## 2 Materials and Methods
### Data  
#### 2.2.1 Satellite Precipitation Dataset  
The GPM Mission uses an international satellite network that provides a new generation of global rainfall and snowfall observations based on the TRMM. The core observation satellite, launched by the National Aeronautics and Space Administration (NASA) and the Japan Aerospace Exploration Agency (JAXA) in February 2014, carried the GPM Microwave Imager (GMI) and the Dual Frequency Precipitation Radar (DPR) [89]. Compared to TRMM data, it combined GPM, multiple satellite precipitation datasets, and microwave-calibrated infrared (IR) satellite estimates, and improved the ability to measure light rain and solid precipitation, resulting in higher-quality precipitation data. This study adopted the final half-hourly scale of GPM-3 IMERGM precipitation data from 2010-2014 [90], covering a global scale with a spatial resolution of 0.1\({}^{\circ}\)\(\times\) 0.1\({}^{\circ}\). The dataset can be obtained from [[https://pmm.nasa.gov/data-access/downloads/gpm](https://pmm.nasa.gov/data-access/downloads/gpm)]([https://pmm.nasa.gov/data-access/downloads/gpm](https://pmm.nasa.gov/data-access/downloads/gpm)) (accessed on 26 August 2022).  
CMORPH is a global satellite precipitation data product developed by the CPC as part of the National Oceanic and Atmospheric Administration (NOAA) that estimates precipitation using microwave data from the U.S. Defense Weather Satellite, the U.S. Marine Weather Service, and the TRMM Microwave Radiometer. The coverage ranged from 60\({}^{\circ}\) S to 60\({}^{\circ}\) N, 180\({}^{\circ}\) E-180\({}^{\circ}\) W [13]. Currently, CMORPH offers two precipitation data products--one with 30 min and 8 km \(\times\) 8 km resolutions, and the other with 3 h and 0.25\({}^{\circ}\)\(\times\) 0.25\({}^{\circ}\) resolutions. In this paper, the 3 h scale, 0.25\({}^{\circ}\) CMORPH dataset in 2010-2014 was employed and data were accumulated as part of a daily scale. The information has been made publicly available at [[https://www.cpc.ncep.noaa.gov](https://www.cpc.ncep.noaa.gov)]([https://www.cpc.ncep.noaa.gov](https://www.cpc.ncep.noaa.gov)) (accessed on 26 August 2022).  
ERA5 is the latest fifth-generation global atmospheric reanalysis dataset of the ECMWF. It provided dozens of commonly used land-surface and atmospheric variables. It adopts data assimilation technology and integrates a large number of ground observations, atmospheric sounding data and remote sensing data [14]. In this paper, the hourly ERA5-land  
Figure 1: The geographical location, topographical overview, major rivers and lakes, and distribution of meteorological stations used in this study in the Three River Headwaters region.  
precipitation data in 2010 were selected with a spatial resolution of 0.1\({}^{\circ}\)\(\times\) 0.1\({}^{\circ}\) and accumulated as daily scale data. The dataset is publicly available at [[https://cds.climate.copernicus.eu](https://cds.climate.copernicus.eu)]([https://cds.climate.copernicus.eu](https://cds.climate.copernicus.eu)) (accessed on 26 August 2022).  
The cloud attribute data were obtained from the Moderate Resolution Image Spectrometer (MODIS) cloud product, MOD06/MYD06, developed by NASA, with a spatial resolution of 1 to 5 km, and can provide 1-4 images per day. The products (MOD06 and MYD06 for Terra and Aqua MODIS, respectively) combine infrared and visible light technologies to enable the pixel-level retrieval of cloud optical and physical properties based on unique spectral and spatial capabilities [72]. In this study, daily cloud product data with a spatial resolution of 1 km from the period of 2010-2014 were selected and accumulated on a daily scale. CER, COT, and CWP are auxiliary variables in the cloud product. The dataset is publicly accessible at [[https://ladsweb.modaps.eosdis.nasa.gov](https://ladsweb.modaps.eosdis.nasa.gov)]([https://ladsweb.modaps.eosdis.nasa.gov](https://ladsweb.modaps.eosdis.nasa.gov)) (accessed on 26 August 2022).