Distinguishing the effects of climate on discharge in a tropical river highly impacted by large dams

Figures & data

Fig. 1 São Francisco River Basin: river reaches and the locations of large dams and gauging stations of interest.

Table 1 Major reservoirs in the São Francisco River

No.	Hydropower plant	State	Owner	Total power (MW)	Volume (10^9 m^3)	Operation since year
1	Três Marias	MG	CEMIG	396	15	1962
2	Sobradinho	BA	CHESF	1050	34	1979
3	Itaparica	PE/BA	CHESF	1500	11	1988
4	Moxotó	BA/AL	CHESF	400	1.15	1975
5	Paulo Afonso (PA) system	BA	CHESF	180	0.026	I: 1955,
				443	(I, II and III)	II: 1961,
				794		III:1971,
				2462	0.128	IV:1979
6	Xingó	AL/SE	CHESF	3000	1	1994

Table 2 Gauging station records

Name	Code	River	Latitude	Longitude	Area (km^2)	Stages begin	Streamflow begin
Morpará	46360000	São Francisco	–11°33′30″	–43°16′57″	344 800	1929	1929
Boqueirão	46902000	Grande	–11°20′41″	–43°49′35″	65 900	1934	1934
Traipu	49660000	São Francisco	–09°58′17″	–37°0′10″	622 600	1927	1939

Fig. 2 Average annual flows upstream of the Sobradinho HPP (Morpará + Boqueirão streamflows) and downstream of the Xingó HPP (at Traipu station) and timing of deployment of HPPs.

Table 3 Classification of HyC based on the anomaly of annual average streamflow and 1σ

Limits	HyC class
Anomaly < –1.5	Very dry
–1.5 < Anomaly < –0.5	Dry
–0.5 < Anomaly < 0.5	Average
0.5 < Anomaly < 1.5	Wet
Anomaly > 1.5	Very wet

Fig. 3 Anomaly time series of annual average flow upstream of the Sobradinho HPP (Morpará and Boqueirão stations).

Fig. 4 Flow duration curves obtained by HyC for different classes in the same periods: (a) 1934–2006, (b) 1963–2006, (c) 1979–2006, and (d) 1995–2006. Flow upstream of Sobradinho HPP.

Fig. 5 Flow duration curves obtained by HyC in different periods for the same classes: (a) dry, (b) average, (c) wet, and (d) very wet. Flow upstream of Sobradinho HPP.

Table 4 Relative error (%) in relation to the streamflow duration curve for the period 1934–2006 (P1). (P2: 1963–2006, P3: 1979–2006, P4: 1995–2006)

Duration	Statistic	Dry			Average			Wet		Very wet
		P2	P3	P4	P2	P3	P4	P2	P3	P2	P3
5–95%	Mean	1	0	−1	−1	0	−5	−1	−1	−5	−2
5–95%	Maximum	12	24	22	11	15	14	8	77	9	22
5–95%	Minimum	−6	−8	−9	−8	−8	−15	−8	−19	−25	−15
5–50%	Mean	−3	−4	−6	−5	−5	−11	−4	4	−10	−7
55–95%	Mean	5	6	4	4	5	0	2	−6	0	4

Fig. 6 Flow duration curves: upstream and downstream, post-Sobradinho Dam (1979–2006), pre-Sobradinho Dam upstream (1934–1977) and downstream (1939–1977).

Table 5 Differences in annual volumes and streamflows according to the HyC classes in 10⁹ m³ (m s^-1)

Reference	Dry	Average	Wet	Very wet
Pre-dam upstream – post-dam upstream = climate effects	2.59 (82)	1.98 (63)	−6.88 (−218)	7.18 (228)
Post-dam upstream – post-dam downstream = dam impacts	6.87 (218)	13.1 (417)	0.18 (6)	−5.96 (−189)

Fig. 7 Flow duration curves for pre- and post-Sobradinho Dam periods (1939–1977 and 1979–2006), upstream and downstream: (a) HyC “dry”, (b) HyC “average”, (c) HyC “wet”, and (d) HyC “very wet”.