The present study examines the impact of the environmental moisture structure in the lower troposphere (below 2 km above sea level, ASL) on the precipitation development, observed in southern France during intensive observation period 13 of the first Special Observation Period of the Hydrological cycle in the Mediterranean Experiment (HyMeX SOP-1), through a series of sensitivity experiments using the non-hydrostatic numerical model Meso-NH. The control simulation (CNTL) and all the other 12 sensitivity experiments examined in this study succeed in reproducing a heavy precipitation event (HPE) in the coastal mountainous region of Var in south-eastern France as observed. The sensitivity experiments are designed to investigate the response of the variability of the water vapour content upstream in the moist marine atmospheric boundary layer (MABL) and the drier air above on the HPE. The comparisons between CNTL and the 12 sensitivity experiments show how the life cycle of precipitation associated with the HPE, but also the upstream flow (over the sea), is modified, even for moisture contents changes of only 1 g kg −1 below 2 km ASL. Within the low-level wind convergence between southerlies and south-westerlies, a small increase of moisture content in the MABL prolongs moderate precipitation (≥ 5 mm in 15 min) and enlarges the area of weak precipitation (≥ 1 mm in 15 min). The moistening in the 1–2 km ASL layer, just above the MABL, prolongs the duration of moderate precipitation, for a similar total precipitation amount as in CNTL. The drier MABL and 1–2 km ASL layer shorten both the life-time of precipitation and the total precipitation amount with respect to CNTL. We also found that the moisture in the MABL has a stronger impact on producing enhanced precipitation (both in terms of amount and intensity) than the moisture just above (1–2 km ASL). Also it is worth noting that adding moisture in the MABL does not necessarily lead to enhanced precipitation amount. At the same time, the duration of moderate precipitation increases with increasing moisture as does the area covered by weak precipitations, while the area covered by the intense precipitation (≥ 30 mm) decreases. Despite a simplified moisture-profile modification approach, this study suggests that moisture structure in lower troposphere is a key for accurate prediction at short-term range of the timing and location of precipitation in the coastal mountainous region in southern France.