Long term evolution of groundwater / surface water interactions in the Indus and Upper Ganges

Northern India and Pakistan face some of the world’s most challenging surface water and groundwater management issues over the coming decades. High groundwater abstraction, widespread canal irrigation, increases in glacier melt and changes to rainfall all impact on the dynamics of surface water/groundwater interactions in the Indus Basin and Upper Ganges. Studies using newly available data from long term hydrographs, high frequency stable isotope sampling and campaign sampling for groundwater residence time indicators are shedding light on the complex interactions between groundwater, surface water and rainfall. Interactions vary spatially: (1) with distance down catchment, related to the prevailing rainfall gradient; and (2) with position in the canal command, both distance from barrage and distance from feeder canals. Interactions are also observed to vary with time due to: (1) the historical evolution of the canal network; (2) patterns in precipitation over the past 120 years; (3) changes in river flow due to glacial melting; and (4) increased pumping, which has also led to increased capture of surface water. Only by understanding and quantifying the different processes affecting groundwater / surface water coupling in the Indus and Upper Ganges is it possibly to forecast future groundwater storage changes.