Study area and data

2.1 Study area

The YRSR, with a drainage area of ~122,000 km2 accounting for ~15% of the area of the Yellow River basin, is located in the north-east of the Qinghai-Tibetan Plateau (roughly ranging between 95°30′103°30′ E and 32°30′36°20 N). With elevations ranging from 2675 to 6253 m that decreases from the south-west to the north-east (Fig. 1 ). The YRSR belongs to a typical alpine climate (Xu and He, 2006), with intense sunshine and diurnal temperature changes. The rainfall predominately concentrates in the flood season (JuneOctober), accounting for ~75% of the annual precipitation, and the snowfall is primarily concentrated from September to May (Hu et al ., 2011). Precipitation runoff is the predominate runoff pattern in the YRSR, accounting for ~96% of the total runoff (Liu and Chang, 2005).
The YRSR has been selected as the study area duo to three reasons: (1) the YRSR provides fresh water to hundreds of millions of people downstream; (2) less impact of human activities with a total of approximately half a million inhabitants (Yuan et al ., 2015); (3) the YRSR is a sensitive zone in response to climate change (Junlianget al ., 2013).

2.2 Data

2.2.1 Precipitation dataset

Five types of precipitation datasets, namely, the GO, IMERG Final Run V6, TRMM 3B42RTV7, CMADS, and CFSR, were selected for this study (Table 2 ).
The GO was derived from the daily surface meteorological data of the China Meteorological Data Network. There are only 11 in-situ gauged observation stations in the YRSR, and most of them are distributed downstream, and there is only one Maduo station upstream [Fig. 1(c) ].
The TRMM was launched in 1979 by the National Aeronautics and Space Administration (NASA) and the Japanese Aerospace Exploration Agency (JAXA) to provide satellite monitoring of global precipitation. In 2015, the TRMM mission ended, the instruments were shut down, and the spacecraft re-entered the Earth’s atmosphere. In this study, the TRMM 3B42RTV7 daily precipitation product from 1 January 2008 to 31 December 2013 was used. The TRMM 3B42RTV7 precipitation products were generated by using the TRMM TMPA Version 7 algorithm (Huffman et al ., 2010b). To the best of our knowledge, the hydrological evaluation of TRMM 3B42RTV7 daily precipitation product in the YRSR has not yet been reported.
The Global Precipitation Measurement (GPM) was launched in February 2014 as the successor to TRMM providing the next generation of global precipitation products. The IMERG precipitation products were GPM’s level-3 products produced by the IMERG algorithm. According to the timeliness of the various products, they can be divided into three levels: Early-Run, Late-Run, and Final-Run. The Final-Run product was generally considered to be more accurate in terms of its results than the quasi-real-time products (Early and Late Run) (Yang et al ., 2020). In this study, the IMERG Final-Run V6 daily precipitation product from 1 January 2008 to 31 December 2016 was selected, of which the precipitation data from January 2008 to February 2014 were calculated from the original remote sensing image of TMPA by IMERG algorithm. TRMM and IMERG precipitation products are currently two satellite precipitation products that were widely used in hydrological simulations (Duan et al ., 2019a; Nhi et al ., 2018; Yuan et al ., 2018).
The CMADS is a reanalysis dataset established using the China Meteorological Administration atmospheric assimilation system technology and multiple other scientific methods (Meng et al ., 2019). The CMADS was completed over nine years (1 January 2008 to 31 December 2016). The application potential of CMADS in hydrological modeling has been verified in many watersheds in China (Li et al ., 2019; Menget al ., 2019; Zhang et al ., 2020).
The CFSR is a reanalysis dataset developed by the National Centers for Environmental Prediction (NCEP) which was completed over 36 years (1 January 1974 to 31 December 2014) (Sorrel, 2010). CFSR in hydrological modeling is currently one of the most widely used reanalysis datasets with worldwide application (Ruan et al ., 2017; Yang et al ., 2020; Zhu et al ., 2015), owing to advantages such as its large time-scale, high-resolution spatial scale, and convenient data acquisition. CMADS and CFSR were both included on the ArcSWAT official website.

2.2.2 Other data

In addition to precipitation data, the following data are needed for model construction and verification:
(1) Digital Elevation Model (DEM): derived from SRTM_DEM data with a spatial resolution of 90 m provided by Geospatial Data Cloud (http://www.gscloud.cn/);
(2) Land use data: derived from the Chinese Academy of Sciences Resource and Environmental Science Data Center (http://www.resdc.cn/), Land-use data for China in 2015 (1980-2015), with a resolution of 1 km;
(3) Soil data: derived from the Harmonized World Soil Database (HWSD) constructed by Food and Agriculture Organization of the United Nations (FAO) and International Institute for Applied Systems Analysis (IIASA), with a resolution of 1 km (http://westdc.westgis.ac.cn/);
(4) Meteorological data: derived from the daily surface meteorological data of the China Meteorological Data Network (Version 3.0) (http://data.cma.cn/), including precipitation, maximum/minimum temperature, relative humidity, wind speed, and hours of sunshine. The solar radiation was calculated by use of the Angtrom-Prescott equation as detailed in Wu et al . (2012);
(5) Streamflow data: observed daily streamflow data at the Tangnaihai station (TNH) and Jimai station (JM) from 1 January 2008 to 31 December 2015 were collected from the Nanjing Hydraulic Research Institute, China.
Fig. 1(c) displays the spatial distribution of meteorological and hydrological stations. We set the projection coordinate system of the DEM, land use, and soil map to that of WGS_1984_Albers, with a central longitude of 100° E and standard latitude (north latitude) of\(\varnothing_{1}\)=33.5°, \(\varnothing_{2}\)=38°.