This document describes the CEH-GEAR dataset, which provides daily and monthly gridded rainfall estimates for the UK at a 1km resolution from 1890 to the present. It was created using raingauge data and a natural neighbor interpolation method. The dataset is freely available online and has various applications, including drought monitoring, land surface modeling, and catchment-scale hydrological analysis. Validation showed the estimates have low error, though error increases with distance from raingauges, particularly for high rainfall events.

1. Maliko Tanguy, V. Keller, I. Prosdocimi, J. Terry,
O. Hitt, S. Cole, M. Fry, D. Morris and H. Dixon
BHS 2014, Birmingham 2-4 September
The new CEH-GEAR dataset:
Fine resolution daily and monthly areal rainfall estimates for the UK

2. Contents
1
Introduction
2
Methodology
3
Analysis
4
Examples of use
5
Access

3. Contents
1
Introduction
2
Methodology
3
Analysis
4
Examples of use
5
Access

4. Introduction Method Analysis Examples Access
Images from: shutterstock, clipartpanda.com
What does CEH-GEAR stand for?
Gridded Estimates of Areal Rainfall

5. Introduction Method Analysis Examples Access
Images from: shutterstock, clipartpanda.com
What is CEH-GEAR dataset?
MAIN PRODUCT:
1 km gridded rainfall
DAILY and MONTHLY totals
for the UK 1890-2012
UPDATED YEARLY
SUB-PRODUCTS:
DAILY and MONTHLY grids of the distance to the closest gauge
Ancillary grids:
- grid of first year of missing data
- grid of last year of missing data
- grid of total days/months of missing data

6. Introduction Method Analysis Examples Access
Hydrological purposes
Long record (back to 1890)
Images from: bestclipartblog.com, metoffice.gov.uk, clipartbest.com, dreamstime.com
CEH-GEAR: Main Features
Based on observed data
FREE
(terms & conditions apply)

7. 0
1000
2000
3000
4000
5000
6000
1860
1870
1880
1890
1900
1910
1920
1930
1940
1950
1960
1970
1980
1990
2000
2010
Number of raingauges
Year
GB daily gauges
Introduction Method Analysis Examples Access
Raingauge network density varies in time.
Peak in 1975: ~5000 gauges
Pre-1961: few stations digitised (500 in 1960)
From1961: most gauges been digitised
Decrease since mid-70s: currently around 2700 raingauges

8. Introduction Method Analysis Examples Access
Raingauge network density varies in time.
1910
1940
1961

9. Contents
1
Introduction
2
Methodology
3
Analysis
4
Examples of use
5
Access

10. NATURAL NEIGHBOUR method
Based on THIESSEN polygons
Image from: ESRI
Intro Methodology Analysis Examples Access
Complies with BS 7843-4:2012 from the British Standards Institution

11. rci,t = calculated rainfall for point i at time interval t
i
rj,t = measured rainfall for raingauge j at time interval t
j=1
j=2
j=3
j=…
j=p
Image from: Wikipedia
Wi,j,t = Weight for raingauge j in time interval t, when used in the estimation of rainfall for target grid point i
Si , Sj = Standard-period Average Annual Rainfall (SAAR) at point i and j
Intro Methodology Analysis Examples Access
Natural neighbour method

12. Normalisation by SAAR
For GB:
Met Office SAAR
(Spackman, 1993)
For Northern Ireland:
Met Eireann SAAR
(Walsh, 2012)
Intro Methodology Analysis Examples Access

13. Intro Methodology Analysis Examples Access
Monthly correction factor  daily and monthly grids consistent
=
Sum of daily rainfall totals for 1 month
Monthly rainfall total

14. Contents
1
Introduction
2
Methodology
3
Analysis
4
Examples of use
5
Access

15. Intro Method Analysis Examples Access
For validation:
14 sites chosen

16. Intro Method Analysis Examples Access
Sites chosen in areas with high spatial variability in rainfall

17. Intro Method Analysis Examples Access
Error:
Some outliers (Scotland)
Larger error for bigger rainfall events
On average: slightly underestimates biggest rainfall events
Low rainfall
High rainfall
rcp: calculated rainfall
rco: observed rainfall
Error
Small error when no or little rain

18. Intro Method Analysis Examples Access
For assessing the effect of network density:
138 SEPA TBRs
(Tipping bucket raingauges)

19. Intro Method Analysis Examples Access
Effect of network density:
Median absolute error vs. Distance to the closest gauge
Low rainfall
High rainfall
Error  with distance for BIGGEST rainfall events
Error  when distance to the closest gauge 
Absolute error
Distance (km)

20. Intro Method Analysis Examples Access
Error  when
distance to the closest gauge 
MINIMUM DISTANCE GRIDS:
Grid of the distance to the closest gauge

21. Contents
1
Introduction
2
Methodology
3
Analysis
4
Examples of use
5
Access

22. Intro Method Analysis Examples Access
Drought Monitoring
Drought indicator:
SPI (Standardised Precipitation Index)
March 2010
June 2010
May 2011
March 2012
June 2012

23. Intro Method Analysis Examples Access
Land surface model
CHESS: JULES applied to the UK
CEH-GEAR used as one of the 7 driving variables to run CHESS.
CEH-GEAR
Images from: jules.jchmr.org

24. Intro Method Analysis Examples Access
Will use CEH-GEAR dataset to derive catchment averaged rainfall time series.
National River Flow Archive
www.ceh.ac.uk/data/nrfa/
Catchment averaged rainfall time series
This data is fictitious. Used for illustration purpose. only
Images from: www.ceh.ac.uk/data/nrfa/

25. Contents
1
Introduction
2
Methodology
3
Analysis
4
Examples of use
5
Access

26. Intro Method Analysis Examples Access
https://gateway.ceh.ac.uk

27. Intro Method Analysis Examples Access
CEH GEAR
First result

28. Intro Method Analysis Examples Access
Images from: http://www.narccap.ucar.edu/
Data stored in NetCDF format
• array oriented scientific data
• highly portable
• built-in metadata

29. Intro Method Analysis Examples Access
Will be fully operational in November 2014
http://doi.org/10.5285/5dc179dc-f692-49ba-9326-a6893a503f6e
THREDDS DATA SERVER
In the meantime:
enquiries@ceh.ac.uk

30. Summary of key ideas
Images from: shutterstock, clipartpanda.com
UK 1km gridded rainfall
DAILY and MONTHLY totals
Back to 1890
and updated yearly
CEH-GEAR
COME AND SEE ME AT THE STAND !

31. For more info:
CEH stand at BHS 2014, Birmingham
Contact:
maliko.tanguy@ceh.ac.uk
Twitter:
@MalikoTanguy
@CEHScienceNews
Thank you