Rain events

Fig. 10-12. Atmospheric processes involved in acidic deposition, The two principal deposition pathways are dry deposition (nonrain events) and wet deposition (rain events).

In developed countries heavy rain events not followed by floods have frequently been associated with outbreaks linked to drinking water supplies derived from... 

Improving education programmes for water professionals in potential climate change impacts and the effect of extreme rain events. 

Figure 7. Log of the excess °Pb and particle concentrations plotted as a function of time after a prolonged rain event in Galveston Bay. Data from Baskaran and Santschi (1993).

Ho et al (2004) showed for SF6 that in low wind conditions short intense rain events accelerate gas exchange in the marine environment. Extending air-sea exchange by including this process is also of interest in the context of climate change, as climate projections suggest that the intensity of rain events will increase [Roeckner et al (2006)]. 

FIGURE 6.3. Diurnal variation in the sulfide concentration of a 4 km pressure main located in North Jutland, Denmark. The typical variation of the residence time during a dry-weather period is between 6 and 14 hours, corresponding to the daily wastewater flow. During a rain event, the residence time may be reduced to about 1 hour. 

In the Asian region with prevalent monsoon climate and heavy rain events during rain seasons, surface runoff plays the most important role in the environmental pathways of many pesticides. The major factors influencing the amount of pesticides carried away by runoff are as follows (Richter, 1999) ... 

As regards the pollutants monitoring, from the measurements available so far it could be concluded that acid rain is coming to be a major problem in Asia. In many industrially developed and new developed countries such as Japan, China, Taiwan, South Korea, Thailand etc., values of pH <5 are encountered at many sites, and they represent more than 50% of monitored rain events on a regional scale. In some developing countries of South-East Asia (Myanmar, Laos, Cambodia) most rainwater pH measurements tend to be around 5.6, the pH of natural rainwater, and the acid rain precipitation is mainly due to localized industrial pollution. There is some evidence that pH values below 5 at unpolluted sites may be due to the contribution of weak organic acids, such as formic and acetic acids (Radojevic, 1998). 

Di-ft-octylphthalate was detected in five of seven ambient air and six of seven rainwater samples collected during rain events that occurred in February through April 1984 in Portland, Oregon. Di-/ -octylphthalate concentrations ranged from 2.6 to 20 ng/L in rain samples and from 0.06 to 0.94 ng/m3 in air samples (Ligocki et al 1985). 

Phenol was detected during seven rain events in Portland, OR, between February and April of 1984. Concentrations in rain ranged from more than 75 to 1,200 ppt, and averaged above 280 ppt. Gas-phase concentrations ranged from 220 (56.1 ppt) to 410 ng/m3 (105 ppt) and averaged 320 ng/m3 (82 ppt) (Leuenberger et al. 1985). 

Knowledge about the isotopic variations in precipitation is increased when single rain events are analyzed from local stations. Especially under mid-latitude weather conditions, such short-term variations arise from varying contributions of tropical, polar, marine, and continental air masses. 

This approach has been used in the well-known model HELP (Hydrological Evaluation of Landfill Performance, Schroeder et al. 1994) and a number of complementary models (Nixon et al. 1997). These models mostly assume the landfilled material to be idealized layers with homogenous properties. One such model, HYDRUS, has been used to model flow through Landfill Lostorf, but it was found that it could not fully catch the dynamics of flow, particularly after rain events (Johnson et al. 2001). Water passes through the... 

Leachate appears to be of more or less constant composition under conditions not affected by rain events. In winter, when the landfills have a higher water content overall, concentrations may be lower due to dilution, but the effect is not dominant (Johnson et al. 1999). This is illus-... 

In the case of Lysimeter Teuftal, most dissolved heavy metal and metalloid concentrations are directly correlated to electrical conductivity. The plot in Fig. 7 shows the relative dilution of different components during a rain event in comparison to that of electrical conductivity. The trend is independent of the speciation of these components. It should be noted that there are three notable exceptions, namely Ni(H), Co(II), and Cu(II). The common property of these cationic species is that they are extremely insoluble under the highly basic conditions encountered in the leachates of cement-stabilized residues (pH 12.8). It is possible that precipitation is the cause of such behaviour. 

Fig. 6. Concentrations of selected leachate components during a rain event in May 1995 at Landfill Lostorf.

Fig. 7. The correlation of changes in dissolved heavy metal concentrations to changes in electrical conductivity for the May 1996 rain event.

Fig. 9. Possible solubility controlling phases for dissolved concentrations of Ca(II), Al(III), SO4- and Si(IV) in Landfill Lostorf leachate. The symbols represent measured concentrations for different rain events and the curves represent model calculations for the conditions given in Table 1.

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