Eos, Vol. 94, No. 11, 12 March 2013
VOLUME 94
NUMBER 11
12 MARCH 2013 EOS, TRANSACTIONS, AMERICAN GEOPHYSICAL UNION
PAGES 105–112
A Network for Observing Great Basin Climate Change
such processes as plant phenology, snow accumulation, and snowmelt (Figure 1, insets C and D). Webcams may be operated manually from any computer connected to the Internet, thus providing visual access of the sites to a wide audience, from researchers to school children. Additional instrumentation can be added to the stations. For example, sap flow sensors and point dendrometers that continuously quantify stem radial growth were added to trees along the transects to measure the timing of transpiration and growth in woody plant species. Further, the actual amounts and timing of precipitation, temperature, and atmospheric vapor pressure deficit (VPD, also known as evaporative demand), as collected by sensors on the networks, can be compared with tree ring growth patterns (from increment cores and microcores) recorded by the new dendrometers to more finely calibrate climate–tree ring relationships and enable more accurate reconstruction of past conditions. In a separate experiment, cold air drainage is being monitored within a wash located between two stations. Sensors have been spatially distributed to measure air temperature, wind speeds, tree sap flow, and plant water status to better understand the geographic and climatic conditions in which cold air drainage is favored and to determine the linkage between cold air movement and plant response. All the instruments in each NevCAN station are located within an area of 1 hectare (0.01 square kilometer). This footprint (1) is an appropriate scale for modeling purposes that rely upon satellite data and gridded remote sensing products and (2) provides sufficient space for establishing replicated experimental plots for future studies. Detailed plant lists have been made for each site, and ongoing studies that combine ground truth with remote sensing data are under way to provide a complete and accurate representation of the plant communities found at each elevation.
PAGES 105 –106 The ability to evaluate accurately the response of the environment to climate change ideally involves long‐term continuous in situ measurements of climate and landscape processes. This is the goal of the Nevada Climate‐Ecohydrology Assessment Network (NevCAN), a novel system of permanent monitoring stations located across elevational and latitudinal gradients within the Great Basin hydrographic region (Figure 1). NevCAN was designed, first, to quantify the daily, seasonal, and interannual variability in climate that occurs from basin valleys to mountain tops of the Great Basin in the arid southwest of the United States; second, to relate the temporal patterns of ecohydrologic response to climate occurring within each of the major ecosystems that compose the Great Basin; and, last, to monitor changes in climate that modulate water availability, sequestration of carbon, and conservation of biological diversity. NevCAN is the only long‐term climate monitoring network specifically designed to measure altitudinal and latitudinal variation in climate change across the Great Basin, a major ecoregion in the conterminous United States. While NevCAN shares several features with the National Ecological Observatory Network (NEON), it has been undertaken at a grassroots level—meaning that its concept, design, and construction were the efforts of field scientists—and is designed to address science questions particularly relevant to semiarid and mountainous environments. In addition to providing free and open access to real‐time data and data products through the Nevada Climate Change Portal (NCCP; http:// sensor.nevada.edu/NCCP/Default.aspx), the network has also been engineered to provide data for immediate use by a wide range of environmental scientists. Further, it has been designed to be a sustainable platform for both experimental and observa-
BY S. MENSING, S. STRACHAN, J. ARNONE, L. FENSTERMAKER, F. BIONDI, D. DEVITT, B. JOHNSON, B. BIRD, AND E. FRITZINGER
tional research, and its sensors have been chosen to enable synergy between hydrological, ecological, and climatological research.
Transect Design NevCAN has been built as two basin‐to‐ mountaintop transects, one in the north across the Snake Range and Great Basin National Park and another in the south across the Sheep Range, about 35 kilometers northwest of the Las Vegas metropolitan center (Figure 1). The Snake Range transect experiences a winter‐dominated precipitation regime characterized by Pacific frontal storm systems with summer thunderstorms still common (see Table S1 in the additional supporting information that can be found in the online version of this article). This west‐to‐ east transect includes seven new stations plus an existing eddy covariance station, located in the center of each major vegetation zone along the transect’s altitudinal gradient. The Sheep Range transect is within a summer‐ dominated precipitation regime with a relatively large component of annual moisture coming from monsoonal systems. This south‐ to‐north transect includes four new stations plus an existing National Resources Conservation Service Soil Climate Analysis Network (SCAN) site. Each station site is instrumented with a common set of equipment selected to monitor aspects of the surface hydrologic balance and key ecological processes. Sensors measure precipitation (snow and rain), air temperature, wind speed and direction, incoming and outgoing long‐ and short‐wave electromagnetic radiation (to help track ecosystem energy balance, changes in the fraction of solar energy absorbed, and nighttime cloud cover), relative humidity, barometric pressure, and soil moisture and temperature. The majority of these sensors are capturing data at intervals as fine as 1 minute so that research across a broad range of temporal scales may be pursued. A webcam that can pan, tilt, and zoom is mounted on each tower to provide real‐time assessment of site conditions as well as archival photographs to quantify temporal and spatial dynamics of
© 2013. American Geophysical Union. All Rights Reserved.
Climate Data During the First Year of NevCAN Operation NevCAN’s first year of operation (1 October 2011 to 30 September 2012) has yielded annual averages and totals for a number of climate variables using 10‐minute values recorded at each transect site. Table S1 illustrates the range of climatic
Eos, Vol. 94, No. 11, 12 March 2013
Fig. 1. Map of the Nevada Climate-Ecohydrology Assessment Network (NevCAN) transects. Inset A shows the subalpine station on the western slope of the Snake Range at an elevation of 3360 meters with Pinus longaeva (bristlecone pine), Picea engelmannii (Engelmann spruce), and Pinus flexilis (limber pine). Inset B illustrates cross-section profiles of tower elevations for each transect. Landscape monitoring by this site’s webcam is illustrated in insets C and D, here showing patterns of snowmelt and snowfall that can be correlated with sensor climatic data. conditions represented by the two transects, and Figure S1 shows how these climate variables change with elevation. The slope of each line in Figure S1 represents the environmental lapse rate, meaning the rate of change in an environmental variable with each unit of increase in elevation. Clear elevational trends were seen in annual measures of climate, including those that codetermine or describe aridity (VPD, mean annual precipitation, mean annual temperature, and wind speed). As expected, air temperature, number of growing degree‐ days (classified as when air temperature is equal to or above freezing, indicating that plant growth can occur), the date of freezing (when air temperature was sustained below −2 °C), and VPD decreased with increasing elevation at both transects. By contrast, precipitation, date of last freezing, number of days with snow cover, the aridity/moisture index that indicates how dry or moist an environment is based on the quotient of mean annual precipitation (measure of water input), and mean annual temperature (a proxy for evaporation potential) increased with elevation (Figure S1). Wind speeds did not vary with any trends among sites at the southern transect but decreased with increasing elevation at the northern transect. All of these elevational patterns observed
during the first year of NevCAN operation, in concert with patterns observed in future years, will provide a quantitative baseline for analyzing possible shifts in the “steepness” of measured lapse rates that may be caused by natural and anthropogenic climate change. Somewhat surprising was that elevational lapse rates for most climate variables differed between the northern and southern transects. Steeper lapse rates observed at the southern transect indicated a greater role of elevation in determining precipitation, moisture (decrease in aridity), and number of days with snow cover (Figure S1). At the northern transect, steeper lapse rates showed faster elevational changes in date of last hard frost, mean annual air temperature, and date of first hard frost (Tables S2 and S3). Latitudinal differences in climate observed during the first year of NevCAN operation occurred mostly as expected. The southern transect exhibited higher mean annual air temperature (by 4.5 °C), more growing degree‐days (69), lower precipitation (by about 80 millimeters), fewer days with snow cover (by 101 days), and lower moisture index values. There was almost no difference between transects in dates of the first and last hard frosts or in vapor pressure deficit.
© 2013. American Geophysical Union. All Rights Reserved.
A Rich Data Source A tiny sample of the data available from these transects has been explored, but they nonetheless illustrate the potential for NevCAN’s use in environmental change research. The great variety of climates expressed across the range of ecosystems represented by NevCAN’s transect sites affords numerous opportunities for research and education. Currently, researchers are analyzing sensor data to determine what ecoclimatic variables control seasonal growth of trees and shrubs across the entire elevational gradient. NevCAN has added various experimental sensor arrays on the landscape centered on individual stations to identify and monitor microclimates that play a critical role in water availability and biological diversity. Archived data and imagery may be queried through the NCCP for each sensor or a combination of sensors at time steps ranging from 1 minute (meteorological) to 1 hour (webcams), with aggregation into longer‐term averages available as an option prior to download. Data are available to anyone, and those interested in studying climate variability and climate change impacts through this new data set are
Eos, Vol. 94, No. 11, 12 March 2013 encouraged to learn more at http://sensor. nevada.edu/NCCP/Default.aspx.
Acknowledgment This material is based upon work supported by the U.S. National Science Foundation under grant EPS‐0814372. — SCOTT MENSING and SCOTTY STRACHAN, Department of Geography, University of Nevada,
Reno; E-mail:
[email protected]; JAY ARNONE, Division of Earth and Ecosystem Sciences, Desert Research Institute, Reno, Nev.; LYNN FENSTERMAKER, Division of Earth and Ecosystem Sciences, Desert Research Institute, Las Vegas, Nev; FRANCO BIONDI, Department of Geography, University of Nevada, Reno; DALE DEVITT, Department of Soil and Water Science, University of Nevada, Las Vegas; BRITTANY JOHNSON, Division of Earth and Ecosystem Sciences, Desert Research Institute, Reno, Nev.; BRIAN BIRD, Department of Soil and
© 2013. American Geophysical Union. All Rights Reserved.
Water Science, University of Nevada, Las Vegas; and ERIC FRITZINGER, Department of Computer Sciences, University of Nevada, Reno
