Beginning Of Rainfall Research Articles

Effect of rain scavenging on altitudinal distribution of soluble gaseous pollutants in the atmosphere

We suggest a model of rain scavenging of soluble gaseous pollutants in the atmosphere. It is shown that below-cloud gas scavenging is determined by non-stationary convective diffusion equation with the effective Peclet number. The obtained equation was analyzed numerically in the case of log-normal droplet size distribution. Calculations of scavenging coefficient and the rates of precipitation scavenging are performed for wet removal of ammonia (NH3) and sulfur dioxide (SO2) from the atmosphere. It is shown that scavenging coefficient is non-stationary and height-dependent. It is found also that the scavenging coefficient strongly depends on initial concentration distribution of soluble gaseous pollutants in the atmosphere. It is shown that in the case of linear distribution of the initial concentration of gaseous pollutants whereby the initial concentration of gaseous pollutants decreases with altitude, the scavenging coefficient increases with height in the beginning of rainfall. At the later stage of the rain scavenging coefficient decreases with height in the upper below-cloud layers of the atmosphere.

Relevance of urban glyphosate use for surface water quality

Relative contributions of agricultural and urban uses to the glyphosate contamination of surface waters were studied in a small catchment (25 km 2) in Switzerland. Monitoring in four sub-catchments with differing land use allowed comparing load and input dynamics from different sources. Agricultural as well as urban use was surveyed in all sub-catchments allowing for a detailed interpretation of the monitoring results. Water samples from the river system and from the urban drainage system (combined sewer overflow, storm sewer and outflow of wastewater treatment plant) were investigated. The concentrations at peak discharge during storm events were elevated throughout the year with maximum concentrations of 4.15 μg L −1. Glyphosate concentrations mostly exceeded those of other commonly used herbicides such as atrazine or mecoprop. Fast runoff from hard surfaces led to a fast increase of the glyphosate concentration shortly after the beginning of rainfall not coinciding with the concentration peak normally observed from agricultural fields. The comparison of the agricultural application and the seasonal concentration and load pattern in the main creek from March to November revealed that the occurrence of glyphosate cannot be explained by agricultural use only. Extrapolations from agricultural loss rates and from concentrations found in the urban drainage system showed that more than half of the load during selected rain events originates from urban areas. The inputs from the effluent of the wastewater treatment plant, the overflow of the combined sewer system and of the separate sewer system summed up to 60% of the total load.

Nematode dispersion by runoff water: Case study of Radopholus similis (Cobb) Thorne on nitisol under humid tropical conditions

To minimize application of nematicides in banana fields, crop systems have been developed in the French West Indies that combine fallow or rotation crops and nematode-free in vitro plants. After two to four years, populations of the burrowing nematode Radopholus similis have developed enough to cause economic losses, leading banana growers to use nematicides. To understand how banana fields are recontaminated, we studied the dissemination of R. similis by water flow. At a 1-m scale, we analyzed the dispersion of R. similis under a rainfall simulator: we isolated a 1-m 2 study plot, placed a R. similis suspension on the upstream soil surface, and simulated a 60 mm/h rainfall for 72 min. We collected soil samples every 10 cm downstream after 12 min of rainfall, and subsequently at 20-min intervals, and extracted the nematodes using a Seinhorst elutriator and then a Baermann funnel. Our results showed that the nematode dissemination follows an inverse exponential law, and depends more on soil moisture at the beginning of rainfall than on the length of rainfall: in fresh soil, 69–80% of the R. similis recovered were found less than 10 cm downstream from the nematode inoculation line, whereas in wetted soil, 76–85% of the recovered individuals were collected in the outlet tub located downstream from the apparatus. This passive dissemination model partially explains the distance covered by individual nematodes but not the low percentage of motile nematodes recovered in the outlet tub (10% and 36% in fresh and wet soils) compared to the percentage of motile nematodes found in the soil (80% and 84% in fresh and wet soils). Indeed, water runoff is likely to disseminate R. similis over long distances only when soil moisture is close to field capacity.

A new installation for treatment of road runoff: up-flow filtration by porous polypropylene media

We installed a new device on a paved road to treat runoff from a roadway surface. All the stormwater runoff was transferred into the device and the runoff equivalent to 10 mm/hr or less was treated. The treatment method consists of sedimentation and up-flow filtration with porous polypropylene (PPL) processes. The treated runoff was discharged into the existing storm drainage pipe. The average removal efficiency of the initial runoff at the beginning of rainfall which has high pollution intensity was about 90% for SS, about 70% for COD, about 40% for total phosphorus (T-P), about 80% for Pb and Cd, about 70% for Zn, Cu, Mn and Cr, and about 60% for polycyclic aromatic hydrocarbons (PAHs). The overall removal efficiencies of the experiment that ran for four months remained > 60% of SS, > 40% of COD, > 60% of heavy metals, and > 40% of PAHs. The PPL is excellent for removing smaller size particulates of suspended solids, which originate basically from diesel exhaust, as well as larger size particulates from automobile tires, asphalt roads, and other accumulated source(s) of clay and sand, etc.

Fixation and chemical analysis of single fog and rain droplets

Last decade, the importance of global environmental problems has been recognized worldwide. Acid rain is one of the most important global environmental problems as well as the global warming. The grasp of physical and chemical properties of fog and rain droplets is essential to make clear the physical and chemical processes of acid rain and also their effects on forests, materials and ecosystems. We examined the physical and chemical properties of single fog and raindrops by applying fixation technique. The sampling method and treatment procedure to fix the liquid droplets as a solid particle were investigated. Small liquid particles like fog droplet could be easily fixed within few minutes by exposure to cyanoacrylate vapor. The large liquid particles like raindrops were also fixed successively, but some of them were not perfect. Freezing method was applied to fix the large raindrops. Frozen liquid particles existed stably by exposure to cyanoacrylate vapor after freezing. The particle size measurement and the elemental analysis of the fixed particle were performed in individual base using microscope, and SEX-EDX, particle-induced X-ray emission (PIXE) and micro-PIXE analyses, respectively. The concentration in raindrops was dependent upon the droplet size and the elapsed time from the beginning of rainfall.

A STUDY ON PONDING TIME AND INFILTRATION CAPACITY DURING STEADY RAINFALL

Natural rainfall has the variation in rainfall intensity during its event. However, the various infiltration models are subjected to rainfall intensities that are higher than the infiltration capacity of the soil at a given location. Diskin and Nazimov (J. Hydrol., 172: 313-330, 1995) proposed recently the infiltration model which is a simple conceptual model and can express the relationship between rainfall intensity and ponding time.‘Ponding time’ is the period from the beginning of rainfall until the occurrence of ponding. This model also can compute the variation in the infiltration capacity for constant or variable rainfall rates. A simple conceptual model is valuable for carrying out the stormwater runoff analysis.The purpose of this paper is to investigate the ponding time and the infiltration capacity for field infiltration data measured using a rainfall simulator under steady rainfall and to evaluate the above infiltration model proposed by Diskin and Nazimov. Comparison of the model calculations with experimental data shows reasonably good for the relationship between rainfall intensity and ponding time and excellent agreement for the infiltration decay curves.

Modeling the dynamics of seal formation and its effect on infiltration as related to soil and rainfall characteristics

The main physical aspects of soil surface seal formation caused by rainfall are modeled. The proposed model relates the surface sealing to the specific hydraulic and mechanical properties of the initially undisturbed soil as well as the physical characteristics of the rainfall applied, under given initial and boundary conditions defining the flow system. The soil disturbance resulting from the raindrop impacts is expressed in terms of an increase of the initial soil bulk density. The dynamics of seal formation at the soil surface are found to be related to the following variables: the rainfall intensity, the second moment of the drop‐size density distribution, the maximal drop diameter, the compaction limit of the given soil, and its initial shear strength, which depends upon the initial soil bulk density and water content. Following Mualem and Assouline [1989], a nonuniform seal is considered, represented by an exponentially decreasing function of the bulk density with depth. The seal thickness is assumed to be dependent upon the rainfall rate. Its steady state value is assumed to be reached shortly after the beginning of rainfall so that it might be considered as constant during the stage of formation. A calibration procedure is presented on the basis of measured infiltration under sealing conditions. The results show that the proposed model addresses the main factors affecting soil sealing formation and is able to simulate the process of infiltration through sealing soils under saturated as well as unsaturated flow conditions.

Rapid change in nitrate and sulfate concentrations observed in early stage of precipitation and their deposition processes

The concentrations of H+, nitrate (NO3-), and sulfate (SO42-) in rainwater and their temporal changes were analyzed on the basis of continuous observation from 1 July 1991 to 30 June 1992 at a suburb of Nagoya, Japan. The yearly average for pH was 4.4. In general, an increasing pH with increase in precipitation amount was observed for rain events. Relatively high pH rainwater was sometimes observed at the beginning of rainfall, even though high concentrations of NO3- and SO42- were involved. The high pH values were considered to be caused by the neutralization process with particulate matter containing cations. The yearly averaged ratio of equivalent concentration of nitrate to sulfate (N/S) in rainwater was 0.58. In the early stage of rain, the N/S value was usually more than 1.0 due to the difference of scavenging process between NO3- and SO42-. High values of N/S ranging from 5 to 10 were found under the atmospheric conditions of calm winds and low humidity, during which it is possible that atmospheric particles float for a long time in the air before a rain event. The adsorption of NO3- in the early stage of rainfall by particulate matter was suggested from the difference in scavenging processes of NO3- and SO42-. A possible scavenging process, called limb cloud scavenging, is presented to explain the interaction of particles and nitrate ions at the early stage of rain. In limb cloud scavenging, the repeated migration of cloud particles or raindrops between the inside and outside of clouds increases the absorption of ions to a highly condensed level, thus increasing the N/S value of rainwater. The influence of global scale seasonal phenomena with large amounts of particulates, such as typhoons or Asian dust storms, was also studied.

STOCHASTIC TIME DISTRIBUTION OF STORM RAINFALL

Increments of rainfall during a storm event were treated as stochastic variates. Statistical distributions of accumulated rain were developed at 2-hour intervals. Three-parameter lognormal distributions were then fitted simultaneously to the twelve 2-hour histograms by making two of the three parameters continuous functions of elapsed time from beginning of rainfall. After evaluation of the parametric functions by nonlinear least squares, stochastic patterns of storm rainfall can be simulated.

A proposed method for calculating stream‐flow

In recent studies of stream‐flow determination from rainfall‐records much emphasis has been placed on antecedent weather. The soil‐moisture deficiencies that occur on a watershed as a result of weather preceding rainfall could be rather closely estimated if the amount of moisture lost by evaporation and transpiration between storms were known. Instruments designed to secure measurements of such losses are only now being perfected [see 5 of “References” at end of paper] and it was in anticipation of them that a proposed method has been developed for calculating contributions of runoff to stream‐flow by reference to soil‐moisture deficiencies at the beginning of rainfall. The details of the method are tentative. Only a brief outline of the procedure and of the results obtained is therefore presented in this paper.