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National Drought Atlas

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.  

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Precipitation

Streamflow

revised 1 Aug 2006

 
 

 


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Precipitation

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