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°.