California Data Exchange Center - Reservoirs

California Reservoirs - Drought Status Percentiles


Change Date:
CA Map of Reservoirs
Percentile
Drought Monitor Category
0.00 - 0.02
D4
 Drought - Exceptional
0.02 - 0.05
D3
 Drought - Extreme
0.05 - 0.10
D2
 Drought - Severe
0.10 - 0.20
D1
 Drought - Moderate
0.20 - 0.30
D0
 Abnormally Dry
0.30 +
N
 Normal

Notes:

Data is preliminary and subject to change. The end-of-month storage values are collected from the California Dept. of Water Resources' RES and STORAGEM reports, and other sources. See: http://cdec4gov.water.ca.gov/cgi-progs/reservoirs/RES and http://cdec4gov.water.ca.gov/cgi-progs/reservoirs/STORAGEM

Background to the Precipitation Drought Status

Reservoir Storage percentiles are based on different periods of record, depending on when the reservoir was filled and data availability:

Reservoir   Period of Record
Trinity   1/1/1963 - Present
Shasta   1/1/1954 - Present
Almanor   1/1/1965 - Present
Oroville   1/1/1969 - Present
New Bullards Bar   1/1/1970 - Present
*Lake Tahoe   1/1/1959 - Present
Folsom   1/1/1956 - Present
Berryessa   1/1/1963 - Present
Camanche / Pardee   1/1/1967 - Present
New don Pedro   1/1/1974 - Present
New Exchequer   1/1/1968 - Present
Friant   1/1/1954 - Present
Pine Flat   1/1/1956 - Present
Isabella   1/1/1968 - Present
San Luis   1/1/1969 - Present
Cachuma   1/1/1960 - Present
Casitas   1/1/1970 - Present
Nacimiento / San Antonio   1/1/1966 - Present
"Statewide"   1/1/1974 - Present

Some reservoirs, like New Melones, did not have a long enough period of record to be included.

Camanche and Pardee reservoirs are operated in tandem and so they are combined as one reservoir. Naciminto and San Antonio reservoirs are operated jointly and so they are combined as one reservoir.

The "Statewide" number accounts for more than 64% of California's total water storage in reservoirs. It is computed from an unweighted sum of all the reservoirs listed above.

* Lake Tahoe often drops below the level of the natural rim (as many as 10 times in 50 years for some months). When Lake Tahoe is below the natural rim the stage elevation of the Lake is used to compute a negative storage and a corresponding percentile.