Analysing the Flood Warning of Negro River in Manaus

Abstract

The magnitude of the Amazon basin, associated with geological, geomorphological and hydrological factors, as well as the distribution of rainfall, contribute to the existence of large rivers, both in extension and flow, such as the Negro and Solimões rivers, which are selected to be evaluated in this study. Manaus city is bathed by the Negro river, near the confluence of the two rivers, in which the water level of Negro river is controlled by Solimões river level. This study proposes to analyse a project named Negro River Flood Warning System that presents a river level or stage forecast about Negro river by the Geological Survey of Brazil in Manaus since 1989, where the annual flood and ebb monitoring process is performed in the Solimões, Negro and Amazonas hydrological system. Flood forecasting models are important for the composition of extreme events alerts, as well as for the knowledge of decisionmakers, representatives of public agencies and affected communities. Many factors contribute to the flooding event: how the various tributaries are integrated down the river main stem and how the basin behaves during the six months of flooding in the rainy season. For the forecast, it is important to monitor the evolution of the level of rivers such as Negro and Solimões, understanding the dynamics of the basin and also the events associated with major floods that have already occurred, as recorded in the historical series of the port of Manaus, all this combined with a statistical methodological approach. In the Manaus alert system, linear regression analysis is used. According to results obtained for the past 15 years, the flood forecast interval reveals that the forecast in 87% of cases has fulfilled the objective of presenting a stage very close to the water level peak. Furthermore, it was noticed that a height of 27 m in Negro river turned to be an alert quota with a return period of 10 years. Once the river water level reaches a height of 29 m, it can be considered a 'severe flood water level' with a return period of 17 years.

Forecasting annual maximum water level for the Negro River at Manaus using dynamical seasonal predictions

“…It is therefore critical to advance the prediction of high water levels of Amazonian rivers, to provide more effective and earlier warnings of impending disasters, for more effective action to safeguard lives and livelihoods (Schöngart and Junk, 2007;Maciel et al, 2020). Operational forecasts of maximum water level for Manaus are provided by Brazilian institutes CPRM (Maciel et al, 2020;Maciel et al, 2022) and INPA (Schöngart and Junk, 2007;Schöngart and Junk, 2020). Chevuturi et al (2021) developed statistical forecast models for the annual maximum water level of the Negro River at Manaus, based on catchment rainfall (the predominant predictor), large-scale teleconnection indices, the long-term linear trend of water level and antecedent water levels.…”

“…Using this premise, Chevuturi et al (2021) developed three statistical forecast models for annual maximum water level for the Negro River at Manaus, that use observed antecedent rainfall, antecedent water level, large-scale modes of variability represented by climate indices and the linear trend of historical water levels as predictors. The models developed by Chevuturi et al (2021) can issue forecasts at three lead times: March (the current earliest operational lead time), February and January; and were compared against the models from INPA (Schöngart and Junk, 2007;Schöngart and Junk, 2020) and CPRM (Maciel et al, 2020;Maciel et al, 2022). The results show that these forecasts gain one month of lead time against the CPRM models with similar forecast performance (Chevuturi et al, 2021).…”

“…1. Currently, the Brazilian Geological Survey (CPRM) uses simple linear regression models to issue forecasts at end of March, April and May for maximum water level at Manaus, using current water levels of the respective issuance month as a predictor (Maciel et al, 2020;Maciel et al, 2022). Another seasonal forecasting model for Manaus was developed collaboratively by Instituto Nacional de Pesquisas da Amazonia (INPA) and Max-Planck Society, using multiple linear regressions of maximum water level against prior Manaus water levels and indices representing large-scale modes of climate variability connected to basin rainfall (Schöngart and Junk, 2007).…”