Integrated Assessment of Land Use Change and Groundwater Trends along the Coastal Stretch of Bharathapuzha River Basin, Kerala, India

Abstract

Groundwater is an essential freshwater supply for the daily activities of people especially for those residing in the coastal areas. Land use change, sea-water intrusion and rapid urbanization have a significant impact on aquifer behavior in these areas. Therefore, this study analyses long-term changes in land use and groundwater levels in the Tavanur-Ponnani region of the Bharathapuzha River Basin, Kerala. Multi-temporal Landsat satellite data were used to assess land use and land cover changes using the spectral indices such as Normalized Difference Vegetation Index (NDVI) and Normalized Difference Built-up Index (NDBI) for the years 2014, 2017, 2021 and 2025. Groundwater level data from eighteen observation wells were analyzed for pre-monsoon and post-monsoon seasons from 2014 to October 2025 using the Mann–Kendall test and Sen’s slope estimator. The results show a continuous decline in vegetation cover, with vegetated area reducing from 32.1 km² in 2014 to 24.9 km² in 2025, while built-up land increased from 2.2 km² to 6.91 km² (approximately 214% increase) during the same period. Mean NDVI values decreased from 0.218 in 2014 to 0.19 in 2025, whereas mean NDBI values increased from −0.12 to −0.07, indicating rapid urbanization in the area. Groundwater level analysis revealed a statistically significant increasing trend in depth to groundwater in both pre-monsoon (up to 3.38 m rise in Well No.1) and post-monsoon seasons (up to 2.5 m rise in Well No.2) across all observation wells. Correlation analysis showed a strong negative relationship between NDVI and groundwater depth (r = −0.82 in 2025) and a strong positive relationship between NDBI and groundwater depth (r = 0.80 in 2025), confirming the influence of land use changes on groundwater. Therefore, the continuous loss in vegetation and increase in built-up areas are strongly associated with long-term groundwater decline in the region, emphasizing the need for sustainable land use planning and groundwater management in coastal river basins of Bharathapuzha.