How to Use the Atlas Precipitation Information
Excel spreadsheets have been prepared for each of the 111 clusters of
precipitation stations in the National Drought Atlas. Users can use
a U.S. map interface to download
the Excel spreadsheet for the cluster or clusters for the region of
interest. The spreadsheet calculates and displays the precipitation
amounts for each station in the cluster for non-exceedance frequencies of
from 2% to 98% and for durations of from 1 to 60 months. The
spreadsheet can provide the same type of information for stations that are
not in the cluster but are nearby.. In that case, the user must
calculate the appropriate mean or median precipitation offline and enter
it by hand into the Excel worksheet. It will not always be
obvious which cluster to use when a station falls between two
clusters. The distributions of nearby clusters are generally similar
at the longer durations, so it may make little practical difference.
When durations are shorter, or when there is a marked change in the
distributions of nearby clusters (say, on either side of a mountain range)
then precipitation contour maps can help determine which cluster a station
should be associated with. Oregon State University has prepared PRISM precipitation maps for all 50 states. Simple low-resolution
maps are available on-line; high resolution prints can be ordered.
How to Use the Atlas Streamflow Information
Excel spreadsheets have been prepared for Hydrologic Regions 1 through
18 (the contiguous 48 states). Users can use a map of those regions
to download the appropriate Excel file(s). Unlike the precipitation
information, the streamflow estimates cannot be extended to stations
outside the Atlas. The spreadsheet calculates and displays the
streamflow (in average cubic feet per second) for each station in the
region for non-exceedance frequencies of
from 2% to 98% and for durations of from 1 to 12 months.
Return to Main Page, National Drought Atlas
Precipitation
Streamflow
revised 1 Aug 2006
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