Should seasonal rainfall forecasts be used for flood preparedness?

Abstract

Abstract. In light of strong encouragement for disaster managers to use climate services for flood preparation, we question whether seasonal rainfall forecasts should indeed be used as indicators of the likelihood of flooding. Here, we investigate the primary indicators of flooding at the seasonal timescale across sub-Saharan Africa. Given the sparsity of hydrological observations, we input bias-corrected reanalysis rainfall into the Global Flood Awareness System to identify seasonal indicators of floodiness. Results demonstrate that in some regions of western, central, and eastern Africa with typically wet climates, even a perfect tercile forecast of seasonal total rainfall would provide little to no indication of the seasonal likelihood of flooding. The number of extreme events within a season shows the highest correlations with floodiness consistently across regions. Otherwise, results vary across climate regimes: floodiness in arid regions in southern and eastern Africa shows the strongest correlations with seasonal average soil moisture and seasonal total rainfall. Floodiness in wetter climates of western and central Africa and Madagascar shows the strongest relationship with measures of the intensity of seasonal rainfall. Measures of rainfall patterns, such as the length of dry spells, are least related to seasonal floodiness across the continent. Ultimately, identifying the drivers of seasonal flooding can be used to improve forecast information for flood preparedness and to avoid misleading decision-makers.

Developing a global operational seasonal hydro-meteorological forecasting system: GloFAS-Seasonal v1.0

“…Recent papers have highlighted the fact that seasonal forecasts of precipitation are not necessarily a good indicator of potential floodiness and called for investment in better forecasts of seasonal flood risk (Coughlan De Perez et al, 2017;Stephens et al, 2015). Coughlan de Perez et al (2017) state that "ultimately, the most informative forecasts of flood hazard at the seasonal scale could be seasonal streamflow forecasts using hydrological models" and that better seasonal forecasts of flood risk could be hugely beneficial for disaster preparedness.…”

“…There are also various ongoing research efforts using seasonal hydro-meteorological forecasting systems for forecast applications and research purposes at regional Bennett et al, 2016;Crochemore et al, 2016;Meißner et al, 2017;Mo et al, 2014;Prudhomme et al, 2017;Wood et al, 2002Wood et al, , 2005Yuan et al, 2013) and global (Candogan Yossef et al, 2017;Yuan et al, 2015b) scales. In addition to the ongoing research into improved seasonal hydro-meteorological forecasts at the global scale, an operational system providing consistent global-scale seasonal forecasts of hydrological variables could be of great benefit in regions where no other forecasting system exists and to organisations operating at the global scale (Coughlan De Perez et al, 2017).…”

“…It has been shown that forecasts of seasonal total rainfall, the most often used seasonal precipitation forecasts, are not necessarily a good indicator of seasonal floodiness (Stephens et al, 2015), and other measures of rainfall patterns, or seasonal hydrological forecasts, would be better indicators of potential flood hazard (Coughlan De Perez et al, 2017).…”

Skilful seasonal forecasts of streamflow over Europe?

“…This is partially due to the complex nature of flood generating mechanisms, still poorly studied on seasonal timescales beyond snowmeltdriven spring floods, as well as the fact that seasonal forecasts reflect the likelihood of abnormal seasonal streamflow totals, but without much skilful information on the exact timing, location and severity of the impact of individual flood events within that season. Coughlan de Perez et al (2017) looked at the usefulness of seasonal rainfall forecasts for flood preparedness in Africa and highlighted the complexities behind using these forecasts as a proxy for floodiness (for a discussion on floodiness, see Stephens et al, 2015). Furthermore, decision-makers in the navigation, reservoir management, drought-risk management, irrigation, water resource management and hydropower sectors are familiar with working on long timescales (i.e.…”

Skilful seasonal forecasts of streamflow over Europe?

“…This is partially due to the complex nature of flood generating mechanisms, still poorly studied on seasonal timescales beyond snowmelt-driven spring floods, as well as the fact that seasonal forecasts reflect the likelihood of 25 abnormal seasonal streamflow totals, but without much skilful information on the exact timing, location and the severity of the impact of individual flood events within that season. Coughlan de Perez et al (2017) looked at the usefulness of seasonal rainfall forecasts for flood preparedness in Africa and highlighted the complexities behind using these forecasts as a proxy for floodiness [for discussion on floodiness see Stephens et al (2015)]. Furthermore, decision-makers in the navigation, reservoir management, drought-risk management, irrigation, water resources management and hydropower sectors are 30 familiar with working on long timescales (i.e.…”