long range forecast update for the 2009 southwest monsoon rainfall india meteorological department...
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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