Weather radar rainfall for hydrological hazard risk management Dawei Han 韩大卫 Department of Civil Engineering University of Bristol, UK
Hydrological hazards related to rainfall Floods Droughts Debris flows
How to measure rainfall?
Rainfall measurements Rain gauge Radar Satellite
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
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 http://www.rmets.org/sites/default/files/pdf/presentation/20100417-allott.pdf
Rainfall is not uniform No rain Rain
Remote sensing could be the answer (?) Radar Satellite
Weather Radar USA UK
Chinese weather radars
Transmitter NOAA Receiver 6 Z D N( D) dd 3.67 R D N( D) dd b Z ar Source: www2010, Univ. of Illinois
Reflectivity Z 200R 1.6
Beam Spreading http://www.srh.noaa.gov/jetstream/doppler/beam_max.htm
Beam refraction Earth curvature Overshooting/beam blocking http://www.srh.noaa.gov/jetstream/doppler/beam_max.htm
Variation of Reflectivity in the Vertical Rico-Ramirez, et al (2007), Meteorological Applications, 14: 117-129.
Height Variation of Reflectivity in the Vertical Radar Range rainfall rate at the ground?
Rain drops falling from the sky
3D wind field (ECMWF Downscaled by WRF)
Rain drop sizes disdrometer http://rpitt.eng.ua.edu/class/erosioncontrol/module3/module3_files/image022.jpg
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) (no validation) 3D wind profiler (Collaborative study with Dr. Yamamoto) 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
Journal papers on radar error modelling 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,
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
Differential Reflectivity Z DR Z h 10 log10 Zv indicator of drop shape
Rinehart, radar for Meteorologists, 2004
Clutter removal using a Bayes classifier Raw reflectivity Clutter Corrected Reflectivity Clutter = Non-precipitation echoes such as echoes from the ground, sea, ship, airplanes
Attenuation Correction differential phase dp
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