Geostatistical space–time mapping of house prices using Bayesian maximum entropy

Mapping spatial processes at a small scale is a challenge when observed data are not abundant. The article examines the residential housing market in Fort Worth, Texas, and builds price indices at the inter- and intra-neighborhood levels. To accomplish our objectives, we initially model price variability in the joint space–time continuum. We then use geostatistics to predict and map monthly housing prices across the area of interest over a period of 4 years. For this analysis, we introduce the Bayesian maximum entropy (BME) method into real estate research. We use BME because it rigorously integrates uncertain or secondary soft data, which are needed to build the price indices. The soft data in our analysis are property tax values, which are plentiful, publicly available, and highly correlated with transaction prices. The results demonstrate how the use of the soft data provides the ability to map house prices within a small areal unit such as a subdivision or neighborhood.     

Facilitating Co-Production of Transdisciplinary Knowledge for Sustainability: Working with Canadian Biosphere Reserve Practitioners

Sustainability scientists argue that diverse knowledge holders should work together in social learning processes to co-produce knowledge in support of sustainability. Yet, how to co-produce such knowledge remains unexplored. A multi-year, national knowledge sharing partnership among Canadian biosphere reserve practitioners, academic researchers and policy advisors revealed that a skilled facilitator was necessary for successful knowledge co-production. We draw attention to the multiple barriers to learning and knowledge co-production, and to the skills required of the facilitator to address them. The facilitator helped draw together local and formalized western knowledge systems (weaving) and diffuse innovations across local sites (out-scaling) and between local sites and the broader program network (up-scaling). Our experience reveals that simply bringing parties together will not generate transformative change for sustainability. Rather, multi-lateral facilitators are needed to ensure deliberate and managed interventions and to institutionalize learning across a diverse collective.     

High‐frequency precipitation and stream water quality time series from Plynlimon,Wales: an openly accessible data resource spanning the periodic table

This scientific briefing announces the availability of a new multi‐element high‐frequency water quality data set that is openly accessible to the research community. The data set comprises up to 2 years of 7‐hourly water quality data for two streams and one rainfall site in the Upper Severn catchment at Plynlimon in Mid‐Wales. The measurements cover 50 analytes ranging from H⁺ to U and spanning six orders of magnitude in concentration, including major, minor and trace elements as well as nutrients, and they complement decades of weekly measurements of the same analytes at the Upper Severn. Together, the weekly and 7‐hourly time series provide a unique data set for studying both long‐term trends and short‐term dynamics. The data show complex behaviour over a wide range of timescales, challenging our understanding of catchment processes and informing future modelling efforts. Copyright © 2013 John Wiley & Sons, Ltd.     

A new strategy for analyzing the chronometry of constructed rock features in deserts

The western Great Basin contains thousands of constructed rock features, including rock rings, cairns, and alignments. Unlike subtractive geoglyphs, such as the Nasca Lines of Peru, that remove desert pavement, these surface features alter the location and positioning of cobble‐ to bouldersized rocks. The chronology of surface rock features has remained unconstrained by numerical ages because no prior chronometric approach has been able to yield age control. We propose a new strategy for studying these features by analyzing anthropogenic modifications to rock coatings, an approach that permits the use of several dating methods, two of which are assessed here: radiocarbon dating of pedogenic carbonate and rock‐varnish microlaminations. Initial results from Searles Valley, eastern California, suggest that constructed rock features may be as old as early Holocene and terminal Pleistocene. Archaeological surveys of desert areas would be greatly enhanced if they noted altered positions of rock coatings. © 2006 Wiley Periodicals, Inc.     

Watershed modelling of hydrology and water quality in the Sacramento River watershed,California

Agricultural pollutant runoff is a major source of water contamination in California's Sacramento River watershed where 8500 km² of agricultural land influences water quality. The Soil and Water Assessment Tool (SWAT) hydrology, sediment, nitrate and pesticide transport components were assessed for the Sacramento River watershed. To represent flood conveyance in the area, the model was improved by implementing a flood routing algorithm. Sensitivity/uncertainty analyses and multi‐objective calibration were incorporated into the model application for predicting streamflow, sediment, nitrate and pesticides (chlorpyrifos and diazinon) at multiple watershed sites from 1992 to 2008. Most of the observed data were within the 95% uncertainty interval, indicating that the SWAT simulations were capturing the uncertainties that existed, such as model simplification, observed data errors and lack of agricultural management data. The monthly Nash–Sutcliffe coefficients at the watershed outlet ranged from 0.48 to 0.82, indicating that the model was able to successfully predict streamflow and agricultural pollutant transport after calibration. Predicted sediment loads were highly correlated to streamflow, whereas nitrate, chlorpyrifos and diazinon were moderately correlated to streamflow. This indicates that timing of agricultural management operations plays a role in agricultural pollutant runoff. Best management practices, such as pesticide use limits during wet seasons, could improve water quality in the Sacramento River watershed. The calibrated model establishes a modelling framework for further studies of hydrology, water quality and ecosystem protection in the study area. Copyright © 2012 John Wiley & Sons, Ltd.     

‘Super-eruptions’ and silicic volcanism from the Yellowstone volcanic field

Yellowstone is perhaps the world's most famous ‘super-volcano’ with an explosive history stretching back more than 2 million years and abundant contemporary evidence of a voluminous magmatic system. The first explosive eruption at Yellowstone was the largest, the Huckleberry Ridge Tuff with a volume estimated at 2500 km³ of deposit. However, recent work using high-precision geochronology has suggested that this ‘poster-child’ of super-eruptions is actually two distinct events separated by at least six thousand years. The geochronological data indicating differences between the constituent parts of the Huckleberry Ridge Tuff is supported by textural, geochemical and isotopic evidence from numerous studies. Advances in both technology and approaches in the sphere of geochronology are allowing for ever more closely spaced events to be temporally resolved; allowing re-investigation of deposits considered to represent ‘super-eruptions’ at much higher resolution. The appreciation that the Huckleberry Ridge Tuff represents two distinct events illustrates that these large, regionally catastrophic events from Yellowstone occurred more frequently than previously thought. Moreover, by being able to better constrain the intervals between super-eruptions we can investigate the timescales of magma generation during quiescent periods.     

Climate change sensitivity assessment of streamflow and agricultural pollutant transport in California's Central Valley using Latin hypercube sampling

Bracketing the uncertainty of streamflow and agricultural runoff under climate change is critical for proper future water resource management in agricultural watersheds. This study used the Soil and Water Assessment Tool (SWAT) in conjunction with a Latin hypercube climate change sampling algorithm to construct a 95% confidence interval (95CI) around streamflow, sediment load, and nitrate load predictions under changes in climate for the Sacramento and San Joaquin River watersheds in California's Central Valley. The Latin hypercube algorithm sampled 2000 combinations of precipitation and temperature changes based on Intergovernmental Panel on Climate Change projections from multiple General Circulation Models. Average monthly percent changes of the upper and lower 95CI limits compared to the present‐day simulation and a statistic termed the “r‐factor” (average width of the 95CI band divided by the standard deviation of the 95CI bandwidth) were used to assess watershed sensitivities. 95CI results indicate that streamflow and sediment runoff in the Sacramento River watershed are more likely to decrease under climate change compared to present‐day conditions, whereas the increase and decrease for nitrate runoff were found to be equal. For the San Joaquin River watershed, streamflow slightly decreased under climate change, whereas sediment and nitrate runoff increased compared to present‐day climate. Comparisons of watershed sensitivities indicate that the San Joaquin River watershed is more sensitive to climate changes than the Sacramento River watershed, which is largely caused by the high density of agricultural land. Copyright © 2012 John Wiley & Sons, Ltd.     

Surface heat flow and CO2 emissions within the Ohaaki hydrothermal field,Taupo Volcanic Zone,New Zealand

Carbon dioxide emissions and heat flow have been determined from the Ohaaki hydrothermal field, Taupo Volcanic Zone (TVZ), New Zealand following 20 a of production (116 MW_e). Soil CO₂ degassing was quantified with 2663 CO₂ flux measurements using the accumulation chamber method, and 2563 soil temperatures were measured and converted to equivalent heat flow (W m⁻²) using published soil temperature heat flow functions. Both CO₂ flux and heat flow were analysed statistically and then modelled using 500 sequential Gaussian simulations. Forty subsoil CO₂ gas samples were also analysed for stable C isotopes. Following 20 a of production, current CO₂ emissions equated to 111 ± 6.7 T/d. Observed heat flow was 70 ± 6.4 MW, compared with a pre-production value of 122 MW. This 52 MW reduction in surface heat flow is due to production-induced drying up of all alkali–Cl outflows (61.5 MW) and steam-heated pools (8.6 MW) within the Ohaaki West thermal area (OHW). The drying up of all alkali–Cl outflows at Ohaaki means that the soil zone is now the major natural pathway of heat release from the high-temperature reservoir. On the other hand, a net gain in thermal ground heat flow of 18 MW (from 25 MW to 43.3 ± 5 MW) at OHW is associated with permeability increases resulting from surface unit fracturing by production-induced ground subsidence. The Ohaaki East (OHE) thermal area showed no change in distribution of shallow and deep soil temperature contours despite 20 a of production, with an observed heat flow of 26.7 ± 3 MW and a CO₂ emission rate of 39 ± 3 T/d. The negligible change in the thermal status of the OHE thermal area is attributed to the low permeability of the reservoir beneath this area, which has limited production (mass extraction) and sheltered the area from the pressure decline within the main reservoir. Chemistry suggests that although alkali–Cl outflows once contributed significantly to the natural surface heat flow (∼50%) they contributed little (<1%) to pre-production CO₂ emissions due to the loss of >99% of the original CO₂ content due to depressurisation and boiling as the fluids ascended to the surface. Consequently, the soil has persisted as the major (99%) pathway of CO₂ release to the atmosphere from the high temperature reservoir at Ohaaki. The CO₂ flux and heat flow surveys indicate that despite 20 a of production the variability in location, spatial extent and magnitude of CO₂ flux remains consistent with established geochemical and geophysical models of the Ohaaki Field. At both OHW and OHE carbon isotopic analyses of soil gas indicate a two-stage fractionation process for moderate-flux (>60 g m⁻² d⁻¹) sites; boiling during fluid ascent within the underlying reservoir and isotopic enrichment as CO₂ diffuses through porous media of the soil zone. For high-flux sites (>300 g m⁻² d⁻¹), the δ¹³CO₂ signature (−7.4 ± 0.3‰ OHW and −6.5 ± 0.6‰ OHE) is unaffected by near-surface (soil zone) fractionation processes and reflects the composition of the boiled magmatic CO₂ source for each respective upflow. Flux thresholds of <30 g m⁻² d⁻¹ for purely diffusive gas transport, between 30 and 300 g m⁻² d⁻¹ for combined diffusive–advective transport, and ?300 g m⁻² d⁻¹ for purely advective gas transport at Ohaaki were assigned. δ¹³CO₂ values and cumulative probability plots of CO₂ flux data both identified a threshold of ∼15 g m⁻² d⁻¹ by which background (atmospheric and soil respired) CO₂ may be differentiated from hydrothermal CO₂.