Climate change and gullies (and ditches) on peatlands are well known factors altering peat hydrology. Yet, exactly how this alteration emerges from interaction of these factors with groundwater dynamics is still not fully understood. In this study, we tackled this issue by coupling field measurement with model simulation using Visual MODFLOW. Groundwater processes and the associated water budget during five months of the wet season, 2017 were examined in the Zoige peatland, located on the northeastern side of Qinghai-Tibet Plateau, China with elevations of 3400–3900 m. Simulations were performed for a peatland area of 3.89 × 104 m2 and three sub-zones within it representing peatland with no gullies (NG), a deep gully cutting through the peat layer (CT), and a shallow gully whose bed is within the peat layer (NCT). Model input parameters were calibrated and validated using the field-measured data. Modeling outcomes led to water budget showing relative contributions of main hydrological pathways (MHPs) (i.e., precipitation (P), evapotranspiration (ET), gully, groundwater flow, and boundary) to changes of water storage in peats (ΔS). Although these MHPs varied differently during rain and inter-rain periods, ΔS values were mainly controlled by the oscillated trend of the difference between P and ET. Variations of MHPs caused by NCT and CT were secondary to those due to those of P and ET during the wet season referred to as the short-term climate change. Vertical groundwater (VGW) flows were strongly correlated with water table (WT) levels in both rain and inter-rain periods, but their directions had different patterns in the two periods. Horizontal groundwater (HGW) flows tended to move into the deep (CT) gully, while move from the shallow (NCT) gully to the neighbor peats during both periods. Since HGW flows were about ten times greater than VGW ones, their effect on ΔS was significant during the long dry season. This would lead to continuous loss of groundwater stored in peats, demonstrating the coupled effect of long-term climate change and gullies on ΔS. These findings underline the necessity of controlling gully development and avoiding ditch excavation in future Zoige peatland management practices.
