Dawei Han 韩大卫

Department of Civil Engineering

University of Bristol, UK

Weather radar rainfall for hydrological hazard risk management

Floods

Droughts

Debris flows

Hydrological hazards related to rainfall

How to measure rainfall?

Rain gauge

Radar

Satellite

Rainfall measurements

Tipping Bucket gauges

Drop counting gauges

Optical gauges

Larson and Peck (1974)

WMO report (1982 by Sevruk) Ground truth ?

Boscastle flood of 16 August 2004

89 mm rain in 60 min, flood peak of 180 cumecs in 1 hour

http://www.rmets.org/sites/default/files/pdf/presentation/20100417-allott.pdf

Is the rain gauge network sufficient (in time and space)?

In Boscastle, the 4 nearest daily gauges showed less than 3 mm of rain that day

No rain Rain

Rainfall is not uniform

Radar

Satellite

Remote sensing could be the answer (?)

Weather Radar

UK

USA

Chinese weather radars

Source: www2010, Univ. of Illinois

Transmitter

Receiver

NOAA

dDDNDZ )(6

dDDNDR )(67.3

baRZ

Reflectivity

1.6200Z R

http://www.srh.noaa.gov/jetstream/doppler/beam_max.htm

Beam Spreading

http://www.srh.noaa.gov/jetstream/doppler/beam_max.htm

Beam refraction

Overshooting/beam blocking

Earth curvature

Variation of Reflectivity in the Vertical

Rico-Ramirez, et al (2007), Meteorological Applications, 14: 117-129.

Range

He

igh

t

Radar

Variation of Reflectivity in the Vertical

rainfall rate at the ground?

Rain drops falling from the sky

3D wind field (ECMWF Downscaled by WRF)

Rain drop sizes

http://rpitt.eng.ua.edu/Class/Erosioncontrol/Module3/Module3_files/image022.jpg

disdrometer

Displacement of rain drops

and time lags

Pairing of radar pixels and rain gauges

Exploration of discrepancy between radar and gauge rainfall estimates driven by wind fields, 2014, Qiang Dai and Dawei Han, Water Resources Research

3D wind field (ECMWF Downscaled by WRF)

3D wind profiler

(Collaborative study with Dr. Yamamoto) (no validation)

How to configure NWP based on wind profile information?

Model Sensitivity Analysis and Uncertainty Analysis

wikipedia

Main error sources with weather radars

1, Hardware error

2, Clutter Errors

3, Screening

4, Attenuation

5, Curvature of the earth

6. Z-R relationship

Radar rainfall error characteristics?

Ideally, radar rain=true rainfall + Noise

A new error model for weather radar data

Multivariate Distributed Ensemble Generator: A new scheme for ensemble radar precipitation estimation over temperate maritime climate, 2014, Qiang Dai, Dawei Han, Migue A. Rico-Ramirez, Prashant K. Srivastava, Journal of Hydrology

Probabilistic radar rainfall nowcasts using empirical and theoretical uncertainty models, 2014, Qiang Dai, Miguel A. Rico-Ramirez, Dawei Han, Tanvir Islam, Sara Liguori, Hydrological Processes,

Journal papers on radar error modelling

Multivariate Distributed Ensemble Generator (MDEG)

MDEG can adopt different kinds of copula functions to simulate the spatial and temporal correlations.

Modeling radar-rainfall estimation uncertainties using elliptical and Archimedean copulas with different marginal distributions, 2014, Qiang Dai, Dawei Han, Miguel A. Rico-Ramirez, Tanvir Islam, Hydrological Sciences Journal

The Thurnham radar

Dual-polarization Radar

3-D film

Rain drop shape

1010log hDR

v

ZZ

Z

Differential Reflectivity

indicator of drop shape

Rinehart, radar for Meteorologists, 2004

Raw reflectivity Clutter Corrected Reflectivity

Clutter removal using a Bayes classifier

Clutter = Non-precipitation echoes such as

echoes from the ground, sea, ship, airplanes

dp

Attenuation Correction

differential phase

Summary

Both rain gauge and weather radar have their own problems.

It is important to understand the strengths and weaknesses of them.

Integration of both data sources would produce better rainfall

estimation

Data uncertainty is important for assessing hydrological modelling

uncertainty