Numerous studies have reported trends in various climate variables over the Indian subcontinent. A decreasing trend in the amount of monsoon rainfall for more than six decades is one. Others include intensifying trends in the occurrence of extreme rainfall events, droughts, heatwaves, and cyclones. The period over which these trends have been estimated vary but global warming has always been invoked as the prime suspect.
A question that isn’t getting as much attention as it deserves to in this milieu is: are these really trends, or are they shifts or decadal cycles?
(A shift is a jump from one state to another, such as a quick transition from one amount of rainfall to another. The best example is seasonal monsoon rainfall: it tends to remain above the long-period average (LPA) for about 20 years and then shifts to a state of less rainfall than the LPA for a similar duration.)
