Strategic Analysis of Water Resources in the Ganga Basin, India

Abstract

GangaWIS is a comprehensive tool that integrates various hydrological components of the Ganga River basin and supports the policymakers in analyzing the impact of future developments and climate change scenarios in combination with multiple interventions. It describes the functioning of the water system of the Ganga basin within India concerning rainfall-runoff, surface water and groundwater flow, storage and diversion of water for various purposes, water quality, and ecology. The hydrology and the rainfall-runoff process has been divided into two different models: SPHY and WFlow. They are both fully distributed models working on a grid of square cells. SPHY is used to describe the hydrological process in the mountainous areas in the Himalaya. The rainfall-runoff processes for the non-mountainous part of the Ganga Basin are simulated with the WFlow model. The river discharges calculated by the SPHY model for the Himalayas are used as upstream boundaries for the WFlow model. The water resources model RIBASIM describes the management and use of water. Its hydrological input is derived from the river discharges calculated by WFlow. RIBASIM uses a schematization of links and nodes to describe the flow of water in the rivers, the storage in reservoirs, the diversion into canals, and the use and return flow by different functions. Furthermore, return flows can be divided over rivers, canals, and Groundwater. The information on discharges and water levels calculated by RIBASIM are used by the groundwater model to describe the interaction between surface and Groundwater. Groundwater movement is simulated with iMOD, the Deltares extension of the well-known MODFLOW code for solving the groundwater flow equation. iMOD uses the same calculation grid as Wflow but is only applied to the alluvial fraction of the basin. The Ganga river basin model is capable of assessing the impacts of future developments/climate change scenarios and various interventions/measures at basin scale by comparison of simulation results. Using this model, different scenarios are developed: present, pristine, and 2040 with three different possible climate change developments: no climate change, climate change following the RCP4.5 scenario, and climate change following the RCP8.5 scenario. The scenarios used model parameters such as precipitation, temperature, land use, infrastructure, population, industry, and agriculture to develop a corresponding model output of the river flow, water quality, and groundwater levels. The dashboard of GangaWIS depicts the various indicators to assess the impact of the different scenarios, such as state of groundwater development, lowest discharge, volume of water stored in reservoirs, agricultural crop production, deficit irrigation, and drinking water, surface water quality index, the amount of Groundwater extracted and ecological, hydrological and socio-economic status. GangaWIS can be used to analyze and visualize various data (temporal/spatial) and model results, and it can provide relevant measured and modeled information to multiple users such as data managers, modelers, policymakers, and decisionmakers.