. Designing an optimum protected areas system for Sri Lanka's natural forests. Volume 1. Data for each station are plotted on a 1:63,360 map, enabling contours of equal rainfall (isohyets) to be drawn. Mean annual rainfall is estimated for each area between adjacent isohyets, weighted by its percentage area. Summation of the mean values for each area provides an estimate of mean armual area for the entire forest, as follows: MAR = A (R^ + Rb)/2 + B (Rb + Rc)/2 + C (R^. + Rq ) + 100 (2) where MAR = Mean annual rainfall, Rft, Rj, Re, and R^ are the rainfall isohyets, and A, B, and C are the area
. Designing an optimum protected areas system for Sri Lanka's natural forests. Volume 1. Data for each station are plotted on a 1:63,360 map, enabling contours of equal rainfall (isohyets) to be drawn. Mean annual rainfall is estimated for each area between adjacent isohyets, weighted by its percentage area. Summation of the mean values for each area provides an estimate of mean armual area for the entire forest, as follows: MAR = A (R^ + Rb)/2 + B (Rb + Rc)/2 + C (R^. + Rq ) + 100 (2) where MAR = Mean annual rainfall, Rft, Rj, Re, and R^ are the rainfall isohyets, and A, B, and C are the areas enclosed within isohyets R^ - Rg, R^ - R<-, and R,; - Rq, respectively. Substituting values from Figure , the mean annual rainfall for Dellawa is calculated as follows: (4050) + (3950) + (3850) + (3750) + (3650) + (3550) MAR MAR 100 3759 mm The value for mean annual rainfall is substimted in Equation (1) in order to calculate an erosivity value for Dellawa as follows: E = + ( x 3759) E = 38375 J m- yr'. Figure Mean aimual rainfall isohyets for Dellawa The erosivity index () is obtained by dividing the erosivity value by 100. It indicates the ability of the rainfall to cause soil erosion. Mean annual rainfall and the respective erosivity values are given in Table for each forest. 50. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original IUCN, WCMC, FAO. Sri Lanka Forest Dept.
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