June Temperature Trends in the Southwest Deserts of the USA (1950–2018) and Implications for Our Urban Areas

Anthony Brazel

doi:10.3390/atmos10120800

Abstract

Within the United States, the Southwest USA deserts show the largest temperature changes (1901–2010) besides Alaska, according to the most recent USA National Climate Assessment report. The report does not discuss urban effects vs. regional effects that might be evident in trends. Twenty-five temperature stations with ca. 68-year records (1950 to 2018) have been accessed from US Global Historical Climate Network archives. Land cover data are accessed from a National Land Cover Database. June results considering both urban and rural sites show an astounding rate per year change among sites ranging from −0.01 to 0.05 °C for maximum temperatures and 0.01 to 0.11 °C for minimum temperatures (−0.8 to 3.2 °C, and 0.8 to 8.0 °C for the entire period). For maximum temperatures, almost half of the sites showed no significant trends at a stringent 0.01 level of statistical significance, but 20 of 25 were significant at the 0.05 level. For minimum temperatures, over 75% of sites were significant at the 0.01 level (92% at 0.05 level of significance). The urban-dominated stations in Las Vegas, Phoenix, Tucson, and Yuma show large minimum temperature trends, indicating emerging heat island effects. Rural sites, by comparison, show much smaller trends. Addressing heat in our urban areas by local actions, through collaborations with stakeholders and political resolve, will aid in meeting future urban challenges in this era of projected global climate change and continued warming.

Highlights

The purpose of this paper is to present a view of the past ca. 68 years of temperature changes for the two desert areas of the Southwest USA
In [36], estimates are presented of maximum nocturnal heat island intensities for North America, Europe, and wet and dry Sub-tropical environments, with the dry Sub-tropical cities’ UHIs ranging from ca. 4 to 7 ◦ C for populations of 0.05 M to 5.0 M
For the cities of Las Vegas and Phoenix, TminU-R is consistent with dry Subtropical places in Africa, India, and the Middle East cited by [36]; whereas, values for Tucson and Yuma are considerably less relative to the population, indicating their peripheral siting and their limited representation for more central urban LCZ locations in these places

Summary

Introduction

The purpose of this paper is to present a view of the past ca. 68 years of temperature changes for the two desert areas of the Southwest USA (see Figure 1—these are the Mojave desert in Nevada and California, and the Sonoran desert in California and Arizona). 68 years of temperature changes for the two desert areas of the Southwest USA (see Figure 1—these are the Mojave desert in Nevada and California, and the Sonoran desert in California and Arizona). The emphasis is on noting that in [1], no temperature trends comparing urban vs rural sites are explicitly analyzed. In some earlier work prior to 1990 [2,3], substantial effects of urbanization on within temperature time series data in the Southwest and USA were identified. The recent national assessment [1] does, present ideas on urban vulnerabilities that are expected, and temperature changes of some individual sites are illustrated. Urban area temperature rates of change are already an order of magnitude greater than rural areas, as demonstrated below, and, it is imperative that

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