The Future of the Indian/Asian Monsoon

A recent study on India's climate change science has generated headline news "Heavier monsoon with climate change" (Times of India November 20 2010) with an assessment that such heavier monsoon rains in the future may adversely impact forests in the "Western Ghats" region of the Peninsular India. The Western Ghats are a coastal mountain range- similar to the US/American Rockies but much smaller overall, just about 600-700 m in average height with peaks ranging between 1000m to 2000m. These Ghats extend from Mumbai (largest city of India) on the west coast to the southern tip of India and support extensive forests and wildlife like tigers and elephants. The lead author (H N Ravindranath) is quoted as saying "The forests in the Western Ghats are vulnerable to this projected climate change."

It is important to closely assess this latest climate change science report and its adverse future impact. The projection of a "heavier monsoon" by 2030 is based on climate models which are not very reliable and cannot be used for any policymaking decisions. The Indian monsoon, and by extension the south Asian monsoon, is the largest seasonal anomaly in the earth's climate system and most models have achieved only limited success so far in simulating many of its complex features (Khandekar, 2009: Shukla, 2007; Gadgil et al., 2005). The IPCC (Intergovernmental Panel on Climate Change) and most climate models project an increase in monsoon activity with rising global temperature associated with increasing CO₂. In reality, the global monsoon, as well as the Asian/Indian monsoon, has declined in strength in the last fifty years (see Chase et al., 2003). Further, a study by Kripalani et al. (2003) shows that the Indian monsoon exhibits decadal variability with above/below normal epochs with an approximately 30-yr period and this decadal variability has NOT been impacted by recent global warming or climate change. Other recent studies (Terray, 1995; Khandekar, 2010) have identified several back-to-back drought/flood patterns in the Indian monsoon. What is of interest here is that such drought/flood patterns occurring irregularly throughout a 150-year dataset can produce regional precipitation changes of 25 to 50 percent from one year to the next. Such large swings in precipitation patterns over many regions including the Western Ghats have often occurred in the past and do not appear to have adversely impacted the forests or wildlife of the region so far.

It is of additional interest to note here that the past summer monsoon (2010) was close to a flood monsoon, which triggered historic flooding in Pakistan and also in many regions of Peninsular India, including parts of the Western Ghats. This past summer's heavy monsoon was followed by a severe drought in 2009 when India-wide summer rains were about 25% below normal (Khandekar, 2009). A deficit rainfall in a given year does impact adversely on the grain yield as it did in 1972, which was a severe drought and adversely impacted rice yield that year. However long-term impacts of such droughts and floods appear to be minimal so far.

In summary the climate model projection of a heavier monsoon by 2030 is fraught with considerable uncertainty when assessed against the reality of monsoonal inter-annual variability. The Indian/Asian monsoon will continue to exhibit regional and large-scale precipitation swings in future, global warming notwithstanding. The best way to cope with such swings in monsoon variability in future is to improve seasonal (1-3 months and longer) prediction skill of summer monsoon. An improved skill will enable policymakers to minimize any adverse impact of future extreme droughts and precipitation.

Additional References
Chase, T.N., Knaff, J.A., Pielke, R.A., Sr. and Kalnay, E. 2003. Changes in global monsoon circulation since 1950. Natural Hazards 29: 229-254.

Gadgil, S., Rajeevan, M. and Nanjundiah, N. 2005. Monsoon prediction- why yet another failure? Current Science 88: 1389-1400.

Khandekar, M.L. 2009. The notoriously unpredictable monsoon. Canadian Meteorological and Oceanographic Society 37: 181-182.

Khandekar, M.L. 2010. 2010 Pakistan floods: climate change or natural variability? Canadian Meteorological and Oceanographic Society 38: 165-167.

Kripalani, R.H., Kulkarni, A., Sabade, S. and Khandekar, M.L. 2003. Indian monsoon variability in a global warming scenario. Natural Hazards 29: 189-206.

Shukla, J. 2007. Monsoon mysteries. Science 318: 204-205.

Terray, P. 1995. Space-time structure of monsoon inter-annual variability. Journal of Climate 8: 2295-2619.