Numerical modeling for the temporal variations of the water interchange between groundwater and surface water in a regional great lake (Poyang Lake, China)

•Variability of GW-SW exchange was dominantly affected by lake level and rainfall.•Monthly groundwater discharge is inversely related to lake level and rainfall.•GW-SW exchange increases while net groundwater discharge decreases in rainy year.•Groundwater is more likely to discharge into rivers during a rainy year.