Reply on CC1

Abstract

<strong class="journal-contentHeaderColor">Abstract.</strong> Climate change, land use land cover (LULC), population, industries, and sewage treatment are factors that can strongly influence river water quality. This paper uses a coupled hydrological-water quality simulation model to assess the influence of each of these drivers on the most polluted river stretch of the Ganga River. The water quality model QUAL2K is driven by these five factors to assess their influence on nine water quality parameters, namely dissolved oxygen (DO), biochemical oxygen demand (BOD), faecal coliform, ammonia, nitrate, total nitrogen, organic-, inorganic-, and total phosphorous. Climate change projections are taken from CMIP5 RCP 4.5 and RCP 8.5 scenarios. Five socio-environmental scenarios which consider sewer network, sewage treatment capacity, level of treatment at sewage treatment plants (STPs), and the type of sewage (domestic or mixed) are also considered. The water quality is simulated using a coupled HEC-HMS-QUAL2K framework. The non-point source pollution is quantified using the export coefficient method, where the export of pollutants from all land use classes are considered. The climate change effect is found to have a larger effect on Kanpur water quality than other drivers, with a percentage contribution of above 70 % because of the large sensitivity of water quality parameters to the amount of streamflow. Climate change projections combined with socio-environmental scenarios imply that the large increase in pollution due to climate change, LULC, industry, and population growth cannot be controlled by the current treatment proposals for 2050. However, providing adequate STPs to meet the population of 2050, and allowing only domestic sewage to reach STPs can help to achieve the objective of the Ganga Action Plan in the mid-21st century.