Arif Mahmood Chief Meteorologist Pakistan Meteorological Department Monsoon Rainfall Prediction Over Pakistan First session of the South Asian Climate Outlook forum (SASCOF-1) pune, India, April 2010

Rainfall over Pakistan 2 The rainfall activity over Pakistan, occurs mainly in two distinct periods (seasons) namely, Winter (January to March) and Summer (July to September). Southwest Monsoon Rains contribute about 60% of total annual rainfall

Average ( ) Annual Precipitation 3

Annual Precipitation Area Weighted Departure

WINTER (Jan-Mar) Precipitation Average

6 Monsoon (Jul-Sep) Precipitation Average

SEASONAL PREDICTION IN PAKISTAN Monsoon seasonal prediction is operationally carried out at PMD by the following methods : Multiple Linear Regression Models Two Models are in use Statistical Downscaling of GCM’s Presently two GCM’s, NCC CGCM and NCEP are being downscaled

Long Range Forecast by PMD Regression Model 1: The Main Predictors of the Pakistan LRF model since 1980’s for Monsoon Rainfall are following: South American Pressure. Punjab (Pakistan) Mean Range of Temperature Equatorial Pressure Western Himalayas Snow Accumulation Regression Model 2: Later Chaudhary (1998) has also developed a regression model using Following six parameters for predicting summer monsoon rainfall over Pakistan: Temperature of a number of cities in Pakistan as well as Northern hemisphere and El-Nino Surface level pressure field over Pakistan and Southern Oscillation Index. 500 hPa ridge position at 75°E in April, 10 hPa zonal pattern in January Eurasian snow cover of December

Long Range Forecast by PMD The departure of the expected monsoon rainfall in Pakistan from the normal monsoon rainfall is calculated by adding up the calculated departures of the all the factors and adding to it the contribution Correlation of all the factors. It is calculated by following equation: Rn = A B C D

Long Range Forecast by PMD Rn = A B C D Where: Rn= Pakistan Monsoon Rainfall Departure. A = South American Pressure Departure; Mean of the Station Level pressure (April & June) of: i. Buonos Aires ii. Cardoba iii. Santaigo B = Equatorial Pressure: i.Mean of station level pressure of Seychlles for March, April and May ii.Mean of sea level pressure of Port Darwin for February and March. C = Mean of temperature range of the following cities of Pakistan (April & May): i.Lahore ii. Islamabad iii. Sialkot iv. Multan D = Snow accumulation at the peaks of Western Himalayas at the end of May. 10

Long Range Forecast by PMD The calculated percentage departure of the expected rainfall in Pakistan from the normal rainfall is classified as follows: Sr. No. Percentage departure of forecast rainfall from normal Classification used for describing the rainfall forecast 1Above 50 %Largely above normal 226 % to 50 %Moderately above normal 311 % to 25 %Slightly above normal 4-10 % to +10 %Normal 5-11 % to -25 %Slightly below normal 6-26 % to -50 %Moderately below normal 7Below -50 %Largely below normal 11

El-Nino and Pakistan Monsoon Relationship (Jul-Sep) RAINFALL ( )

Statistical Model Two statistical downscaling models are used for seasonal precipitation prediction: 1. Coupled Pattern Projection Model (CPPM) 2. Multiple Linear Regression Model (MLRM)

µ x for predictor field µ y is standard dev. of predictand,

Rainfall for Monsoon 2007 Predicted Observed

Rainfall for Winter ObservedPredicted

Rainfall for Monsoon 2008 ObservedPredicted

Rainfall for Winter Predicted precipitation Seasonal Anomaly (%)

Predicted & Observed Rainfall (Jun-Jul) Summer 2009

Anomalies Summer,2009 Observed rainfall from Predicted rainfall

Time Series

Forecast Winter ( ) Predicted Rainfall (Winter ) % Anomalies of Rainfall

Forecast Winter ( ) Likely to normal precipitation is expected in northern parts of the country; while Southern Punjab, Northern Sindh and eastern Balochistan may receive greater than normal rains.

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