NWRFC

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NWRFCCHPS Forcing Study

Goal of Forcings Study

• Compare the current operational process with the calibration Mean Areal Precipitation (MAP).

• Create a historical grid or Local Analysis of Record (LAOR) for use in the evaluation process and bias assessments.

• Develop a method to produce an unbiased grid MAP, representing the volumes used in the calibration phase.

• Consider methods that can be employed in future calibration activities that use historical grids in lieu of point data.

HIC Meeting - 2/2010

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Rationale for Gridded Data Forcings

• CAT-I decision to retire the OFS Preprocessors.

• Data sets (becoming) readily available in gridded form.

• Preparation to use new/advanced modeling systems, ie., distributed modeling.

• Aligns hydrology with agency direction in data assimilation, verification, and research programs.


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Steps of Study Procedure

1. Generate quality and consistent hourly point precipitation from the point data network used in the calibration process

+ OHD provided special MAP program+ Post point data to a new database

2. Create 6-hour and 24-hour aggregates from hourly point data (output from MAP program).

3. Use auto_mpe_dailyQC to generate historical 6 and 24 hour grids for the calibration period of 1949 to 2003.

4. Employ an instance of a CHPS stand alone system to compare calibration (OFS point) MAPS and new generated historical MAPX (MPE).

5. Use CHPS and Excel to generate statistics for analysis.


4HIC Meeting - 2/2010


Sample of Grids Produced by MPE dailyQC

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OHD MAPProgram

Database Tables

Database Tables

MPEAuto_dailyQC

55 Years6 and 24

GridsCHPS Excel

Evaluation

Schematic of Process

1 hr Precip calibration sites 6 and 24 hr Precip values

6 and 24 hr Precip values

Grids

Grids MAP and MAPX

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Issues

• MAP fails to accurately disaggregate the 6-hour data to 1-hourly values. Values are lumped in a single 1-hr data point.

• Address multiple time zones. For an RFC that crosses multiple time zones, data must be loaded taking actual time into account. • MAP program renders 6-hour MAP in local time. Supplied MPE 6 hour data in local time. Adjustments must be made in CHPS so MAP and MAPX represent the same period.

• CHPS limited to 20 years of data for historical calculation. The full 55 years of grids split into multiple groups.

• CHPS generates historical time series with output used by Excel for analysis and scatter plot generation.


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Sites Include in Evaluation


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Site-Zone R2 Bias MAE

DWRI1U .7123 .915 .08

DWRI1L .815 .952 .05

HHWM8U .754 1.029 .06

HHWM8L .764 .992 .05

PLDI1U .832 .708 .04

PLDI1L .841 .778 .03

SAKW1G .894 .662 .16

SAKW1U .893 1.002 .08

SAKW1L .896 1.138 .08

WFBM8U .413 .998 .07

WFBM8L .439 1.159 .06

TOPI1 .865 .95 .05

DARM8U .540 .883 .06

DARM8L .598 1.080 .04

BONM8U .701 .848 .06

BONM8L .773 .832 .03

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Typical Comparison

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Typical Comparison

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Bitterroot Basin Has Issues

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Results

• The majority of sites analyzed exhibited R2 > .80 over the 55 years.• Considerable scatter for all sites and also need to look at categories.• Bitterroot basin has the weakest relationship.• Bias between sites is not consistent.• Bias for a site is not consistent from month to month.• Analysis using 1971-2000 only shows a minor improvement in the relationships.• Process is very simple and easy to update.


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Future

• Develop QC points for Western Oregon. Needed for final LAOR grid.

• Develop method to disaggregate values from MAP that were not time distributed.

• Analysis runs (today) on 6-hour data.

• Analysis using simulations and runoff to determine impacts of this solution.

• Automate the bias correction process.


Documents

NWRFC