Precipitation rain rainfall

The rainfall regime in arid areas is characterized by low, irregular and unpredictable precipitation, often concentrated in a few rainstorms, creating humid conditions in the soil for a short period and over a limited area. In many arid areas, several years may elapse between successive rainfalls. The moisture supplied to the soil from rain is offset by evaporation, that is related to air temperature, air humidity and intensity of solar radiation. Because of the irregular rainfall distribution, mean precipitation values have little meaning, if not also the range of variation is indicated. 

Because of the irregular rainfall distribution, mean precipitation values have little meaning in the (semi)-arid zone, if not also the range of variation is indicated. This variability refers to both temporal and spatial variability. Temporal variability affects not only the onset and duration of the rains in the year, but plays also a role in year-by-year differences. The variability is highest in the hyper-arid zone, where the mean precipitation value is composed of a few intensive rainstorms. When these fall on a heated barren surface - as is often the case in the arid zone - a part of it is immediately evaporated and lost for soil processes. High rainfall intensity results on the other hand in a rapid saturation of the surface layers and creates lateral runoff and erosion, in particular on sloping land. Many arid and semi-arid soils show therefore features of gully and sheet erosion. 

We can see that the Tropical Rain Green Forest ecosystems occupy about 1/5 of the African equatorial belt, whereas about 1/2 of this area is Woody and Tall Grass Savanna ecosystems. The rest of the area are occupied by various Dry Steppe and Dry and even Extra-Dry Desert ecosystems, like the Sahara, with annual rainfall less than 200 mm. As it has been mentioned above, the amount of precipitation is of high significance for exposure pathways of pollutants. 

Endrin may also be found in atmospheric precipitation. In an analysis of pesticides in rainfall from four stations in Canada in 1984, detectable concentrations of endrin were found at each site (Strachan 1988). There was a noticeable pattern of decline in detections within the summer season (May-August). In more recent studies in the Great Lakes area, endrin was found in 5% of 450 wet deposition (rain/snow) samples collected between 1986 and 1991, at volume weighted mean concentrations ranging from 0.02 to 0.98 ng/L (ppt) (Chan et al. 1994). 

Mirex has been detected in wet precipitation over rural areas at concentrations of less than 1 ng/L (ppt) (EPA 1981b). Rainfall samples collected at several sites in 1985-1986 as part of the Great Lakes Organics Rain Sampling Network contained from >0.2 to <0.5 ng/L (ppt) of mirex. Mirex was not detected consistently at many stations throughout the sampling period therefore, quantitative results for mirex were not presented (Strachan 1990). Air samples taken over southern Ontario in 1988 showed mirex in 5 of 143 samples, at an annual mean concentration of 0.35 pg/sol m (range, 0.1-22 pg/m ) with all of the positive samples detected in polluted environments (Hoff et al. 1992). 

The toxicity characteristic leaching procedure may be subject to misinterpretation if the compounds under investigation are not included in the methods development or the list of contaminants leading to the potential for technically invalid results. However, an alternative procedure, the synthetic precipitation leaching procedure (SPLP, EPA SW-846 Method 1312) may be appropriate. This procedure is applicable for materials where the leaching potential due to normal rainfall is to be determined. Instead of the leachate simulating acetic acid mixture, nitric and sulfuric acids are utilized in an effort to simulate the acid rains resulting from airborne nitric and sulfuric oxides. 

For this storm, precipitation collections started at 1200 PST, January 20 from Crescent City southward to Pescadero light rain began at Vandenberg and Goleta after 1200 PST, January 21, and at La Jolla, collections did not occur until 1200 PST on January 22. The rainfall and radiochemical data for this storm are given in Table IV. 

Precipitation. Precipitation as rain, snow, sleet, or hail is governed by movement of ah and is generally abundant wherever air currents are predominately upward. The greatest precipitation should therefore occur near the equator. The average annual rainfall in the United States is about 79 cm. 

Figure 6. Topography (solid), precipitation (gray), and 8180 and 8D values along a transect across the southern South Island of New Zealand. The modern Southern Alps create a strong rain shadow on the eastern side of the mountain range that is characterized by a reduction in rainfall from up to 3000 mm/a on the western side to values <300 mm/a on the eastern side of the range. Similarly, hydrogen and oxygen isotopic compositions of meteoric water are strongly depleted in D and 180, and decrease by ca. —40%o and -4.5%o, respectively. Circles SlsO values, diamonds 8D values. Data from Chamberlain et al. (1999) and Stewart et al. (1983). After Chamberlain et al. (1999).

Surface wind speed and direction from six sites were available at four hour intervals during the 24 hour sample collection. These data indicate that surface winds in the Tacoma-Seattle area were consistently southwesterly at 10 knots on February 14-15. A rawindsonde confirmed southwesterly flow aloft. Frontal precipitation as rain occurred with the mean rainfall accumulation across the network of 0.5 cm. in a 3 hour period. 

Acid rain was at one time an important point of contention between the United States and Canada. Much of this acid was the result of the emission of sulfur oxides by coal-fired electricity generating plants in southern Indiana and Ohio. These sulfur oxides, when dissolved in rainwater, formed sulfuric acid and hence acid rain. How many metric tonnes of Indiana coal, which averages 3.5% sulfur by weight, would yield the H2S04 required to produce a 0.9 in. rainfall of pH 3.90 precipitation over a 104 mile2 area ... 

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