Abstract River deltas all over the world are sinking
beneath sea-level rise, causing significant threats to natural
and social systems. This is due to the combined effects of
anthropogenic changes to sediment supply and river flow,
subsidence, and sea-level rise, posing an immediate threat
to the 500–1,000 million residents, many in megacities that
live on deltaic coasts. The Mississippi River Deltaic Plain
(MRDP) provides examples for many of the functions and
feedbacks, regarding how human river management has
impacted source-sink processes in coastal deltaic basins,
resulting in human settlements more at risk to coastal
storms. The survival of human settlement on the MRDP is
arguably coupled to a shifting mass balance between a
deltaic landscape occupied by either land built by the
Mississippi River or water occupied by the Gulf of Mexico.
We developed an approach to compare 50 % L:W isopleths
(L:W is ratio of land to water) across the Atchafalaya and
Terrebonne Basins to test landscape behavior over the last
six decades to measure delta instability in coastal deltaic
basins as a function of reduced sediment supply from river
flooding. The Atchafalaya Basin, with continued sediment
delivery, compared to Terrebonne Basin, with reduced
river inputs, allow us to test assumptions of how coastal
deltaic basins respond to river management over the last
75 years by analyzing landward migration rate of 50 %
L:W isopleths between 1932 and 2010. The average landward
migration for Terrebonne Basin was nearly 17,000 m
(17 km) compared to only 22 m in Atchafalaya Basin over
the last 78 years (p\0.001), resulting in migration rates of
218 m/year (0.22 km/year) and\0.5 m/year, respectively.
In addition, freshwater vegetation expanded in Atchafalaya
Basin since 1949 compared to migration of intermediate
and brackish marshes landward in the Terrebonne Basin.
Changes in salt marsh vegetation patterns were very distinct
in these two basins with gain of 25 % in the Terrebonne
Basin compared to 90 % decrease in the Atchafalaya
Basin since 1949. These shifts in vegetation types as L:W
ratio decreases with reduced sediment input and increase in
salinity also coincide with an increase in wind fetch in
Terrebonne Bay. In the upper Terrebonne Bay, where the
largest landward migration of the 50 % L:W ratio isopleth
occurred, we estimate that the wave power has increased
by 50–100 % from 1932 to 2010, as the bathymetric and
topographic conditions changed, and increase in maximum
storm-surge height also increased owing to the landward
migration of the L:W ratio isopleth. We argue that this
balance of land relative to water in this delta provides a
much clearer understanding of increased flood risk from
tropical cyclones rather than just estimates of areal land
loss. We describe how coastal deltaic basins of the MRDP
can be used as experimental landscapes to provide insights
into how varying degrees of sediment delivery to coastal
deltaic floodplains change flooding risks of a sinking delta
using landward migrations of 50 % L:W isopleths. The
nonlinear response of migrating L:W isopleths as wind
fetch increases is a critical feedback effect that should
influence human river-management decisions in deltaic
coast. Changes in land area alone do not capture how
corresponding landscape degradation and increased water
area can lead to exponential increase in flood risk to human
populations in low-lying coastal regions. Reduced land
formation in coastal deltaic basins (measured by changes in
the land:water ratio) can contribute significantly to
increasing flood risks by removing the negative feedback
of wetlands on wave and storm-surge that occur during
extreme weather events. Increased flood risks will promote
population migration as human risks associated with living
in a deltaic landscape increase, as land is submerged and
coastal inundation threats rise. These system linkages in
dynamic deltaic coasts define a balance of river management
and human settlement dependent on a certain level of
land area within coastal deltaic basins (L).
more »
« less
Spatially interactive modeling of land change identifies location-specific adaptations most likely to lower future flood risk
Impacts of sea level rise will last for centuries; therefore, flood risk modeling must transition from identifying risky locations to assessing how populations can best cope. We present the first spatially interactive (i.e., what happens at one location affects another) land change model (FUTURES 3.0) that can probabilistically predict urban growth while simulating human migration and other responses to flooding, essentially depicting the geography of impact and response. Accounting for human migration reduced total amounts of projected developed land exposed to flooding by 2050 by 5%–24%, depending on flood hazard zone (50%–0.2% annual probability). We simulated various “what-if” scenarios and found managed retreat to be the only intervention with predicted exposure below baseline conditions. In the business-as-usual scenario, existing and future development must be either protected or abandoned to cope with future flooding. Our open framework can be applied to different regions and advances local to regional-scale efforts to evaluate potential risks and tradeoffs.
more » « less- NSF-PAR ID:
- 10472195
- Publisher / Repository:
- Nature Publishing Group
- Date Published:
- Journal Name:
- Scientific Reports
- Volume:
- 13
- Issue:
- 1
- ISSN:
- 2045-2322
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
more » « less
Abstract Floods are among the costliest natural hazards and their consequences are expected to increase further in the future due to urbanization in flood-prone areas. It is essential that policymakers understand the factors governing the dynamics of urbanization to adopt proper disaster risk reduction techniques. Peoples’ relocation preferences and their perception of flood risk (collectively called human behavior) are among the most important factors that influence urbanization in flood-prone areas. Current studies focusing on flood risk assessment do not consider the effect of human behavior on urbanization and how it may change the nature of the risk. Moreover, flood mitigation policies are implemented without considering the role of human behavior and how the community will cope with measures such as buyout, land acquisition, and relocation that are often adopted to minimize development in flood-prone regions. Therefore, such policies may either be resisted by the community or result in severe socioeconomic consequences. In this study, we present a new Agent-Based Model (ABM) to investigate the complex interaction between human behavior and urbanization and its role in creating future communities vulnerable to flood events. We identify critical factors in the decisions of households to locate or relocate and adopt policies compatible with human behavior. The results show that when people are informed about the flood risk and proper incentives are provided, the demand for housing within 500-year floodplain may be reduced as much as 15% by 2040 for the case study considered. On the contrary, if people are not informed of the risk, 29% of the housing choices will reside in floodplains. The analyses also demonstrate that neighborhood quality—influenced by accessibility to highways, education facilities, the city center, water bodies, and green spaces, respectively—is the most influential factor in peoples’ decisions on where to locate. These results provide new insights that may be used to assist city planners and stakeholders in examining tradeoffs between costs and benefits of future land development in achieving sustainable and resilient cities.
-
more » « less
Abstract Tide gauge water levels are commonly used as a proxy for flood incidence on land. These proxies are useful for projecting how sea‐level rise (SLR) will increase the frequency of coastal flooding. However, tide gauges do not account for land‐based sources of coastal flooding and therefore flood thresholds and the proxies derived from them likely underestimate the current and future frequency of coastal flooding. Here we present a new sensor framework for measuring the incidence of coastal floods that captures both subterranean and land‐based contributions to flooding. The low‐cost, open‐source sensor framework consists of a storm drain water level sensor, roadway camera, and wireless gateway that transmit data in real‐time. During 5 months of deployment in the Town of Beaufort, North Carolina, 24 flood events were recorded. Twenty‐five percent of those events were driven by land‐based sources—rainfall, combined with moderate high tides and reduced capacity in storm drains. Consequently, we find that flood frequency is higher than that suggested by proxies that rely exclusively on tide gauge water levels for determining flood incidence. This finding likely extends to other locations where stormwater networks are at a reduced drainage capacity due to SLR. Our results highlight the benefits of instrumenting stormwater networks directly to capture multiple drivers of coastal flooding. More accurate estimates of the frequency and drivers of floods in low‐lying coastal communities can enable the development of more effective long‐term adaptation strategies.
-
Flooding is a natural hazard that touches nearly all facets of the globe and is expected to become more frequent and intensified due to climate and land-use change. However, flooding does not impact all individuals equally. Therefore, understanding how flooding impacts distribute across populations of different socioeconomic and demographic backgrounds is vital. One approach to reducing flood risk on people is using indicators, such as social vulnerability indices and flood exposure metrics, to inform decision-making for flood risk management. However, such indicators can face the scale and zonal effect produced by the Modifiable Areal Unit Problem (MAUP). This study investigates how the U.S. Census block group, tract, and county scale selection impacts social vulnerability and flood exposure outcomes within coastal Virginia, USA. Here we show how (1) scale selection can obstruct our understanding of drivers of vulnerability, (2) increasingly aggregated scales significantly undercount highly vulnerable populations, and (3) hotspot clusters of social vulnerability and flood exposure can identify variable priority areas for current and future flood risk reduction. Study results present considerations about using such indicators, given the real-life consequences that can occur due to the MAUP. The results of this work warrant understanding the implications of scale selection on research methodological approaches and what this means for practitioners and policymakers that utilize such information to help guide flood mitigation strategies.more » « less
-
more » « less
Abstract Flooding is a function of hydrologic, climatologic, and land use characteristics. However, the relative contribution of these factors to flood risk over the long-term is uncertain. In response to this knowledge gap, this study quantifies how urbanization and climatological trends influenced flooding in the greater Houston region during Hurricane Harvey. The region—characterized by extreme precipitation events, low topographic relief, and clay-dominated soils—is naturally flood prone, but it is also one of the fastest growing urban areas in the United States. This rapid growth has contributed to increased runoff volumes and rates in areas where anthropogenic climate changes has also been shown to be contributing to extreme precipitation. To disentangle the relative contributions of urban development and climatic changes on flooding during Hurricane Harvey, we simulate catchment response using a spatially-distributed hydrologic model under 1900 and 2017 conditions. This approach provides insight into how timing, volume, and peak discharge in response to Harvey-like events have evolved over more than a century. Results suggest that over the past century, urban development and climate change have had a large impact on peak discharge at stream gauges in the Houston region, where development alone has increased peak discharges by 54% (±28%) and climate change has increased peak discharge by about 20% (±3%). When combined, urban development and climate change nearly doubled peak discharge (84% ±35%) in the Houston area during Harvey compared to a similar event in 1900, suggesting that land use change has magnified the effects of climate change on catchment response. The findings support a precautionary approach to flood risk management that explicitly considers how current land use decisions may impact future conditions under varying climate trends, particularly in low-lying coastal cities.
