Harry F. Lins

Regional streamflow regimes and hydroclimatology of the United States

The dominant regions of interannual streamflow variability in the United States are defined, and their seasonality and persistence characteristics identified, using an orthogonally rotated principal components analysis (RPCA) of a climatically sensitive network of 559 stream gages for the period 1941-1988. This classification of streamflow regimes is comprehensive and unique in that separate analyses of the streamflow record, for each month of the year, are carried out to detail the month-to-month changes in the dominant streamflow patterns. Streamflow variations, or anomalies, in the Upper Mississippi, South Atlantic/Gulf, Far West, Ohio Valley, Northeast, and Eastern/Mid- Atlantic regions, as well as a pattern of opposing streamflow anomalies in the West, are observed in all seasons of the year. Anomalies in the Southern Plains and New England regions are observed in autumn, winter, and spring; those in the Rocky Mountains and Middle Mississippi regions occur in late spring and summer.

SEASONAL AND REGIONAL CHARACTERISTICS OF U.S. STREAMFLOW TRENDS IN THE UNITED STATES FROM 1940 TO 1999

J. R. Mather (1981) observed that runoff (streamflow) constitutes a significant phase of the hydrologic cycle. He also noted that it takes at least 15-25 years of systematic observations to characterize statistically the spatial and temporal patterns in streamflow. With this in mind, a recent assessment of temporal trends in streamflow (Lins and Slack, 1999) is updated to encompass the 60-year period 1940-1999, using data from 435 climate-sensitive stream-gauging stations and expanded to include regional and seasonal characteristics. The previously documented pattern of increasing discharge in the low to moderate range of flows is corroborated, with this pattern being most pronounced in the central two-thirds of the U.S. and to a lesser extent in the eastern coastal regions and in the Great Basin. Relatively few trends are observed in the annual maximum flow. No systematic shift in the timing of the annual minimum, median, or maximum flow is detected in any region on a monthly time scale. The observed increases in low to moderate streamflows, typical of the warm and transitional seasons, are consistent with documented trends in warm and transition season precipitation, and indicate that natural U.S. surface water supply has increased without a concomitant increase in flooding.

Increasing U.S. streamflow linked to greenhouse forcing

Although considerable effort has gone into assessing and projecting climatic change, continental-scale analyses of trends in only one component of the hydrologic cycle—precipitation—have been described. With few exceptions [see Zektser and Loaiciga, 1993], assessments of temporal variations in runoff, evaporation, and soil water storage have been neglected, to some degree because of a lack of adequate observational data. On a regional basis, have there been any changes in seasonal patterns of streamflow in the United States? If so, are these changes consistent with documented variations in other hydroclimatic variables? To answer these questions, we examined a set of climate-sensitive streamflow data recently collected by the U.S. Geological Survey. This data set covers the years 1941–1988 and presents data from 559 gaging stations across the conterminous United States.

Climate, hydrology and freshwater: towards an interactive incorporation of hydrological experience into climate research

DEMETRIS KOUTSOYIANNIS, ALBERTO MONTANARI, HARRY F. LINS & TIMOTHY A. COHN 1 Department of Water Resources and Environmental Engineering, Faculty of Civil Engineering, National Technical University of Athens, Heroon Polytechneiou 5, GR-157 80 Zographou, Greece dk@itia.ntua.gr 2 Dipartimento di Ingegneria delle Strutture, dei Trasporti, delle Acque, del Rilevamento del Territorio, Faculty of Engineering, University of Bologna, I-40136 Bologna, Italy alberto.montanari@unibo.it 3 US Geological Survey, MS 415, Reston, Virginia 20192, USA hlins@usgs.gov; tacohn@usgs.gov

Recent directions taken in water, energy, and biogeochemical budgets research

Understanding and predicting global change is a major scientific focus of the late 20th century. Although atmospheric scientists have made substantial progress in developing models that account for many components of the climate system, significant progress is needed in understanding processes associated with the exchange of water, energy, and carbon between terrestrial systems and the atmosphere. To strengthen terrestrial process research, especially research associated with the interactions of water, energy, gases, nutrients, and vegetation, the U.S. Geological Survey initiated an intensive study of Water, Energy, and Biogeochemical Budgets (WEBB). WEBB is aimed at improving understanding of processes controlling terrestrial water, energy, and biogeochemical fluxes, their interactions, and their relations to climatic variables; and the ability to predict continental water, energy, and biogeochemical budgets over a range of spatial and temporal scales.

Scale and modeling issues in water resources planning

Resource planners and managers interested in utilizing climate model output as part of their operational activities immediately confront the dilemma of scale discordance. Their functional responsibilities cover relatively small geographical areas and necessarily require data of relatively high spatial resolution. Climate models cover a large geographical, i.e. global, domain and produce data at comparatively low spatial resolution. Although the scale differences between model output and planning input are large, several techniques have been developed for disaggregating climate model output to a scale appropriate for use in water resource planning and management applications. With techniques in hand to reduce the limitations imposed by scale discordance, water resource professionals must now confront a more fundamental constraint on the use of climate models—the inability to produce accurate representations and forecasts of regional climate. Given the current capabilities of climate models, and the likelihood that the uncertainty associated with long-term climate model forecasts will remain high for some years to come, the water resources planning community may find it impractical to utilize such forecasts operationally.

Trend analysis of monthly sulfur dioxide emissions in the conterminous United States, 1975–1984

Abstract Trends in monthly sulfur dioxide emissions for the 48 conterminous United States during the decade 1975–1984 are identified using a robust nonparametric procedure. Statistically significant downward trends are indicated in 32 States, upward trends appear in 10 States, and no significant trend is apparent in six States. Geographically, a distinct regional pattern of emission increases and decreases is evident with declines dominating the Eastern and Western States; increases aligning longitudinally from border to border in most of the Great Plains States, in several New England States, and in Georgia; and no trends frequently occurring in proximity to the upward trending emissions in the Plains States. A time-series decomposition of the monthly values indicates that one distinct emissions pattern commonly occurred through the period of record. This pattern is characterized by an initial emissions increase that peaks between 1977 and 1978, followed by a shallow and undulating decrease through the end of 1984. It is suggested that this signature represents the ‘national’ trend for the period. In addition, five regions of coherent sulfur dioxide emissions behavior are defined on the basis of seasonal occurrence of maximum and minimum emission loadings. A winter-summer, latitudinal opposition is apparent in the timing of emissions maxima, whereas an equinox-summer, longitudinal opposition is apparent in the timing of emissions minima.

The scientific legacy of Harold Edwin Hurst (1880–1978)

ABSTRACT Emanating from his remarkable characterization of long-term variability in geophysical records in the early 1950s, Hurst’s scientific legacy to hydrology and other disciplines is explored. A statistical explanation of the so-called “Hurst Phenomenon” did not emerge until 1968 when Mandelbrot and co-authors proposed fractional Gaussian noise based on the hypothesis of infinite memory. A vibrant hydrological literature ensued where alternative modelling representations were explored and debated, e.g. ARMA models, the Broken Line model, shifting mean models with no memory, FARIMA models, and Hurst-Kolmogorov dynamics, acknowledging a link with the work of Kolmogorov in 1940. The diffusion of Hurst’s work beyond hydrology is summarized by discipline and citations, showing that he arguably has the largest scientific footprint of any hydrologist in the last century. Its particular relevance to the modelling of long-term climatic variability in the era of climate change is discussed. Links to various long-term modes of variability in the climate system, driven by fluctuations in sea surface temperatures and ocean dynamics, are explored. Several issues related to the Hurst Phenomenon in hydrology remain as a challenge for future research. Editor M. Acreman; Associate editor A. Carsteanu

Recent patterns of sulfate variability in pristine streams

Abstract Systematic modes of spatial and temporal variation in a 13-y record of stream sulfate from a nationwide network of headwater sampling stations are defined using principal components. Based on the undisturbed nature of the sampling network, it is suggested that these modes of stream sulfate variability are analogues for variations in acid deposition. Three statistically significant components, accounting for approximately 50% of the total stream sulfate variance, are identified. Analysis of component loadings and scores indicates that a major transition occurred in the early 1970s when stream sulfate concentrations in the northeast changed from persistently above mean levels to persistently below. At the same time concentrations of sulfate in Gulf and Southeast Atlantic coast streams shifted from persistently below to persistently above mean concentrations. Significantly, these changes occurred contemporaneously with regional trends in sulfate emissions which can generally be characterized as decreasing in the northeast and increasing in the southeast.

Storm-generated variations in nearshore beach topography

Abstract A series of nearshore beach profile measurements from the Outer Banks of North Carolina spanning a four-month period have been examined for temporal variations in nearshore topography. Principal component analysis of the profile data indicates that most of the variation in nearshore topography occurs in four principal modes, two quasiseasonal and two subseasonal. The first principal component, or eigenvector, corresponds to a bar-berm function. The second, to a terrace function. Combined, the first two vectors explain 76.3% of the total variance. The third and fourth components, representing subseasonal modes, are a ridge and runnel and a storm bar function, respectively. Both occur in direct response to storm wave activity. Although the bar-berm and terrace modes of profile variation have been previously identified using principal component analysis techniques, the subsequent modes have not. The ridge and runnel function accounts for 10.6% of total profile variability and the storm bar function accounts for 5.0%.