Comprehensive Analysis of Rainfall Distribution, Trends, and Extremes Across Indian Subdivisions

By abhishek.verma75000 · May 5, 2026

This study presents a detailed statistical analysis of rainfall patterns across Indian subdivisions using long-term data (1901–2015). The analysis…

The analysis identified the subdivisions with the highest average annual rainfall across the full period (1901–2015). A horizontal bar chart and data tables have been generated showing the top 10 wettest subdivisions ranked by their average annual rainfall in millimeters.

The analysis breaks down India's annual rainfall into four seasons across all subdivisions from 1901–2015. The Jun–Sep monsoon season overwhelmingly dominates, contributing 75.22% of total annual rainfall. The remaining three seasons share the rest fairly modestly. A pie chart and bar chart were generated to visualize these shares clearly.

The analysis reveals which Indian subdivisions rely most heavily on the June–September monsoon season for their annual rainfall totals. A horizontal bar chart has been generated showing all subdivisions ranked by the percentage of their annual rainfall that comes from the Jun-Sep monsoon window, along with supporting data tables.

The analysis identified the subdivisions with the highest annual rainfall variability and climate risk. Saurashtra & Kutch tops the list with a Coefficient of Variation (CV) of 40.8%, meaning its rainfall is highly unpredictable year to year — a strong indicator of drought and flood risk. Two charts and data tables were generated to visualize these findings.

Average annual rainfall across India has remained relatively stable from 1901 to 2015, with a very slight declining trend of about -0.21 mm per year. Over the full 114-year period, this amounts to a total decrease of roughly 24 mm — quite small compared to the overall average of 1,411 mm. A chart has been generated showing the annual values, a 10-year rolling average, and the linear trend line.

The analysis examined national annual rainfall from 1901 to 2015, identifying the most extreme flood (wettest) and drought (driest) years. Two visualizations were produced: a bar chart showing rainfall anomalies across all years (with blue bars for the top 5 wettest years and red bars for the top 5 driest), and a comparison chart directly contrasting those extreme years against the long-term national mean of 1,411 mm.

The analysis identified 179 extreme rainfall years across Indian subdivisions using a 2-standard-deviation threshold. A stacked bar chart shows the top 15 subdivisions most prone to extreme years, and the top 5 most extreme individual records are listed. Orissa leads with 9 extreme years (6 wet, 3 dry), followed by Bihar, Chhattisgarh, Jammu & Kashmir, Konkan & Goa, and Madhya Maharashtra each with 7 extreme years. The single most extreme record belongs to Coastal Karnataka in 1961 with 5,553.9mm annual rainfall (z-score: 4.45), followed by West Rajasthan in 1917 and Naga Mani Mizo Tripura in 1970. Notably, all top 5 most extreme individual records are wet events, suggesting the most dramatic deviations tend to be excess rainfall rather than drought.

The Pearson correlation matrix for all 12 monthly rainfall columns has been computed across 4,116 records from 36 subdivisions (1901–2015). Two visualizations were generated: a full 12×12 heatmap with annotated correlation values, and a bar chart highlighting the 10 month pairs with correlation 0.5. The strongest positive correlation is between June and July (r = 0.742), reflecting the core monsoon season. The weakest/most negative relationship is between January and July (r = -0.052), showing near-zero association between peak winter and peak monsoon months. All 10 significant pairs are positively correlated — no strong negative correlations exist — indicating that months with high rainfall tend to cluster together rather than offset each other.

The analysis successfully grouped 115 years of rainfall data (1901–2015) into four periods and calculated average monthly rainfall for each. A grouped line chart and supporting tables were generated to visualize the seasonal shifts. Across all four periods, the monsoon season (June–September) dominates rainfall, with July being the wettest month in every period. The earliest period (1901–1928) shows July averaging 341.6 mm, while the latest (1987–2015) shows a slight decline to 335.3 mm. January and February show modest decreases in the latest period, while March shows a slight increase. Overall, the seasonal pattern has remained relatively stable, but subtle shifts are visible — particularly a general softening of peak monsoon intensity in the most recent decades.

The analysis successfully calculated average seasonal rainfall for all Indian subdivisions across four seasons and produced two grouped horizontal bar charts plus detailed ranking tables. The charts compare Winter (Jan-Feb), Pre-Monsoon (Mar-May), Monsoon (Jun-Sep), and Post-Monsoon (Oct-Dec) rainfall side by side for the top-performing subdivisions. The first chart shows all top performers together, while the second chart displays separate top-10 rankings per season.