Average annual temperature has increased 2.7°F since 1900. Warming is particularly evident as an increase in very warm nights and a below-average occurrence of very cold nights over the past three decades. Under a higher emissions pathway, historically unprecedented warming is projected by the end of the 21st century.
Key Message 2
Droughts are a serious threat in this water-scarce state. The intensity of naturally occurring future droughts and the frequency and severity of wildfires are projected to increase in Utah.
Key Message 3
Projected changes in winter precipitation include an increase in the fraction falling as rain rather than snow, potentially decreasing snowpack water storage. The number and magnitude of heavy precipitation events are projected to increase, which could increase the risk of flooding.
Utah is a geographically diverse state with forested, mountainous,
and desert regions. It has a varied climate due to its inland
continental location and wide range of topography. Elevations across
the state range from approximately 2,500 feet in the Virgin River
Valley to 13,500 feet in the Uinta Mountains. Based on records from
long-term stations, temperatures in the mountains average around
20°F during the winter months, while lower elevations in the southern
portion of the state frequently experience days over 100°F in the
summer. In the northern part of the state, the Great Salt Lake has
a moderating effect on temperatures in its vicinity. The hottest
year on record for Utah was 1934 with an average annual temperature
of 51.3°F, followed by 2012 with an average annual temperature of
Figure 1: Observed and projected changes (compared to the 1901–1960 average) in near-surface air temperature for Utah. Observed data are for 1900–2018. Projected changes for 2006–2100 are from global climate models for two possible futures: one in which greenhouse gas emissions continue to increase (higher emissions) and another in which greenhouse gas emissions increase at a slower rate (lower emissions)<sup>1</sup>. Temperatures in Utah (orange line) have risen 2.7°F since 1900. Shading indicates the range of annual temperatures from the set of models. Observed temperatures are generally within the envelope of model simulations of the historical period (gray shading). Historically unprecedented warming is projected to continue through the 21st century. Less warming is expected under a lower emissions future (the coldest years being about 2 degrees cooler than the hottest year in the historical record; green shading) and more warming under a higher emissions future (the hottest years being about 13°F warmer than the hottest year in the historical record; red shading). Source: CICS-NC and NOAA NCEI. <br><br><sup>1</sup>Technical details on models and projections are provided in an appendix, available online at: <a href="https://statesummaries.ncics.org/pdfs/TechInfo.pdf">https://statesummaries.ncics.org/pdfs/TechInfo.pdf</a>.
The early 21st century has been the warmest period on record for
Utah (Figure 1). The period from 2000 to 2004 was particularly warm,
with the state seeing the largest number of extremely hot days (days
with maximum temperature at or above 100°F) in the historical record
(Figure 2). In addition to the overall trend of higher temperatures,
the state has experienced a dramatic increase in the number of very
warm nights (minimum temperature at or above 75°F) and a decrease
in the number of very cold nights (minimum temperature at or below
0°F) since 1990 (Figures 3 and 4a).
Figure 2: The observed number of extremely hot days (annual number of days with maximum temperature at or above 100°F) for 1900–2018, averaged over 5-year periods (bars; last bar represents 4-year average). Filled circles connected by black line segments show annual values. The horizontal black line shows the long-term average for 1900–2018 is 11 days per year. These values are averages from 12 long-term reporting stations. With the exception of the 2010–2014 period, the number of extremely hot days has been above the long-term average since the late 1980s, reaching a peak in 2000–2004. Source: CICS-NC and NOAA NCEI.
Figure 3: The observed number of very warm nights (annual number of days with minimum temperature at or above 75°F) for 1900–2018, averaged over 5-year periods (bars; last bar represents 4-year average). Filled circles connected by black line segments show annual values. The horizontal black line shows the long-term average for 1900–2018 is 1.6 nights per year. These values are averages from 12 long-term reporting stations. While high nighttime temperatures are historically rare for Utah due to its semiarid climate and high average elevation, the frequency of very warm nights has risen dramatically over the past three decades. During the 2000–2004 period, the number of such nights was more than double the long-term average. Source: CICS-NC and NOAA NCEI.
Most of the state is quite dry because the Sierra Nevadas
and the Rocky Mountains block moisture from the Pacific
Ocean and Gulf of Mexico, respectively. In the northwest
part of the state, most precipitation falls during the winter
and spring months, while thunderstorms fueled by moisture
from the North American Monsoon provide summer
precipitation in the east and south. Annual precipitation is
highly variable across the state, with annual totals ranging
from less than 5 inches in portions of the Great Salt Lake
Desert to more than 20 inches in some portions of the
Wasatch Mountains. Statewide average annual precipitation
has ranged from 8.1 inches in 1956 to 20.3 inches in 1941.
The driest multiyear periods were in the early 1900s and
the 1950s to early 1960s, and the wettest periods were
the late 1900s and early 1980s (Figure 4b). Average annual
precipitation has ranged from 10.7 inches during the driest
consecutive 5-year interval (1952–1956) to 17.2 inches during
the wettest consecutive 5-year interval (1980–1984). Long-
term periods of wet and dry spells can have critical impacts
on water supplies.
Snowfall varies widely across the state, with portions of the
south receiving less than 10 inches annually and areas in
the mountains receiving over 400 inches per year. The area
around the Great Salt Lake can receive significant snowfall
due to lake-effect snow events. The lake’s high salt content
prevents it from freezing, and the open waters can efficiently
warm and moisten cold air masses as they pass over the lake,
occasionally triggering bands of heavy snowfall over areas to
the east and south of the lake. As the state has warmed, the
percentage of precipitation falling as snow during the winter
has decreased, as has snow depth and snow cover.
Unlike many areas of the United States, Utah and other
southwestern states have not experienced an upward trend
in the frequency of extreme precipitation events (Figure 4c).
Although floods are rare in the state, both heavy rainfall
and snowmelt can result in severe flooding. Historically,
floods of both types have had devastating impacts. In 1983,
melting of a large snowpack during the months of April and
June caused mudslides and extensive flooding in the Salt Lake
Valley (Figure 4d). In January 2005, heavy rains in the Virgin
River basin caused severe flooding along the Virgin and Santa
Clara Rivers in Washington County, resulting in over $225
million in damage.
Figure 4: The observed (a) number of very cold nights (annual
number of days with minimum temperature at or below 0°F; 1900–
2018), (b) annual precipitation (1895–2018), and (c) number of
extreme precipitation events (annual number of days with precipitation
of 1 inch or more; 1900–2018), averaged over 5-year periods (bars;
last bar represents 4-year average). Filled circles connected by
black line segments show annual values. Horizontal black lines show
the long-term averages. The values in Figures 2a and 2c are averages
from all available long-term reporting stations (12 for temperature,
7 for precipitation). The values in Figure 2b are from NCEI’s version
2 climate division dataset. Graph (d) shows variations in the April
1 snow water equivalent at the Ben Lomond Peak, Utah, SNOTEL site
(1979–2018). Since 1990, Utah has experienced a below-average number
of very cold nights, indicative of warming in the region. Annual
precipitation during the most recent fourteen years (2005–2018) has
been near the long-term average. There is no long-term trend in the
number of extreme precipitation events. Snow water equivalent (SWE)
is the amount of water contained within the snowpack. SWE varies
widely from year to year and was well above the long-term average
in 2017 but was well below that average in 2018. Source: CICS-NC
and NOAA NCEI.
Utah frequently experiences droughts. Since snowmelt from
the snowpack provides water for many river basins, abnormally
low winter and spring precipitation is often the trigger for
drought conditions. In 2012, Utah experienced one of its driest
springs since records began in 1895, resulting in severe drought
conditions in areas across the entire state. The historical record
indicates periodic occurrences of extended wet and dry
periods (Figure 5). Dry conditions since 2000 have resulted in
near-record-low water levels in the Great Salt Lake (Figure 6). El
Niño and La Niña events can have major effects on precipitation
in others part of the western U.S., but in Utah the effects are not
consistent and thus the occurrence of such events cannot be
used as a reliable prediction tool.
Figure 5: Time series of the Palmer Drought Severity Index from the year 1000 to 2018. Values for 1895–2018 (red) are based on measured temperature and precipitation. Values prior to 1895 (blue) are estimated from indirect measures such as tree rings. The thick black line is a running 20-year average. In the modern era, the wet periods of the early 1900s and the 1980s–1990s and the dry period of the 1950s are evident. The extended record indicates periodic occurrences of similarly prolonged wet and dry periods. Source: CICS-NC and NOAA NCEI.
Under a higher emissions pathway, historically
unprecedented warming is projected by the end of the
21st century (Figure 1). Even under a pathway of lower
greenhouse gas emissions, average annual temperatures are
projected to most likely exceed historical record levels by the
middle of the 21st century. However, there is a large range of
temperature increases under both pathways, and under the
lower pathway, a few projections are only slightly warmer
than historical records. Increases in average temperatures
will be accompanied by increases in heat wave intensity and
decreases in cold wave intensity.
Climate models are not consistent in their projections of
precipitation for Utah, including winter precipitation (Figure
7). However, projected rising temperatures will increase the
average lowest elevation at which snow falls (the snow line).
Continuing recent trends, this will increase the likelihood that
precipitation will fall as rain instead of snow, reducing water
storage in the snowpack, particularly at lower elevations
that are currently on the margins of reliable snowpack
accumulation. In addition, extreme precipitation is
projected to increase, potentially increasing the frequency
and intensity of floods.
Droughts, a natural part of Utah’s climate, are expected
to become more intense. Higher temperatures will amplify
the effects of naturally occurring dry spells by increasing the
rate of loss of soil moisture. Most of Utah’s water is supplied
by the snowpack, and changes to the snow/rain ratio could
result in less water storage. Additionally, higher spring
temperatures can cause early melting of the snowpack,
decreasing water availability during the already dry summer
months. The projected increase in the intensity of naturally
occurring droughts will increase the occurrence and severity
Figure 6: Annual time series of the water level of the Great Salt Lake at Saltair Boat Harbor for 1880–2019. Water levels in the Great Salt Lake have varied widely over the years. Record snowpack levels during the winter of 1982–1983 resulted in severe flooding. Recent years have seen some of the lowest levels in the historical record. Source: USGS.
Figure 7: Projected changes in winter precipitation (%) by the middle of the 21st century compared to the late 20th century under a higher emissions pathway. Hatching represents areas where the majority of climate models indicate a statistically significant change. Utah is part of a large area across the United States with projected increases in winter precipitation, but the changes in Utah are not statistically significant. Source: CICS-NC, NOAA NCEI, and NEMAC.
Rebekah Frankson, Kenneth E. Kunkel
Laura Stevens, David Easterling
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