Sean W. Fleming

Tracer tests in a fractured dolomite: 2. Analysis of mass transfer in single‐well injection‐withdrawal tests

We investigated multiple-rate diffusion as a possible explanation for observed behavior in a suite of single-well injection-withdrawal (SWIW) tests conducted in a fractured dolomite. We first investigated the ability of a conventional double-porosity model and a multirate diffusion model to explain the data. This revealed that the multirate diffusion hypothesis/model is consistent with available data and is capable of matching all of the recovery curves. Second, we studied the sensitivity of the SWIW recovery curves to the distribution of diffusion rate coefficients and other parameters. We concluded that the SWIW test is very sensitive to the distribution of rate coefficients but is relatively insensitive to other flow and transport parameters such as advective porosity and dispersivity. Third, we examined the significance of the constant double-log late time slopes (−2.1 to −2.8), which are present in several data sets. The observed late time slopes are significantly different than would be predicted by either conventional double-porosity or single-porosity models and are believed to be a distinctive feature of multirate diffusion. Fourth, we found that the estimated distributions of diffusion rate coefficients are very broad, with the distributions spanning a range of up to 3.6 orders of magnitude. Fifth, when both heterogeneity and solute drift are present, late time behavior similar to multirate mass transfer can occur. Although it is clear that multirate diffusion occurs in the Culebra, the number of orders of magnitude of variability may be overestimated because of the combined effects of drift and heterogeneity.

Pacific Decadal Oscillation and the Hydroclimatology of Western Canada—Review and Prospects

The Pacific Decadal Oscillation (PDO) is a large-scale climate system feature that influences the surface climate and hydrology of western North America. In this paper, we review the literature describing the PDO and demonstrate its effects on temperature, precipitation, snowfall, glacier mass balance, and streamflow with a focus on western Canada, and particularly British Columbia. We review how the PDO index was developed and discuss other North Pacific climate patterns that resemble the PDO. The impacts of PDO on glacier mass balance and streamflow from retrospective studies are also reviewed and illustrated with specific examples from BC. We assess the current state of knowledge regarding the PDO and provide a critical assessment of its use in hydroclimatology. This information should provide insight on the sensitivity of projects to climatic variability.

Glacial Control of Water Resource and Related Environmental Responses to Climatic Warming: Empirical Analysis Using Historical Streamflow Data from Northwestern Canada

We applied nonparametric statistical techniques to historical streamflow data from five glacierized and four nonglacierized watersheds in southwest Yukon and northwestern British Columbia, Canada, to determine whether rivers with and without catchment glacial cover respond in significantly different ways to a warming climate. The analysis was posed in terms of contrasts between the two groups with respect to long-term trends in annual time series of total river flow volume. We found that glacier-fed rivers grew larger and nival streams progressively smaller over the historical record under an observed regional warming trend. Although some of these trend effects are subtle, the overall result was statistically significant at restrictive confidence levels. Combined consideration of hydrological, meteorological and glaciological trends suggests that the streamflow consequences of increasing temperature exceed those from a concurrent rise in precipitation in the study area, causing increases in both glacial meltwater production and evapotranspiration; the former appears to have the dominant net hydrologic effect in glacierized catchments, and the latter in glacier-free watersheds. By empirically demonstrating that catchment glacial cover can result in opposite trends in total annual flow volume from river to river within an otherwise hydroclimatologically uniform area, the analysis presents strong evidence that climatic warming can materially affect downstream water resources specifically via glaciological pathways, and also implies that regional generalizations of interpreted or projected hydrologic trends may not be tenable in variably-glacierized regions.

Spatiotemporal mapping of ENSO and PDO surface meteorological signals in British Columbia, Yukon, and southeast Alaska

Abstract We assessed the impacts of some key Pacific ocean‐atmosphere circulation patterns on annual cycles of temperature and precipitation across British Columbia, Yukon, and southeast Alaska. The El Niño‐Southern Oscillation (ENSO), the Pacific Decadal Oscillation (PDO), and ENSO conditional on PDO states were considered in composite analyses of 71 long, high‐quality datasets from surface meteorological stations. Month‐by‐month, station‐by‐station Monte Carlo bootstrap tests were employed to assess statistical significance. The results trace precipitation and temperature responses as a function of location, season, and climate mode. In summary, temperature responses were relatively uniform, with higher (lower) temperatures during the warm (cool) phases of these circulation patterns. Nevertheless, strength and seasonal persistence varied considerably with location and climate mode. Impacts were generally most consistent in winter and spring but could extend through most of the year. Overall spatiotemporal patterns in precipitation response were decoupled from those in temperature and were far more heterogeneous. Complexities in precipitation signals included north‐south inverse teleconnectivity along the Pacific coast, with a zero‐response hinge point in the approximate vicinity of northern Vancouver Island; seasonally opposite anomalies in several interior regions, which might conceivably reflect contrasting effects of Pacific climate modes on wintertime frontal storms versus summertime convective storms; and a consistent lack of substantial response in northwestern British Columbia and possibly southwestern Yukon, conjectured to reflect complications associated with the Icefield Ranges. The product is intended primarily as a basic‐level set of climate response maps for hydrologists, biologists, foresters, and others who require empirical assessments of relatively local‐scale, year‐round ENSO and PDO effects across this broad region.

Autoregressive Noise, Deserialization, and Trend Detection and Quantification in Annual River Discharge Time Series

The evaluation of long-term trends in yearly discharge records, such as annual peak daily flow or total annual runoff, is important to a variety of issues including water resource planning, flood hazard studies, and the assessment of historical data for evidence of anthropogenic climate change effects. Prewhitening or deserialization procedures have recently been developed and applied to adjust statistical tests of monotonic trend, and the nonparametric Mann-Kendall test in particular, for sensitivity to serial dependence. Deserialization attributes much or all of the observed serial correlation in a time series to an autoregressive process; however, deterministic processes can also lead to a large lag-1 serial correlation coefficient, and the physical basis for autoregressive noise may be weaker for annual rather than more finely-discretized (e.g., daily) streamflow records. In this paper, the potential consequences of using such procedures are investigated through a suite of Monte Carlo simulations. We find that prewhitening can substantially and inappropriately reduce the power of trend significance tests and increase slope estimate errors. The choice of whether deserialization is applied is to some degree left to the judgement and conservatism of the individual practitioner. We suggest that such procedures not be applied to a given annual hydrologic time series unless there is a strong site-specific physical basis for the assumption of AR(1) noise and that if deserialization is performed, very recently-developed multi-stage techniques appear preferable. We also present a number of useful ancillary results regarding trend identification in streamflow-derived data.

Crustal structure beneath the central Oregon convergent margin from potential‐field modeling: Evidence for a buried basement ridge in local contact with a seaward dipping backstop

Models of magnetic and gravity anomalies along two E-W transects offshore central Oregon, one of which is coincident with a detailed velocity model, provide quantitative limits on the structure of the subducting oceanic crust and the crystalline backstop. The models indicate that the backstop-forming western edge of the Siletz terrane, an oceanic plateau that was accreted to North America-50 million years ago, has a seaward dip of less than 60o3. Seismic, magnetic, and gravity data are compatible with no more than 2 km of subducted sediments between the Siletz terrane and the underlying crystalline crust of the Juan de Fuca plate. The data also suggest the presence of a N-S trending, 200-km-long basaltic ridge buried beneath the accretionary com- plex from about 43oN to 45oN. Although the height and width of this ridge probably vary along strike, it may be up to 4 km high and several kilometers wide in places and appears to be locally in contact with the Siletz terrane beneath Heceta Bank. Several models for the origin of this ridge are discussed. These include: a sliver of Siletz terrane detached from the main Siletz terrane dur- ing a late Eocene episode of strike-slip faulting; imbrication and thickening of subducted oceanic crust in place; an aseismic ridge rafted in on the subducting oceanic crust during the past 1.2 mil- lion years; and a series of ridges and/or seamounts rafted in over a longer period of time and trans- ferred from the subducting plate to the overlying plate. The last model is the most consistent with the complicated history of local uplift, subsidence, and slope instability recorded in the ridges, basins, and banks of this part of the margin. We speculate that the massive seaward dip- ping western edge of the Siletz terrane in this region inhibits subduction of seamounts and sedi- ments, resulting in fomation of buried ridge as the accumulated flotsam and jetsom of subduction. This process may also be responsible for thickening of lower accretionary complex material, over- steepening of slopes leading to massive slumping, and north-south extension through strike-slip faulting in the accretionary complex to the west of the buried ridge. Regardless of its origin, the ridge may currently be acting as an asperity inhibiting subduction.

Modeling solute diffusion in the presence of pore-scale heterogeneity: method development and an application to the Culebra dolomite Member of the Rustler Formation, New Mexico, USA

Previous studies have revealed the presence of pore-scale variability in diffusivity in the Culebra (dolomite) member of the Rustler Formation, NM. In this study, eight laboratory-scale diffusion experiments on five Culebra samples were analyzed using a methodology for modeling solute diffusion through porous media in the presence of multiple matrix diffusivities, Dp. A lognormal distribution of Dp is assumed within each of the lab samples. The estimated standard deviation (sigma d) of ln(Dp) within each sample ranges from 0 to 1, with most values lying between 0.5 and 1. The variability over all samples leads to a combined sigma d in the range of 1.0-1.2, which is consistent with the distribution of independently determined formation factor measurements for similar Culebra samples. A comparison of our estimation results to other rock properties suggests that, at the lab-scale, the geometric mean of Dp increases with bulk porosity and the quantity of macroscopic features such as vugs and fractures. However, sigma d appears to be determined by variability within such macroscopic features and/or by micropore-scale heterogeneity. In addition, comparison of these experiments to those at larger spatial scales suggests that increasing sample volume results in an increase in sigma d.

Parabolic northern-hemisphere river flow teleconnections to El Niño-Southern Oscillation and the Arctic Oscillation

It is almost universally assumed in statistical hydroclimatology that relationships between largescale climate indices and local-scale hydrometeorological responses, though possibly nonlinear, are monotonic. However, recent work suggests that northern-hemisphere atmospheric teleconnections to El Nino-Southern Oscillation (ENSO) and the Arctic Oscillation can be parabolic. The effect has recently been explicitly confirmed in hydrologic responses, though associations are complicated by land surface characteristics and processes, and investigation of water resource implications has been limited to date. Here, we apply an Akaike Information Criterion-based polynomial selection approach to investigate annual flow volume teleconnections for 42 of the northern hemisphere’s largest ocean-reaching rivers. Though we find a rich diversity of responses, parabolic relationships are formally consistent with the data for almost half the rivers, and the optimal model for eight. These highly nonlinear water supply teleconnections could radically alter the standard conceptual model of how water resources respond to climatic variability. For example, the Sacramento river in drought-ridden California exhibits no significant monotonic ENSO teleconnection but a 0.92 probability of a quadratic relationship, reducing mean predictive error by up to 65% and suggesting greater opportunity for climate index-based water supply forecasts than previously appreciated.

Modulation of linear and nonlinear hydroclimatic dynamics by mountain glaciers in Canada and Norway: Results from information-theoretic polynomial selection

Historical streamflow and climate datasets were analyzed for low- and high-frequency hydroclimatic variability. Four glacial/non-glacial catchment pairs were considered, two from the southern Canadian Rocky Mountains and two from arctic coastal Norway. Analyses were performed using daily data, providing high seasonal resolution and facilitating the identification of possible nonlinear hydroclimatic processes. Spearman rank correlation, and an information theory-based polynomial selection method, were employed in parallel. The latter permits straightforward identification of highly nonlinear relationships, simultaneous consideration of multiple models and estimation of the probability of a given relationship, as distinct from conventional p-values. Highly nonlinear (parabolic) atmospheric teleconnections to the Arctic Oscillation and El Niño-Southern Oscillation were confirmed in Norway and Canada, respectively, and their corresponding hydrologic effects were detected; conversely, little evidence for deviation from linearity was found for long-term monotonic trends. Presence or absence of watershed glacial cover was found to fundamentally alter streamflow responses to climate variability and change. In particular, for ecologically highly relevant late-summer low flows, glaciers induced: (1) stronger negative long-term trends than observed for non-glacial basins, presumably reflecting net mass balance declines seen in nearby glaciers, and (2) parabolic teleconnections, largely absent in non-glacial basins, reflecting parabolic air temperature teleconnections and the presence or absence of glacial ice available for melting.

Exploring the nature of Pacific climate variability using a “toy” nonlinear stochastic model

The Pacific Decadal Oscillation (PDO) is the leading mode of North-Pacific temperature variability. This climatic oscillation is nominally dominated by regime shifts having wide-ranging impacts. An ongoing point of discussion around the PDO regards whether such regimes genuinely represent multiple, stable, discrete states in a nonlinear dynamical system, or instead simply extended runs of above- or below-normal values in a continuous stochastic memory process. A simple nonlinear Markov time series model, involving a (hybrid) stochastically driven tipping-point process, is considered as a vehicle to explore the fundamental nature of the PDO. This toy model is found to be sufficiently plausible for our purposes, insofar as it reproduces some key observational PDO dynamics: in particular, de facto regime shifts and a 1/f power spectrum. The primary conclusion is that the line between the two competing general views may be blurred, and the red-noise and bi-stability hypotheses might be better considered as en...