Investigating climate and land use change impacts on design flood estimation over Indian tropical catchments

Abstract

Land use and climate change studies have emerged as a critical component of current natural resource management and environmental monitoring strategies. Remote sensing and geographic information systems (GIS) have proven to be instrumental in assessing and analysing changes in land use and land cover (LULC) and understanding the climate dynamics. In this study, a decadal analysis of annual maximum rainfall, LULC changes, and in turn, design runoff, is carried out to investigate the impact of the above factors on extreme events in the tropical basins of India. To this end, daily rainfall data from the year 1980 to 2019, LULC maps of 1985, 1995, 2005, and 2015 for four catchments of Mahanadi Basin and six catchments of Godavari Basin are utilized to estimate 50-year, 100-year and 200-year design rainfall, and in turn, design runoff, from four different decades, viz, 1980–89, 1990–99, 2000–09 and 2010–19. The design rainfall is estimated after fitting suitable distributions on the respective decadal rainfall series while the design runoff is estimated using the popular Natural Resources Conservation Service-Curve Number (NRCS-CN) method. Results showed that the decadal mean of annual maximum rainfall series increased from 1980–89 to 1990–99 and from 1990–99 to 2000–09 in seven out of ten catchments but declined in most catchments from the period 2000–09 to 2010–19, which indicates the dynamic nature of rainfall patterns over the tropical basins and highlights the importance of considering climate dynamics for hydrologic design purposes. Also, an increase in CN values from 1985 to 2015 in most of the catchments is mainly due to increased urbanization and reduced forest lands. This indicates intensification of runoff potential, which may lead to increased flood risk, soil erosion, and water quality degradation. The inferences from the study will aid policymakers in designing appropriate policies like sustainable land use practices, rainwater harvesting, and afforestation to ensure the well-being of communities in the face of changing climate and land use.