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 (?)
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