Bihar, located in the eastern part of India, is endowed with a diverse climatic regime heavily influenced by the southwest monsoon. The state, primarily agrarian, relies significantly on rainfall for its agriculture, water resources, and socio-economic activities. This article provides a detailed analysis of the rainfall distribution across Bihar, examining its spatial and temporal patterns, factors influencing rainfall variability, and its implications for agriculture, water management, and disaster mitigation.
Geographic and Climatic Overview of Bihar
Bihar spans a geographical area of 94,163 square kilometers and is bordered by Nepal to the north and other Indian states like Uttar Pradesh, Jharkhand, and West Bengal. The state is primarily a part of the Indo-Gangetic Plain, with the Ganges River serving as its lifeline. Bihars climate is characterized by:
Subtropical Monsoon Climate: High temperatures and humidity dominate, especially during the monsoon season.
Three Distinct Seasons:
Summer (March to May)
Monsoon (June to September)
Winter (November to February)
Rainfall Patterns in Bihar
1. Annual Rainfall Distribution
Average Annual Rainfall: Bihar receives an average annual rainfall of approximately 1,200 mm, with significant regional variations.
North Bihar: This region, closer to the foothills of the Himalayas, receives heavier rainfall, averaging 1,3001,500 mm annually.
South Bihar: Rainfall in this region is relatively lower, averaging 1,0001,200 mm annually.
2. Seasonal Rainfall
Southwest Monsoon (JuneSeptember): Accounts for about 85% of the annual rainfall.
Post-Monsoon Period (OctoberNovember): Contributes approximately 10% of the annual rainfall.
Winter and Summer Seasons: Receive scanty rainfall, primarily from western disturbances and pre-monsoon thunderstorms.
3. Spatial Variability
Rainfall in Bihar shows significant spatial variability, with the northern districts like West Champaran, Sitamarhi, and Madhubani experiencing heavier rainfall compared to the southern districts like Gaya, Nalanda, and Jehanabad.
4. Temporal Variability
The onset of the monsoon typically occurs in mid-June, with rainfall peaking in July and August.
Temporal variability is marked by periods of excess rainfall leading to floods and periods of deficit rainfall causing drought-like conditions.
Factors Influencing Rainfall in Bihar
Southwest Monsoon Winds: The primary source of rainfall, influenced by low-pressure systems in the Bay of Bengal.
Topography: The Himalayan foothills to the north enhance orographic rainfall.
Western Disturbances: Occasionally bring rainfall during the winter months.
Cyclonic Systems: Cyclones originating in the Bay of Bengal impact rainfall during the post-monsoon season.
Climate Change: Recent trends indicate an increase in the frequency of extreme rainfall events.
Implications of Rainfall Distribution
1. Agriculture
Bihars agriculture is highly dependent on monsoonal rainfall.
Uneven distribution often leads to challenges:
Excess rainfall in the north causes floods, damaging crops.
Deficient rainfall in the south leads to water scarcity, affecting paddy and wheat cultivation.
2. Water Resources
Rainfall replenishes surface and groundwater resources.
Over-dependence on monsoon rains for irrigation has highlighted the need for improved water management strategies.
3. Floods
The northern regions, particularly along the Kosi, Gandak, and Bagmati rivers, are prone to recurrent flooding during heavy monsoonal rains.
Floods disrupt livelihoods, damage infrastructure, and lead to significant economic losses.
4. Droughts
Southern Bihar occasionally faces drought conditions due to erratic rainfall.
Drought adversely affects agriculture and drinking water supply.
Recent Trends and Challenges
Erratic Rainfall Patterns: The past two decades have witnessed irregular rainfall patterns, attributed to climate change.
Increasing Intensity of Rainfall Events: Instances of intense rainfall over short periods have increased, causing flash floods.
Delayed Onset and Early Withdrawal of Monsoons: These trends disrupt the agricultural calendar.
Rainfall Deficiency: Certain districts have reported a decline in average annual rainfall, necessitating adaptation measures.
Measures for Sustainable Rainfall Management
1. Flood Management
Strengthening embankments along rivers.
Implementation of early warning systems for flood-prone areas.
Integrated watershed management to reduce surface runoff.
2. Drought Mitigation
Promotion of drought-resistant crop varieties.
Expansion of irrigation infrastructure to reduce dependence on monsoon rains.
3. Rainwater Harvesting
Encouraging rainwater harvesting to recharge groundwater levels.
Construction of check dams and percolation tanks.
4. Policy Interventions
Development of a comprehensive state action plan for climate change.
Enhanced focus on disaster preparedness and mitigation.