Assessing Effectiveness of National Flood Policy Through Spatiotemporal Monitoring of Socioeconomic Exposure1

Abstract: After a century of evolving flood policies, there has been a steady increase in flood losses, which has partly been driven by development in flood prone areas. National flood policy was revised in 1994 to focus on limiting and reducing the amount of development inside the 100‐year floodplain, with the goal of decreasing flood losses, which can be measured and quantified in terms of population and property value inside the 100‐year floodplain. Monitoring changes in these measurable indicators can inform where and how effective national floodplain management strategies have been. National flood policies are restricted to the spatial extent of the 100‐year floodplain, thus there are no development regulations to protect against flooding adjacent to this boundary. No consistent monitoring has been undertaken to examine the effect of flood policy on development immediately outside the 100‐year floodplain. We developed a standardized methodology, which leveraged national data to quantify changes in population and building tax value (exposure). We applied this approach to counties in North Carolina to assess (1) temporal changes, before and after the 1994 policy and (2) spatial changes, inside and adjacent to the 100‐year floodplain. Temporal results indicate the Piedmont and Mountain Region had limited success at reducing exposure within the 100‐year floodplain, while the Coastal Plain successfully reduced exposure. Spatially, there was a significant increase in exposure immediately outside the 100‐year floodplain throughout North Carolina. The lack of consistent monitoring has resulted in the continuation of this unintended consequence, which could be a significant driver of increased flood losses as any flood even slightly higher than the 100‐year floodplain will have a disproportionately large impact since development is outside the legal boundary of national flood policy.     

Thallium in marine plankton

Concentrations of thallium in phytoplankton (0.02 to 0.8 g g^–1), zooplankton (0.03 to 0.5 g g^–1) and ichthyoplankton (0.1 g g^–1) from the central Pacific were comparable , as were the atomic ratios of thallium to calcium (3x10^–6) and to potassium (1x10^–6) in those organisms. These relatively constant ratios, plus the biounlimited ocean profile of thallium, indicate that it is rapidly cycled through plankton in the same manner as potassium, its principal biogeochemical analogue. The higher atomic ratios of thallium to potassium in pelagic clays (6x10^–6) and ferromanganese nodules (4x10^–3) suggest that both biological transport processes and abiotic transport processes influence this trace element's oceanic cycle.     

Sampling duration calculations

Routine air quality monitoring produces filter samples that, when analyzed, yield the total amount of the aerosol present in the volume of air drawn by the pump in the monitoring device during the given sampling period. From this we obtain an average concentration of the aerosol for the given duration. The samples are therefore really aggregate samples. A natural question then is "what is the effect of the duration of aggregation on the accuracy and precision of the estimate of the quantity of interest?" The answer depends on a number of factors, such as the quantity that is being estimated: a mean, or an extreme value, or some other quantity; the nature of the measurement error--additive versus multiplicative; the costs of laboratory analyses, and so on. In this paper, we investigate these issues when the interest is in estimating the mean concentration of a specified aerosol species over a fixed time period. In particular, we propose a method for determining a sampling duration that will yield the "best estimate" of the mean concentration for a given cost whenever appropriate statistical assumptions hold.     

Lifestyle and polybrominated diphenyl ethers in human milk in the United States: A pilot study

Polybrominated diphenyl ethers (PBDE) are a class of brominated flame retardants with some congeners having the ability to accumulate in body lipids. The incorporation of PBDE in consumer products found primarily in the indoor environment suggests that routes of exposure include inhalation of indoor air and contact with indoor dust. The purpose of this study was to test the hypothesis that lifestyle factors, and in particular the proximity and use of products likely to contain PBDE in the indoor environment, are primarily responsible for levels of PBDE found in human milk. Human milk samples were taken from two populations of lactating women in the same geographic region of the United States: one “typical” of US suburban lifestyle, and the other practicing a traditional Amish lifestyle, which excludes many modern amenities containing PBDE, such as computers and televisions. For a subset of the cohort, persistent organic pesticides and polychlorinated biphenyls (PCB) were also measured in human milk samples. Despite the small number of participants, there is evidence suggestive of Amish women having lower PBDE concentrations in their milk. In addition, the nonsignificant differences in levels of PCBs and pesticides between the two groups of women as compared to the significant differences in levels of PBDE suggest an important route of exposure for PBDE other than diet. Information prepared for study participants is provided to initiate a dialogue on how to best communicate biomonitoring findings to study participants and to the public in general.     

Convergent validity between willingness to pay elicitation methods: an application to Grand Canyon whitewater boaters

We directly compare trip willingness to pay (WTP) values between dichotomous choice contingent valuation (DCCV) and discrete choice experiment (DCE) stated preference surveys of private party Grand Canyon whitewater boaters. The consistency of DCCV and DCE estimates is debated in the literature, and this study contributes to the body of work comparing the methods. Comparisons were made of mean WTP estimates for four hypothetical Colorado River flow-level scenarios. Boaters were found to most highly value mid-range flows, with very low and very high flows eliciting lower WTP estimates across both DCE and DCCV surveys. Mean WTP precision was estimated through simulation. No statistically significant differences were detected between the two methods at three of the four hypothetical flow levels.     

A Nationwide Analysis of U.S. Army Corps of Engineers Reservoir Performance in Meeting Operational Targets

The United States (U.S.) Army Corps of Engineers operates reservoirs across the U.S. with 89% of reservoirs constructed prior to 1980. Many reservoirs have experienced changes in environmental conditions (e.g., climate and sediment yield) and societal conditions (e.g., water/energy demand and ecological flows) since construction. These changes may challenge the potential for reservoirs to meet their operational targets (OTs) (management goals). Historic daily reservoir data and OTs were collected for 233 reservoirs. Analyses were developed to identify when and where reservoirs may be systematically departing from OTs in terms of the frequency and magnitude of departure. Fifty‐six percent of reservoirs consistently met operating targets, 30% were borderline, and 13% experienced frequent and large magnitude departures. Fifty‐two percent of reservoirs with large departures were due to shortages and were located in the South Pacific and Southwestern divisions. This work provides a framework to identify reservoir performance in relation to management goals, a necessary step for moving toward adaptive management under changing conditions. All individual reservoir analyses are provided via an interactive data visualization tool: https://nicholasinstitute.duke.edu/reservoir-data .     

Characterization of Drought in the South Atlantic,United States

Drought has been less extensively characterized in the humid South Atlantic compared to the arid western United States. Our objective was to characterize drought in the South Atlantic and to understand whether drought has become more severe in this region over time. Here we used monthly streamflow to characterize hydrological drought. Hydrological drought occurred when streamflow fell below the 20th percentile over three consecutive months and terminated once streamflow remained above the 20th percentile for three consecutive months. We characterized the frequency, duration, magnitude, and severity of events using the above definition. Significant changes in drought characteristics were tested with Mann‐Kendall over three periods: 1930‐2010, 1930‐1969, and 1970‐2010. We show that 71% of drought events were shorter than six months, while 7% were multiyear events. There was little evidence of trends in drought characteristics to support the claim of drought becoming more severe in the South Atlantic over the 20th Century. The one exception was a significant increase in the joint probability of nearby basins being simultaneously in drought conditions in the southern portion of the study area from 1970 to 2010. While drought characteristics have changed little through time, decreasing average streamflow in non drought periods coupled with increasing water demand provide the context within which recent multiyear drought events have produced significant stress on existing water infrastructure.