Temperature Changes across an Elevational Gradient

This article was originally published in The Midden – Great Basin National Park: Vol. 20, No. 2, Winter 2020.

Figure 1. Vertical schematic representing the ESN sensor location by elevation and ecosystem. Numbered panels show examples of thee specific Lascars dataloggers in locations with radiation shields, also identified by number and elevation:

(1) Wheeler Peak Summit (WPS), 3976 m a.s.l.; (2) Buck Ridge 1 (BR1), 3034 m a.s.l; and (3) Great Basin Visitor Center (VC), 1639 m a.s.l.

By Bryan Mark & James DeGrand, Ohio State University; David Porinchu, University of Georgia; & Scott Reinemann, Sinclair Community College

How have temperatures been changing in Great Basin National Park (GBNP) over the past decade? This is an interesting question, especially considering that temperature is highly variable across the diverse terrain of the Park. Globally, the average temperatures of the planet have been rising. Furthermore, studies in other mountain regions suggest temperatures in higher elevations might be increasing at an even faster rate than at lower elevations. How consistent are these patterns of change throughout the various biomes contained within the Park that span from the desert floor to the mountain summits? This article summarizes a study we published this year addressing such questions in a long-term collaboration between universities and National Park staff.

To investigate patterns of ongoing temperature changes throughout the Park, we set up a network of “embedded” sensors in different locations, usually in trees, distributed across the 2,300 m (7,800 feet) elevation range in the Park (Fig. 1). These sensors have provided a unique collection of hourly readings of near-surface air temperature and humidity, shaded from direct sunlight, at about the height of a person above the landscape. The expansive nature of the network, i.e. multiple sensors located at varying elevations, gives us a way to consider trends in temperature change over time and for different landcover. We installed the embedded sensor network (ESN) in 2006, and it now comprises 29 sensors. From a maximum elevation near the summits of Wheeler, Bald and Buck mountains, the sensor locations are distributed along ridgelines and streams in adjoining eastern-draining watersheds all the way down to the Great Basin Visitor Center. The network spans multiple ecological zones including tundra, sub-alpine forest, sub-alpine lakes, sagebrush meadows, and a rock glacier. We have maintained this network in partnership with NPS staff during annual visits to GBNP with undergraduate and graduate students as part of an educational research experience we have entitled, “GBEx (Great Basin Expedition)” (Fig. 2).

Figure 2. For over 12 years, students, faculty and staff from Ohio State University and
University of Georgia have maintained the ESN during annual educational research
expeditions to Great Basin National Park (GBNP) called “GBEx.”

Photos show team atop Wheeler Peak during the 2017 expedition (top), and recovery of Lascar temperature and humidity dataloggers in different locations.

We focused on assessing temperature changes from the GBEX ESN over 12 years, from 2006-2018. We were able to make use of the other weather stations in GBNP and regional climate data to independently verify our results. Specifically, we compared our sensors to the Mather Overlook RAWS and the Wheeler Peak SNOTEL weather stations, as well as the PRISM climate dataset (https://prism.oregonstate. edu/), which provides a gridded interpolation of temperatures distributed across the topography. When we did those validation checks, we find very consistent findings.

Following a robust quality control assessment of all available hourly observations, we were able to analyze the resulting spatially distributed temperature record for GBNP and report on key patterns of variability. From 2006 to 2018, there were significantly increasing trends in daily maximum, minimum, and mean temperatures for all elevations. The average daily minimum temperature increased by 2.1°C (3.8°F). The trend in daily maximum temperatures above 3500 m was significantly greater than the increasing trends at lower elevations, suggesting that daytime forcings may be driving enhanced warming at GBNP’s highest elevations.

The results from the ESN indicate that existing weather stations, such as the Wheeler Peak SNOTEL site, are not sufficient to fully capture the small-scale spatial variability in temperature that exists in GBNP. Our study offers an alternative, lowcost methodology for sustaining long-term, distributed observations of conditions in heterogeneous mountainous environments at finer spatial resolutions. In arid mountainous regions with vulnerable water resources and fragile ecosystems, it is imperative to maintain and extend existing sensor networks and observations as climate change continues to alter conditions.