Climate and Human Impacts on Hydrological Processes and Flood Risk in Southern Louisiana

Abstract

River deltas are home to more than half a billion people worldwide, support some of the most productive agricultural land and aquaculture, and their revenue and ecosystem services are conservatively valued at trillions of US dollars (Giosan et al., 2014). Current scientific literature defines sea level rise (SLR) as a major factor in increasing global coastal flood risk in recent and future decades (Oppenheimer et al., 2019;Taherkhani et al., 2020). Coastal flood risk, particularly over deltas, is exacerbated by natural and human-induced subsidence (Kolker et al., 2011;Syvitski et al., 2009), as well as local processes such as wave effects, storm surges, tides,

Unsustainable groundwater-fed irrigation drives deltaic water scarcity and compound flooding

“…Indeed, the current literature on compound coastal flooding accounting for both natural processes and human interventions, is limited. This is especially true for analyses attempting to isolate the impacts of multiple factors (27). Based on a heavily data-driven modeling system, we perform multiple "what-if" scenarios to prove our Cascading Effect hypothesis and to determine the relative impacts of human intervention, including irrigation and flood control structures (i.e., levees), as well as sea level change and land subsidence under historical (2002-2021) hydrological events on flood risk over the GBM delta.…”

“…It is demonstrated that well known factors contributing to compound coastal flooding (e.g., sea level change and land subsidence) (38) have low impact on flood risk over the GBM delta when compared to those induced by direct human interventions, such as GWI and levees. Climateinduced hydrological change is another factor that may have major impacts on compound coastal flooding, as recently demonstrated over southern Louisiana (27). Indeed, compound coastal flooding accounting for inland hydrology and human activities is still poorly known, and new methodologies to numerically represent and measure processes must be put in place.…”

“…Increasing climate and human-induced alterations will only place already exposed communities and ecosystems at greater risk (43). Well known factors driving compound coastal flooding in mega-deltas are sea level rise, land subsidence, sediment starvation, storm surges, and climate-induced hydrological changes (27,42,(44)(45)(46). It is also known that groundwater extraction can be a major cause of subsidence and sediment starvation, leading to further delta land loss (45)(46)(47)(48).…”

“…However, its capability of simulating backwater effects combined with interactions between rivers and floodplains and bifurcations (see below) results in a pseudo twodimensional representation of surface water dynamics (51). HyMAP has been extensively evaluated in the Amazon basin (61,65) and adopted as a tool for deltaic (27,51), regional (66)(67)(68)(69) and global (53) water cycle studies.…”

“…This means that water availability in the ocean is assumed unlimited and sufficient to flow inland whenever the model computes inflow (i.e., water flow from the ocean to land/river). More details on the representation of coastal backwater flooding in HyMAP can be found in Getirana et al (27).…”