| A unit of Lasting Forests
evolving since March 30, 1999 |
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A Total Forest Management Plan
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Precipitation needs to be dealt with as the sum of:
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| Inputs to the land and plants there over the year (suggested by the dotted line) need to be evaluated in terms of the removals from runoff, evapotranspiration, and storage (only some of which is available to photosynthetically active plants). |
Effective precipitation, that for plant use, is a function of the amount that evaporates quickly, runs off quickly (as when soil is very steep, frozen, hard-packed, or saturated), or enters the soil beyond the rooting zone (as with sand).
Anderson (1981) analyzed temperature records in Virginia for 170 weather stations over 30 years and computed the temperatures for each 27-acre map cell of the state based on multiple regression. Independent variables were elevation and latitude. He failed to create similar estimates of precipitation because the record was so poor. There were gaps that could mean "no rain" or "not collected by an observer." There were abnormally large amounts in some rain collectors indicating that several rains had accumulated. Wajda (1993) attempted similar analyses and found missing collectors, missing data, and collectors in inappropriate locations. She found that coastal and continental variables improved estimates. Trying to estimate the highly variable, sporadic precipitation for the wildlands of Virginia has been very difficult.
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| The context is relative humidity and its local limits. With additions of steet, hail, and ocean spray, this figure shows most pathways that need to be modeled and understood to explain and predict and respond to likely water-related phenomena of the rural areas. Water combed from clouds by trees, called fog drip or hoarfrost (winter) (shown here as melt and drip), is under estimated in some areas. Gutation may be of interest in some arweas. Dew is rarely considered, especially that which is not evaporated but shaken to the ground by people and animals. Uptake by micorhizzae should be noted. |
Subjective judgements about general wind patterns, topography, storm patterns, and other factors may help in estimating adjustments for the rainfall amount estimates most appropriate for the area.
Where, for example, the annual precipitation is 35 inches, this is 35 / 0.0394 (inches per mm) or 888.3 mm total. The cube root of 888.3 is 9.61 and this value is hypothesized to relate more closely to ecological phenomena than the simple linear measure.
The source of precipitation is clouds and these are from two sources or " types" These are convective clouds in summer and fall and frontal clouds in winter and spring. For convenience at this time (but it may be possible later to achieve an obective criterion for discriminating the date) the periods are separated on the basis of the hydrologic year, convective cloud sources starting with the Julianized date of ____, or _____, and frontal sources assumed to be starting on ____.
Portman et.al. 1965 :5-9 said that the largest precipitation particles are associated with clouds of great vertical development whereas smaller ones are characteristic or relatively laminar clouds. As clouds move eastward and are pared from below by the mountains, they become thin. This suggests the hypothesis that smaller particles as well as less rainfall occurs on the southern slopes of Havens and similar Virginia areas. Portman (1965:5-9) said that precipitation data are extremely irregular.
Precipitation particles are greater than 100 microns in diameter.
The largest amount of water occurs in clouds formed from warm air. The range of water content in clouds is from 10 grams/m3 to 1 mg /m3
Giles recommended in 2001 transforming all readings of inches of rain to a value that is likely to be relevant in the world of nature, namely taking the inches, transforming them to millimeters and then using the the cube root of such numbers for analyses.
| Precipitation (inches) |
Precipitation Index (inches/0.0394)0.333 |
| 0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0 45.0 50.0 |
0.0 5.0 6.3 7.2 8.0 8.6 9.1 9.6 10.0 10.4 10.8 |
Plants, for example, do not respond to water in linear increments. In the adjoining table, transformations are made for a range of precipitations. For high rainfall amounts, the changes are small. The critical conditions for plants and dependent animals is in the lower values which are sensitive to the cube-root transformation.
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| The general pattern of a classical climatograph. The monthly mean is plotted for the two important ecological variables. |
Under Development: A table (with elevation, Latitude, and Longitude) with monthly maximum, mean, and minimum for the center point of the site.
A gross estimate of the annual precipitation was derived for a linear equation with independent variable elevation , e, by Lee et al. in 1975 for West Virginia sites.
P = 28.32 + 0.5095 e 0.05
For example, at 2320, the rainfall in inches is 52.8.
The farther from West Virginia and the dates, the less confidence a person may have. Perhaps similar analyses can be performed and an improved precipitation model developed.
Monthly means, minimum, and maximum are presented for high and low elevation for the site. Here, data are from the 3 nearest weather stations.
| Month | Average | Least 30-year average |
Greatest 30-year average |
| January | 3.82 2.98 3.95 … |
1.69 0.0 1.32 … |
8.93 9.42 7.57 … |
Climatic Sine Day
The trigonometric sine of the Julian date (which is the calendar day sequence counting from one on January 1) has been found to be well correlated with precipitation events. It acknowledges that precipitation does not occur in a uniform or regular way but in a cyclic pattern that fits a sine wave.
The major use of climatic sine day numbers may shed special insight into precipitation as it affects soil moisture, stream flow, sediment discharges, and a variety of fish observations. The numbers may correlate well with various seasonal events. By using the sine day rather than day, some variance in statistical analyses of watershed data is likely to be controlled or reduced. Using sine day is hypothesized to improve future estimators developed to predict precipitation at any point in the state. Other climatic variables are likely similarly related. The numbers are partially to alert field staff to new hypotheses and new ways of analyzing their data.
The sine day is the julian day number beginning with November 21 (day zero) converted to the sine of the day plus 2. The two is added to avoid negative numbers and zeros in the data set. November 21 was selected by regression techniques. The data upon which this approach was based were from the Appalachians.
References
Anderson, D. R. 1981. A climatological information system for natural resource management: temperature. M.S. Thesis, Virginia Polytechnic Institute and State Univ., Blacksburg, Va. viii + 220 pp.
Wajda, R. K. 1993. A site-specific rainfall model for Western Virginia ecosystems. M.S. Thesis, Va. Poly. Inst. and State Univ., Blacksburg, Va. xi + 143 pp.
Findley, S. H. 1994. Hydrologic modeling as a decision-making tool in wildlife management. Unpub. M.S. Thesis, Virginia Polytechnic Institute and State University, Blacksburg, VA. ix + 164 pp.
Klopfer, S. D. 1998. Insolation, precipitation, and moisture maps for a Virginia geographic information system. M.S. Thesis, Virginia Polytechnic Institute and State University, Blacksburg, VA. 184 pp.
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Last revision February 17, 2003.