Climate change and anthropogenic stresses on the sediment load variation in the Western Ghat Rivers

Rivers globally experiencing a regime shift in sediment load during the Anthropocene. Substantial alterations in sediment transport patterns were also reported in fluvial systems of Indian Peninsula, attributed mainly to the climate change and human activities. This study focuses on small-sized rivers originating from the Western Ghats, flowing over 50 km and debouching into the Arabian Sea with two major objectives: (i) identifying factors governing temporal changes in sediment load over recent decades, and (ii) to evaluate the potential geomorphic and ecological implications to the fluvial settings. To address these inquiries, hydro-meteorological data (discharge, suspended sediment concentration, and rainfall) from the Central Water Commission (CWC) and the India Meteorological Department (IMD) spanning from the mid-1970s to 2018 were examined. Various statistical methods such as the non-parametric Mann-Kendall test, Pettitt test, and double mass plot were employed to recognize trends, abrupt changes, and the interplay of climate and human activities. Results reveals a temporal variation of sediment load in most studied rivers unfolds in four significant episodes: (i) pre-dam construction before 1985, (ii) a phase marked by an equilibrium between rapid deforestation and dam construction during 1985-1995, (iii) reduced deforestation coupled with swift dam construction from 1995 to 2010, and (iv) a relatively stable period post-dam construction since 2010.   Our findings also show a declining trend in sediment load for all the southern rivers of Kerala. Nevertheless, it was found that Netravati, Chaliyar, Bharathapuzha, and Periyar rivers emerge as the leading contributors of sediment to the Arabian Sea among the 18 rivers studied.  This system response has wider implications, including effective management of water resources, sedimentation control, and understanding the ecological responses within the Western Ghats, influencing both human communities and biodiversity in the region.