IITM study finds land retains rainfall memory for up to 35 days

The team developed a non-parametric, model-free approach to quantify memory in complex systems such as soil, oceans, and atmosphere

A new study by scientists from the Indian Institute of Tropical Meteorology (IITM), Pune, has decoded how long land “remembers” past rainfall events, offering deeper insights into how soil moisture influences local weather and broader climate patterns. The research found that soil moisture across India’s core monsoon zone retains traces of past rainfall for nearly 35 days — a duration that is shorter but considered more realistic than earlier scientific estimates.

The approach departs from conventional statistical models, which tend to overestimate memory at shorter time scales — typically from a few days to weeks — where extreme weather events like heavy rainfall or droughts are more frequent. (HT)

Published in Physical Review Letters on October 14 and made available online on November 4, the study titled “Persistence in Physical Systems: An Application to Soil Moisture Memory” introduces a novel framework to measure memory in natural systems using the principles of information theory. Madhusudan Ingale led the work under the guidance of Bhupendra Bahadur Singh at IITM’s Centre for Climate Change Research (CCCR).

The team developed a non-parametric, model-free approach to quantify memory in complex systems such as soil, oceans, and atmosphere. The approach departs from conventional statistical models, which tend to overestimate memory at shorter time scales — typically from a few days to weeks — where extreme weather events like heavy rainfall or droughts are more frequent.

By providing a more refined measure, the new method captures how the land surface “remembers” rainfall and gradually loses that memory, influencing evaporation, temperature, and future rainfall. “The method refines our understanding of how the land-atmosphere system behaves and can help improve climate predictions,” said Singh.

Using both model-based simulations and observational data, the IITM study estimated soil moisture memory over India’s monsoon zone at around 35 days, while site-based measurements from IITM’s COSMOS observatory in Pune suggested a 21-day memory at the local scale.

According to the researchers, the findings could have significant implications for monsoon variability forecasting, water resource management, and agricultural planning. Understanding how long land retains rainfall memory can also improve predictions of drought persistence, crop yield, and groundwater recharge — key factors in building resilience against climate extremes.