2 Study area and data

The Tao’er River basin is located in northeastern China, with elevations ranking from 100 m a.s.l. to 1600 m a.s.l. (Fig. 1). The drainage area is 41,200 km2, of which the bed rock mountain area accounts for about 65% and mainly distributed above the Zhenxi station (Chen, Li, Li, & Liu, 2016; Kou, 2016). The forest and grassland coverage in the basin are about 25% and 36%, respectively, and the rest is mostly cultivated with corn. This basin belongs to the temperate continental monsoon climate zone, with an average annual rainfall of 463.6 mm (from 1953 to 2015).
The daily average precipitation, streamflow and water level of the four hydrological stations in Tao’er River basin (Suolun, Dashizhai, Chaersen and Zhenxi) have been monitored since 1964. The Zhenxi station is 63 km away from the downstream of Chaersen reservoir, the Chaersen station is located at the outlet of the reservoir, and the Suolun and Dashizhai stations are located in the upstream watersheds (Fig. 1). The main purpose of the paper is to analysis the influence of Chaersen reservoir on the streamflow and baseflow recession characteristics of Zhenxi station.
Figure 1. Location and topography of the Tao’er River basin.
The Chaersen Reservoir is a large-scale reservoir mainly used for flood prevention, irrigation, combined power generation, and fish farming. This reservoir started construction in 1987 and was completed in September 1989. The drainage area it controls is 7872 km2, the total design storage capacity is 11.48 × 108m3, the design peak discharge is 420 m3/s, and the design irrigation area is 590 km2. The dam of the reservoir is a loam core wall dam with a maximum height of 40 m, a crest width of 6 m and a length of 1712 m (Li, 2018). The streamflow regulation of Chaersen reservoir is usually carried out from May to October every year. From 2009 to 2013, the average daily discharge of the reservoir is between 20 to 110 m3/s, with an average of 45 m3/s (Fig. S1). After the construction of the reservoir, the streamflow process of Chaersen station is obviously flattened, and the flood peak originally concentrated in July and August is evenly distributed to May to October.
After excluding the construction period (1987-1989) and the initial impoundment stage (1989-1995), based on the similarity of rainfall‑runoff characteristics, 1982-1986 was determined as the pre-disturbance period, and 2009-2013 was the post-disturbance period. These two periods are the same length and the annual precipitation is basically the same. Precipitation and runoff in both periods are all increasing year by year (Fig. S2, Fig. S3). The unpublished streamflow data was provided by Songliao Water Resources Commission, Ministry of Water Resources, China.