Estimating Additional Water Yield from Changes in Management

• File Number: 8461.250
• Description: Water Issues
• State: CO
• Basin: South Platte
• Water Division: 1
• Date: 5/12/2000
• Author: Charles A. Troendle, James M. Nankervis
• Title: Estimating Additional Water Yield from Changes in Management
• Water Supply Pro - Doc Type: Report/Study

Precipitation
Forest Service staff assisted us by superimposing the Oregon State
University Climate Center Precipitation Map for Colorado and Wyoming on
the DEM's for the respective Forests to estimate mean annual precipitation
as a function of elevation for the polygons. Mean monthly precipitation data
for a number of precipitation gauges in Colorado and Wyoming, were then
used by us to estimate the percentage of annual precipitation occurring in
each month, as a function of elevation (table 1). As a general observation,
the amount of annual precipitation increases with elevation (about 20
percent increase per 1000 ft rise in elevation) while the percent of the annual
precipitation (storms) that occurs in the summer months increases with
decreasing elevation (table 1).
The percent of annual precipitation occurring in each month, table 1 was
used to partition the estimates of annual precipitation, generated by the U.S.
Forest Service from the GIS layers, into monthly values, for each of the
elevarion zones. Estimates of monthly precipitation are the required input
for the electronic version of the WRENSS hydrologic model we used.
Fr } However, the monthly values are in turn aggregated to the seasonal values
sripulated as input in the original WRENSS procedure (Troendle and Leaf
1980).
Table 1. Percent of annual precipitation occurring in each month by
elevation zone.
Elevation Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
500 0.041 0.035 0.071 0.111 0.194 0.140 0.103 0.068 0.074 0.074 0.048 0.039
600 0.045 0.053 0.077 0.119 0.170 0.124 0.098 0.073 0.073 0.078 0.064 0.048
700 0.056 0.050 0.081 0.106 0.142 0.106 0.112 0.083 0.073 0.080 0.065 0.053
800 0.092 0.071 0.098 0.107 0.100 0.072 0.073 0.064 0.070 0.069 0.088 0.098
900 0.104 0.089 0.107 0.106 0.092 0.058 0.056 0.057 0.060 0.068 0.098 0.106
1000 0.105 0.093 0.110 0.123 0.103 0.054 0.052 0.046 0.058 0.070 0.092 0.097
"1100 0.105 0.093 0.110 0.123 0.103 0.054 0.052 0.046 0.058 0.070 0.092 0.097
'1200 0.105 0.093 0.110 0.123 0.103 0.054 0.052 0.046 0.058 0.070 0.092 0.097
*For observatioris over 11,000' use 10,000' values.
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