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The daily rise and fall of the tides are intimately familiar to those living on the coast. However, due to sea‐level rise, what communities in the United States now experience as the highest, lowest, and average water levels on a typical day no longer corresponds to the official definitions of high tide, low tide, and mean sea level, respectively. Water levels now regularly exceed official high tide along parts of the Chesapeake Bay, Gulf Coast, and Puerto Rico. In other words, yesterday's high tide is becoming today's new normal. This demonstrates how sea‐level rise is radically redefining the American shore. Plain Language Summary Due to sea‐level rise, coastal elevations that we once knew as marking the highest water level over a typical daily tidal cycle now correspond more closely to the average level of the sea: yesterday's high tide is becoming today's new normal. This illustrates how profoundly sea‐level rise is altering how we live, work, and play by the sea. Key Points Sea‐level rise is altering how we live, work, and play by the sea Elevations that marked high tide only decades ago are now closer to mean sea level This has implications for transportation, construction, and policy

Wang, H.; Li, W.; Zuo, C.; Dong, J.; Li, C.; Xu, H.; Liu, Q., and Pan, S., 2020. Saltwater intrusion in the Pearl River estuary (China): Variation characteristics and cause analysis. Journal of Coastal Research, 36(6), 1145–1153. Coconut Creek (Florida), ISSN 0749-0208. The characteristics and influence factors of saltwater intrusions in the Pearl River Estuary were analyzed with tide gauge observation data, sea-level rise impact investigation data, and discharge data. The results show that (1) Seasonal variations in saltwater intrusion in the Pearl River estuary are obvious. Intrusion usually begins in September–October and ends in March–April of the following year. More saltwater is present in January, February, and October, which all had more than 10 events in the last 10 years. The number of saltwater intrusions fluctuated during 2009–2018, with the highest number of 14 in 2010 and the lowest of 2 in 2015. The annual saltwater intrusion duration increased obviously during 2015–2018 and lasted 171 days in 2018. (2) The integrated influence factor of sea level and discharge is closely related to frequency and duration of saltwater occurrence, with correlation coefficients of 0.7 and 0.5, respectively (95% confidence). From January to March, the Pearl River is in the dry season, and the integrated influence factor of sea level and discharge is positive, corresponding to more saltwater intrusions. From April to August, the seasonal sea level is low and discharge is high, resulting in a negative integrated influence factor of sea level and discharge and nearly no saltwater intrusion. From September to December, the seasonal sea level is high and the discharge is low. The integrated influence factor of sea level and discharge is higher than 1, corresponding to the high occurrence of saltwater intrusions. (3) Astronomical high tides mostly occur during return tides. The combination of astronomical tides and storm surges aggravates saltwater intrusions and their influence. (4) Countermeasures, including saltwater monitoring and forecasting, river basin management, and water conservation, are suggested to effectively address saltwater intrusion.

Coastal flooding has become a major issue for low‐lying coastal cities in China, and a lot of research has focused on assessing flood risk from storms and associated extreme sea levels. High‐tide flooding (HTF), however, which leads to minor inundation and occurs more frequently as sea level continues to rise has not been assessed comprehensively. Here, we analyze HTF along the China coastline using tide gauge records. We show that the frequency of HTF has increased (Xiamen doubled HTF frequency every 11.5–37.4 years, with the median being 17.5 years). As a result, the cumulative loss ratios of HTF are higher than those of major (or extreme) flooding events in several locations. To gain insights into the processes driving HTF changes, we decompose still water levels that occurred during HTF into five components, including non‐linear trend, interannual to decadal mean sea level (MSL) variability, seasonal MSL cycle, tidal anomaly, and nontidal residuals. It is evident that due to sea‐level rise (SLR) fewer components need to combine to raise the water levels above HTF thresholds. We show that the South China Sea coast already experiences HTF purely driven by high spring tides, and will also see the fastest future increase in the number of tide‐only HTF events. In general, China will experience more HTF days under all warming scenarios as SLRs. This long‐term trend will be modulated by the nodal cycle of ocean tides leading to more rapid increases in HTF in the 2030s and 2050s. Plain Language Summary High‐tide flooding (HTF), which usually occurs during high tides in coastal areas, is one of the most apparent consequences of sea‐level rise (SLR). Analyses of HTF in the past and future have been carried out for the United States, Australia, and Europe, but no comprehensive analysis exists for the coast of China. Here, we analyze HTF along the China coast based on available sea level records. We find, for example, that the frequency of HTF has increased and doubled every 17.7 years. High tidal levels alone will lead to more HTF days due to SLR along the South China Sea coast. In the future, the China coast will experience more HTF days under different warming scenarios, with more rapid increases in the 2030s and 2050s due to long‐term cycles in ocean tides. The analysis presented here advances our understanding of HTF along the China coastline, providing a basis for future research and adaptation planning. Key Points The frequency of High‐tide flooding (HTF) along China coastline has increased, with a doubling time of 11.5–37.4 years in Xiamen Cumulative loss ratios of HTF are higher than those of extreme flooding at several locations China will experience more HTF days under all warming scenarios, with more rapid increases in the 2030s and 2050s

Stormwater infrastructure can manage precipitation‐driven flooding when there are no obstructions to draining. Coastal areas increasingly experience recurrent flooding due to elevated water levels from storms or tides, but the inundation of coastal stormwater infrastructure by elevated water levels has not been broadly assessed. We conservatively estimated stormwater infrastructure inundation in municipalities along the Atlantic United States coast by using areas of high‐tide flooding (HTF) on roads as a proxy. We also modeled stormwater infrastructure inundation in four North Carolina municipalities and measured infrastructure inundation in one of the modeled municipalities. Combining methodologies at different scales provides context and allows the scope of stormwater infrastructure inundation to be broadly estimated. We found 137 census‐designated urban areas along the Atlantic coast with road area impacted by HTF, with a median percent of total road area subject to HTF of 0.16% (IQR: 0.02%–0.53%). Based on 2010 census block data, the median number of people per urban area that live in census blocks with HTF on roads was 1,622 (IQR: 366–5,779). In total, we estimate that over 2 million people live in census blocks where HTF occurs on roadways along the US Atlantic coast. Modeling results and water level measurements indicated that extensive inundation of underground stormwater infrastructure likely occurs at water levels within the mean tidal range. These results suggest that stormwater infrastructure inundation along the US Atlantic coast is likely widespread, affects a large number of people, occurs frequently, and increases the occurrence of urban flooding. Plain Language Summary Urban areas are often drained by underground pipes that convey stormwater runoff downstream when it rains, but coastal urban areas can experience recurrent “high‐tide” flooding (HTF) that may block stormwater pipes from draining. We estimated where stormwater pipes may be influenced by recurrent flooding in urban areas along the Atlantic United States coast by finding where HTF occurs on roads. We also modeled the impacts of stormwater pipe inundation in four North Carolina municipalities and measured inundation in one of the modeled municipalities. Over 130 east coast urban areas had road area impacted by HTF and the number of people estimated to live in census blocks that had HTF on roads was more than 2 million. Modeling results and water level measurements in the four North Carolina municipalities indicated that stormwater pipes likely have reduced capacity to convey stormwater at water levels within the average tidal range. These results suggest that stormwater infrastructure inundation is common and increases the occurrence of urban flooding along the east coast of the United States. Key Points Proxy measurements suggest that inundation of coastal stormwater networks from high water levels is common along the US Atlantic coast Measurements and modeling in coastal North Carolina showed stormwater network inundation at water levels within mean tidal range Stormwater network inundation likely increases risk of overland flooding in coastal urban areas

High‐tide flooding—minor, disruptive coastal inundation—is expected to become more frequent as sea levels rise. However, quantifying just how quickly high‐tide flooding rates are changing, and whether some places experience more high‐tide flooding than others, is challenging. To quantify trends in high‐tide flooding from tide‐gauge observations, flood thresholds—elevations above which flooding begins—must be specified. Past studies of high‐tide flooding in the United States have used different data sets and approaches for specifying flood thresholds, only some of which directly relate to coastal impacts, which has lead to sometimes conflicting and ambiguous results. Here we present a novel method for quantifying, with uncertainty, high‐tide flooding thresholds along the United States coast based on sparsely available impact‐based flood thresholds. We use those newly modeled thresholds to make an updated assessment of changes in high‐tide flooding across the United States over the past few decades. From 1990–2000 to 2010–2020, high‐tide flooding rates almost certainly (probability P>99%$P > 99\\%$ ) increased along the United States East Coast, Gulf Coast, California, and Pacific Islands, while they very likely (P=93%)$(P=93\\%)$decreased along Alaska during that time; significant changes in high‐tide flooding rates between the two decades were not detected in Oregon, Washington, and the Caribbean. Averaging spatially, we find that high‐tide flooding rates probably (P=85%)$(P=85\\%)$more than doubled nationally between 1990–2000 and 2010–2020. Our approach lays a foundation for future studies to more accurately model high‐tide flood thresholds and trends along the global coastline. Plain Language Summary As climate warms, and sea level rises, high‐tide flooding will happen more frequently. High‐tide flooding is recurrent, minor and disruptive coastal inundation. To quantify how high‐tide flood rates are changing, we need observations of coastal water levels and data on high‐tide flooding thresholds. With this information, we define high‐tide flooding when water level rises above a flood threshold. A challenge is that we seldom have sufficient knowledge to define flood thresholds in terms of impacts. Thus, past high‐tide flooding studies in the U.S. used alternative methods to define thresholds. As a result, there can be discrepancies between published estimates of high‐tide flooding in the U.S., which are not always interpretable in terms of impacts. We analyzed sparsely available impact‐based flood threshold data using a probabilistic model to estimate high‐tide flood thresholds everywhere on the U.S. coast, and we used those estimates to quantify recent high‐tide flood trends. We find that, on average, high‐tide flooding rates in the U.S. more than doubled over the past three decades. More regionally, high‐tide flooding rates increased along the East Coast, Gulf Coast, California, and Pacific Islands, decreased along Alaska, and held steady along Oregon, Washington, and the Caribbean over that same period. Key Points Past estimates of high‐tide flooding for the U.S. feature systematic uncertainty related to their different choices of flood thresholds We develop a probabilistic spatial model for inferring impact‐based high‐tide flood thresholds everywhere along the U.S. coastline We determine that high‐tide flooding rates in the U.S. likely more than doubled between 1990–2000 and 2010–2020

Fishery management relies on forecasts of fish abundance over time and space, on scales of months and kilometres. While much research has focussed on the drivers of fish populations, there has been less investigation of the decisions made day-to-day by fishers and their subsequent impact on fishing pressure. Studies that focus on the fisher decisions of smaller vessels may be particularly important due to the prevalence of smaller vessels in many fisheries and their potential vulnerability to bad weather and economic change. Here we outline a methodology with which to identify the factors affecting fisher decisions and success as well as quantifying their effects. We analyse first the decision of when to leave port, and then the success of the fishing trip. Fisher behaviour is here analysed in terms of the decisions taken by fishers in response to bio-physical and socio-economic changes and to illustrate our method, we describe its application to the under 10-meter fleet targeting sea bass in the UK. We document the effects of wave height and show with increasing wave height fewer vessels left port to go fishing. The decision to leave port was only substantially affected by time of high tide at one of the four ports investigated. We measured the success of fishing trips by the landings of sea bass (kg) per metre of vessel length. Fishing success was lower when wave height was greater and when fish price had increased relative to the previous trip. Fuel price was unimportant, but a large proportion of the variation in success was explained by variation between individual vessels, presumably due to variation in skipper ability or technical restrictions due to vessel characteristics. The results are discussed in the context of management of sea bass and other small-scale inshore fisheries.

High tide flooding (HTF) occurs when astronomically driven water levels rise above flooding thresholds in coastal areas, which can happen on sunny days. In a warming climate, sea‐level rise (SLR) is expected to change the frequency of HTF via a direct non‐linear change in the mean water level. In this study, we investigate the impacts of SLR on HTF along the Gulf and Atlantic Coasts of the United States. We quantify the extent to which SLR is expected to exacerbate the HTF regime in the coming decades if no more flood protection is implemented. We estimate SLR at 10 km intervals using regression models, add it to numerically simulated tidal levels, and compare the results with estimated HTF thresholds. Our results provide continuous spatial coverage along the Atlantic and Gulf Coasts, showing a projected average rise of 0.35 ± 0.10 m in tidal levels above the mean higher high water (MHHW) by 2050, whereas Chesapeake Bay is projected to experience a greater rise of 0.39 ± 0.05 m, and Maine is expected to see a lower increase of 0.27 ± 0.08 m. This yields an increase of 10 days/year and 110 days/year in HTF hours in the years 2050 and 2100, respectively. Moreover, Pamlico Sound and Chesapeake Bay are expected to experience the most significant changes in HTF frequency, with more than 90 days of HTF by 2050s. Our results show that HTF regime in mesotidal semidiurnal systems are, on average, more sensitive to the projected SLR than the rest. Plain Language Summary High tide flooding (HTF) happens when coastal water levels (a combination of mean sea level, harmonic tides, and non‐tidal residuals) rise above certain flood levels without extreme weather, even on sunny days. As a result of global warming, sea level rise (SLR) directly increases the average water level, leading to more frequent occurrences of HTF. This study shows how SLR is projected to increase HTF frequency along the Gulf and Atlantic Coasts of the United States. Regression and process‐based modeling methods are used to achieve tidal‐level projections that further our understanding of expected changes in the HTF regime. In view of the increase in the 95th percentile of the tidal levels, regions such as Pamlico Sound in North Carolina and Chesapeake Bay are expected to endure more than 90 days of exposure to HTF by the mid‐21st century. This study identifies hotspots requiring urgent attention to implement mitigation strategies. We underscore the urgent need for coastal communities to consider flood protection measures that prepare them for such impacts based on local SLR information. Additionally, this study suggests that local governments should prioritize adaptation and mitigation strategies to protect vulnerable regions from the growing threat of HTF. Key Points This study presents spatially distributed estimates of changes in high tide flooding (HTF) regimes along the coasts of the United States The largest HTF increases are expected in the Chesapeake Bay, North Carolina, Louisiana, and Texas by the end of this century Our findings highlight the need for region‐specific flood strategies based on high‐resolution SLR and HTF information

A growing demand for sustainable energy has led to an increase in construction of offshore windfarms. Guishan windmill farm will be constructed in the Pearl River Estuary, China, which sustains the world's largest known population of Indo-Pacific humpback dolphins (Sousa chinensis). Dolphin conservation is an urgent issue in this region. By using passive acoustic monitoring, a baseline distribution of data on this species in the Pearl River Estuary during pre-construction period had been collected. Dolphin biosonar detection and its diel, lunar, seasonal and tidal patterns were examined using a Generalized Linear Model. Significant higher echolocation detections at night than during the day, in winter-spring than in summer-autumn, at high tide than at flood tide were recognized. Significant higher echolocation detections during the new moon were recognized at night time. The diel, lunar and seasonal patterns for the echolocation encounter duration also significantly varied. These patterns could be due to the spatial-temporal variability of dolphin prey and illumination conditions. The baseline information will be useful for driving further effective action on the conservation of this species and in facilitating later assessments of the effects of the offshore windfarm on the dolphins by comparing the baseline to post construction and post mitigation efforts.

Limited information exists on the occurrence of microplastics (MPs) in East African coastal waters. A 300 μm manta net was used to collect surface water from 8 sites in the regions Dar es Salaam (DES) and Zanzibar (ZZ) during low and high tides. DES had a higher (p < 0.05) abundance of MPs than ZZ. Fragments and fibers were the dominant MP types at all sites. The number of fibers was significantly higher (p = 0.002) in DES than in ZZ. MPs were more prevalent during high tide in both DES and ZZ. The MPs within the 2–5 mm size range were identified most often. White and blue MPs were the most common in study sites comprising 45% and 18% of the total MPs respectively. Three polymers polypropylene (PP) high-density polyethylene (HDPE) and low-density polyethylene (LDPE) were identified. The occurrence of MPs in nearshore waters of DES and ZZ is probably due to their proximity to industrial areas, poor solid waste management, and high population pressure.

Recreational water quality, as measured by culturable fecal indicator bacteria (FIB), may be influenced by persistent populations of these bacteria in local sands or wrack, in addition to varied fecal inputs from human and/or animal sources. In this study, pyrosequencing was used to generate short sequence tags of the 16S hypervariable region ribosomal DNA from shallow water samples and from sand samples collected at the high tide line and at the intertidal water line at sites with and without FIB exceedance events. These data were used to examine the sand and water bacterial communities to assess the similarity between samples, and to determine the impact of water quality exceedance events on the community composition. Sequences belonging to a group of bacteria previously identified as alternative fecal indicators were also analyzed in relationship to water quality violation events. We found that sand and water samples hosted distinctly different overall bacterial communities, and there was greater similarity in the community composition between coastal water samples from two distant sites. The dissimilarity between high tide and intertidal sand bacterial communities, although more similar to each other than to water, corresponded to greater tidal range between the samples. Within the group of alternative fecal indicators greater similarity was observed within sand and water from the same site, likely reflecting the anthropogenic contribution at each beach. This study supports the growing evidence that community-based molecular tools can be leveraged to identify the sources and potential impact of fecal pollution in the environment, and furthermore suggests that a more diverse bacterial community in beach sand and water may reflect a less contaminated site and better water quality.