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NRCS_ NATIONAL SCIENCE _amp; TECHNOLOGY CONSORTIUM National Water

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NRCS_ NATIONAL SCIENCE _amp; TECHNOLOGY CONSORTIUM National  Water Powered By Docstoc
					Climatology of Precipitation and
 Precipitation Extremes in the
         United States
            Greg Johnson
         Applied Climatologist
              USDA-NRCS
   National Water and Climate Center
            Portland, Oregon
    Characteristics of the Mean
      Precipitation Climate
   The principal controlling factors are the
    availability of atmospheric moisture and
    lifting mechanisms
   Moisture controlled by flow from or
    proximity to large water bodies
   Propensity for lifting influenced by
    topography, convergence zones (seabreeze,
    etc.), preferred storm tracks (jet dynamics)
    Orographic Precipitation
     Enhancement Factors
 Wind Direction (relative to topography)
 Wind Speed
 Atmos. Moisture (precipitable water)
 Elevation Rise
 Slope Angle
         Issues of Scale
     (Spatial and Temporal)
 Over long averaging times (say, the 30
  year normal maps), only the most
  important and consistent
  meteorological factors are evident
 Progressively shorter time spans reveal
  ever-increasing nuances of the
  atmospheric system
A Snapshot in Time
24 Hour Time Integration
July normal
Precipitation
(top)

    versus

July 1993
Precipitation
(bottom)
 Statistical Properties of Precipitation

 Persistence, or lack thereof
 Average amount of precipitation
 Variability in precipitation amount, and
  theoretical maximum
 Frequency of precipitation
 Duration of precipitation
Annual Mean of Wet-Dry Day Prob. (x1000), Southwest Idaho
     A Spatial Climate Modeling
               System
   PRISM (Parameter-elevation Regressions on
    Independent Slopes Model)
   Statistical/Dynamical/Topographic approach
   Funded primarily by the NRCS-NWCC since
    1993 for development of spatial climate
    products for the U.S.
   Developed by Dr. Chris Daly of the Spatial
    Climate Analysis Service, Oregon State
    University
What is PRISM?
               PRISM
 Grid based model, approx. 4 km horiz.
  resolution
 Any given grid cell value is determined
  by a linear regression of station values
  against elevation
 Stations assigned weights
 Combined weight of a station is a
  function of many factors
    Form of Grid Cell Prediction
               Y = 1X + 0 ,
      where Y is the predicted climate
    element and X is the DEM elevation at
    the target cell. 0 and 1 are regression
    slope and intercept, and are
    determined by x,y pairs of elevation
    and climate observations from nearby
    climate stations
           Station Weighting
   Combined weight of a station is:

     W = f {Wd, Wz, Wc, Wl, Wf, Wp, We} ,

    where Wd, Wz, Wc, Wl, Wf, Wp, We are
    the distance, elevation, cluster, vertical
    layer, topographic facet, coastal
    proximity and effective terrain height
    weights.
Vermont
Annual
Precipitation
Olympic Mtns Terrain
         Olympic Mtns Annual Precipitation
           Facets On + Vertical Extrapolation On




Inches
         Olympic Mtns Annual Precipitation
           Facets On + Vertical Extrapolation Off




Inches
         Olympic Mtns Annual Precipitation
           Facets Off + Vertical Extrapolation Off




Inches
         Olympic Mtns Annual Precipitation
                    No elevation




Inches
         Olympic Mtns Annual Precipitation
           Facets On + Vertical Extrapolation On




Inches
Hawaii Annual
Precipitation

No Layer
Weighting
Hawaii Annual
Precipitation

Two Layers
SNOTEL Coverage
     PRISM-derived Products
 Mean Mon. and Ann. Precipitation
 Mean Mon. and Ann. Temps (mx/mn)
 Frost dates and freeze-free season
 Extreme winter min. temps & probs.
 Growing, heating, cooling degree days
 Snow-water equivalent
Oregon Annual Precipitation
Annual
Precipitation
Map of Elmore
County, Idaho
Produced by the
NRCS NCGC
“Cut-out” of
State Map
PRISM - SWE Map - Oregon
PRISM Product Dissemination
                    Web Sites:
OSU:
 www.ocs.orst.edu/prism/prism_new.html
 (Raster and polygon coverages of practically
 everything produced to date (Arc, GRASS);
 documentation; metadata; DEM’s)
NRCS:
 www.ftw.nrcs.usda.gov/prism/prism.html
 (U.S., Regional and State mean annual
 precipitation cartographic products)
 http://www.ftw.nrcs.usda.gov/prism/prism.html:




 Cartographic state mean annual precipitation maps
 Full repository of “official” NRCS PRISM layers
PRISM Product Dissemination

                Compact Discs:
All precipitation layers for all of the U.S.
  3 CD’s (East, Central, West) of the lower 48
  states. Includes Arc Explorer viewing
  software, and all documentation.
Available from the NRCS-NCGC:
  800-672-5559
PRISM Product Dissemination
               Hardcopy maps:
Cartographic-quality, walls-size maps of mean
 annual precipitation for each state
Available from the NRCS Climate Data
 Liaison in each state
Extreme Precipitation
    Climatology
        Spatial Considerations
   Means and extremes are not always
    correlated, especially over large spatial
    domains, or even in small regions with
    significant climate variations:
      Portland OR MAP 37.39”
        Max24 2.62”
      Washington DC MAP 39.00”
        Max24 7.19”
    Elevational Effect: Reynolds Creek
             Watershed Idaho
 Valley bottom: MAP: 11.14”
     50 yr 1-hour value: 1.18”
 Mountain top location: MAP: 43.58”
     50 yr 1-hour value: 1.26”

    Distance between stations: 10 miles
    Elevation difference: 3500 feet
Example of Variations over Small
Regions: Reynolds Creek, Idaho
        (values in mm precipitation):
     10 Year Return
                  3500 feet   Atlas 2   7000 feet   Atlas 2
     30 min.          14          9       13          9
     1 hour           21         20       29         20
     24 hours         41         43       103        48
  
     50 Year Return
     30 min.          21         13       19         13
     1 hour           30         28       32         29
     24 hours         54         53       129        64
Geographic Effect on Extreme vs. Mean Precipitation
      Precipitation Frequency
             Definition

   100 - Year Event: “An event which has
    a 1 percent chance of occurrence IN
    ANY YEAR; NOT ONE event every 100
    years.”
  Hydrometeorological Design
  Studies Center (HDSC) of the
             NWS:

http://www.nws.noaa.gov/oh/hdsc/index.
                html
TP-40 100 Yr 24-hour pcpn. (in.) from SCS TR-55, 1986
100 Year, 24-hour NOAA Atlas 2 Values (inches)
             Northwest Colorado
          Probable Maximum
          Precipitation (PMP)
   “Theoretically, the greatest depth of
    precipitation for a given duration that is
    physically possible over a given size
    storm area at a particular geographical
    location at a certain time of the year.”
Storm Characteristics
Dimensionless Mass Curves
                                       1.0
  Dimensio nless Depth, fraction       0.9
                                       0.8
                                       0.7
                                       0.6
                                       0.5
                                       0.4
                                   c
                                   a
                                   r
                                   f
                                   ,
                                   h
                                   t
                                   p
                                   l
                                   o
                                   s
                                   n
                                   e
                                   m
                                   i
                                   D




                                       0.3
                                       0.2
                                       0.1
                                       0.0
                                             0.0   0.1   0.2   0.3   0.4   0.5   0.6   0.7   0.8   0.9 1.0
                                                    Dimensionless Duration, fraction
 Synthesis of Within-Storm
        Intensities
                                1.0
Dimensionless Depth, fraction




                                0.9
                                                            90%
                                0.8                          80%                      .
                                0.7                               70%


                                0.6
                                                                    60%
                                                                        50%
                                                                           .
                                                                   .      40%
                                0.5
                                                                            30%
                                0.4                                             20%
                                c
                                a
                                r
                                f
                                ,
                                h
                                t
                                p
                                l
                                o
                                s
                                n
                                e
                                m
                                i
                                D


                                                                                  10%
                                0.3             B
                                0.2

                                0.1
                                            A

                                0.0
                                      0.0       0.1   0.2     0.3         0.4     0.5     0.6   0.7   0.8   0.9   1.0

                                                      Dimensionless Duration, fraction

				
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posted:4/14/2013
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