Weather radar rainfall for hydrological hazard risk management

Transcription

1 Weather radar rainfall for hydrological hazard risk management Dawei Han 韩大卫 Department of Civil Engineering University of Bristol, UK

2 Hydrological hazards related to rainfall Floods Droughts Debris flows

3 How to measure rainfall?

4 Rainfall measurements Rain gauge Radar Satellite

5 Tipping Bucket gauges Drop counting gauges Optical gauges

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8 Larson and Peck (1974)

9 WMO report (1982 by Sevruk) Ground truth?

10 Boscastle flood of 16 August mm rain in 60 min, flood peak of 180 cumecs in 1 hour

11 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

12 Rainfall is not uniform No rain Rain

13 Remote sensing could be the answer (?) Radar Satellite

14 Weather Radar USA UK

15 Chinese weather radars

16 Transmitter NOAA Receiver 6 Z D N( D) dd 3.67 R D N( D) dd b Z ar Source: www2010, Univ. of Illinois

17 Reflectivity Z 200R 1.6

18 Beam Spreading

19 Beam refraction Earth curvature Overshooting/beam blocking

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21 Variation of Reflectivity in the Vertical Rico-Ramirez, et al (2007), Meteorological Applications, 14:

22 Height Variation of Reflectivity in the Vertical Radar Range rainfall rate at the ground?

23 Rain drops falling from the sky

24 3D wind field (ECMWF Downscaled by WRF)

25 Rain drop sizes disdrometer

26 Displacement of rain drops and time lags

27 Pairing of radar pixels and rain gauges

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

29 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?

30 Model Sensitivity Analysis and Uncertainty Analysis wikipedia

31 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

32 Radar rainfall error characteristics? Ideally, radar rain=true rainfall + Noise

33 A new error model for weather radar data

34 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,

35 Multivariate Distributed Ensemble Generator (MDEG) MDEG can adopt different kinds of copula functions to simulate the spatial and temporal correlations.

36 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

37 The Thurnham radar Dual-polarization Radar

38 3-D film

39 Rain drop shape

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41 Differential Reflectivity Z DR Z h 10 log10 Zv indicator of drop shape

42 Rinehart, radar for Meteorologists, 2004

43 Clutter removal using a Bayes classifier Raw reflectivity Clutter Corrected Reflectivity Clutter = Non-precipitation echoes such as echoes from the ground, sea, ship, airplanes

44 Attenuation Correction differential phase dp

45 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