Mekonnen Gebremichael, and Dawit ZeweldiCivil & Environmental Engineering DepartmentUniversity of Connecticut

Evaluating Satellite Rainfall Products for Hydrological Applications

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Outline

Introduction+ The Approach+ The Study Region

Evaluating Satellite Rainfall Products (PERSIANN)+ Performance Statistics

Evaluating Utility in Hydrological Applications+ A Blueprint

Conclusions

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Two validation approaches:1. Evaluating against independent rainfall observations

2. Evaluating error propagation in hydrological applications

Introduction

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Introduction

High-resolution satellite rainfall products analyzed: PERSIANN, CMORPH (to follow)

PERSIANN+ IR-PMW merged algorithm: Neural Network+ 4-km hourly over the United States

Validation Approach+ Evaluation against NEXRAD radar rainfall observations+ Evaluation in hydrological applications (to follow)

Study region+ Little Washita watershed in Oklahoma, USA+ Good quality NEXRAD data; subject of several major experiments (NASA,

USDA, etc.)

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Area ~ 600 km2

Introduction: The Little Washita Watershed

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Introduction: Inter-annual variability

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Performance Statistics: 4-km, hourly time scale

Bias

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Performance Statistics: watershed-averaged, hourly time scale

JJADJF

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Performance Statistics: e-folding distance

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Performance Statistics of the Largest Storm

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Storm Duration Storm rainfall , mm E-folding distance:eP / eN

Peak Storm Rate:qP / qN

RMSEmm

Corr elati on

Beginning Ending NEXRAD PERSIANN

06/04/02:22 06/05/02:16 37.31 47.62 8.60 0.92 6.11 0.57

08/11/04:07 08/11/04:14 30.07 26.46 8.17 0.62 2.76 0.63

03/03/04:18 03/04/04:23 53.82 58.12 0.89 0.94 8.59 0.63

10/07/04:09 10/07/04:18 36.21 28.16 0.94 0.70 2.82 0.40

09/19/02:04 09/19/02:13 24.90 14.95 4.26 1.34 8.45 0.23

05/17/02:07 05//17/02:12 36.59 18.78 0.41 0.42 3.20 0.40

05/14/03:03 05/14/03:13 21.56 9.30 1.07 0.46 5.74 0.46

10/08/02:06 10/09/02:22 72.46 15.84 0.55 0.26 7.16 0.48

10/28/02:19 10/29/02:06 30.73 13.40 0.71 0.79 5.07 0.25

09/08/02:16 09/09/02:19 44.95 5.49 0.63 0.09 8.00 0.76

Performance Statistics of Storms

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Performance Statistics: Scaling with Temporal Scale

38.0−∝TR

RMSE55.0−∝T

RRMSE

RRMSE

DJF JJA

What is the appropriate spaceWhat is the appropriate space--time scale?time scale?

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Numerical simulations of catchment hydrologic processes require a method for representing a basin. Methods can be categorized as lumped versus distributed modeling (contours, grids, polygons, TINs).

Basin-Averaged Models (e.g. HEC-HMS)

Raster-Grid Models (e.g. MIKE SHE)

Which is the hydrologic model apt for the satellite rainfall obsWhich is the hydrologic model apt for the satellite rainfall observations?ervations?

versus

Predictive performance of hydrologic models as a function of model complexityand data availability (Grayson and Bloschl 2001).

Hydrological Application

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SatelliteRainfall Products

Simulated Watershed Response

Satellite Rainfall Error PropagationHydrologic Model

ReferenceRainfall Products Hydrologic Model

Simulated Watershed Response

Observed Watershed Response Hydrologic

Model Error

Performance Statistics: A Blueprint for Hydrological Applications

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Conclusions

Need for rigorous validation of high-resolution satellite rainfall products, at various space-time scales, for different regimes

Need for identifying hydrologic model complexity level apt for satellite- rainfall inputs, and sensitivity to space-time resolutions

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Thank you