9494

• UCREFRP Catalog Number: 9494
• Author: Briggs, M. K.
• Title: Editor
• USFW Year: Series
• USFW - Doc Type: 1996
• Copyright Material: YES

From a Watershed Perspective / 17

shed, whereas the term drainageway refers to principal areas of water ac-

cumulation (i.e., channels).

Climate

The climate of the watershed is one of the primary factors (with geology being
the other) that affect the pattern of streamflow, shape of the landscape, and
density and diversity of vegetation communities. Understanding the climate of
the degraded riparian area's watershed and how it may have changed is an
important step toward understanding the reasons for the vegetation and hy-
drologic changes that have occurred. Climate is often classified based on the
moisture budget and potential evapotranspiration, requiring the measurement
of temperature, relative humidity, and precipitation.
Collecting precipitation data is important because relations between pre-
cipitation and runoff can be developed, using as parameters some of the fac-
tors that affect runoff. Such a relationship can be useful because it can be
extrapolated to areas that lack hydrologic data or be used to estimate runoff
for the area of interest. However, the relation is often unsatisfactory, unless
other parameters (such as storm frequency, initial soil-moisture condition,
storm duration, and time of year) are also taken into consideration.
Precipitation data are often available from various agencies and institu-
tions. Global precipitation data are available at the National Climatic Data
Center in Asheville, North Carolina; regional offices have data more specific to
a certain part of the United States. In addition, each state has an Office of the
State Climatologist that collects and distributes precipitation data for its asso-
ciated state. Precipitation data for large urban areas are often available in the
"World Weather Almanac," a publication that pulls together precipitation
data from around the world. In addition, precipitation data are often collected
for areas managed by the National Park Service, Forest Service, and Bureau of
Land Management.

Watershed Size

The size of the watershed area is an important descriptor because it influences
water yield and the number and size of streams. Watershed boundaries can be
located using the contour lines on a topographic map. After the watershed is
delineated on a map, its size can be determined in a number of ways. A
planimeter can be used to measure the area directly. Watershed size can also be