Rainfall Distribution within an Hydro-Estimator Pixel

Ian Garcia1, E. W. Harmsen2 and Jorge Canals Garcia3

1. Undergraduate Research Assistant, Dept. of Biology

2. Associate Professor, Dept. of Ag. and Biosystems Eng.

3. Graduate Research Assistant, Dept. of Computer Engineering,

University of Puerto Rico – Mayagüez Campus

Acknowledgements We would like to thank the following students for their help

on this project: Marcel Giovanni Prieto, Victor Hugo Ramirez, Yaritza Perez, Romara Santiago, Alejandra Roja, Julian Harmsen and Lua Harmsen. Dr. Luis Perez and Dr. Nazario Ramirez for use of their GPS equipment. We also want to thank NOAA CREST for their financial support of this project. Additional support was received from NASA EPSCoR, USDA-TSTAR and NSF-CASA projects.

This work made use of Engineering Research Centers Shared Facilities supported by the National Science Foundation under NSF Cooperative Agreement No. EEC-0313747. Any Opinions, findings and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect those of the National Science Foundation.

 Problem

The QPE validation study of Cruz Gonzalez (2006) raised a concern relative to the validation methodology itself; specifically, is it appropriate to compare a single rain gauge value of rainfall with estimates from the HE algorithm, which covers an area of 16 km2? Other potential sources of error include: rain gauge inaccuracy, and assumptions made in the development of the HE algorithm that may be violated under tropical rainfall conditions.

Definitions: QPE = quantitative precipitation EstimationHE = Hydro-Estimator

Long-term Objectives

Validate and enhance QPE methods in Puerto (HE, SCaMPR, GMSRA)

Understand pixel-scale rainfall vaiability

Develop a satellite QPE flash flood Nowcast for a testbed in western PR.

Short-term Objectives

Install 16 digital rain gauges within a HE pixel

Collect data from the rain gauges for at least a one year period

Evaluate rainfall statistics Compare rain gauge data with HE-

estimated data

Methodology

1. The center points of the HE pixels were obtained from NOAA-1. The center points of the HE pixels were obtained from NOAA-NESDIS. NESDIS.

2. An appropriate HE pixel was selected, which included a relatively 2. An appropriate HE pixel was selected, which included a relatively large range of topographic relief east of the Mayagüez Bay in large range of topographic relief east of the Mayagüez Bay in western Puerto Rico. western Puerto Rico.

3. Using ArcGIS, sixteen points were located (evenly spaced) within 3. Using ArcGIS, sixteen points were located (evenly spaced) within the HE pixel. These sixteen areas will be referred to as sub-areas.the HE pixel. These sixteen areas will be referred to as sub-areas.

4. With the assistance of a ground positioning system (GPS), students 4. With the assistance of a ground positioning system (GPS), students located properties which were as close as possible to the center located properties which were as close as possible to the center point locations identified in step no. 3. In each case it was point locations identified in step no. 3. In each case it was necessary to obtain permission from the property owner before necessary to obtain permission from the property owner before installing the rain gauges.installing the rain gauges.

5. The actual coordinates of the installed rain gauges were recorded 5. The actual coordinates of the installed rain gauges were recorded and entered into ArcGIS. and entered into ArcGIS.

MayaguezBay

Miradero

Study Area

Final rain gauge locations

Results

RESULTS

Pixel Rainfall Statistics

Date

Storm Start Time

Storm End Time

Storm Duration (hours)

Total Rainfall

(mm)St. Dev (mm)

Max (mm)

Min (mm)

Max - Min (mm)

6-Aug 13:32 14:42 1.17 30.8 13.6 55.5 9.2 46.314-Aug 17:12 18:37 1.42 9.3 9.6 27.2 0.0 27.216-Aug 12:54 16:49 3.92 16.6 4.7 27.5 9.6 17.918-Aug 12:53 18:38 5.75 33.8 22.7 64.1 0.0 64.120-Aug 16:28 19:48 3.33 14.3 10.3 27.5 0.0 27.522-Aug 15:00 23:23 8.38 19.4 13.3 44.0 0.0 44.025-Aug 14:03 14:53 0.83 5.2 3.3 10.4 0.0 10.426-Aug 12:18 13:13 0.92 4.4 2.8 8.6 0.0 8.6

1-Oct 21:19 0:32 3.22 18.2 12.2 37.7 0.0 37.72-Oct 21:06 22:26 3.22 2.7 2.2 7.5 0.0 7.5

Average 3.2 15.5 9.5 31.0 1.9 29.1

 Gauges with Zero Rain

Instrument is at 200 cm Height

Date

Gauge No. with

zero Rain

Gauge No. with

zero Rain

Gauge No. with

zero Rain6-Aug

14-Aug 14 15 1616-Aug18-Aug 520-Aug 5 9 1622-Aug 925-Aug 3 11 1626-Aug 10

1-Oct 4 162-Oct 4 7 16

 

0

2

4

6

8

10

12

12:43 PM 1:12 PM 1:40 PM 2:09 PM 2:38 PM 3:07 PM 3:36 PM 4:04 PM

Time (hour)

Rai

nfa

ll (

mm

)

Rainfall Variation with TimeAugust 6th, 2006

Comparison of rain gauges with the Hydro Estimator (HE) NESDIS provide us with HE data for

Aug 1st through Aug 8th, 2006. A comparison was made with the

Aug 6th rain gauge data The HE did not register any

rain on Aug 6th, whereas the rain gauges recorded an average depth of 30.8 mm.

Conclusions

Nine storms were evaluated between Aug and Oct, 2006.

Measured rainfall within an HE pixel (4 km x 4 km) can be highly variable.

The HE did not register any rain in the pixel as compared to 30.8 mm measured by the rain gauges.

Future Work

Continue collecting and analyzing rain gauge data.

Obtain additional HE data from NESDIS to compare with the rain gauge data.

Obtain SCaMPR and GMSRA data for comparison with the rain gauge.

Questions?