A NEW APPROACH TO THE ESTIMATION OF PRECIPITATION FIELDS IN MOUNTAINOUS ENVIRONMENTS

Elsa Nickl and Cort Willmott

University of Delaware

Department of Geography

HIGH-RESOLUTION DIGITAL ELEVATION INFORMATION

GTOPO30 (USGS)30 arc sec resolution

EROS Data Center (used by PRISM)3 arcsec resolution

Shuttle Radar Topography Mission (USGS) 1 arcsec resolution

METHODS OF PRECIPITATION FIELDS ESTIMATION

1. Precipitation interpolation methods:• e.g. ordinary kriging, elevational cokriging, etc• Few have been able to adequately explain the complex variability of precipitation in mountain regions

2. The PRISM model

Principal aspects taken into account in PRISM model:

1. Relationship between precipitation and elevation:

• Precipitation increases with elevation, with a maximum in mountain crests• Relationship between precipitation and elevation can be described by a

linear function

2. Spatial scale of orographic precipitation (orographic elevation)

• Mismatch in scale when using actual elevation of stations• “Orographic” elevation estimation in order to avoid this mismatch• The orographic scale depends on the scale of the prevailing storm type• 5 min-DEM appears to approximate the scale of orographic effects

explained by available data

3. Spatial patterns of orographic precipitation (facets)

• PRISM divides the mountainous areas into “facets “• Each “facet” is a contiguous area of constant slope orientation

OBJECTIVES

To explore the relationships between the spatial arrangements of orientation, slope, winds and precipitation.

To develop a new approach for estimating precipitation fields in mountain regions

DATA

• Monthly precipitation National Climatic Data Center (NCDC) (2001-2005)

• Digital Elevation information 2.5 minutes (used by PRISM, derived from EROS Data Center 3 arc sec)

ELEVATION, ORIENTATION AND PRECIPITATION GREATER THAN 200 mm

December

DECEMBER, JANUARY, FEBRUARY (seasonal? MAM, JJA, SON?, zoom?)

December

dz/dx dz/dy

January

January

dz/dx dz/dy

February

February

dz/dx dz/dy

MAM, JJA, SON?, ZOOMS?

ELEVATION, ORIENTATION, STEEPNESS AND PRECIPITATION (2.5min)

DJF (December-February)

JJA (June-August)

ELEVATION, ORIENTATION, STEEPNESS AND PRECIPITATION (2.5min)

ELEVATION, ORIENTATION, STEEPNESS AND PRECIPITATION (2.5min)

December

January

ELEVATION, ORIENTATION, STEEPNESS AND PRECIPITATION (2.5min)

February

ELEVATION, ORIENTATION, STEEPNESS AND PRECIPITATION (2.5min)

CELLS TO TAKE INTO ACCOUNT FOR DIFFERENT RESOLUTIONS

5 min (~9.2 km)

CELLS TO TAKE INTO ACCOUNT FOR DIFFERENT RESOLUTIONS

7 min (~12.8 km)

CELLS TO TAKE INTO ACCOUNT FOR DIFFERENT RESOLUTIONS

10 min (~18.3 km)

ELEVATION, ORIENTATION, STEEPNESS AND PRECIPITATION (7.5min)

DJF (December-February)

ELEVATION, ORIENTATION, STEEPNESS AND PRECIPITATION (7.5min)

JJA (June-August)

ELEVATION, ORIENTATION, STEEPNESS AND PRECIPITATION (12.5min)

CONCLUSIONS

FUTURE RESEARCH

•Most largest precipitation events take place in lower-elevation areas (0-500m) with no-orientation (flat terrain)

•During DJF period, strong precipitation events in moderate elevation (500-1000m), present a SW orientation tendency.

•During JJA period, strong precipitation events are more related to convection.

•To quantify relationships between precipitation and elevation, steepness and orientation.•To identify relationship between wind and precipitation based on these relationships.