Climate change and ENSO significantly enhances seasonal flood occurrence
in the Ganges-Brahmaputra-Meghna Basin
Abstract
Seasonal hydrological dynamics have profound socio-economic implications
for communities in the Ganges-Brahmaputra-Meghna (GBM) River basin.
Climate change and El Niño-Southern Oscillation (ENSO) phase are known
to impact extreme flood magnitude in GBM River, however how they affect
seasonal flooding pattern is not revealed. Utilizing large ensemble
climate data (comprising 6000 years of non-warming and warming climate
scenarios) and the global hydrodynamic model CaMa-Flood, we assess the
influence of climate change and ENSO on seasonal hydrological patterns
specially focusing on maximum river flow. The quantitative effects of La
Niña and El Niño are calculated utilizing the Fractional Attribution
Risk (FAR) method, separately for non-warming and historical climate
scenarios. We assess climate change’s impact on flooding by contrasting
historical and non-warming climate conditions using the FAR method.
Climate change has substantially increased the maximum river flow for
all seasons. In the monsoon season, climate change amplifies the
likelihood of flooding with a 10-year return period of 34%, 46%, and
31% at the Hardinge Bridge, Bahadurabad, and Bhairab Bazar gauge
stations of the Ganges, Brahmaputra, and Meghna Rivers, respectively.
The influence of ENSO still remains significant even with the influence
of climate change. ENSO influence presents a nuanced picture, exhibiting
variations both between seasons and across different rivers within the
GBM basin. The relationship between ENSO and seasonal flood occurrence
in the GBM basin can be effectively elucidated by the upward movement of
moisture through vertical wind velocity, which serves as a large-scale
controlling factor for flood variation.