Madhav Khandekar is a former research scientist from Environment Canada and is presently on the editorial board of the Journal Natural Hazards (Kluwer Netherlands). Khandekar was an Expert Reviewer for the IPCC 2007 climate change and his current interests are global warming, climate change and monsoon inter-annual variability.
Guest Post by Madhav Khandekar – Indian Monsoon 2011: Progress & Prognostics
The summer (June-September) monsoon over India and vicinity is the most important annual climate event impacting about 1.7 billion people (close to 25% of world’s humanity) of the Indian sub-continent. The timely arrival and steady progress of the monsoon through the four months is crucial for socioeconomic development of the seven countries (India, Pakistan, Nepal, Bhutan, Bangladesh, Sri Lanka and Myanmar/Burma) on the continent. Most climate models have achieved only a limited success in simulating the arrival, progress and the seasonal prediction of the Indian monsoon, which still remains notoriously unpredictable (Khandekar 2009).
Normally the monsoon arrives on the southern tip of India by 1st June and progresses steadily over central India by 15th June. By 25th to 30th June, monsoon normally establishes over most of the continent. A communiqué issued by the India Meteorological Department (IMD) on 19th April 2011has projected a normal monsoon for this year (within 96-104% of long period average (LPA) rainfall over India as whole which is about 89cm) with a very low probability for seasonal rainfall to be below 90% or above 110% of LPA. The IMD uses a statistical forecasting system with parameters involving indices of ENSO phase in the equatorial Pacific, equatorial south Indian ocean SST (Sea Surface temperature), North Atlantic SST plus NW Europe land-surface temperatures.
This year, the monsoon rains have already begun in Kerala, the southernmost State in India by 1st June and appears to be progressing rather ‘quickly’ over west coast as well as in the northeast part of India including Bangladesh & Myanmar. A strong cross-equatorial flow over the Arabian Sea (off the west coasty of India) together with a development of an off-shore trough seems to be providing an impetus for the monsoon to progress quickly over the rest of the continent. So far the ‘lingering La Nina’ conditions in the Pacific plus a positive phase of the EQINOO (Equatorial Indian Ocean Oscillation) appear to favor a steady progress of the monsoon over next few weeks. Per the latest (June 7 2011) communiqué from IMD, heavy rains have already occurred on the west coast (with daily amounts varying from 20-75mm at some locales) and it appears that this year’s monsoon season will be close to normal.
Recent studies by Gadgil and her associates (Gadgil et al 2004) have identified the ENSO phase and the EQUINOO as the two most important parameters for predicting seasonal rainfall over India and vicinity. The EQUINOO is linked with the Indian Ocean Dipole (IOD), an oceanic feature characterized by anomalies of opposite sign of SST and Sea Surface Height (SSH) between the west and east Equatorial Indian Ocean. According to Gadgil, these two indices (ENSO and EQUINOO) can provide a more skilful prediction of seasonal rainfall than most climate models on a regional or global scale.
The monsoon 2009 was predicted to be a normal monsoon by most climate models, weeks before the beginning of the monsoon season. As it turned out, the 2009 monsoon season started at the southern tip of India about a week earlier, but later the monsoon progress stalled and resulted in a massive deficit for June 2009. This deficit was due to an unfavorable phase of EQUINOO (Francis & Gadgil 2009) which inhibited convective activity over the Bay of Bengal during June 2009. The monsoon rains for the rest of the three months of 2009 could not make up for this deficit and this eventually led to a deficient monsoon (by as much as 23%) for the entire season June-September.
The monsoon 2010 was also predicted to be a normal monsoon by most climate models. In reality, the monsoon rains were deficient in June 2010 by 16% but later in July and early August heavy rains in the northwest led to massive flooding in Pakistan (August 2010) and also in the nearby Indian States of Punjab & Rajasthan. Overall, monsoon 2010 was declared a “flood monsoon” with about 110% of rains country-wide, while northwest regions received as much as 125% of normal rains.
The above discussion exemplifies the complexities of Indian monsoon and its unpredictable progress through the season, from one year to next. For agriculturally dominated countries of the Indian continent, it is imperative that existing climate models provide a much more improved skill than what is available at present.
Francis P A & Sulochana Gadgil 2009: The aberrant behaviour of the Indian monsoon in June 2009. Current Science 97 10 November 2009 p.1291-1295
Gadgil Sulochana et al 2004: Extremes of the Indian summer monsoon rainfall, ENSO and equatorial Indian Ocean Oscillation. Geophysical Research Letters 31 L12213 doi:10.1029/2004GL019733
Khandekar Madhav 2009: The notoriously unpredictable monsoon. CMOS (Canadian Met & Oceanographic Society) Bulletin, 37 December 2009 p.181-182
Acknowledgement: I am thankful to Prof Pielke Sr for his encouragement to invite guest posts on his weblog.
Map of India & vicinity showing the countries in the sub-continent.