Validation of satellite rainfall estimation in the summer monsoon dominated area
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Validation of satellite rainfall estimation in the summer monsoon dominated area of the Hindu Kush Himalayan Region Sagar Ratna Bajracharya , Mandira Shrestha and Pradeep Mool [email protected] Integrated Water and Hazard Management

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Validation of satellite rainfall estimation in the summer monsoon dominated areaof the Hindu Kush Himalayan Region

Sagar Ratna Bajracharya, Mandira Shrestha and Pradeep Mool

[email protected]

Integrated Water and Hazard Management

International Centre for Integrated Mountain Development (ICIMOD)

www.icimod.org

4th Workshop of the

International Precipitation Working Group

13-17 October, 2008, Beijing, CHINA


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Outline monsoon dominated area

  • General description and climatic condition of HKH region

  • What is NOAA CPC-RFE 2.0

  • Methodology and Analysis

  • Results

  • Recommendations and Road Ahead


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The Himalayan Region monsoon dominated area

  • Extends over 3500 km from Afghanistan, Pakistan, India, China, Nepal, Bhutan to Bangladesh and Myanmar

  • Geologically youngest mountain range in the world, giving rise to the high degree of slope instability and landslide hazards

  • High mountains, Plane and Tibetan Plateau

  • Variable background – snow cover etc

  • High spatial variations with widely varying physical and climatic conditions


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The Hindu Kush-Himalayan Context monsoon dominated area

  • Meteorologically diverse

  • Orography and continental influences

  • Convective precipitation, Cloud burst, Monsoon Influence

  • Seasonal variations – Extremely cold vs hot and humid temperatures

  • Variety and variability of climate due to complex topography

  • Plenty of intense rain intensities…


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Track of Monsoon Depression monsoon dominated area


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Active Monsoon Trough monsoon dominated area

L, 990 mbar


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Kitini Khola 1993 flood monsoon dominated area


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Orography and Rain Shadow monsoon dominated area

Orographic lift occurs when an air mass is forced

a low elevation to higher elevation as it moves

over rising terrain. As the air mass gains altitude

it expands and cools adiabatically. This cooler air

cannot hold the moisture as well as warm air and

this effectively raises the relative humidity to 100%,

creating clouds and frequently precipitation.


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Note: -ve value indicates Ocean monsoon dominated area

Precipitation

  • Southern part of the Himalayas receive higher rainfall whereas northern receive less rainfall

  • Higher in the east and gradually decreases towards west

  • More than 80% rainfall during monsoon (June-September)

  • High seasonal and spatial variation

Source: World Water and Climate Atlas, IWMI


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Seasonal Variation of Precipitation monsoon dominated area

Monsoon

Pre Monsoon

Winter

Post Monsoon


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NOAA CPC RFE2.0 monsoon dominated area

  • Initial version became operational in May 2001

  • Originally run over the African continent then expanded to southern Asia and western Asia / eastern Europe

  • Product is a combination of surface and satellite precipitation information

  • Spatial resolution: 0.1 degree

  • Temporal resolution: daily

  • Availability: 5°-35°N; 70°-110°E


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Final Product monsoon dominated area

Source: Tim Love


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NOAA CPC RFE Domain monsoon dominated area


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GTS Inputs monsoon dominated area

15

15

Source: Tim Love


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Methodology for validation monsoon dominated area

Data Preparation

Daily independent rain gauge data in

word file convert into appropriate format provided

by individual country from 2002-2004

  • Estimated Data

  • NOAA CPC_RFE Product

  • Whole HKH Daily product (24 hours)

  • 0.1 degree spatial resolution

  • In Lambert Azimuthal Area

Data Quality Control

Data Conversion

- RFE2 Data downloaded by NOAA ftp server

- Observed rain gauge data in GIS format

Comparison or Overlay

Change the projection parameter

of GIS dataset

Interpolation

a) Kriging

- 0.1˚ spatial resolution for individual

country

-0.25 to 2.5˚for regional level

Validation

a) Visual analysis

b) Descriptive statistics

- through contingency tables

- POD, FAR

(e.g. with zero and 1mm/day rain/no rain threshold)

c) Statistical analysis

-Bias

-RMSE

-linear correlation coefficient

-Skill score index

-% error

-etc

Working Area

- ICIMOD Whole HKH (Regional)

- Partner institutes their individual country

Considered Scales

Individual country

- 0.1 to 0.25˚ spatial resolution

- 24 hours, 10 and 30 days temporal

ICIMOD

-0.25 to 2.5˚spatial resolution

- 24 hours, 10 and 30 days temporal


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Comparison monsoon dominated area


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Validation of RFE monsoon dominated area

  • Visual Analysis

  • Scatter plot of Observed V Estimated rainfall

  • Descriptive statistics

  • Contingency tables use of POD and FAR

  • Statistical analysis

  • Bias, RMSE, Correlation, Skill, % error etc


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Results monsoon dominated area

  • The CPC-RFE technique overestimates rainfall particularly over a region where there is persistence of cirrus cloud, snow and ice.

  • Underestimates rainfall in a region where there is orographic precipitation and precipitation by warm cloud.

  • Rainfall occurrence is underestimated by about half and more than half in monsoon during heavy rainfall and overestimates in pre monsoon

  • Limitation of SRE is that it cannot produce more than certain amount of rainfall in 24 hours


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Next Steps in SRE application monsoon dominated area

  • How lag time of the data can be reduced?  

  • Improving Orographic effects in rainfall estimation .

  • RFE- the shape of precipitation is given by the combination of satellite estimates, magnitude is inferred from GTS station data, need the maximum availability of the rain gauge stations

  • Including radar data for validation where available in HKH and Incorporate more gauge data for validation

  • Validation considering different rainfall regimes.

  •  Validation considering temporal variable like decadal, monthly, yearly, rainy season etc using different spatial resolution (0.25˚, 0.5˚, 1˚, etc)

  • Improve Satellite estimates over the ice and snow cover estimates over the Himalayas

  • Application of improved RFE in flood early warning and flood monitoring activities in flood season. 


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Thank You! monsoon dominated area


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