Mapping abrupt streamflow shift in an abrupt climate shift through multiple change point methodologies: Brazil case study

Figures & data

Figure 1. Location of streamflow stations. Key stations are highlighted (triangles) and labelled. The stations colour represents its region according to ONS standards

Figure 2. Penalty values of the synthetic series obtained from different penalty functions and CROPS method. Maximum, minimum and median values of each penalty function are shown at the bottom left, bottom right and top, respectively. CROPS maximum, minimum and median values were 6.53, 0.05 and 0.65

Table 1. Detection and convergence rate of Pettitt test, Bai and Perron’s algorithm and Pruned Exact Linear Time method for the synthetic series

Detection rate (%)				Convergence rate with PELT (%)
Method	Single change point	Double change points		Method	Correct change points			Incorrect change points
		All	Any		Single	Double (all)	Double (any)	Single	Double
PELT	66.17	47.83	89.00	BP	95.10	90.31	91.27	52.52	57.92
BP	57.83	37.83	88.17	Pettitt	97.79	–	97.88	20.59	25.97
Pettitt	45.33	–	39.33	BP and Pettitt	95.59	–	91.27	12.61	23.12

Table 2. Statistical properties of each segment: mean (μ), standard deviation (σ) and coefficient of variation (CV)

Index	Period	µ	σ	CV	Duration
AMO	1931–1963	0.12	0.11	0.97	33
	1964–1994	−0.17	0.12	−0.69	31
	1995–2016	0.15	0.11	0.77	22
PDO	1931 − 1943	0.66	0.81	1.21	13
	1944–1975	−0.61	0.62	−1.02	32
	1976–1998	0.57	0.64	1.11	23
	1999–2013	−0.36	0.67	−1.88	15
	2014–2016	1.44	0.27	0.19	3

Figure 3. Change point results for the mean value (bold lines) of climate indices and of the streamflow series of key stations

Figure 4. Percentage difference between the complete series mean value and the latest change point mean value, along with the convergence among the three change-point methodologies

Figure 5. Comparison between mean value change point results of climate indices and annual streamflow. Numbers on the right are station numbers; 168, 6 and 266 refer to the key stations Sobradinho, Furnas and Itaipu, respectively

Figure 6. Wavelet coherence results between the key stations and climate indices, AMO (left) and PDO (right). The thick black contour line indicates the 5% significance level. The cone of influence is represented in white and indicates a border effect in the highlighted results