This dataset contains 74 weekly/bi-weekly precipitation sum samples recorded at An Long, in the northern part of the Mekong Delta (Plain of Reed, Dong Thap province, Vietnam). The data were collected as part of a study analyzing the influence of local and regional climatic factors on the stable isotopic composition of rainfall in the Mekong delta as part of the Asian monsoon region (Le Duy et al., 2017)..

Samples were taken on a weekly basis between June 2014 and May 2015 and twice a week between June 2015 and December 2015. The rain collector was a dip-in sampler type as described in the guidelines of the IAEA technical procedure for precipitation sampling (IAEA, 2014). It consists of a 5 liters accumulation glass bottle fitted with a vertical 14 cm diameter plastic funnel that reaches almost to the bottom to prevent evaporative losses, and a pressure equilibration plastic tube (2 mm in diameter and 15 m in length) to minimize evaporation out of the collection device. All collected samples were stored in 30 mL plastic sample bottles with tight screw caps to avoid evaporation effects. Between collection and laboratory analysis, the samples were stored in the dark.

All stable isotope samples were analyzed at the laboratory of the Alfred-Wegener-Institute (AWI) in Potsdam, Germany. The measurements were performed with a Finnigan MAT Delta-S mass spectrometer using equilibration techniques to determine the ratio of stable oxygen (18O/16O) and hydrogen (2H/1H) isotopes. Analytical results were reported as δ2H and δ18O (‰, relative to Vienna Standard Mean Ocean Water - VSMOW) with internal 1σ errors of better than 0.8‰ and 0.1‰ for δ2H and δ18O, respectively. The deuterium excess (d-excess) was calculated with the equation of Dansgaard (1964):

d-excess = δ2H - 8*δ18O