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Monsoon Rainfall Prediction Over Pakistan. Arif Mahmood. Chief Meteorologist. Pakistan Meteorological Department http://www.pakmet.com.pk. First session of the South Asian Climate Outlook forum (SASCOF-1) pune, India, 13-15-April 2010. Rainfall over Pakistan.
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Monsoon Rainfall Prediction Over Pakistan Arif Mahmood Chief Meteorologist Pakistan Meteorological Department http://www.pakmet.com.pk First session of the South Asian Climate Outlook forum (SASCOF-1) pune, India, 13-15-April 2010
Rainfall over Pakistan • 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
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 = 0.3575A - 14.3989B - 0.7612C + 0.8147D + 0.3902
Long Range Forecast by PMD Rn = 0.3575A - 14.3989B - 0.7612C + 0.8147D + 0.3902 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: • Mean of station level pressure of Seychlles for March, April and May • 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): • Lahore ii. Islamabad iii. Sialkot iv. Multan D = Snow accumulation at the peaks of Western Himalayas at the end of May.
Long Range Forecast by PMD The calculated percentage departure of the expected rainfall in Pakistan from the normal rainfall is classified as follows:
El-Nino and Pakistan Monsoon Relationship (Jul-Sep) RAINFALL (1961-2009)
Two statistical downscaling models are used for seasonal precipitation prediction: Coupled Pattern Projection Model (CPPM) Multiple Linear Regression Model (MLRM) Statistical Model
µx for predictor field µy is standard dev. of predictand,
Rainfall for Monsoon 2007 Observed Predicted
Rainfall for Winter 2007 - 08 Observed Predicted
Rainfall for Monsoon 2008 Observed Predicted
Rainfall for Winter 2008-09 Predicted precipitation Seasonal Anomaly (%)
Summer 2009 Predicted & Observed Rainfall(Jun-Jul)
Forecast Winter (2009-2010) Predicted Rainfall (Winter2009-10) % Anomalies of Rainfall
Forecast Winter (2009-2010) • 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.