Academic literature on the topic 'Sea-inland gradient'
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Journal articles on the topic "Sea-inland gradient"
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Wermter, Joseph, Stephen Noble, and Brian Viner. "Impacts of the Thermal Gradient on Inland Advecting Sea Breezes in the Southeastern United States." Atmosphere 13, no. 7 (June 22, 2022): 1004. http://dx.doi.org/10.3390/atmos13071004.
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Sea breezes are frequently observed in the South Carolina/Georgia region of the Southeastern United States (SEUS) and can reach upwards of 150km inland. This region is unique among the places frequently affected by sea breeze due to it being a continental location with relatively flat topography. The thermal gradient between land and water environments is a factor in introducing the sea breeze, but its role in the inland extent of sea breeze propagation isn’t as well known. We investigate the role of the thermal gradient in previously catalogued sea breeze events observed at the Savannah River Site (SRS) by taking differences of temperature measurements at inland and coastal weather stations for the days that the events occurred. We saw that the temperature differences for those days were much higher than in the non-sea breeze days during the mornings and afternoon. Numerical models were also used to conduct a sensitivity study on a sea breeze case, using simple modifications of the temperature gradient. We found that while the modifications did not stop the generation of a sea breeze circulation, the extent of the inland propagation was dependent on the magnitude of the thermal gradient.
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You, Cheng, Jimmy Chi-Hung Fung, and Wai Po Tse. "Response of the Sea Breeze to Urbanization in the Pearl River Delta Region." Journal of Applied Meteorology and Climatology 58, no. 7 (July 2019): 1449–63. http://dx.doi.org/10.1175/jamc-d-18-0081.1.
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AbstractThe Pearl River delta (PRD) region has undergone rapid urbanization since the 1980s, which has had significant effects on the sea-breeze circulation in this region. Because the sea breeze plays an important role in pollutant transportation and convective initiation in the PRD region, it is meaningful to study the effects of urbanization on the sea breeze. In this study, three numerical experiments were conducted from 2 June to 31 August 2010 with land-use data from 1988, 1999, and 2010. For each simulation, characteristics of the sea breeze such as the start time, end time, intensity, height, pumping ability, and inland penetration distance were quantified. By comparing the characteristics of the sea breeze in these simulations, its response to urbanization was quantified. The results show that urbanization enhances the duration, height, and intensity of the sea breeze but blocks its inland penetration. One physical mechanism is proposed to dynamically elucidate the response of the sea breeze to urbanization. Because the urban area in the PRD region is concentrated near the coast, urbanization imposes a positive heating gradient on the coastal region and a negative heating gradient on the region farther inland. The positive heating gradient may intensify the sea breeze, and the negative heating gradient may prevent the sea breeze from propagating farther inland.
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Zheng, Xiaoxue, Yan Tao, Zhongqiang Wang, Chen Ma, Hong He, and Xiuqin Yin. "Soil macro-fauna respond to environmental variations along a coastal-inland gradient." PeerJ 8 (July 14, 2020): e9532. http://dx.doi.org/10.7717/peerj.9532.
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Varied environmental conditions in coastal-inland zones tend to influence soil faunal communities. However, few studies have focused on the responses of soil fauna to environmental variations along the coastal-inland gradient. In order to better understand the aforementioned responses, a total of 80 soil macro-faunal samples were collected at the five different distances from the coastline of China’s Bohai Bay. The results revealed that the compositions, structural characteristics and diversity of the soil macro-fauna varied among the different habitats. With the increases in the distance from the sea, the individual density, richness and diversity levels of the soil macro-fauna all first increased and then decreased. The individual density, richness and diversity values were all at their maximum at 30 km from the sea. The Edge effect promoted unique and rare soil macro-faunal taxa. Formicidae, Curculionidae and Aphodiidae were found to be the edge taxa. Agelenidae, Liocranidae and Nematocera were considered to be indicator taxa of severe sea effects. Paradoxosomatidae was an indicator taxon of slight effects. Overall, the environmental variations along the coastal-inland gradient were found to have the potential to affect the soil macro-faunal communities, and the different taxa of the soil macro-fauna responded to those variations in different ways. This study further revealed the processes and mechanisms of the sea influencing the soil macro-faunal communities, which had been caused by the coastal-inland gradient. The results of this study also provided a theoretical basis for developing future biodiversity guidelines for coastal ecosystems.
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Yu, Xiaojie, Xinyu Guo, and Hidetaka Takeoka. "Fortnightly Variation in the Bottom Thermal Front and Associated Circulation in a Semienclosed Sea." Journal of Physical Oceanography 46, no. 1 (January 2016): 159–77. http://dx.doi.org/10.1175/jpo-d-15-0071.1.
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AbstractSummer hydrographic data from 1971 to 2000 demonstrate the presence of bottom cold water (BCW) and a bottom thermal front around the BCW in a semienclosed sea in the Seto Inland Sea of Japan. The horizontal gradient of water temperature across the bottom front was larger in neap tide than in spring tide, which is the opposite the pattern observed in the fortnightly variations in other areas (e.g., the Irish Sea). A numerical model for the Inland Sea reproduced the presence of BCW and a bottom front as well as the same fortnightly variation in the horizontal gradient of water temperature across the bottom front as in observational data. Being the same BCW as those in other areas, the presence of BCW in the Inland Sea is also caused by spatial variation in tidal mixing. The intensification of the bottom front in neap tide in the Inland Sea results from a combination of tidal mixing and horizontal advection of warm water to the BCW. The presence of a bottom residual current in the direction across the bottom front results in the horizontal advection of warm water to the BCW, and its fortnightly variation is responsible for the fortnightly variation of the bottom front in the Inland Sea. The presence of the BCW induces a surface cyclonic circulation in the direction approximately along the bottom front; the intensification and weakening of the bottom front with the spring–neap tidal cycle, combined with the fortnightly variation in the bottom boundary layer thickness, produce a slightly stronger surface cyclonic circulation in neap tide than in spring tide.
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Molinet, Carlos, Carlos A. Moreno, Edwin J. Niklitschek, Manira Matamala, Mónica Neculman, Alejandra Arévalo, José Codjambassis, Patricio Diaz, and Manuel Diaz. "Reproduction of the sea urchin Loxechinus albus across a bathymetric gradient in the Chilean Inland Sea." Revista de biología marina y oceanografía 47, no. 2 (August 2012): 257–72. http://dx.doi.org/10.4067/s0718-19572012000200008.
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LOHAR, D., B. CHAKRAVARTY, and B. Pal. "Sensitivity studies on the air flow characteristics In Kharagpur using a meso-scale model." MAUSAM 44, no. 4 (January 1, 2022): 329–36. http://dx.doi.org/10.54302/mausam.v44i4.3903.
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A three-dimensional hydrostatic model has been employed for the study of sea breeze circulations over south West Bengal with special reference to an inland station Kharagpur (22°.21' N, 87° 19'E). A series of sensitivity experiments have been performed to stress the Importance of differential heating on circulation over south West Bengal during pre-monsoon period. It is found that due to differential heating rate between land and sea surfaces, sea breezes can penetrate to the inland station Kharagpur and beyond even in case of moderate gradient wind. Surface observations at Kharagpur and pilot balloon observation at nearby station Kalaikunda are used to compare the model results. The onset of sea breezes, variation of the air temperature and humidity are In fairly good agreement whereas It over estimates the depth of the circulation and cannot predict the variation of the late morning hours surface wind.
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RAO, D. VENKATESWARA. "The speed and some other features of the sea-breeze Front at Madras." MAUSAM 6, no. 3 (December 3, 2021): 233–42. http://dx.doi.org/10.54302/mausam.v6i3.4479.
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The speed with which the sea breeze advances inland at Madras under various meteorological conditions and Its dependence on the time of onset and depth of penetration are discussed in this paper, utilising the records for the year 1945 and 1946 of autographic instruments at three stations located at different distances from the coast. A velocity of 10-15 mph, a south southeasterly direction of the resultant wind, the months April to September and a time of onset during the early afternoon are favoured most by the sea breeze at Madras. The average speed of the sea- breeze front is found to be 37 mph. It is accelerated with depth of penetration inland independently of the wind speed. It varies with the hour of onset of the sea-breeze, being lowest during the epoch of maximum temperature. The variation of the ratio of the speed inland to that near the coast with time of onset and direction of the on-shore wind is investigated. The results are explained on t he basis of the temperature gradient and its variation with distance inland. The mean temperature drop and vapour pressure rise caused by the sea-breeze for different times of incidence and magnitudes of wind velocity in the various months have also been studied. The changes are maximum in the proximity of the epoch of maximum temperature and in the month of July in the year. The results of this study would help in anticipating with sufficient accuracy and sufficiently in advance for aviation needs the time of onset of the sea-breeze and the accompanying meteorological changes at the airfield at Meenambakkam given the time of incidence and the direction of the on shore wind earlier at a point closer to the coast.
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Yoshikado, Hiroshi. "Intense Summer Heat in Tokyo and Its Suburban Areas Related with Variation in the Synoptic-Scale Pressure Field: A Statistical Analysis." Journal of Applied Meteorology and Climatology 52, no. 9 (September 2013): 2065–74. http://dx.doi.org/10.1175/jamc-d-12-0315.1.
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AbstractIntense summer heat in Tokyo, Japan, and its suburban areas between 1990 and 2010 was statistically analyzed. Sample days were selected from among days with a sea breeze and sufficient sunshine duration, because sea breeze is the dominant summertime meteorological system in the region. Excess in the daily maximum temperature of an inland urban site in Tokyo over a site facing the outer sea where the sea breeze originates was selected as a key index. A comparison of a group of days for which the temperature excess was large with an opposing group of days for which it was small revealed a distinct difference in diurnal wind variations: persistent southwesterly winds overwhelmed the sea breeze in areas facing the outer sea in the former case, whereas in the latter case a diurnal sea-breeze cycle was typically observed in those areas as well as in the inland areas. This difference could furthermore be connected to differences in the pressure gradient in the region, that is, differences in the synoptic-scale pressure field. As a result, slight shifts in the pressure field affect urban heat, suggesting that, in addition to general warming, changes in the pressure field resulting from future climate change can be of great importance.
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Khodzher, T. V., L. P. Golobokova, E. Yu Osipov, Yu A. Shibaev, V. Ya Lipenkov, O. P. Osipova, and J. R. Petit. "Spatial–temporal dynamics of chemical composition of surface snow in East Antarctica along the Progress station–Vostok station transect." Cryosphere 8, no. 3 (May 19, 2014): 931–39. http://dx.doi.org/10.5194/tc-8-931-2014.
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Abstract. In January of 2008, during the 53rd Russian Antarctic Expedition, surface snow samples were taken from 13 shallow (0.7 to 1.5 m depth) snow pits along the first tractor traverse from Progress to Vostok stations, East Antarctica. Sub-surface snow/firn layers are dated from 2.1 to 18 yr. The total length of the coast to inland traverse is more than 1280 km. Here we analysed spatial variability of concentrations of sulphate ions and elements and their fluxes in the snow deposited within the 2006–2008 time interval. Anions were analysed by high-performance liquid chromatography (HPLC), and the determination of selected metals, including Na, K, Mg, Ca and Al, was carried out by mass spectroscopy with atomization by induced coupled plasma (ICP-MS). Surface snow concentration records were examined for trends versus distance inland, elevation, accumulation rate and slope gradient. Na shows a significant positive correlation with accumulation rate, which decreases as distance from the sea and altitude increase. K, Ca and Mg concentrations do not show any significant relationship either with distance inland or with elevation. Maximal concentrations of these elements with a prominent Al peak are revealed in the middle part of the traverse (500–600 km from the coast). Analysis of element correlations and atmospheric circulation patterns allow us to suggest their terrestrial origin (e.g. aluminosilicates carried as a continental dust) from the Antarctic nunatak areas. Sulphate concentrations show no significant relationship with distance inland, elevation, slope gradient and accumulation rate. Non-sea salt secondary sulphate is the most important contribution to the total sulphate budget along the traverse. Sulphate of volcanic origin attributed to the Pinatubo eruption (1991) was revealed in the snow pit at 1276 km (depth 120–130 cm).
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Lebassi, Bereket, Jorge González, Drazen Fabris, Edwin Maurer, Norman Miller, Cristina Milesi, Paul Switzer, and Robert Bornstein. "Observed 1970–2005 Cooling of Summer Daytime Temperatures in Coastal California." Journal of Climate 22, no. 13 (July 1, 2009): 3558–73. http://dx.doi.org/10.1175/2008jcli2111.1.
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Abstract This study evaluated 1950–2005 summer [June–August (JJA)] mean monthly air temperatures for two California air basins: the South Coast Air Basin (SoCAB) and the San Francisco Bay Area (SFBA). The study focuses on the more rapid post-1970 warming period, and its daily minima temperature Tmin and maxima temperature Tmax values were used to produce average monthly values and spatial distributions of trends for each air basin. Additional analyses included concurrent SSTs, 40-yr European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-40) sea level coastal pressure gradients, and GCM-downscaled average temperature Tave values. Results for all 253 California National Weather Service (NWS) Cooperative Observer Program (COOP) sites together showed increased Tave values (0.23°C decade−1); asymmetric warming, as Tmin values increase faster than Tmax values (0.27° versus 0.04°C decade−1) and thus decreased daily temperature range (DTR) values (0.15°C decade−1). The spatial distribution of observed SoCAB and SFBA Tmax values exhibited a complex pattern, with cooling (−0.30°C decade−1) in low-elevation coastal areas open to marine air penetration and warming (0.32°C decade−1) in inland areas. Results also showed that decreased DTR values in the basins arose from small increases at inland sites (0.16°C decade−1) combined with large decreases (−0.58°C decade−1) at coastal sites. It is also possible that some of the current observed temperature trends could be associated with low-frequency decadal variability, expected even with a constant radiative forcing. Previous studies suggest that cooling JJA Tmax values in coastal California were a result of increased irrigation, coastal upwelling, or cloud cover. The current hypothesis is that they arise (as a possible “reverse reaction”) from the global warming of inland areas, which results in increased sea-breeze flow activity. GCM model Tave warming decreased from 0.13°C decade−1 at inland sites to 0.08°C decade−1 in coastal areas. Sea level pressure increased in the Pacific high and decreased in the thermal low. The corresponding gradient thus showed a trend of 0.04 hPa 100 km−1 decade−1, supportive of the hypothesis of increased sea-breeze activity.
Dissertations / Theses on the topic "Sea-inland gradient"
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BONARI, GIANMARIA. "DIFFERENT HABITAT AND TAXA: VARIOUS APPROACHES AND THEIR IMPLICATIONS FOR A LONG-SIGHTED MANAGEMENT AND CONSERVATION." Doctoral thesis, Università di Siena, 2017. http://hdl.handle.net/11365/1010508.
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The thesis starts in the continental context of the White Carpathians Protected Landscape Area and UNESCO Biosphere Reserve (Czech Republic), a protected area famous for its grasslands with the globally highest fine-scale plant species richness. The effects of management on species richness and composition of both plants and animals were tested in relation to different management practices (mowing, grazing, abandonment and mixed management) for several years at several sites, clarifying the disagreements that have occurred among conservationists and practitioners to date. The thesis continues with a focus on the Mediterranean context. Here, the distribution patterns of understorey assemblages of coastal pine stands on sand dunes were studied, given the scarcity of literature due to scholarly disdain. Using more than a hundred plots along Italian coastlines in different pine forest types, community similarity and specificity was assessed in order to provide lacking management clues. Subsequently, focusing on a pine forest stand located in Southern Tuscany, the thesis aimed to solve another pivotal question, namely by investigating the concordance of species assemblages between vascular plants, oribatid mites and soil chemical properties with special attention to the role of vegetation structure (i.e. tree, shrub and herbaceous cover) for biological components. This part provides new answers about congruence among communities and following appropriate management practices to be fulfilled for communities. The last part, performed along a wide range of Tuscan coasts, deals with one of the most extreme habitats in the Mediterranean basin: coastal dunes. Here, the understanding of the response of plant species to soil factors was estimated. This provides concrete proposals for the effective conservation of coastal habitats.
Book chapters on the topic "Sea-inland gradient"
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Bayly, Brian. "Disequilibrium 1: Potential Gradients and Flows." In Chemical Change in Deforming Materials. Oxford University Press, 1993. http://dx.doi.org/10.1093/oso/9780195067644.003.0008.
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As in Chapter 2, so again here the intention is to review ideas that are already familiar, rather than to introduce the unfamiliar; to build a springboard, but not yet to leap off into space. The familiar idea is of flow down a gradient—water running downhill. Parallels are electric current in a wire, salt diffusing inland from the sea, heat flowing from the fevered brow into the cool windowpane, and helium diffusing through the membrane of a helium balloon. For any of these, we can imagine a linear relation: . . . Flow rate across a unit area = (conductivity) x (driving gradient) . . . where the conductivity retains a constant value, and if the other two quantities change, they do so in a strictly proportional way. Real life is not always so simple, but this relation serves to introduce the right quantities, some suitable units and some orders of magnitude. For present purposes, the second and fourth of the examples listed are the most relevant. To make comparison easier we imagine a barrier through which salt can diffuse and through which water can percolate, but we imagine circumstances such that only one process occurs at a time. Specifically, imagine a lagoon separated from the ocean by a manmade dike of gravel and sand 4 m thick, as in Figure 3.1. If the lagoon is full of seawater but the water levels on the two sides of the dike are unequal, water will percolate through the dike, whereas if the levels are the same and the dike is saturated but the lagoon is fresh water, salt will diffuse through but there will be no bulk flow of water. (More correctly, because seawater and fresh water have different densities, and because of other complications, the condition of no net water flow would be achieved in circumstances a little different from what was just stated. For present purposes all we need is the idea that conditions exist where water does not percolate but salt does diffuse.) For flow of water driven by a pressure gradient, suitable units are shown in the upper part of Table 3.1 and for diffusion of salt driven by a concentration gradient, suitable units are shown in the lower part.
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Woodroffe, Colin D. "Southeast Asian Deltas." In The Physical Geography of Southeast Asia. Oxford University Press, 2005. http://dx.doi.org/10.1093/oso/9780199248025.003.0024.
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Deltas and estuaries are actively evolving suites of landforms formed where rivers meet the sea. Deltas are characteristically subaerial (and subaqueous) sediment wedges that protrude from the shoreline, whereas estuaries are typically tidally influenced lower parts of rivers in which the shoreline recedes inland. However, the individual distributaries of deltas, which may themselves be cuspate, exhibit estuarine characteristics, and it is convenient to use the term ‘deltaic–estuarine’ to describe river mouth tidal and alluvial plains. There are extensive low-lying coastal and deltaic–estuarine plains throughout Southeast Asia. These represent productive and relatively easily settled land, which has led to clearance of the natural vegetation of many of these plains for agriculture, silviculture, or settlement. Deltaic–estuarine plains are geologically young, responding to Late Quaternary sea-level and climatic fluctuations, and actively undergoing change in the modern landscape. Most have adopted their present form only in the past few thousand years, and are still active centres of deposition. Worldwide expansion of deltas occurred in the early to mid-Holocene as a result of deceleration of postglacial sea-level rise and the coincidence of sea level with extensive low-gradient shorelines (Stanley and Warne 1994). The formation of deltaic–estuarine plains in semi-arid areas may have been a catalyst for the appearance of civilizations based upon cultivation (Stanley and Warne 1993). Deltas in Southeast Asia, however, presented major challenges to pre-technical societies, as a result of their propensity to flood, poor access across the many bifurcating channels, and malaria, and were slower to be colonized (Büdel 1966). However, they have subsequently become important areas supporting large populations, particularly as a result of successful management of inundation for the cultivation of rice (van de Goor 1966). Overbank flooding is a prominent feature of most deltas and assures nutrient re-enrichment of fertile, but immature, soils supporting intensive farming. On the other hand, such flooding can also represent a major hazard, damaging property and in some cases resulting in loss of life. It is often controlled, or control over the extent of flooding is sought through engineering works.
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Cretescu, Igor, Zsofia Kovacs, Liliana Lazar, Adrian Burada, Madalina Sbarcea, Liliana Teodorof, Dan Padure, and Gabriela Soreanu. "Danube Delta: Water Management on the Sulina Channel in the Frame of Environmental Sustainability." In River Deltas - Recent Advances [Working Title]. IntechOpen, 2021. http://dx.doi.org/10.5772/intechopen.97877.
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The Danube Delta is the newest land formed by both transporting sediments brought by Danube River, which flows into the Black Sea and by traversing an inland region where water spreads and deposits sediments. Diurnal tidal action is low (only 8–9 cm), therefore the sediments would wash out into the water body faster than the river deposits it. However, a seasonal fluctuation of water level of 20 cm was observed in the Black Sea, contributing to alluvial landscape evolution in the Danube Delta. The Danube Delta is a very low flat plain, lying 0.52 m above Mean Black Sea Level with a general gradient of 0.006 m/km and only 20% of the delta area is below zero level. The main control on deposition, which is a combination of river, wind-generated waves, and tidal processes, depends on the strength of each one. The other two factors that play a major role are landscape position and the grain size distribution of the source sediment entering the delta from the river. The Danube Delta is a natural protected area in the South-Eastern part of Romania, declared a Biosphere Reserve through the UNESCO “Man and Biosphere” Programme. Water is a determining factor for all the human settlements in the Biosphere Reserve, the whole Danube Delta being structured by the three branches of the Danube (Chilia, Sulina and Sfantu Gheorghe (Saint George)). Our case study is focused on the Sulina branch, also named Sulina Channel, which offers the shortest distance between the Black Sea (trough Sulina Port) and Tulcea (the most important city of the Danube Delta from economic, social and cultural points of view) for both fluvial and marine ships. The improvement of water resources management is the main topic of this chapter, in terms of water quality indicators, which will be presented in twenty-nine monitoring points, starting since a few years ago and updated to nowadays. During the study period, significant exceedances of the limit value were detected in case of nitrate-N (3.9–4.6 mg/L) at the confluence (CEATAL 2) with the Saint George branch and in the Sulina Channel after the Wastewaters Treatment Plant (WWTP) discharge area, as well as near two settlements, namely Gorgova and Maliuc. The higher concentrations of Nitrogen-based nutrients were caused by the leakage from the old sewage systems (where these exist) and the diffuse loads.
Conference papers on the topic "Sea-inland gradient"
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Sequera, Pedro, Yanelly Molina, Jorge E. Gonzalez, and Robert Bornstein. "Energy Demand Projections in the 21st Century for Coastal California." In ASME 2012 6th International Conference on Energy Sustainability collocated with the ASME 2012 10th International Conference on Fuel Cell Science, Engineering and Technology. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/es2012-91243.
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Previous studies conducted by Lebassi et al. (2010) and Sequera et al. (2011) have showed a strong correlation between summer temperature and electricity demand per capita trends for the past four decades for California. Decreasing summer temperature trends in low elevation coastal California sites between 1970–2010 resulted in decreasing electricity demand for the same locations. On the other hand, increasing temperature trends in high-elevation and inland California sites for the same period showed increasing electricity demand during summers. As a consequence of an increased gradient of the concurrent sea breeze potential for the same period, the authors suggested that this increased in sea breeze was responsible for the observed coastal cooling, attributing the seabreeze increase to a counter effect of global warming. The authors also reported increasing temperatures during winter throughout California for the same period, resulting in decreasing natural gas consumption. This work extends this analysis by determining spatial and temporal trends in residential electricity and natural gas consumption using 1990 to 2009 data from the California Energy Commission. Results show yearly electricity consumption per person is lower for coastal counties than inland counties. In contrast, yearly natural gas consumption per capita is decreasing for both coastal and inland counties. Additional work includes the examination of future summer axysymmetric warming and winter homogenous warming as well as their implications on energy demands into the 21st century. Results from 16 downscaled Global Circulation Models for 2 green-house gas emissions scenarios are used to forecast future average temperatures. These projections are correlated with electricity consumption during the summer and natural gas consumption during the winter. Statistical analysis of these results is provided in order to quantify uncertainty on these forecasts.
Reports on the topic "Sea-inland gradient"
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Rine, Kristin, Roger Christopherson, and Jason Ransom. Harlequin duck (Histrionicus histrionicus) occurrence and habitat selection in North Cascades National Park Service Complex, Washington. National Park Service, April 2022. http://dx.doi.org/10.36967/nrr-2293127.
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Harlequin ducks (Histrionicus histrionicus) are sea ducks that migrate inland each spring to nest along fast-flowing mountain streams. They are considered one of the most imperiled duck species in North America and occur in two distinct populations on the Atlantic and Pacific coasts. The Pacific coast population includes Washington State, where harlequin ducks breed in the Olympic, Cascade, and Selkirk Mountains. This species is designated as a Management Priority Species by the National Park Service within North Cascades National Park Service Complex (NOCA). This report summarizes harlequin duck surveys conducted during 15 years across a 27-year period (1990 and 2017) on major streams within NOCA, and incidental observations collected from 1968–2021. The primary objectives of these surveys were to 1) document the distribution and abundance of harlequin duck observations within NOCA boundaries, 2) describe productivity (number of broods and brood size), 3) describe breeding chronology of harlequin ducks, and 4) describe habitat characteristics of breeding streams. Sixty-eight stream surveys over 15 years resulted in observations of 623 individual harlequin ducks comprising various demographics, including single adults, pairs, and broods. In addition, we collected 184 incidental observations of harlequin ducks from visitors and staff between 1968–2021. Harlequin ducks were observed on 22 separate second- to sixth-order streams throughout NOCA across the entire 53-year span of data, both incidentally and during harlequin duck surveys by Park staff. Harlequin ducks were detected on 8 of the 13 streams that were actively surveyed. Excluding recounts, 88.7% (n = 330) of individual harlequin duck observations during surveys occurred in the Stehekin River drainage. Between all surveys and incidental observations, 135 unpaired females without broods were sighted across all NOCA waterways. Thirty-nine broods were recorded between NOCA surveys and incidental observations, with a mean brood size of 3.61 (± 1.44 SD; range = 2–10). Breeding pairs were recorded as early as April 5 and were seen on streams until June 15, a period of less than seven weeks (median: May 2), but most pairs were observed within a 3-week span, between April 26 and May 17. Single females (unpaired with a male, with (an)other female(s), or with a brood) were observed on streams between April 26 and August 25 (median: July 3), though most observations were made within a 5-week period between June 12 and July 19. Habitat data collected at adult harlequin duck observation sites indicate that the birds often used stream reaches with features that are characteristic of high-energy running water. While adults occupied all instream habitat types identified, non-braided rapids and riffles were used most frequently, followed by pools and backwaters. Larger instream substrate sizes (cobbles and boulders) were present at most observation sites. Adult harlequin ducks were more often found at locations that lacked visible drifting or lodged woody debris, but drift debris was a slightly more abundant debris type. The presence of gravel bars and at least one loafing site was common. Adult harlequin ducks were more often observed in association with vegetation that offered some cover over the channel, but not where banks were undercut. The average channel width at adult observation sites was 34.0 m (range: 6-80 m; n = 114) and 27.6 m (± 15.7 m; range: 10-60 m; n = 12) at brood observation sites. Compared to adult harlequin duck sites, broods were observed more frequently in low velocity habitat (pools, backwaters), but rarely in rapids. Cobble and boulder substrates were still the most dominant substrate type. Contrary to adult ducks, broods were observed most often observed in meandering stream channels, a morphology indicative of low gradient, low velocity stream reaches. Most broods were observed in stream reaches with gravel bars, loafing sites, and...