Weather in India is like the heartbeat of a vast organism. Across the country, the pulse beats differently: steady in some places, like a sleeping person, and erratic in others, as if after a sprint. Scientists set out to understand how the rhythm of this pulse changes over the long term. To do so, they took temperature and humidity data from 1948 to 2022 at 15 sites across India.
Each weather measurement was turned into a point on a special map, where nearby points indicate similar weather. Then they moved through time with a window of roughly seven years, watching how often weather returned to previously seen states. If returns are frequent and regular, weather is easy to predict, like a pendulum. If rare and disorderly, it is like raindrops on a windowpane. This method is called recurrence analysis, that is, the search for repeating states.
It turned out that nearly all 15 locations experienced a shift toward more chaotic weather between 1972 and 1979. During those years, strong El Niño and La Niña events occurred: warm and cold currents in the Pacific Ocean that affect weather worldwide. India's climate, like a sensitive orchestra, fell out of rhythm under the influence of these distant events. After 2000, the dynamics became more regular again, as if the orchestra had found its former tempo. For humidity, the picture was different: regularity dominated until 1970, followed by scattered shifts.
This work shows that climate change is not just a rise in temperature or a change in humidity. The very character of weather changes: it becomes more predictable at times, more disorderly at others. And if we want to understand when disruptions might occur, we need to listen not to average values but to the rhythm itself.
The analysis window of 5000 time steps corresponds to about 7 years—comparable to the typical period of El Niño. This choice allowed capturing an entire ENSO cycle within one window and seeing its influence on dynamics.