Heat Wave reducing water supply

Overview

It’s August 3, 2026, with a temperature expected to hit 113 degrees here in Clark County, Nevada.

For Clark County, August is typically the hottest or second-hottest month of the year, depending on the location within the county, and this year, the average daytime high is 103–104°F (39–40°C) with an average overnight low of 79–81°F (26–27°C)

Temperatures vary substantially with elevation, with Las Vegas Valley: 103–104°F average high, Lake Mead and lower Colorado River: 106–108°F average high, while Spring Mountains (Mt. Charleston) remains often 20–30°F cooler than the valley and Red Rock Canyon: around 94°F average high because of its higher elevation.  

These higher temperatures coincide with peak outdoor irrigation demand, while increasing the maximum evaporative losses from Lake Mead and reservoirs, in addition to peaking electricity demand for air conditioning and increasing seasonal water use by many municipal customers.

Nevada’s extreme heat is the result of both long-term climate trends and short-term weather patterns. The exact mix varies from one heat wave to another, but the main drivers are well understood.

Most major Nevada heat waves occur when a strong high-pressure ridge, sometimes called a “heat dome,” settles over the Southwest.

Under these conditions, air sinks and compresses, warming as it descends; clouds suppress, allowing nearly continuous sunshine; winds are generally light, reducing cooling; and weather patterns can persist for days or weeks, thus producing temperatures above 110°F in Las Vegas and above 100°F across much of western and central Nevada.

With the driest climate in North America, Nevada’s desert geography and desert soils contain little moisture, so more incoming solar energy heats the Air rather than evaporating water.

And its mountain ranges trap hot Air, while clear skies allow intense summer solar radiation.

And Human-caused climate change has increased average temperatures across Nevada over the past century, adding to higher average annual temperatures, more frequent extremely hot days, longer heat waves, warmer overnight temperatures, and earlier spring warming and longer summers.

Nevada has experienced prolonged drought conditions during much of the 21st century, which can amplify summer heat. Cities such as Las Vegas are often several degrees warmer than surrounding desert areas because asphalt and concrete absorb heat, buildings reduce nighttime cooling, and Air conditioning systems release waste heat.

Then natural climate variability makes individual summers hotter or cooler. For example, La Niña, which can favor hotter, drier conditions in parts of the Southwest during some seasons, adds to Variations in Pacific Ocean temperatures while influencing atmospheric circulation patterns that influence where high-pressure systems develop.

Water impacts

Lake Mead

Higher temperatures impact both groundwater and surface water but in different ways.

Heat increases evapotranspiration [1]around Lake Mead and evaporation from the reservoir itself; evaporation is water lost directly from the lake surface. Both processes increase during hotter conditions and reduce the amount of water remaining in the Lower Colorado River system.

Lake Mead loses enormous amounts of water to evaporation. US Geological Survey (USGS) measurements show Average annual evaporation from Lake Mead is about 1,896 mm (6.2 ft) of water from the lake surface. In comparison, earlier direct measurements during 2010–2012 found annual evaporation between 1,881 and 2,074 mm (74–82 inches) depending on weather conditions.

Because Lake Mead’s surface area changes with reservoir elevation, the annual volume is lost. When the reservoir is relatively large, evaporation can approach 500,000–600,000 acre-feet per year, roughly comparable to or exceeding Nevada’s entire annual Colorado River apportionment of 300,000 acre-feet in some years.

USGS researchers found that Lake Mead stores heat during spring and summer and, instead of evaporation peaking exactly when solar radiation peaks, solar energy first warms the reservoir. Then it is released during late summer and autumn; as a result, evaporation remains high well into the fall, even after air temperatures begin to decline.

Recent research in the Colorado River Basin shows that during hotter, drier summers, vegetation can continue extracting groundwater to sustain transpiration, further reducing runoff to streams and the river system.

Higher temperatures and drought reinforce one another: warmer Air dries soils, dry soils increase sensible heating, vegetation becomes stressed, runoff efficiency declines, causing losses in incoming water to ET before reaching rivers and reservoirs.

This feedback helps explain why Colorado River runoff has declined more than would be expected from precipitation changes alone.

Groundwater Basins

High temperatures affect groundwater mostly indirectly, by changing how much water infiltrates into aquifers, how much water remains available for withdrawals, and how much is lost through evapotranspiration.

The effects are especially important in arid regions like Nevada.

For hydrographic basins that support data center development such as Las Vegas Valley designated (Basin 212) [2], Garnet Valley designated Basin (216), Ivanpah Valley (164A/164B), and Truckee Meadows (87), sustained higher temperatures reduce recharge while increasing withdrawals, placing additional stress on groundwater resources.

Meanwhile, Nevada Governor Joe Lombardo pushes water-consuming data center growth. At the same time, the US Bureau of Reclamation (BOR) acting Commissioner Scott J. Cameron proposes to cut up to 3 million acre-feet of Colorado River water annually from Arizona, California, and Nevada over the next ten years.

In addition, Nevada Democratic Governor challenger Attorney General Aaron Ford is not taking positions on a proposal that taxpayers subsidize a water-consuming data center approved on federal land outside Boulder City while stopping short of endorsing fellow Democrat US Rep. Dina Titus’ request last week that Lombardo halt tax abatements to data centers on federal land until the Legislature can weigh in. 

[1] Technically, evapotranspiration (ET) refers to water lost from soil and vegetation through evaporation and plant transpiration, while evaporation is water lost directly from the lake surface.

[2] A designated order requires that withdrawals from domestic wells must conform to a restriction policy. In addition, under NRS 533.370, the State Engineer must refuse to issue the requested permit where:  “There is no unappropriated water in the proposed source of supply, or its proposed use or change conflicts with existing rights or with protectable interests in existing domestic Wells, or the Water right threatens to prove detrimental to the public interest.”