Rising Flood Risk in Northwest India

Scientists have reported that northwestern South Asia (including northwest India) is becoming increasingly flood-prone due to changes in two key subseasonal weather patterns.
Changing Rainfall Pattern in NWSA
•  Northwestern South Asia (NWSA), including parts of Pakistan and northwest India, has traditionally been a semi-arid region with low rainfall. 
•  Monsoon rainfall in South Asia generally shows an east–west contrast, with higher rainfall in eastern regions and lower rainfall in the northwest. 
•  However, recent decades have witnessed an increase in persistent heavy rainfall events in NWSA, leading to frequent floods.
Intra-Seasonal Oscillation (ISO)
•  Intra-Seasonal Oscillations (ISOs) are weather patterns that vary within a season and influence rainfall over periods ranging from 10 to 90 days. 
•  These oscillations play a crucial role in determining active and break phases of the monsoon.
Two key drivers of increasing floods :
1. Strengthening of Tropical Monsoon ISO
•  The tropical monsoon ISO refers to rainfall systems that originate near the equatorial Indian Ocean and move towards the Indian subcontinent. 
•  Recent changes show that these systems are becoming stronger and penetrating deeper into inland regions like NWSA. 
•  This results in enhanced and prolonged rainfall in areas that were previously dry. 
2. Slowing of Mid-Latitude Oscillation
•  Mid-latitude oscillations are atmospheric waves associated with the jet stream (high-altitude winds). 
•  These waves influence weather systems such as rainfall and storms. 
•  Recent trends indicate that these oscillations are slowing down, causing rain-bearing systems to remain stationary over NWSA for longer durations.
Combined Impact
•  The interaction of stronger tropical ISO and slower mid-latitude oscillations leads to persistent heavy rainfall events. 
•  This persistence increases the likelihood of floods, especially in semi-arid regions that lack resilience to excess rainfall. 
•  Together, these two factors account for about 44% of the increase in flood frequency in the region. 
Role of Climate Change
•  Global warming is intensifying these changes by increasing atmospheric moisture and altering wind patterns. 
•  Enhanced land-sea temperature contrast supports stronger monsoon systems. 
•  Weakening of the jet stream contributes to slower movement of weather systems.
Significance
•  Semi-arid regions like NWSA are more vulnerable to sudden floods compared to traditionally wet regions. 
•  Understanding these oscillations improves flood prediction beyond short-term weather forecasts. 
•  Incorporating ISO patterns into forecasting models can enhance early warning systems and disaster preparedness.