## 2 Materials and Methods
### Sampling  
During two cold periods from November to mid-March (winter 2019-2020 and 2020-2021), snowfalls and snow cover samples were recovered to study their water isotopic (\(\delta\)D and \(\delta^{18}\)O) composition. Sampling was carried out in the catchment area of the Ob River from Biysk city to Kamen-na-Obi city (Figure 1b), while the main work and experiments were carried out in the center part of this area--in and around Barnaul city (Figure 1c). The sampling scheme was as follows:  
1. Samples of snow event-based precipitation during the cold period were collected immediately after their fallout on experimental site III, located on the roof of the building of the Institute for Water and Environmental Problems of the Siberian Branch of the Russian Academy of Sciences (IWEP SB RAS) at the height of 25 m from the earth's surface (Figure 1c). Snowfalls were collected in internal removable high-density polyethylene bags attached inside the barrel, equipped with blowing protection (Supplementary, Figure S1a). A total of 97 event-based snowfalls samples were collected during two cold periods.
2. The bulk snowpack samples were taken during the period of maximum snow accumulation (at the beginning of March) at the sites of the network (Figure 1b). All sites were located in a field on a flat territory free from trees and bushes. Sampling was performed using the envelope method (10 \(\times\) 10 m). The composite sample consisted of 5 snowpits collected with a plastic pipe (4.5 cm inner diameter). In March 2020, the bottom layers of snowpack samples (thickness \(\sim\)5-7 cm) were taken in addition to the bulk ones. In total, 111 snow samples were taken and analyzed.
3. The following experiments were carried out on three experimental sites (Figure 1c, sites I, II, III) in 2019-2021:  
Experiment No. 1. At the beginning of winter 2019-2020, the 1.5 m high plastic barrel was installed on the roof of the IWEP SB RAS building (site III) in addition to sampling the individual snowfalls. In this barrel, after each heavy snowfall, a layer of fallen snow was separated from subsequent precipitation with a plastic disk. The 11 layers of snow obtained in this way were removed at the end of the winter (Supplementary, Figure S1b) and analyzed separately.  
Experiment No. 2. In the winter of 2020-2021, two barrels equipped with wind protection devices were installed on the ground of each of the two sites (Figure 1c, sites I, II). One barrel was intended to sample integral snow precipitation, the second one for a separate sampling of snow layers (similar to experiment No. 1). The barrels' contents were removed for isotopic analysis at the end of winter. Moreover, we sampled two snowpack  
Figure 1: (**a**) Location of the studied area; (**b**) snowpack sampling network. The sampling points are the numbers 1–14; (**c**) location sites for conducting experiments (I, II) and atmospheric precipitation sampling (III).  
pits (bulk and layer-by-layer) on the earth's surface near the experimental barrels at the end of winter. Layer-by-layer sampling was carried out with a step as equal as possible to the layers of snow in the corresponding second barrel. For this, we selected nine horizontal layers in each pit (equal to the number of layers in each barrel) and determined their density. Then, we took samples of the pit layers, the height of which in water equivalents was equal to the corresponding layers in the barrel.  
After collection, samples of snow (precipitation and snowpack) were placed in clean tight-closing plastic bags and stored frozen until analysis.