What is the most useful approach for forecasting hydrological extremes during El Niño?

Abstract

In the past, efforts to prepare for the impacts of El Niño-driven flood and drought hazards have often relied on seasonal precipitation forecasts as a proxy for hydrological extremes, due to a lack of hydrologically relevant information. However, precipitation forecasts are not the best indicator of hydrological extremes. Now, two different global scale hydro-meteorological approaches for predicting river flow extremes are available to support flood and drought preparedness. These approaches are statistical forecasts based on large-scale climate variability and teleconnections, and resource-intensive dynamical forecasts using coupled ocean-atmosphere general circulation models. Both have the potential to provide early warning information, and both are used to prepare for El Niño impacts, but which approach provides the most useful forecasts? This study uses river flow observations to assess and compare the ability of two recently-developed forecasts to predict high and low river flow during El Niño: statistical historical probabilities of ENSO-driven hydrological extremes, and the dynamical seasonal river flow outlook of the Global Flood Awareness System (GloFAS-seasonal). Our findings highlight regions of the globe where each forecast is (or is not) skilful compared to a forecast of climatology, and the advantages and disadvantages of each forecasting approach. We conclude that in regions where extreme river flow is predominantly driven by El Niño, or in regions where GloFAS-seasonal currently lacks skill, the historical probabilities generally provide a more useful forecast. In areas where other teleconnections also impact river flow, with the effect of strengthening, mitigating or even reversing the influence of El Niño, GloFAS-seasonal forecasts are typically more useful.

Bias-corrected and spatially disaggregated seasonal forecasts: a long-term reference forecast product for the water sector in semi-arid regions

“…Moreover, the Blue Nile Basin, which will undergo tremendous changes due to the construction of the Grand Ethiopian Renaissance Dam (GERD) near the Ethiopian-Sudanese border, has been controversially debated in the public and the scientific literature (Kidus, 2019) as the filling and operation of the GERD will change downstream flow patterns significantly (e.g., Wheeler et al, 2020). This underlines the urgent need for longer-term forecasts to mitigate the impacts of climatically extreme events and improve the regions' disaster preparedness (e.g., Tall et al, 2012) as well as improve the regional water management, especially in transboundary catchments (e.g., Gerlitz et al, 2020).…”

Exploring the ENSO Impact on Basin‐Scale Floods Using Hydrological Simulations and TRMM Precipitation

“…Consequently, ENSO can impact global floods (e.g., Chiew & McMahon, 2002;Emerton et al, 2017;Lee et al, 2018aLee et al, , 2018bWard, Eisner, et al, 2014;Ward, Jongman, et al, 2014;Ward et al, 2016), given the intrinsic connections between precipitation and the occurrence of flood events. Precipitation has thus even been applied as a direct predictor for floods (e.g., Stephens et al, 2015), even though the occurrence of floods also depends on antecedent surface conditions and other factors (e.g., Berghuijs et al, 2016;Emerton et al, 2017Emerton et al, , 2018Emerton et al, , 2019Sharma et al, 2018).…”

Attribution of Amazon floods to modes of climate variability: A review

“…east Pacific versus central Pacific). Doing so could provide added predictability over the use of a single index as a predictor (Emerton et al ., 2019), and would provide a more complete picture of a range of different climate scenarios. Finally, the analysis could be further broken down to consider the probabilities of exceeding a particular percentile or threshold of river flows for different intensities of climate phases (e.g.…”