish the optimum rates of N and P fertilizers, optimal ratio of basal to top dressed N and time for top dressing the balance of total N in rainfed wheat in the high rainfall zone of northern Zambia. Grain yield, number of spikes per unit area and number of kernels per spike increased with both N and P rates. Except for kernel weight, the other yield components were positively correlated with grain yield. Split application with a ratio favouring top dressing, and applied four weeks after seeding gave higher yields than ratios favouring basal dressing. Initial fertility levels and rainfall distribution influence on the effects of these factors are discussed.

Pesticide Runoff Simulations: Long-Term Annual Means vs. Event Extremes?

The GLEAMS model (Groundwater Loading Effects of Agricultural Management Systems) is used to illustrate model application in evaluating potential pesticide runoff of two similar pesticides from one soil. This limited application was chosen for simplicity in illustrating relationships between annual means and single events. When using annual totals of simulated pesticide runoff for comparing two pesticides or assessing risks, long-term 50-yr simulations are preferable to short 10-yr simulations. When short-term simulations are performed, care must be exercised in selecting representative climatic periods. For short half-life pesticides, as demonstrated in this study, initial rainfall events on or near the day of application will often contribute most to annual pesticide lost. In these cases, single event analysis may be required. Procedures are demonstrated for expressing annual total pesticide losses and single rainfall event losses probabilistically in terms of expected recurrence intervals.

Washoff of Ultra‐Low‐Volume‐Oil‐Applied Insecticides from Cotton Plants as a Function of Time between Application and Rainfall

AbstractModel development for predicting the movement of foliar‐applied pesticides depends on being able to characterize the dynamics of pesticide disappearance from plants, including washoff by rainfall. This study was conducted to determine the effect of elapsed time between spray application and initial rainfall on pesticide washoff from foliage. Methyl parathion [0, 0‐dimethyl,0‐(p‐nitrophenyl) phosphorothioate] and fenvalerate [(RS)‐α‐cyano‐3‐phenoxybenzyl (RS)‐2‐(4‐chlorophenyl)‐3‐methylbutyrate] were applied in oil by rotary‐atomizer controlled‐droplet applicators to mature cotton (Gossypium hirsutum L.) plants. Simulated rainfall (51 mm in 1 h) was applied to the plants at different times after insecticide application to determine washoff characteristics for both compounds. Residues of both insecticides became increasingly resistant to washoff with increasing time interval between pesticide application and initial rainfall. The mean amounts of both insecticides washed from the plants (i) were related to the square of the mean insecticide loads on the plants and (ii) decreased exponentially with time.

Contributions to the Implementation of the Arakawa-Schubert Cumulus Parameterization in the GLA GCM

Several integrations were made with a coarse (4° × 5° nine-sigma level) version of the GLA GCM, which has the Arakawa–Schubert cumulus parameterization, predicted fractional cloud cover, and a parameterization of evaporation of falling rainfall. All model simulation experiments started from the ECMWF analysis for 15 December 1982 and were integrated until 31 January 1983 using climatological boundary conditions. The first ten days of model integrations show that the model-simulated tropics dries and warms as a result of excessive precipitation. Three types of model development-cum-analysis studies were made with the cumulus scheme. First, the Critical Cloud Work Function (CCWF) dataset for different sigma layers were reworked using the Cloud Work Function (CWF) database of Lord et al. as representative of time-average CWF and not the actual CCWF values as in the Arakawa–Schubert implementation of cumulus convection. The experiments with the new CCWF dataset helped to delineate the influence of changing CCWF on model simulations. Larger values of CCWF partially alleviated the problem of excessive heating and drying during spinup and sharpened the tropical ITCZ (Intertropical Convergence Zone). Second, by comparing two simulations, one with and one without cumulus convection, the role of cumulus convection in maintaining the observed tropical rainfall and 850 mb easterly winds is clarified. Third, by using Simpson's relations between cloud radii and cumulus entrainment parameter, λ, in the Arakawa–Schubert cumulus scheme, realistic upper and lower bounds on λ were obtained. This improvement had a significant impact on the time evolution of tropical temperature and humidity simulation. It also significantly suppressed the excessive rainfall during spinup. Finally, by invoking λmin = 0.0002 m−1 (Rmax = 1.00 km) another simulation was made. In this simulation, not only the excessive initial rainfall was virtually eliminated, but a more realistic vertical distribution of specific humidity in the tropics was produced. Despite the conceptual simplicity of the latter, it has made some very significant improvement to the monthly simulation in the tropics.

Rangeland Experiments to Parameterize the Water Erosion Prediction Project Model: Vegetation Canopy Cover Effects

The Water Erosion Prediction Project (WEPP) is a new water erosion prediction technology being developed by the USDA-Agricultural Research Service to replace the Universal Soil Loss Equation. Rangeland field experiments were designed to parameterize the WEPP rangeland erosion model. Included in the field experiments were plot treatments designed to separate direct from indirect effects of vegetation canopy on runoff and soil erosion. Nine rangeland sites from a wide range of soil and vegetation types were evaluated using rainfall simulation techniques. Natural versus clipped treatment surface characteristics and runoff and erosion responses were compared using regression analyses. These analyses showed that there were no significant differences between natural and clipped plot surface characteristics, runoff ratios, final infiltration rates, or initial rainfall abstractions. Erosion rates were different between treatments with the clipped plots having slightly less erosion than the natural plots. Results indicated that, under the rainfall conditions simulated, canopy cover was not directly contributing to initial abstractions through rainfall interception loss or significantly affecting runoff or erosion.

Physical initialization for numerical weather prediction over the tropics

The current operational World Weather Watch over the tropical latitudes exhibits large data gaps. This paper proposes a detailed physical initialization procedure where the combined use of the World Weather Watch and detailed satellite data sets are used to enhance the definition of initial surface fluxes of water vapor and sensible heat, the initial rainfall rates and the earth's radiation budget. The satellite radiances are used to unify the physical initializations of the fluxes, rainfall, and the clouds. This is carried out using a Newtonian relaxation during a pre integration phase between day — 1 and day 0 where the fluxes, the rainfall rates, and the cloud distributions provide a consistent humidity analysis and a spin up of the diabatic heating and the divergent circulations. A comparison of medium range forecasts from a control experiment (that utilizes the standard nonlinear normal mode initialization, with physics, at day 0) with an experiment based on the unified physical initialization is carried out to demonstrate the effective enhancement of the World Weather Watch over the tropics by the proposed method. These experiments are carried out with a global spectral model which is run at a resolution of 106 wave triangular truncation. DOI: 10.1034/j.1600-0889.1991.t01-2-00007.x

Physical initialization for numerical weather prediction over the tropics

The current operational World Weather Watch over the tropical latitudes exhibits large data gaps. This paper proposes a detailed physical initialization procedure where the combined use of the World Weather Watch and detailed satellite data sets are used to enhance the definition of initial surface fluxes of water vapour and sensible heat, the initial rainfall rates and the earth's radiation budget. The satellite radiances are used to unify the physical initializations of the fluxes, rainfall, and the clouds. This is carried out using a Newtonian relaxation during a-pre integration phase between day — 1 and day 0 where the fluxes, the rainfall rates, and the cloud distributions provide a consistent humidity analysis and a spin up of the diabatic heating and the divergent circulations. A comparison of medium range forecasts from a control experiment (that utilizes the standard nonlinear normal mode initialization, with physics, at day 0) with an experiment based on the unified physical initialization is carried out to demonstrate the effective enhancement of the World Weather Watch over the tropics by the proposed method. These experiments are carried out with a global spectral model which is run at a resolution of 106 wave triangular truncation. DOI: 10.1034/j.1600-0870.1991.t01-3-00007.x

Initial Storm Effects on Macropore Transport of Surface‐Applied Chemicals in No‐Till Soil

AbstractPrevious research has established that macropores can rapidly transmit water through soil. This observation has raised concern that macropores may also promote rapid movement of agricultural chemicals to groundwater. This is a particular concern for no‐till fields where lack of disruption by tillage can lead to the development of extensive macropore systems. In order to investigate the effect of initial rainfall on chemical transport, strontium bromide hexahydrate (SrBr2·6H2O) and atrazine (2‐chloro‐4‐ethylamino‐6‐isopro‐pylamino ‐s‐triazine) were surface‐applied to six 30 by 30 by 30 cm blocks of undisturbed soil obtained from a 25‐yr‐old, no‐till corn (Zea mays L.) field with evidence of well‐defined macropores attributable to earthworm activity. Half of the blocks then received a 1‐h 5‐mm simulated rain, which did not produce percolate. Two days later, the blocks received a 0.5‐h 30‐mm simulated rain, followed by another 0.5‐h 30‐mm rain 1 wk later. The remaining blocks received only the two 30‐mm events. An average of 12% of the applied water passed through all the blocks during and shortly after the first 30‐mm rain. Bromide, Sr, and atrazine losses in this percolate were 7, 10, and 2 times less, respectively, from blocks that received the 5‐mm rain than from blocks not receiving this initial, light rain. The second 30‐mm rain on the blocks not receiving the initial 5 mm produced 1.6× more percolate than the first 30‐mm rain. Yet, transport and flow‐weighted average concentrations of Br, Sr, and atrazine were all reduced. These results indicated that the first storm after application can move solutes into the soil matrix, thereby reducing the potential for transport in macropores during subsequent rainfall events.

Rainfall-runoff relationship based on the model of runoff formation at the natural storage

An attempt is mad~ to establish a relationship between rainfall and runoff. The basic input data are (i) rainfall, (ii) run off and (iii) evapotranspiration. The moisture content prior to rainfall under consideration and after the termination of rainfall is computed by water balance technique this method is applied in small agricultural catchments in Soil Conservation Research Farm at Ballary, Karnataka, which is categorised its semiarid zone of black soil region. The relationship between rainfall and runoff under different initial moisture content and rainfall intensities are found out. Attempts are also made to get relationship between moisture condition of the catchment after the end of rainfall and runoff with rainfall intensities as an additional factor. The estimated runoff obtained from various equations are compared with the observed runoff. The rainfall-runoff relationship with initial moisture content as third parameter gives encouraging results for estimation of runoff.

Movement of Tebuthiuron Applied to Wet and Dry Rangeland Soils

Tebuthiuron was applied at 1 kg ai/ha to wet and dry Hathaway gravelly, sandy loam soil in the spring and fall to determine the amount of tebuthiuron removed in runoff water and the depth to which it would move within the soil profile by simulated rainfall. When pellets containing 20% ai of tebuthiuron were broadcast onto dry soil in the spring, the first simulated rainfall event, 37 mm, removed 5% of the applied tebuthiuron in runoff water and sediment. The second and third simulated rainfall events, 22 and 21 mm, respectively, removed an additional 2%. When tebuthiuron was applied to wet soil in the spring, the initial simulated rainfall events, totaling 42 mm, removed 15% of the tebuthiuron. When tebuthiuron was applied to wet soil in the fall, the initial rainfall events, totaling 40 mm, removed a total of 48% of the tebuthiuron in runoff water and sediment. No significant differences were found in the total amount of tebuthiuron within the soil profile after application to dry and wet soils. More than half of the tebuthiuron had moved into the surface 7 cm 1 day after application. Tebuthiuron was not detected below 90 cm after 165 mm of simulated rainfall and 270 mm of natural rainfall.

Evaluating the Effect of Puddling on Infiltration Using the Green and Ampt Equation

ABSTRACT AFTER exposure to several different initial rainfall durations and rainfall sequences, the constant-head cumulative infiltration of water into disturbed Hagerstown silt loam Ap horizon soil samples of two aggregate sizes was measured. The Green-Ampt equation was fit to the cumulative infiltration data using nonlinear regression to yield hydraulic conductivity and capillary suction parameters for each treatment. The Green and Ampt equation fit the results of all treatments very well. The hydraulic conductivities an capillary suction values obtained were unique and characteristic of the flow process for all treatments containing a surface puddle or partial surface puddle caused by rainfall energy. These parameters were not unique for treatments which had no surface puddling. The infiltration responses to rainfall of 0 to 20 min duration (0 to 436 J/m^ rainfall energy) showed that the hydraulic conductivities decreased from 576 mm/h for the no rain treatment to 5.4 mm/h for the coarse aggregates receiving 20 min of rain. For all treatments the capillary suction was very small indicating that flow through the surface puddle was controlled by the very thin surface layer of partially broken aggregates and primary particles. The breakdown of surface aggregates by raindrop impact was found to be a two stage process. During the initial stage, the surface layer's hydraulic conductivity decreased very rapidly (15.1 mm/h for every J/m^ of rainfall energy). During the second stage, the surface layer's hydraulic conductivity decreased more slowly (0.034 mm/h for every J/m^ of rainfall energy). Surface puddling resulting from a sequence of rainfall events was also evaluated. It was found that the flow characteristics of the surface layer reflected the condition created as a result of the most recent rainfall event. Surface puddling from previous events was less important.

ESTIMATING RUNOFF VOLUMES FROM URBAN AREAS1

ABSTRACT: Estimations of runoff volumes from urban areas can be made by the equation Q = a A σ(Pe– b), where Q is the runoff volume, a is the part of the total area A Contributing to runoff, Pe is the rainfall amount for a single event, and b is the initial rainfall losses. For the evaluation of a and b, rainfall/runoff measurements were made in five areas of sizes between 0.035 km2 and 1.450 km2. By linear regression analysis of rainfall volumes versus runoff volumes, the initial rainfall losses were found to vary from 0.38 mm to 0.70 mm for the different areas. The parts of the areas contributing to runoff were found to be proportional to the impermeable parts of the mas. The equation is applicable in urban areas with well defined paved surfaces and roofs and with a negligible amount of runoff from permeable areas.

Warm Rain Development in a Three-Dimensional Cloud Model

Abstract A warm rainshower was simulated in a shallow, anelastic, three-dimensional cloud model with detailed microphysics. After many features of the drop growth process were successfully simulated in a symmetric cloud, wind shear effects on both microphysical and dynamic properties were investigated. A number of special characteristics appeared under wind shear conditions: 1) the development of stronger downdrafts and a shortened cloud lift; 2) weak rainfall occurs early in the process; 3) a sharp raindrop size distribution; 4) initial rainfall localized in a narrow area at the ground with a large rainfall intensity gradient near the upshear side; 5) greater movement of the cloud system during rainfall; and 6) formation of cyclonic-anticyclonic circulations near the cloud top. Many of these characteristics may be explained by the transport of horizontal momentum by updrafts/downdrafts, as shown by close correspondence with the detailed microphysical processes.