Context:
A recent study, published in Geophysical Research Letters on March 17, 2025, investigates the spatial rainfall trends in India over the last decade (2011-2020) using GSMaP-ISRO data. The findings reveal notable regional shifts in both the amount and timing of rainfall compared to the previous decade (2001-2010).
Key Findings
Regional Rainfall Variations
- West-Central India:
- The study observed a slight increase in rainfall, about 2 mm per day, during 2011-2020 compared to 2001-2010.
- Indo-Gangetic Plain & Southern India:
- These areas also experienced a slight increase in rainfall, but it was less than that seen in west-central India.
- Eastern India:
- Contrarily, the eastern region saw a 1 mm per day decrease in rainfall during 2011-2020 compared to the previous decade, whereas the northeastern and eastern areas had experienced a slight increase in rainfall from 2001 to 2010.
Link to Vegetation and Soil Moisture
- Increased Vegetation in West-Central India:
- The Normalized Difference Vegetation Index (NDVI), a measure of vegetation density, increased significantly in west-central India, from 0.2 to 0.4.
- This rise in vegetation is linked to the increased rainfall in the region. Vegetation boosts transpiration, releasing water vapour into the atmosphere, thus influencing the local climate.
- Soil Moisture:
- The study also observed a significant increase in soil moisture content in west-central India, positively correlating with the increased rainfall. In contrast, the eastern region saw a notable decrease in soil moisture over the same period.
Shift in Rainfall Timing
- Peak Rainfall Time:
The timing of the peak rainfall has shifted in various regions:- In the Indo-Gangetic Plain, the peak rainfall time advanced by 2-4 hours.
- In west-central India, the peak time was delayed by 1-2 hours.
- Influence of Aerosols:
- The study linked these shifts to changes in aerosol loading in the atmosphere. In areas like the Indo-Gangetic Plain, where aerosol levels are higher, rainfall peaks earlier.
- This was observed in a previous study in Beijing, where polluted conditions caused earlier rainfall peaks. Conversely, west-central India, with relatively lower aerosol levels, experienced a later peak in rainfall.
Implications and Insights
- The findings highlight the complex interplay between climate, vegetation, and aerosols in shaping India’s rainfall patterns.
- The shifts in rainfall timing and changes in regional rainfall can have significant implications for water management, agriculture, and climate adaptation strategies across the country.
- These results can also help in understanding the broader impacts of climate change on rainfall distribution and the hydrological cycle in India.
This study provides valuable insights into the spatial variability of rainfall in India, emphasizing the role of both biophysical and atmospheric factors, such as vegetation growth and aerosol concentration, in shaping rainfall patterns. The findings could assist in developing more accurate rainfall prediction models and climate adaptation strategies in the country.
