Scotty Strachan

Dendroecological testing of the pyroclimatic hypothesis in the central Great Basin, Nevada, USA

In the Great Basin region of western North America, records of past climate and wildfire variability are needed not only for fire use, but also for understanding the mechanisms behind the century-long expansion of pinon-juniper woodlands. The Mt. Irish area (Lincoln County, south-eastern Nevada) is a remote mountain ecosystem on the hydrographic boundary between the Great Basin and the Colorado River Basin. Non-scarred ponderosa pines (Pinus ponderosa C. Lawson var. scopulorum Engelm.) and single-needle pinyons (Pinus monophylla Torr. & Frem.) were used to develop a tree-ring reconstruction of drought (mean PDSI for May–July from NV Climate Division 3) from 1396 to 2003. A hypothetical fire regime was obtained from the PDSI reconstruction and from explicitly assumed relationships between climate and wildfire occurrence. A census of fire-scarred trees was then sampled at the study area, and crossdated fire-scar records were used to generate the fire history, independently of the pre-existing pyroclimatic m...

550-Year Reconstruction of Streamflow Variability in Spring Valley, Nevada

Spring Valley, Nevada, is one of several areas proposed for the pumping and export of ground-water to Las Vegas by the Southern Nevada Water Authority. Long-term annual-to-decadal variability of water supply in the region is not well understood, so tree-ring records were used to develop a longer baseline of variability in streamflow and drought episodes. Long-lived (up to about 600 years), climatically sensitive single-leaf pinyon pine (Pinus monophylla) trees within the Cleve Creek watershed provided a 550-year (1458-2007) tree-ring chronology that was compared to water-year mean monthly runoff from USGS gauge 10243700. Using a proxy record from within the watershed under study increased confidence in the statistical relationships used for streamflow reconstruction. Linear correlation between the tree-ring chronology and the streamflow record over 34 years of overlap was 0.73, explaining 53% of the instrumental variance. After comparison with multiple linear regression and linear regression with transformed data, the line of organic correlation (LOC) method was used to develop a streamflow reconstruction with water-year resolution from 1458 to 2007. During these 550 years, a total of 257 wet and dry episodes were quantified according to their duration, magnitude, and peak. The longest episode was 1848-1855 (an 8-year wet spell); the greatest magnitude belonged to the drought of the mid-1600s (1652-1655); the three highest peaks all corresponded to dry episodes, 1506-1508, 1590, and 1933-1936. Using a numerical scoring rule, the 1930s drought (1933-1936) was in eighth position, making it one of the most remarkable episodes in the past half millennium. This result is not entirely consistent with recent dendroclimatic reconstructions for the eastern Sierra, suggesting that regional drought severity varies by locality within the Great Basin. Evaluating the responses of trees at multiple elevations to various local climate and hydrological parameters through in situ monitoring will help refine tree-ring reconstructions of past ecohydrological conditions. DOI: 10.1061/(ASCE)WR.1943-5452.0000180.

Architecting Climate Change Data Infrastructure for Nevada

The NSF EPSCoR-funded Nevada Climate Change Project seeks to create a central, reusable, extensible infrastructure that can be used to collect geospatial climate data and information. Housing climate data for Nevada and its surrounding regions during the initial construction phases, the newly created system (with its central component: the Nevada Climate Change Portal) will ultimately be capable of storing any kind of geospatial data for multiple types of research, education and outreach activities. In order to meet the varied needs of the climate researchers, educators, students, and policy makers involved in the project, it was necessary to research and implement a new system architecture. The novelty of this architecture is that it addresses, in an extensible and robust manner, the end-to-end needs of all project stakeholders, implementing multiple sub-levels of architectural design that incorporate data acquisition from sensor networks, data storage using high-performance geospatially-enabled databases, asset tracking and management to improve data validation and verification, metadata collection and management, data curation, and advanced web-based data management and retrieval. The paper describes the proposed system architecture, discusses the major design challenges encountered, addresses some implementation points, and highlights the capabilities of the Nevada Climate Change Portal.

Land Surface Temperature and Surface Air Temperature in Complex Terrain

Land surface temperature (LST) is a fundamental physical property relevant to many ecological, hydrological, and atmospheric processes. There is a strong relationship between LST and near surface air temperature (Tair), although the two temperatures have different physical meaning and responses to atmospheric conditions. In complex terrain, these differences are amplified; yet it is in these environments that remotely sensed LST may be most valuable in prediction and characterization of spatial-temporal patterns of Tair due to typical paucity of meteorological stations in mountainous regions. This study presents an analysis on the suitability and limitations of using LST as a proxy or an input variable for predicting Tair in complex mountainous topography. Explicitly, we investigated the influence of key environmental, topographic, and instrumental factors on the relation between LST and measured Tair in two mountainous ecoregions of Nevada. The relation between LST and Tair was found to be strongest during late summer and fall, and weakest during winter and early spring. Increasing terrain roughness was found to diminish the relation between between LST and Tair. There was a strong agreement between nighttime Tair lapse rates and LST lapse rates. Given the inadequacy of several gridded Tair products in capturing minimum temperature cold-air pooling and inversions, using LST as an input variable in the interpolation process would enhance capture of temperature inversions in grid-ded data over complex terrain. Crucially, the relationship between LST and Tair did not differ significantly across the two distinct mountainous ecoregions.

Filling the Data Gaps in Mountain Climate Observatories Through Advanced Technology, Refined Instrument Siting, and a Focus on Gradients

The mountain research community is still contending with the need to monitor ecosystems, both to improve local management practices and to address regional and global science questions related to the Future Earth themes of Dynamic Planet, Global Sustainable Development, and Transformations Towards Sustainability. How such efforts may be designed and coordinated remains an open question. Historical climate and ecological observatories and networks typically have not represented the scope or spatial and topographic distribution of near-surface processes in mountains, creating knowledge gaps. Grassroots, in situ investigations have revealed the existence of topoclimates that are not linearly related to general atmospheric conditions, and are also not adequately represented in gridded model products. In this paper, we describe how some of the disconnects between data, models, and applications in mountains can be addressed using a combination of gradient monitoring, uniform observational siting and standards, and modern technology (cyberinfrastructure). Existing observational studies need to expand their topographic niches, and future observatories should be planned to span entire gradients. Use of cyberinfrastructure tools such as digital telemetry and Internet Protocol networks can reduce costs and data gaps while improving data quality control processes and widening audience outreach. Embracing this approach and working toward common sets of comparable measurements should be goals of emerging mountain observatories worldwide.

Testing the daily PRISM air temperature model on semiarid mountain slopes

Studies in mountainous terrain related to ecology and hydrology often use interpolated climate products because of a lack of local observations. One dataset frequently used to develop plot-to-watershed-scale climatologies is PRISM (Parameter-elevation Regression on Independent Slopes Model) temperature. Benefits of this approach include geographically-weighted station observations and topographic positioning modifiers, which become important factors for predicting temperature in complex topography. Because of the paucity of long-term climate records in mountain environments, validation of PRISM algorithms across diverse regions remains challenging, with end users instead relying on atmospheric relationships derived in sometimes distant geographic settings. Presented here are results from testing observations of daily temperature maximum (TMAX) and minimum (TMIN) on 16 sites in the Walker Basin, California-Nevada, located on open woodland slopes ranging from 1967 to 3111 m in elevation. Individual site mean absolute error varied from 1.1 to 3.7 °C with better performance observed during summertime as opposed to winter. We observed a consistent cool bias in TMIN for all seasons across all sites, with cool bias in TMAX varying with season. Model error for TMIN was associated with elevation, whereas model error for TMAX was associated with topographic radiative indices (solar exposure and heat loading). These results demonstrate that temperature conditions across mountain woodland slopes are more heterogeneous than interpolated models (such as PRISM) predict, that drivers of these differences are complex and localized in nature, and that scientific application of atmospheric/climate models in mountains requires additional attention to model assumptions and source data.

Near Real-time Autonomous Quality Control for Streaming Environmental Sensor Data

Abstract In this paper, we present a novel and accessible approach to time-series data validation: the Near-Real Time Autonomous Quality Control (NRAQC) system. The design, implementation, and impacts of this software are explored in detail within this paper. This software system, created in close conference with environmental scientists, leverages microservice design patterns employed for high volume web applications to develop a contemporary solution to the problem of data quality control with streaming sensor data. Through a comparative analysis between NRAQC and the GCE Toolbox, we argue that the web based deployment of QC software enhances accessibility to crucial tools required to make a robust and useful data product from raw measurements. Additionally, a key innovation of the NRAQC platform is its positive impact on modern data management practices and quality data dissemination.

Application of Dendrochronology to Historical Charcoal-Production Sites in the Great Basin, United States

During the Comstock mining era of the late 1800s, forested lands in the North American Great Basin were used for charcoal production to fuel mining smelters and related industries. Archaeological studies within or near mining districts include assessments of charcoal-production sites when such remnant features are present. Minimal historical documentation exists for individual production sites, and so the science of dendrochronology (tree-ring dating) is used to provide calendar dates and other information on the nature of historical activity within forests and woodlands. A synthesis of the dendrochronological approach to historical charcoal-production investigation is presented in the context of four recent studies, including a comprehensive strategy, new processing techniques, and unique results. This approach provides charcoal-production archaeologists with precise temporal and spatial data that are applied to questions such as patterns and timing of deforestation, or differences in technology and practices among immigrant laborers.