Hydrological changes caused by the construction of dams and reservoirs: The CECP analysis

Abstract

We investigated the influence of the construction of cascade dams and reservoirs on the predictability and complexity of the streamflowof the São Francisco River, Brazil, by using complexity entropy causality plane (CECP) in its standard and weighted form. We analyzeddaily streamflow time series recorded in three fluviometric stations: São Francisco (upstream of cascade dams), Juazeiro (downstream ofSobradinho dam), and Pão de Açúcar station (downstream of Sobradinho and Xingó dams). By comparing the values of CECP information quantifiers (permutation entropy and statistical complexity) for the periods before and after the construction of Sobradinho (1979) and Xingó(1994) dams, we found that the reservoirs’ operations changed the temporal variability of streamflow series toward the less predictable regimeas indicated by higher entropy (lower complexity) values. Weighted CECP provides some finer details in the predictability of streamflow dueto the inclusion of amplitude information in the probability distribution of ordinal patterns. The time evolution of streamflow predictabil-ity was analyzed by applying CECP in 2 year sliding windows that revealed the influence of the Paulo Alfonso complex (located betweenSobradinho and Xingó dams), construction of which started in the 1950s and was identified through the increased streamflow entropy in thedownstream Pão de Açúcar station. The other streamflow alteration unrelated to the construction of the two largest dams was identified inthe upstream unimpacted São Francisco station, as an increase in the entropy around 1960s, indicating that some natural factors could alsoplay a role in the decreased predictability of streamflow dynamics.