Sierra Nevada Water Supply Forecast

The United States Department of Agriculture released a water supply forecast on May 1 for Nevada and parts of the Eastern Sierra Nevada in California. The results are good news for the mountains, lakes, and rivers of the area.

The biggest finding from these reports is that Lake Tahoe is expected to reach 100 percent capacity for the first time since 2019 based on snowmelt runoff predictions.

“The dam at Lake Tahoe’s outlet provides up to six feet of storage totaling 744,500 acre-feet. Once full the stored water in Lake Tahoe typically provides sufficient supply to meet demand for three years even if snowpacks are below normal,” states the report.

This is crucial to the ecology, environment, and business of the area because the Truckee River provides drinking water to 85 percent of the population in the Truckee Meadows area, which includes Truckee, Reno, Sparks, and more.

The Truckee River is also irrigated to farmland around Fallon, used by the US Fish and Wildlife Department for threatened and endangered fish species, operates hydroelectric facilities, and of course provides for recreational activities and businesses.

The important points to take away from this report are the snowpack, water year precipitation, soil moisture, streamflow forecast, reservoir capacity, and drought status.

Snowpack:

This winter’s snowpack reached above normal levels at 102-184 percent as of May 1, which is crucial because most of the annual river flow in the Western United States comes from snowmelt runoff.

A good snow year is always a good sign for water level and drought predictions.

Water year precipitation:

The term “water year” is a period of time, October through September of the next year, when surface-level water levels are measured. In this case, the water year precipitation for the area as of May 1 is at 93-132 percent.

Soil moisture:

According to reports, the soil moisture for the Sierra Nevada is “high and will help with an efficient runoff.” While a solid snowpack is good, it doesn’t always mean it will runoff efficiently into important basins and bodies of water.

High soil moisture means that less snow will melt into the soil because it already has sufficient moisture, and in turn it will melt into rivers, streams, and lakes more efficiently.

Reservoirs:

This report measured 16 reservoirs in Nevada and the part of the Eastern Sierra Nevada, most of which are expected to fill completely including Lake Tahoe, Lahontan, and Rye Patch.

Streamflow forecast:

Streamflow forecasting is a difficult measure to predict because of its complexity and layers of information. It plays directly into the evaluation of dams and reservoirs, operation and performance, and watershed management.

“The NRCS May 1 streamflow forecasts predict near normal to well above normal runoff across Nevada and the eastern Sierra based on the 50% exceedance forecasts. May through July volumes range from 93-652% of median across northern Nevada and the eastern Sierra,” according to reports from the US Department of Agriculture.

Drought status:

The US Drought Monitor statistics has shown that there are currently no droughts in Nevada except for an “abnormally dry” section of Southern Nevada.

The report goes on to say that Nevada is “well on its way to receiving an A on its final report card.” However, we still need additional precipitation by September to reach normal water year totals because the water year ends in September.