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  • 1
    Electronic Resource
    Electronic Resource
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Environment and Resources 22 (1997), S. 47-74 
    ISSN: 1056-3466
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract Projections of the effect of climate change on future water availability are examined by reviewing the formulations used to calculate moisture transport between the ground and the atmosphere. General circulation models and climate change impact models have substantially different formulations for evapotranspiration, so their projections of future water availability often disagree, even though they use the same temperature and precipitation forecasts. General circulation models forecast little change in tropical and subtropical water availability, while impact models show severe water and agricultural shortages. A comparison of observations and modeling techniques shows that the parameterizations in general circulation models likely lead to an underestimate of the impacts of global warming on soil moisture and vegetation. Such errors would crucially affect the temperature and precipitation forecasts used in impact models. Some impact model evaporation formulations are probably more appropriate than those in general circulation models, but important questions remain. More observations are needed, especially in the vicinity of forests, to determine appropriate parameterizations.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    OR spectrum 15 (1993), S. 83-94 
    ISSN: 1436-6304
    Keywords: Sequential asset-selling ; dynamic programming ; Sequentielle Verkaufsprobleme ; Dynamische Optimierung
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Economics
    Description / Table of Contents: Zusammenfassung Wir untersuchen folgende „symmetrische“ Verallgemeinerung des bekannten Hausverkaufsproblems. Ein Unternehmen betreibt zwei verschiedene Aktivitäten, von denen pro Periode genau eine ausgeführt werden muß. Für jede Aktivität ist vorgeschrieben, wie oft sie durchzuführen ist. Ein Beispiel ist die Entsorgung voni bzw.j Containern mit Giftmüll. Die zufälligen (eventuell negativen) Gewinne für die Durchführung der Aktivitäten sind unabhängig und identisch verteilt mit bekannter gemeinsamer zwei-dimensionaler Verteilung. Ferner entstehen pro Periode feste Kosten (evtl. negativ) der Höhec bzw.c 1 bzw.c 2, solange noch beide Arten bzw. nur die erste Art bzw. nur die zweite Art der Aktivitäten durchgeführt werden müssen. Aufgrund der Beobachtungen der beiden möglichen Gewinne muß in jeder Periode entschieden werden, welche der beiden Aktivitäten bearbeitet werden soll, damit der erwartete Gesamtgewinn maximal wird. Wir zeigen für beliebigen Diskontierungsfaktor die Existenz einer optimalen Kontrollgrenzen-Politik mit rekursiv berechenbaren kritischen Zahlend ij . Einige explizit lösbare Fälle werden angegeben. Unter bestimmten Bedingungen sind die kritischen Zahlend ij monoton ini und/oderj. Dies erlaubt trotz eines 4-dimensionalen Zustandsraums die Darstellung der optimalen Politik durch eine Familie 2-dimensionaler monotoner Entscheidungsregionen. Die Grenzwerte derd ij gestatten dann die Bestimmung „großer“ Mengen von Zuständen, in denen optimale Entscheidungen ohne numerische Rechnungen gefunden werden können. Das wesentliche Hilfsmittel ist die integrierte Verteilungsfunktion der Differenz der Gewinne. Die Arbeit verallgemeinert viele bekannte Resultate über das Hausverkaufsproblem ohne Rückgriff.
    Notes: Summary We consider the following “symmetric” generalization of the well-known asset-selling problem. Assume that there are two activities, each of which must be carried out a given number of times. An example is the disposal ofi andj containers of toxic waste of two different kinds. Exactly one of the activities is performed per time period. The random rewards (possibly negative) for performing the different tasks are i.i.d. and have a known two-dimensional joint distribution. In addition, there are fixed costsc, c 1 andc 2 (possibly negative) per period as long as activities of both kinds, or only of the first or only of the second kind must be performed. Based on a realization of the two random rewards, each period a choice must be made which of the two activities to perform such that the expected total reward becomes maximal. We show for arbitrary discount factor the existence of an optimal control limit policy with recursively computable critical numbersd ij . Some explicitly solvable cases are presented. Under appropriate assumptions thed ij 's are monotone ini and/orj which allows, despite a 4-dimensional state space, to represent the optimal policy by a family of 2-dimensional monotone decision regions. And then, the limits of thed ij 's can be used to identify “large” sets of states where the optimal decision can be found without numerical computations. The basic tool is the integrated distribution function of the difference of the two rewards. The paper generalizes many of the known results on asset-selling problems without recall.
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  • 3
    Publication Date: 2014-02-13
    Description: While river-borne materials are recognized as important resources supporting coastal ecosystems around the world, estimates of river export from the North Slope of Alaska have been limited by a scarcity of water chemistry and river discharge data. This paper quantifies water, nutrient, and organic matter export from the three largest rivers (Sagavanirktok, Kuparuk, Colville) that drain Alaska's North Slope and discusses the potential importance of river inputs for biological production in coastal waters of the Alaskan Beaufort Sea. Together these rivers export ~297,000 metric tons of organic carbon and ~18,000 metric tons of organic nitrogen each year. Annual fluxes of nitrate-N, ammonium-N, and soluble reactive phosphorus are approximately 1750, 200, and 140 metric tons per year respectively. Constituent export from Alaska's North Slope is dominated by the Colville River. This is in part due to its larger size, but also because constituent yields are greater in the Colville watershed. River-supplied nitrogen may be more important to productivity along the Alaskan Beaufort Sea coast than previously thought. However, given the dominance of organic nitrogen export, the potential role of river-supplied nitrogen in support of primary production depends strongly on remineralization mechanisms. Although rivers draining the North Slope of Alaska make only a small contribution to overall river export from the pan-arctic watershed, comparisons with major arctic rivers reveal unique regional characteristics as well as remarkable similarities among different regions and scales. Such information is crucial for development of robust river export models that represent the arctic system as a whole.
    Print ISSN: 0043-1397
    Electronic ISSN: 1944-7973
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 4
    Publication Date: 2019
    Description: Abstract Depth transects of benthic foraminiferal oxygen isotopes from the Atlantic Ocean show that glacial‐interglacial changes are larger at deep (〉 ~2,000 m) than at intermediate water levels. Our model results suggest that the smaller changes in the upper 1,000 m of the water column are a result of the glacial sea level lowering of about 120 m, leading to warmer temperatures of around 1 °C and hence a smaller glacial‐interglacial stable oxygen isotope difference. In contrast, a shoaling of the water mass boundary to ~2,000‐m water depth between the northern and southern source waters is caused by the expansion of a cold (close to the freezing point) southern source water in the abyssal ocean, increasing the oxygen isotope values of benthic foraminifera from the Last Glacial Maximum in the deep Atlantic. These two effects explain the different amplitudes of glacial‐interglacial stable oxygen isotope differences in the upper and deeper water column of the Atlantic Ocean.
    Print ISSN: 0883-8305
    Electronic ISSN: 2572-4525
    Topics: Geosciences
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 5
    Publication Date: 1993-06-01
    Print ISSN: 0171-6468
    Electronic ISSN: 1436-6304
    Topics: Mathematics , Economics
    Published by Springer
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  • 6
    Publication Date: 2002-09-01
    Print ISSN: 0304-3800
    Electronic ISSN: 1872-7026
    Topics: Biology
    Published by Elsevier
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  • 7
    Publication Date: 2007-11-08
    Print ISSN: 0148-0227
    Electronic ISSN: 2156-2202
    Topics: Geosciences
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  • 8
    Publication Date: 2011-03-23
    Description: An assessment of regional similarity in catchment stream response is often needed for accurate predictions in ungauged catchments. However, it is not clear whether similarity among catchments is preserved at all flow conditions. We address this question through the analysis of flow duration curves for 25 gauged catchments located across four river basins in the northeast United States. The coefficient of variation of streamflow percentiles is used as a measure of variability among catchments across flow conditions. Results show that similarity in catchment stream response is dynamic and highly dependent on flow conditions. Specifically, within each of the four basins, the coefficient of variation is high at low flow percentiles and gradually reduces for higher flow percentiles. Analysis of the inter-annual variation in streamflow percentiles shows a similar reduction in variability from low flow to high flow percentiles. Greater similarity in streamflows is observed during the winter and spring (wet) seasons compared to the summer and fall (dry) seasons. Results suggest that the spatial variability in streamflow at low flows is primarily controlled by the dominance of high evaporative demand during the warm period. On the other hand, spatial variability at high flows during the cold period is controlled by the increased dominance of precipitation input over evapotranspiration. By evaluating variability over the entire range of streamflow percentiles, this work explores the nature of hydrologic similarity from a seasonal perspective.
    Print ISSN: 1027-5606
    Electronic ISSN: 1607-7938
    Topics: Geography , Geosciences
    Published by Copernicus on behalf of European Geosciences Union.
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  • 9
    Publication Date: 2012-02-23
    Description: Prediction of streamflow at ungauged catchments requires transfer of hydrologic information (e.g., model parameters, hydrologic indices, streamflow values) from gauged (donor) to ungauged (receiver) catchments. A common metric used for the selection of ideal donor catchments is the spatial proximity between donor and receiver catchments. However, it is not clear whether information transfer among nearby catchments is suitable across a wide range of climatic and geographic regions. We examine this issue using the data from 756 catchments within the continental United States. Each catchment is considered ungauged in turn and daily streamflow is simulated through distance-based interpolation of streamflows from neighboring catchments. Results show that distinct geographic regions exist in US where transfer of streamflow values from nearby catchments is useful for retrospective prediction of daily streamflow at ungauged catchments. Specifically, the high predictability catchments (Nash-Sutcliffe efficiency NS 〉 0.7) are confined to the Appalachian Mountains in eastern US, the Rocky Mountains, and the Cascade Mountains in the Pacific Northwest. Low predictability catchments (NS 〈 0.3) are located mostly in the drier regions west of Mississippi river, which demonstrates the limited utility of gauged catchments in those regions for predicting at ungauged basins. The results suggest that high streamflow similarity among nearby catchments (and therefore, good predictability at ungauged catchments) is more likely in humid runoff-dominated regions than in dry evapotranspiration-dominated regions. We further find that higher density and/or closer distance of gauged catchments near an ungauged catchment does not necessarily guarantee good predictability at an ungauged catchment.
    Print ISSN: 1027-5606
    Electronic ISSN: 1607-7938
    Topics: Geography , Geosciences
    Published by Copernicus on behalf of European Geosciences Union.
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  • 10
    Publication Date: 2011-10-19
    Description: Prediction of streamflows at ungauged catchments requires transfer of hydrologic information (e.g., model parameters, hydrologic indices, streamflow values) from gauged (donor) to ungauged (receiver) catchments. One of the most reliable metrics for selection of ideal donor catchments is the spatial proximity between donor and receiver catchments. However, it is not clear whether information transfer among nearby catchments is suitable across a wide range of climatic and geographic regions. We examine this issue using the data from 756 catchments within the continental United States. Each catchment is considered ungauged in turn and daily streamflow is simulated through distance-based interpolation of streamflows from neighboring catchments. Results show that distinct geographic regions exist in US where transfer of streamflow values from nearby catchments is useful for retrospective prediction of daily streamflow at ungauged catchments. Specifically, the high predictability catchments (Nash-Sutcliffe efficiency NS 〉 0.7) are confined to the Appalachian Mountains in eastern US, the Rocky Mountains, and the Cascade Mountains in the Pacific Northwest. Low predictability catchments (NS 〈 0.3) are located mostly in the drier regions west of Mississippi river, which demonstrates the limited utility of gauged catchments in those regions for predicting at ungauged basins. The results suggest that high streamflow similarity among nearby catchments (and therefore, good predictability at ungauged catchments) is more likely in humid runoff-dominated regions than in dry evapotranspiration-dominated regions. We further find that higher density and/or closer distance of gauged catchments near an ungauged catchment does not necessarily guarantee good predictability at an ungauged catchment.
    Print ISSN: 1812-2108
    Electronic ISSN: 1812-2116
    Topics: Geography , Geosciences
    Published by Copernicus on behalf of European Geosciences Union.
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