Anatomizing spatiotemporal LULC changes and anthropogenic drivers of forest loss in Eastern Assam of India

Technical Summary: Anatomizing spatiotemporal LULC changes and anthropogenic drivers of forest loss in Eastern Assam of India

Problem Statement
Rapid Land Use Land Cover (LULC) change and forest loss constitute critical environmental challenges, particularly in regions undergoing intense anthropogenic pressure. The Dibrugarh district in Eastern Assam, India—renowned as the "Tea City of India" and recently designated as the state's second capital—exhibits significant LULC transitions. Despite the district's known rapid urbanization and infrastructural development, there is a scarcity of empirical studies quantifying forest cover loss and identifying the specific anthropogenic drivers behind these transformations. Existing literature often addresses urban heat islands or general vegetation decline without a comprehensive, quantitative assessment of the drivers linking population dynamics, agricultural expansion (specifically tea), and urban growth to forest degradation. This study aims to fill these research gaps by analyzing spatiotemporal LULC dynamics and quantifying forest loss from 2000 to 2023.

Methodology
The study employs a mixed-methods approach combining geospatial analysis with socio-economic field investigations.

• Data Sources: Multi-temporal satellite imagery was utilized, specifically Landsat TM (2000) with 30m resolution and Sentinel-2 (2023) with 10m resolution, sourced from the USGS EarthExplorer archive. Ancillary data included high-resolution Google Earth Pro imagery for ground sample points (GSP), government statistics, and field observations.
• Classification Scheme: Eleven distinct LULC classes were defined based on literature review and local knowledge:
  1. Agricultural Land (Kharif crop, Rabi crop, Two-crop area)
  2. Agricultural Plantation (Tea Garden)
  3. Built-up (Urban)
  4. Forest (Dense Evergreen/Semi-evergreen, Open Evergreen/Semi-evergreen, Scrub Forest)
  5. Agri-plantation/Settlement
  6. Water Bodies
  7. River Sand
• Analytical Techniques:
  • Pre-processing: Radiometric calibration, geometric registration, and cloud/shadow masking were applied to correct distortions.
  • Classification: Supervised classification was performed using training samples derived from high-resolution imagery and field data.
  • Change Detection: Post-classification comparison was used to generate class-to-class transition matrices and calculate Net Change (NC) and Annual Rate of Change (AR) using standard formulas.
  • Accuracy Assessment: Reliability was evaluated using Producer's Accuracy, User's Accuracy, Overall Accuracy, and Kappa Statistics based on 60 ground sample points.
  • Driver Analysis: Anthropogenic drivers were identified through spatial overlay analysis (correlating forest loss with urban/agricultural expansion) and qualitative data from key informant interviews, focus group discussions, and published statistics.

Key Results
The study period (2000–2023) reveals significant landscape transformations in the Dibrugarh district:

• Classification Accuracy: The classified maps demonstrated high reliability with an Overall Accuracy of 96% and a Kappa coefficient of 0.9554. Most classes achieved 100% user accuracy, with the exception of Rabi crop agriculture (77.78%).
• LULC Dynamics:
  • Forest Loss: Total forest cover (combining dense, open, and scrub) declined from 11.86% (401.09 sq. km) in 2000 to 11.05% (373.90 sq. km) in 2023. Specifically, dense and open evergreen/semi-evergreen forests decreased by 30.12 sq. km and 17.25 sq. km, respectively.
  • Urban Expansion: Built-up areas increased from 0.96% (32.42 sq. km) to 1.26% (42.47 sq. km), representing a net gain of 10.05 sq. km. Growth was concentrated in Dibrugarh City, Duliajan, and Namrup.
  • Agricultural and Tea Expansion: Total agricultural land increased from 46.87% to 47.35%. Tea plantation areas, a dominant land use, rose from 15.84% (535.81 sq. km) to 16.48% (557.24 sq. km), a net increase of 21.43 sq. km.
  • Other Changes: Water bodies increased slightly (18.12% to 18.31%), likely due to riverbank erosion and capture, while river sand areas decreased by 15.7 sq. km, transforming partly into scrub forest.
• Annual Rate of Change: The district experienced an annual forest loss rate of approximately 0.81% (net), with tea plantation expansion occurring at an annual rate of 0.93 sq. km.

Anthropogenic Drivers Identified
The study identifies a hierarchy of drivers responsible for forest loss:

1. Primary Drivers:
   • Tea Plantation Expansion: The conversion of forest land and existing cropland into tea gardens is a major driver, with 29,771 registered small tea growers contributing to this trend.
   • Urban and Industrial Growth: Rapid expansion of settlements in Dibrugarh, Duliajan (oil production), and Namrup (petrochemicals) necessitated land clearing for infrastructure and housing.
   • Agricultural Encroachment: General expansion of agricultural land to meet food demands.
2. Underlying Drivers:
   • Population Explosion: The district's population grew significantly (from ~1.55 lakh in 1901 to ~13.26 lakh in 2011), driving demand for shelter, food, and employment.
   • Limited Livelihood Sources: Dependence on forest resources (timber, fuel wood, medicinal plants) due to limited alternative income.
   • Resettlement: Displacement of flood and erosion-affected populations from the Brahmaputra riverbanks to forest peripheries.
   • Governance and Awareness: Weak governance, lack of environmental awareness, and insufficient implementation of land-use policies.

Significance and Claims
The paper claims that its primary contribution is providing the first empirical, quantitative assessment of forest loss drivers in the Dibrugarh district, addressing a specific gap in existing literature which often lacks driver analysis. By integrating geospatial quantification with socio-economic field data, the study establishes a clear correlation between the district's development trajectory (urbanization, tea cultivation, industrialization) and the degradation of its forest cover.

The authors conclude that the rapid transformation of the Dibrugarh landscape necessitates a shift toward consolidated town planning, the strict implementation of land-use and forest policies, and enhanced forest restoration efforts. They emphasize that without strong governance and grassroots environmental awareness, the current trend of forest loss will continue to intensify, threatening the region's ecological resilience and biodiversity. The study serves as a baseline for effective land management and sustainable economic planning in the region.