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

Abstract

Three change-point methodologies were used to detect changes in the mean value of annual streamflow series and analyse simultaneous changes in large-scale global sea surface temperature (SST) oscillations. To verify the relationship between the variables we used wavelet coherence analysis. A preliminary detection skill test was performed using asynthetic series and Pruned Exact Linear Time (PELT) presented the best results among the methods used (Pettitt test, Bai and Perron algorithm) when combined with a penalty selection via the Changepoints for a Range of Penalties (CROPS) method. However, the use of classical penalty functions resulted in a poor performance of PELT. The three methods showed an extremely high convergence rate (> 90%) for the correct change points and a smaller rate for false positives (< 24%). Changes in the streamflow mean value coincided with phase shift of the low-frequency indices Atlantic Multidecadal Oscillation (AMO) and Pacific Decadal Oscillation (PDO), also corroborated by the wavelet results. Most of the changes can be associated with phase shift impacts in the South Atlantic Convergence Zone.

Density and classification of the rainfall network and spatiotemporal analysis of rain in the upper Parana river region, Brazil

“…Perez et al (2021) proposed that was not until 1995 that the region presented a decrease trend of hydrological variables. After this period, La Plata basin presented mostly negative trends of river discharge (Perez et al, 2021;Rocha & Souza Filho, 2020). However, the Andean side (western) shows an increase of river discharge for the same latitude range (Castino et al, 2017).…”

“…River discharge in La Plata basin showed significant increase in early 1970s, associated with positive (negative) ENSO and PDO (AMO) phases (Castino et al, 2017;Perez et al, 2021;Rocha & Souza Filho, 2020). Perez et al (2021) proposed that was not until 1995 that the region presented a decrease trend of hydrological variables.…”

Wavelet transform for medium-range streamflows projections in national interconnected system

“…These variability modes occur in the Pacific and Atlantic Oceans, overlapped and influenced by interannual modes, such as ENSO, and, as already mentioned, can influence the effects of these variabilities on South America. Rocha and Souza Filho (2020) detected low-frequency anomalies in the SST of Pacific (PDO) and Atlantic (AMO) in the period 1931-2016 with change-point analysis. The cold (C) and warm (W) phases of PDO and AMO detected were in the following periods: W-AMO (1931-1963 and 1995-2016), W-PDO (1931-1943, 1976-1998, and 2014), C-AMO (1964-1994), and C-PDO (1944-1975and 1999-2013.…”

“…The period from 1963 to 1970 is a transition period between phases of AMO and a weak cold phase of the PDO, which is consistent with annual flow close to the historical mean. According to Rocha and Souza Filho (2020), the period between 2014 and 2016 was a warm phase of both PDO and AMO. In this period, the annual average streamflow of Sobradinho reached to the minimum of the entire series.…”

“…Grimm et al (2020) and references quoted therein pointed to the influence of ENSO and Atlantic Multidecadal Oscillation (AMO) on precipitation over South America, in the respective interannual and interdecadal oscillation scale. Rocha and Souza Filho (2020) have identified a strong coherence between the changes of ONS streamflow time series and SST interdecadal oscillation patterns (AMO and PDO) in the key stations of ONS, including Sobradinho, Itaipú, and Furnas.…”