Incorporating Sea Level Change in Civil Works Programs

U.S. Army Corps of Engineers (USACE) | December 31st, 2013

Increased flood exposure due to climate change and population growth in the United States

American Geophysical Union (AGU) | October 30th, 2021

Precipitation extremes are increasing globally due to anthropogenic climate change. However, there remains uncertainty regarding impacts upon flood occurrence and subseq

Precipitation extremes are increasing globally due to anthropogenic climate change. However, there remains uncertainty regarding impacts upon flood occurrence and subsequent population exposure. Here, we quantify changes in population exposure to flood hazard across the contiguous United States. We combine simulations from a climate model large ensemble and a high‐resolution hydrodynamic flood model—allowing us to directly assess changes across a wide range of extreme precipitation magnitudes and accumulation timescales. We report a mean increase in the 100‐year precipitation event of ~20% (magnitude) and >200% (frequency) in a high warming scenario, yielding a ~30–127% increase in population exposure. We further find a nonlinear increase for the most intense precipitation events—suggesting accelerating societal impacts from historically rare or unprecedented precipitation events in the 21st century.

Increased Interannual Precipitation Extremes over California under Climate Change

American Meteorological Society (AMS) | August 10th, 2015

Changes to mean and extreme wet season precipitation over California on interannual time scales are analyzed using twenty-first-century precipitation data from 34

Changes to mean and extreme wet season precipitation over California on interannual time scales are analyzed using twenty-first-century precipitation data from 34 global climate models. Models disagree on the sign of projected changes in mean precipitation, although in most models the change is very small compared to historical and simulated levels of interannual variability. For the 2020/21–2059/60 period, there is no projected increase in the frequency of extremely dry wet seasons in the ensemble mean. Wet extremes are found to increase to around 2 times the historical frequency, which is statistically significant at the 95% level. Stronger signals emerge in the 2060/61–2099/2100 period. Across all models, extremely dry wet seasons are roughly 1.5 to 2 times more common, and wet extremes generally triple in their historical frequency (statistically significant). Large increases in precipitation variability in most models account for the modest increases to dry extremes. Increases in the frequency of wet extremes can be ascribed to equal contributions from increased variability and increases to the mean. These increases in the frequency of interannual precipitation extremes will create severe water management problems in a region where coping with large interannual variability in precipitation is already a challenge. Evidence from models and observations is examined to understand the causes of the low precipitation associated with the 2013/14 drought in California. These lines of evidence all strongly indicate that the low 2013/14 wet season precipitation total can be very likely attributed to natural variability, in spite of the projected future changes in extremes.

Increasing precipitation volatility in twenty-first-century California

Nature Portfolio (Springer Nature) | April 23rd, 2018

Mediterranean climate regimes are particularly susceptible to rapid shifts between drought and flood—of which, California’s rapid transition from record multi-yea

Mediterranean climate regimes are particularly susceptible to rapid shifts between drought and flood—of which, California’s rapid transition from record multi-year dryness between 2012 and 2016 to extreme wetness during the 2016–2017 winter provides a dramatic example. Projected future changes in such dry-to-wet events, however, remain inadequately quantified, which we investigate here using the Community Earth System Model Large Ensemble of climate model simulations. Anthropogenic forcing is found to yield large twenty-first-century increases in the frequency of wet extremes, including a more than threefold increase in sub-seasonal events comparable to California’s ‘Great Flood of 1862’. Smaller but statistically robust increases in dry extremes are also apparent. As a consequence, a 25% to 100% increase in extreme dry-to-wet precipitation events is projected, despite only modest changes in mean precipitation. Such hydrological cycle intensification would seriously challenge California’s existing water storage, conveyance and flood control infrastructure.

Increasing threat of coastal groundwater hazards from sea-level rise in California

Nature Portfolio (Springer Nature) | August 17th, 2020

Projected sea-level rise will raise coastal water tables, resulting in groundwater hazards that threaten shallow infrastructure and coastal ecosystem resilience. Here we

Projected sea-level rise will raise coastal water tables, resulting in groundwater hazards that threaten shallow infrastructure and coastal ecosystem resilience. Here we model a range of sea-level rise scenarios to assess the responses of water tables across the diverse topography and climates of the California coast. With 1 m of sea-level rise, areas flooded from below are predicted to expand ~50–130 m inland, and low-lying coastal communities such as those around San Francisco Bay are most at risk. Coastal topography is a controlling factor; long-term rising water tables will intercept low-elevation drainage features, allowing for groundwater discharge that damps the extent of shoaling in ~70% (68.9–82.2%) of California’s coastal water tables. Ignoring these topography-limited responses increases flooded-area forecasts by ~20% and substantially underestimates saltwater intrusion. All scenarios estimate that areas with shallow coastal water tables will shrink as they are inundated by overland flooding or are topographically limited from rising inland.

Increasing water cycle extremes in California and in relation to ENSO cycle under global warming

Nature Portfolio (Springer Nature) | October 21st, 2015

Since the winter of 2013–2014, California has experienced its most severe drought in recorded history, causing statewide water stress, severe economic loss and

Since the winter of 2013–2014, California has experienced its most severe drought in recorded history, causing statewide water stress, severe economic loss and an extraordinary increase in wildfires. Identifying the effects of global warming on regional water cycle extremes, such as the ongoing drought in California, remains a challenge. Here we analyse large-ensemble and multi-model simulations that project the future of water cycle extremes in California as well as to understand those associations that pertain to changing climate oscillations under global warming. Both intense drought and excessive flooding are projected to increase by at least 50% towards the end of the twenty-first century; this projected increase in water cycle extremes is associated with a strengthened relation to El Niño and the Southern Oscillation (ENSO)—in particular, extreme El Niño and La Niña events that modulate California’s climate not only through its warm and cold phases but also its precursor patterns.

Indicators of Climate Change in California

California Environmental Protection Agency (CalEPA) | May 16th, 2018

From record temperatures to proliferating wildfires and rising seas, climate change poses an immediate and escalating threat to California’s environment, public health,

From record temperatures to proliferating wildfires and rising seas, climate change poses an immediate and escalating threat to California’s environment, public health, and economic vitality. Recent climate-related events – such as the devastating 2017 wildfires and the record-setting 2012-16 drought – have highlighted the challenges that confront the state as its climate continues to evolve.  California has been a pioneer in addressing climate change. This report helps support policy decisions and facilitates communication about climate change by providing, in a single document, indicators characterizing its multiple aspects in California.  Indicators are scientifically-based measurements that track trends in various aspects of climate change. Many indicators reveal discernable evidence that climate change is occurring in California and is having significant, measurable impacts in the state.  The report’s 36 indicators are grouped into four categories, as listed below. The report discusses what these indicators show, why they are important, and the factors that may be influencing them.  * Human-influenced (anthropogenic) drivers of climate change, such as greenhouse gas emissions * Changes in the state’s climate * Impacts of climate change on physical systems, such as oceans, lakes and snowpack * Impacts of climate change on biological systems – humans, vegetation and wildlife

Inequitable patterns of US flood risk in the Anthropocene

Nature Portfolio (Springer Nature) | January 31st, 2022

Current flood risk mapping, relying on historical observations, fails to account for increasing threat under climate change. Incorporating recent developments in inundati

Current flood risk mapping, relying on historical observations, fails to account for increasing threat under climate change. Incorporating recent developments in inundation modelling, here we show a 26.4% (24.1–29.1%) increase in US flood risk by 2050 due to climate change alone under RCP4.5. Our national depiction of comprehensive and high-resolution flood risk estimates in the United States indicates current average annual losses of US$32.1 billion (US$30.5–33.8 billion) in 2020’s climate, which are borne disproportionately by poorer communities with a proportionally larger White population. The future increase in risk will disproportionately impact Black communities, while remaining concentrated on the Atlantic and Gulf coasts. Furthermore, projected population change (SSP2) could cause flood risk increases that outweigh the impact of climate change fourfold. These results make clear the need for adaptation to flood and emergent climate risks in the United States, with mitigation required to prevent the acceleration of these risks.

Influence of agricultural managed aquifer recharge on nitrate transport: The role of soil texture and flooding frequency

Soil Science Society of America (SSSA) | June 9th, 2021

Agricultural managed aquifer recharge (Ag-MAR) is a concept in which farmland is flooded during the winter using excess surface water to recharge the underlying groundwat

Agricultural managed aquifer recharge (Ag-MAR) is a concept in which farmland is flooded during the winter using excess surface water to recharge the underlying groundwater. In this study, we show how different recharge practices affect NO3− leaching and mineralization–denitrification processes in different soil systems. Two contrasting soil textures (sand and fine sandy loam) from the Central Valley, Califor- nia, were repeatedly flooded with 15 cm of water at varying time intervals in field and soil column experiments. Nitrogen species (NO3–, NH4+, total N), total C, dis- solved O2, and moisture content were measured throughout the experiments. Results show that when flooding occurs at longer intervals (every 1–2 wk), N mineralization increases, leading to an increase of mobile NO3− in the upper root zone and leach- ing of significant quantities of NO3− from both soil textures (137.3 ± 6.6% [sand] and 145.7 ± 5.8% [fine sandy loam] of initial residual soil NO3−) during subsequent flooding events. Laboratory mineralization incubations show that long flooding inter- vals promote mineralization and production of excess NO3− at rates of 0.11–3.93 mg N kg–1 wk–1 (sand) and 0.08–3.41 mg N kg–1 wk–1 (fine sandy loam). Decreasing the flooding frequency to 72 h reduces potential mineralization, decreasing the amount of NO3− leached during flooding events (31.7 ± 3.8% [sand] and 64.7 ± 10.4% [fine sandy loam] of initial residual soil NO3–). The results indicate that implementing recharge as repeated events over a long (multiple-week) time horizon might increase the total amount of NO3− potentially available for leaching to groundwater.

Landslide-channel feedbacks amplify channel widening during floods

Nature Portfolio (Springer Nature) | January 24th, 2025