## 3 Materials and Methods
### Sampling and Testing  
#### 3.2.1 Sampling  
The water samples described in this paper include information about the soil moisture of profile 3E, rainfall from the field test, and the groundwater of SYC-01 from the field test. We also took soil samples for water content testing in a vertical direction inside the field test site. We put a plastic bucket on the open-air roof of resident's house near the field test site and collect rainfall samples after each rainfall. The resting rainfall in the plastic bucket was all poured out after sampling every time. The rainfall sample was collected into clean PET bottles (their volume is 50 cm\({}^{3}\)) without bubbles after the rain stopped. Then, we sealed the PET bottle with elastic film to ensure that the rainfall sample was isolated from air. All the rainfall samples collected for stable isotopes (D, \({}^{18}\)O) testing were saved at a low temperature, about 3-4 \({}^{\circ}\)C.  
We put down a stainless steel sampler with the function of a water inlet from its bottom into SYC-01 at the depth of 16 m and pulled up a full sampler of groundwater. Then, the groundwater sample was collected from the stainless steel sampler into clean PET bottles (their volume is 50 cm\({}^{3}\)) without bubbles. Finally, we sealed the PET bottles with elastic film to ensure that the rainfall sample was isolated from air. All the groundwater samples collected for stable isotopes (D, \({}^{18}\)O) testing were saved at a low temperature, about 3-4 \({}^{\circ}\)C.  
Figure 1: Monitoring and data collection systems of the field test site. The number “1–8” in the north-eastern part of this figure are the numbers of horizontal holes for instrument installation. The CS257 and CS650 probes were installed inside holes “3–6” at the east direction of WELL 3. Soil moisture samples for stable isotopes (D, \({}^{18}\)O) testing  
It was not easy to collect soil moisture stable isotopes (D, \({}^{18}\)O) test samples. First of all, we used a drilling machine (QY-100L, Jiangsu Wuxi Mineral Exploration Machinery General Factory Ltd., Wuxi, JiangSu, China) to obtain a soil column in the vertical direction inside the field test site. In order to avoid taking contaminated samples, we needed to cut a 2 cm thickness of the soil on the surface part of the soil column away before taking the soil samples. Then, we used glass bottles (their volume is 8 cm\({}^{3}\)) to take clean soil samples from the soil column every 0.1 m from 0 to 14.30 m. The glass bottles full of the soil samples were sealed by elastic film isolated from air and transported to the laboratory at a low temperature, about 3-4 \({}^{\circ}\)C.  
In the laboratory, we put medical-use cotton balls into the sampled glass bottles (their volume is 8 cm\({}^{3}\)) in preparation for soil water extraction. Then, we put the sampled glass bottles (their volume is 8 cm\({}^{3}\)) into an LI-2100 automatic water extraction system (LICA Inc., Beijing, China) for soil water extraction. The LI-2100 automatic water extraction system created a 1500 Pa vacuum environment with the temperature set at 105-110 \({}^{\circ}\)C for 300 min for every soil water extraction process. At the same time, we also used a condensation vapor collection part of the same vacuum environment. The soil moisture extracted by LI-2100 included strongly bound water, weakly bound water, capillary water, and gravity water. We extracted soil moisture samples into new glass bottles (their volume is 2 cm\({}^{3}\)) without bubbles from the soil samples. Then, we sealed each new glass bottle with elastic film to ensure that the water sample was isolated from air. All the soil moisture samples collected for stable isotopes (D, \({}^{18}\)O) testing were saved at a low temperature, about 3-4 \({}^{\circ}\)C.  
Soil samples for soil volume water content testing  
Before taking soil samples, we weighed, recorded, and numbered every standard steel ring knife and every porous aluminum box.