This dataset was collected during field-based monitoring in the Kali Gandaki River catchment be-tween the years 2013 and 2017. The monitoring aims to understand the hydrological fluxes and feedback with weathering and erosion processes across the mountain range. The Kali Gandaki River sources its water in the North and traverses through the Himalayan Mountain Range, along a north-south transect. The field-based monitoring comprises targeted field campaigns to revisit locations at different years and seasons in order to constrain the annual and intra-annual variability.

This is complemented by permanent installations and routine river and rain sampling at two loca-tions, Lete and Purtighat. Lete is situated at the orographic barrier, at ~2500 m asl. and the up-stream catchment integrates the northern part of the Himalayan Range as well as some of the southern edge of the Tibetan Plateau. Purtighat is located further south and integrates the north-ern part as well as south-facing flanks of the Higher and Lower Himalayas. At both locations, auto-mated river monitoring is installed as well as a trained station ward for daily routine sampling. At Lete, rainfall samples are obtained on a daily resolution during the monsoon. This sampling was not feasible at Purtighat for logistic reasons. Instead, rain was sampled daily in Kathmandu.

This dataset contains five tables of stable water isotope analysis. One containing grab samples from the Kali Gandaki river in its vicinities and 4 tables with time series sampling from the Kali Gandaki River and from rainfall.

Grab sampling: Grab samples were obtained from all hydrological compartments (spring, river, tributary, snow, ice, and rain) in the Kali Gandaki catchment and its surroundings. The samples were taken during repeated field campaigns covering all seasons during the years 2013 to 2016. Samples were filtered in the field and stored 30ml Nalgene bottles. Snow and ice samples were melted at ambient temperatures before filtering and storing.

Stable water isotope time series of rainfall: Samples were collected by a local, trained station ward, during rainfall periods 2016 and 2017. Samples were recuperated always between 8 and 9 o’clock local time (GMT+5:45) if sufficient rainwater was accumulated. At both locations Lete and Kathmandu we used Palmex Rain Sampler RS1 (Gröning et al., 2012). The following isotope ratios, expressed as δ values with VSMOW as a standard, were measured: δ18O and δ2H.

Stable water isotope time series of river water: Samples were collected by a local, trained station ward, between the 10th of June 2015 and October 2018 daily during the monsoon (June to Septem-ber) and bi-weekly (October to May) during the dry season. Sampling time was always between 8 and 9 o’clock local time (GMT+5:45). Samples were typically analyzed for stable water isotopic com-position with weekly resolution. The following isotope ratios, expressed as δ values with VSMOW as a standard, were measured: δ18O and δ2H.

River time series samples in Purtighat were first obtained at Mirmi Hydropower Intake, upstream of the confluence with Andhi Khola from a suspension bridge in the middle of the river. The sampling location was later moved upstream to Purthighat village, roughly 10km upstream with no major tributary in between.