Table 1. Estimate reference evapotranspiration (ETo) rates (inches/day) for geographic areas shown on the California evaporative demand map*

 

Region

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

1.

North coast, coastal valleys and plains

0.02

0.04

0.06

0.08

0.11

0.12

0.11

0.11

0.09

0.05

0.04

0.02

2.

North coast interior valleys

0.03

0.05

0.08

0.11

0.16

0.20

0.21

0.19

0.15

0.09

0.04

0.02

3.

Northeastern mountain valleys

0.02

0.04

0.07

0.12

0.16

0.19

0.25

0.23

0.16

0.09

0.03

0.02

4.

Sacramento valley floor

0.04

0.06

0.10

0.15

0.19

0.24

0.26

0.22

0.17

0.11

0.05

0.03

5.

San Joaquin valley floor

0.03

0.06

0.10

0.15

0.21

0.25

0.25

0.21

0.16

0.11

0.05

0.02

6.

Central coast interior valleys

0.05

0.08

0.11

0.14

0.18

0.21

0.22

0.19

0.16

0.12

0.08

0.05

7.

Sierra Nevada foothill valleys

0.04

0.06

0.09

0.14

0.19

0.24

0.26

0.23

0.18

0.11

0.05

0.03

8.

Central coast, coastal valleys and plains

0.06

0.08

0.10

0.13

0.15

0.16

0.17

0.15

0.13

0.10

0.07

0.05

9.

South coast, coastal valleys and plains

0.06

0.09

0.10

0.13

0.15

0.17

0.18

0.18

0.15

0.11

0.09

0.06

10.

South coast interior valleys

0.05

0.09

0.11

0.14

0.16

0.20

0.22

0.22

0.17

0.12

0.08

0.06

11.

Southern California desert

0.09

0.13

0.19

0.25

0.33

0.38

0.37

0.31

0.28

0.20

0.12

0.06
*Actual ETo rates vary within each zone and can be adjusted upward or downward depending on the local climate relative to average for the region. A monthly ETo rate more than 10 percent above or below the values listed would be unusual. ETo values for winter months in snow-covered high Sierra valleys are lower than those listed in the table. The evaporative demand map was developed by the California Department of Water Resources (DWR). Sources for the ETo data include: DWR Bulletin 113-3 and Pruitt et al. (1987).