Impact of 2018 Kerala Floods on Soil Erosion: Need for Post-Disaster Soil Management

Abstract

Extreme precipitation events lead to flash floods, which can trigger soil erosion and landslides. While damages to infrastructure and livelihoods are rapidly assessed on economic terms, damages to natural resources are not estimated due to limited observation record. This study conducted an analysis using remote sensing data to estimate changes in soil erosion rates before, during and after the Kerala 2018 floods, based on the Universal Soil Loss Equation (USLE). The USLE was driven by multiple data including: in situ rainfall data from Indian Meteorological Department (to estimate rainfall erosive factor), soil maps prepared by Food and Agriculture Organization (to estimate the soil erodibility factor from the properties of soil that consists of the percentage of clay, loam and silt), digital elevation model (to estimate topographic slope and length) from Shuttle Radar Topography Mission and multispectral imagery (to estimate cover management factor and conservation practice factor) from Landsat-8 satellite. Data from these sources were analysed using a Geographic Information System (GIS) platform. Results indicate a state-wise average increase of 80% (31–56 metric tons ha−1 year−1) in soil erosion rate during the floods. Of the districts, Idukki showed the highest increase, of 220% and more susceptibility to soil erosion, which is in comparison with government survey records. Results show that the floods and associated erosion were not only due to the rainfall event but also due to the rapid change in land use and land cover, from natural to human settlements. Therefore, government agencies need to protect land cover and reduce unsustainable development in ecologically sensitive environments, which if managed properly can act as a buffer for soil erosion extremes in Kerala.