The 2021-22 water year has been marked by climate-driven extremes far outside the historical norm in California. Following on the heels of intensely dry conditions in 2020 and 2021, the current water year continued a fundamental break from historical norms and required the use of new tools and partnerships to understand rapidly changing conditions and implications for our water supply.
Snowmelt this year began sooner and peaked earlier than usual. This acceleration can be expected to continue for the remainder of the year as warm and dry conditions persist. Across nearly all measurable indicators, California’s climate is becoming hotter and more unpredictable with larger and more frequent swings between wet and dry periods. These dramatic climate-induced changes create unprecedented forecasting challenges, and DWR is investing heavily to adapt. The Bulletin 120 and Water Supply Index (WSI) forecast for April 2022 utilizes data from more sources than ever before, including updated state-of-the-art electronic monitoring stations, Airborne Snow Observatory flights, satellite data, and modeling techniques that DWR will continue to refine and leverage in coming years to prepare for a new climate reality.
Ongoing collaboration with research partners will also help us understand post-fire impacts on snow and hydrology and better model snowmelt and runoff, soil conditions, sublimation, changes to landscape from climate change, fire, and tree mortality. DWR’s Snow Surveys and Water Supply Forecasting teams are coordinating with hundreds of scientists, researchers, and partner agencies across the state to present the best picture of runoff conditions possible in the face of unprecedented drought conditions and climate whiplash.
DWR is taking an all-hands-on-deck approach to meet the increasing challenges posed by a warming climate. Our current investments and new forecasting efforts plus funding opportunities we are continuing to seek will help get us better answers crucial to the future of forecasting our water supply.
The projected median April-July (AJ) runoff in the major Southern Cascades/Sacramento River basins ranges from 25% of average for the Trinity River basin to 53% of average for the Pit River, in the major San Joaquin River basins ranges from 29% of average for the Cosumnes River basin to 55% of average for the San Joaquin River basin, and in the major Tulare Lake river basins ranges from 21% of average for the Tule River basin to 47% of average in the Kings River basin. The statewide seasonal AJ median forecast is 5.8 MAF which is 41% of the historic average.
The projected median Water Year (WY) runoff in the major Sierra Nevada river basins ranges from 29% on the Tule River to 67% for the San Joaquin River. The projected statewide median WY runoff is 16.2 MAF which is 54% of the historic average.
The WSI forecast is based on precipitation, snow, and flows observed through March 2022 and can be summarized as follows:
Sacramento River Unimpaired Runoff Water Year Forecast
(55% of average)
Sacramento Valley Index (SVI)
San Joaquin Valley Index (SJI)
Water Year 2022 flows fell considerably after the October and December storms and were relatively steady until late March. Flows in late March and early April increased in most basins, primarily as a result of the accelerated snow melt. Increases have been most significant in the central and southern Sierras. Despite these increases, average flow rates for all major basins are below average for April, ranging from 24% of average in the Cosumnes to 84% of average in the San Joaquin. Flows have begun to recede in many northern basins.
For unimpaired flows through March 2022, the Sacramento Valley (includes the Sacramento River at Bend Bridge, Feather River, Yuba River, and American River) accumulated unimpaired runoff of 6.7 MAF is 64% of average. For the San Joaquin Valley (includes the Stanislaus River, Tuolumne River, Merced River, and San Joaquin River), the accumulated unimpaired runoff of 2.0 MAF is 79% of average. For the Tulare Lake Basin (Kings River, Kaweah River, Tule River, and Kern River), the accumulated unimpaired runoff of 451 TAF is only 56% of average.
Despite a very wet October and December, Water Year 2022 has continued to drop further below average with March precipitation falling well below average for all three precipitation indices. The Northern Sierra 8-Station Precipitation Index (8SI) saw a total of only 3.0 inches of precipitation from the beginning of January through the end of March. During this period average precipitation would be 26.1 inches. The San Joaquin 5-Station Precipitation Index (5SI) and the Tulare Basin 6-Station Precipitation Index (6SI) each accrued only 1.9 inches over this three-month period, well below their respective averages of 20.9 inches and 15.1 inches.
Precipitation for Water Year 2022 accumulated at the following rates of average:
Monthly Precipitation to date in Percent of Average for Water Year 2022 for Regional Precipitation Indices
San Joaquin River
Tulare Lake Basin
Statewide Weighted Average
Snowpack is monitored using two complementary methods: automatic snow sensor (or “pillow”) readings and manual snow course measurements. The snow sensors give us a daily snapshot of snow conditions while the manual snow course measurements provide a monthly verification of snow conditions in locations where snow has been measured in the same manner as far back as over 100 years.
Snow course measurements were conducted during the April 10-day measurement period which ran from March 25 through April 3. Snow courses that were not measured were due to limited staff or access issues.
The 2022 statewide snowpack was 62% of average for April 1 based on the snow course data collected by cooperators of the California Cooperative Snow Surveys Program. This year’s snowpack was the 5th smallest snowpack on record dating back to 1950 behind WYs 2015, 1977, 2014, and 1988.
Results of the April 1 snow course measurements are as follows:
Avg WC (inches)
San Joaquin River
Statewide Average (weighted)
The statewide snowpack was 10.2 inches on April 1 which is 37% of the April 1 average based on the automated snow sensor network.
The state saw a series of significant storm events in December leading to large accumulations of snowpack across the state especially in the Central Sierras. However, since the first of the year there has been minimal additional snow accumulation, and snowmelt has increased dramatically across the state since the last week of March.
The snowpack as of the morning of April 8, 2022 stands at the following (based on snow sensors):
No. of Stations
% of April 1
% of Average
Airborne Remote Sensing of Snow (ARSS):
During the month of March as well as the April snow surveying window, the ARSS program conducted Airborne Snow Observatory (ASO) flights over the Feather, Yuba, Truckee, Carson, Tuolumne, Merced, San Joaquin, Kings, and Kaweah River basins.
In all watersheds where data has been collected, ASO data continues to reveal that the snowpack is not only very much below average, but it also has a limited distribution throughout the watersheds. This more limited distribution of the snowpack has not been evident in other remote sensing products derived from satellites imagery and snow sensor data. As a result, the amount of snow water content in the Sierra Nevada is much lower than other remote products such as SNODAS would suggest. As is evident in the snow sensor network, ASO data captured the onset of melt conditions and the rapid depletion of the snowpack particularly in the Northern Sierra Nevada especially when multiple ASO data flights were conducted during the month.
ASO data from these flights, as shown below, were considered in this forecast and the updated forecasts throughout March as the data became available.
*Note: SWE volumes are based on ASO data assimilated into iSnoBal models
More flights are underway or planned for these watersheds during April and May. Data from all ASO flights will be available on the Snow Product Comparison Dashboard and will be scrutinized to aid in future updates of the Bulletin 120 forecasts.
Weather and Climate Outlooks:
According to CNRFC 6-day forecast, there is precipitation forecasted across the majority of the state. The North Coast is forecast to receive up to 2.0 inches of precipitation while the Sierra Nevada will see totals between 0.25 to over 0.5 inches. The Central Valley and Coastal Southern California are forecasted to receive less than 0.1 inch of precipitation. Freezing levels are currently between 10,000 to 12,000 feet for most of the state but will drop to around 4,000-6,000 feet by the end of the forecast window.
The NWS Climate Prediction Center (CPC) one‐month revised outlook for April 2022 issued on March 31, 2022, suggests below normal chances of precipitation across the entire state. The same outlook suggests increased chances of above normal temperatures for the southern two-thirds of the state with the northern third seeing equal chances of above or below normal temperatures.
The CPC three-month (April-May-June) outlook, issued on March 17, 2022, suggests equal chances of above or below normal temperatures for the central coast and northern third of the state; for the rest of the state increased chances of above average temperatures are expected. The outlook also shows equal chances of above or below normal precipitation for the southern half of the state and increased chances of below normal precipitation for the northern half.
According to the latest El Niño/Southern Oscillation (ENSO) discussion issued by the Climate Prediction Center on April 4, 2022, La Niña conditions are present. Equatorial sea surface temperatures are below average across the east-central to eastern Pacific Ocean. The tropical Pacific atmosphere is consistent with La Niña. La Niña is likely to continue into the Northern Hemisphere spring (53% chance during June-August 2022), with a 40-50% chance of La Niña or ENSO-neutral chance thereafter.
A Bulletin 120 update forecast for conditions as of April 12 will be available by Thursday, April 14. The May 1, 2022 Bulletin 120 and Water Supply Index forecasts will be available by Monday, May 9. If you have any questions regarding this forecast or need additional help, please contact a member of the Snow Surveys and Water Supply Forecasting Unit.