Long Range Forecast Update for the 2009 Southwest Monsoon Rainfall

India Meteorological Department

Presents

April

June

All India June – September

Rainfall

Update for All India

June – September Rainfall

All India Monthly(July & August)

Rainfall

June – September Rainfall for Four Homogeneous

Regions

Long range Forecast Schedule

In addition, Forecast for Date of Monsoon Onset over Kerala in May

1st Stage Forecast

2nd Stage Forecast

Long Range Forecast of 2009 South-west Monsoon Season (June-September) Rainfall

issued on 17th April, 2009

IMD’s operational Long Range Forecast for the 2009 South-west Monsoon season (June-September) is that the rainfall for the country as a whole is likely to be Near Normal.

Quantitatively, monsoon season rainfall is likely to be 96% of the Long Period average (LPA) with a model error of ± 5 %.

S.No Predictor Used for forecasts in

F/N/U

1 NW Europe Land Surface Air Temperatures (January)

April Neutral

2 Equatorial Pacific Warm Water Volume(February +March)

April Neutral

3 East Asia Mean Sea Level Pressure(February + March)

April and June

Unfavorable

4 North Atlantic SST (December +January) April and June

Favorable

5 Equatorial SE Indian Ocean SST (February + March)

April and June

Neutral

6 Central Pacific (Nino 3.4) SST Tendency(Mar+Apr+May) – (Dec+Jan+Feb)

June Unfavorable

7 North Atlantic Mean Sea Level Pressure(May)

June Unfavorable

8 North Central Pacific wind at 1.5 Km above sea level (May)

June Unfavorable

Predictors Used in the Ensemble Forecasting System for the Seasonal Rainfall over the Country as a Whole

Rajeevan et al. ( 2006), Climate Dynamics

Geographical Locations of the 8 Predictors

DR. PAI PARAMETERS FOR 2007

EAST ASIA PR ANOMALY

WARM WATER VOLUME

N. ATL SST ANOMALY

EQ. SE INDIAN OCEAN SST ANOMALY

NORTH WEST EUROPE TEMP ANOMALY

NINO 3.4 SST ANOMALY

NATL PR ANOMALY

NCPAC U850 ANOMALY

Second Stage Forecasts: Method

a) Forecast update for the southwest monsoon season (June-September) rainfall over the country as a whole using a 6-parameter ensemble statistical model with a model error of ± 4%.

b) Forecast for the monthly rainfall over the country as a whole for the months of July & August using separate principle component regression models with a model error of ± 9%.

c)    Forecasts for the southwest monsoon season (June-September) rainfall for the following four broad geographical regions of India using separate multiple linear regression models with a model error of ± 8%.

PREDICTORS(5/6)

MR MODEL

PPRMODEL

ENSEMBLE AVERAGE OF

BEST MODELS

ENSEMBLE AVERAGE OF

BEST MODELS

MEAN FORECAST

ALL POSSIBLE MODELS(31/63)

ALL POSSIBLE MODELS(31/63)

Ensemble Forecasting System for Seasonal Rainfall over Country as a whole:

The average of the ensemble forecasts from best out all possible MR (multiple regression) models and that from PPR

(projection pursuit regression) models gives the final forecast.

Linear Models

Non-Linear Models

• Excess : Above 110% of LPA (16% Prob)

• Above Normal: 104-110% of LPA (17% Prob)

• Near Normal: 96-104% of LPA (33% Prob)

• Below Normal: 90-96% of LPA (16% Prob)

• Deficient: Below 90% of LPA (17% Prob)

Definitions of Rainfall Categories

based on 1901-2005 data

2nd Stage Forecasts

IMD’ s Experimental Dynamical Model Forecasts

May SST Persisted

10 Initial Conditions

21 – 30 May 2009

Forecasts suggest positive rainfall anomalies over most parts of the country, except along some part of west coast where the anomalies are positive.

For the country as a whole, the ensemble dynamical forecast suggests normal monsoon season rainfall (104% of LPA).

2009 Rainfall Predictions from Various Institutes

IMD has also taken into account the experimental forecasts prepared by the national institutes like Indian Institute of Tropical Meteorology (IITM), Pune, Indian Institute of Science (IISc), Bangalore, Space Applications Centre (SAC), Ahmedabad, National Aerospace Laboratories (NAL), Bangalore, Centre for Mathematical Modelling and Computer Simulation (CMMACS), Bangalore, National Centre for Medium Range Weather Forecasting (NCMRWF), Noida and Centre for Development of Advanced Computing (C-DAC), Pune and

Operational/experimental forecasts prepared by international institutes like World Meteorological Organization (WMO)’s Lead Centre for Long Range Forecasting - Multi-Model Ensemble (LRFMME), the National Centers for Environmental Prediction (NCEP), USA, International Research Institute for Climate and Society (IRI), USA, Meteorological Office, UK, the European Center for Medium Range Weather Forecasts (ECMWF), UK , the Experimental Climate Prediction Center (ECPC), USA, and Asian-Pacific Economic Cooperation (APEC) Climate Centre, Korea.

7 Models were used for prepareing the multi-

model ensemble:

ECHAMp5CCM3v6

NCEPNSIPP-1COLAECPCGFDL

IRI, US: Multi-Model Probability Forecast: July to August, 2009

Below normal rainfall over most parts of the country.

3 Models:ECMWFUKMO

Meteo-France

Below normal rainfall over the north and northwestern parts of the coutnry. Normal to above normal rainfall over all other areas.

WMO Lead Center for LRF-MME: JAS

Models: From 10 GPCs, Beijing ECMWF Exeter

Melbourne  Montreal Moscow

Seoul Tokyo

ToulouseWashington

Below normal rainfall over North and northwestern parts of the country. Normal rainfall over south Peninsula and northeast.

• In general, the experimental forecasts based on statistical models suggest below normal monsoon season rainfall over the country as whole and that based on the dynamical models suggest normal to above normal rainfall.

2009 Rainfall Predictions from Various Institutes

La Nina Conditions over Pacific and Prediction 1st stage

forecast

oCurrently Atmospheric and oceanic conditions reflect neutral ENSO conditions.

Latest ENSO Forecast

oForecasts from both dynamical and statistical models suggest high probability (about 60%) for El Nino conditions to prevail during the monsoon season

oAbout 40% probability for ENSO neutral conditions.

oLa Niña is ruled out .

Indian Ocean Dipole

IOD forecast: weak positive IOD during the monsoon season

FRCGC, Japan: June, 2009

Second Stage Long Range Forecast for

2009 South-west Monsoon Season(June –September )

Rainfall

25th June, 2009

Summary of the Update Forecasts for 2009 Southwest Monsoon Rainfall

i) South-West Monsoon Season RainfallIMD’s long range forecast update for the 2009 south-west monsoon season (June to September) is that the rainfall is likely to be below normal. Quantitatively, monsoon season rainfall for the country as a whole is likely to be 93% of the long period average with a model error of ±4%. The Long period average rainfall over the country as a whole for the period 1941-1990 is 89 cm.

ii) Monthly (July & August) Rainfall Rainfall over the country as a whole in the month of July 2009 is likely to be 93% of its LPA and that in the month of August is likely to be 101% of LPA both with a model error of ± 9 %.

Summary of the Update Forecasts for 2009 Southwest Monsoon Rainfall

iiI) Rainfall over Broad Geographical RegionsOver the four broad geographical

regions of the country, rainfall for the 2009 South-West Monsoon Season is likely to be

81% of its LPA over North-West India, 92% of its LPA over North-East India, 99% of its LPA over Central India and 93% of its LPA over South Peninsula, all with a model error of ± 8 %.

Thank you

31-YEAR MOVING AVERAGE OF SEASONAL MONSOON RAINFALL

y = -7E-10x6 + 2E-07x5 - 3E-05x4 + 0.0017x3 - 0.039x2 + 0.2492x

R2 = 0.8208

-4

-3

-2

-1

0

1

2

3

4

1905 1915 1925 1935 1945 1955 1965 1975 1985 1995 2005

YEAR ENDING 31-YEAR SLIDING WINDOW

RA

INF

AL

L A

NO

MA

LY

(%

DE

P. F

RO

M L

PA

)Epochal Variation of ISMR

119

101 100

9193

100

110

100

103 102

105

96

9291

81

102

87

99100

106

98

113

102101

9492

103

92

97 96

92

99

108

99 98

101

98100

98

92 93

99

80

85

90

95

100

105

110

115

120

125

1988

1989

1990

1991

1992

1993

1994

1995

1996

1997

1998

1999

2000

2001

2002

2003

2004

2005

2006

2007

2008

YEAR

RA

INF

AL

L %

OF

LP

A

Actual

Forecast

PERFORMANCE OF OPERATIONAL FORECAST (1988-2008)

Region PeriodIssued

onForecast Actual

All IndiaJune to

September

16 April, 2008

99% of LPA ± 5%

98% of LPA30 June,

2008100% of LPA ± 4%

All India July30 June,

200898% of LPA ± 9% 83% of LPA

NW India

June toSeptember

30 June, 2008

96% of LPA ± 8% 105% of LPA

NE India 101% of LPA ± 8% 97% of LPA

Central India 101% of LPA ± 8% 96% of LPA

S. Peninsula 98% of LPA ± 8% 96% of LPA

The forecast for onset over Kerala was 29th May.The actual monsoon onset over Kerala was 31st May.

Verification of 2008 Operational Forecasts