Comprehensive Climatology of ENSO Events and California Precipitation

Summary: With the periodic reoccurrence of El Niño and La Niña there are efforts to try and assess what the impact will be on California, especially the state's water supply. This project examines the precipitation for both warm and cool ENSO events across California.

Overview: The various ENSO (El Niño-Southern Oscillation) events have are defined from the Oceanic Niño Index (ONI) into Weak, Moderate and Strong events. The moderate and strong events are highlighted in the tables below. Then the seasonal (July 1 through June 30) percent of normal precipitation for each category, plus a collective category of "all" warm and cool events, was collated for a number of cities and geographic areas. One of these areas is the Northern Sierra Nevada Eight Station index (8SI) which is the average of the precipitation totals for Mt. Shasta City, Shasta Dam, Brush Creek, Mineral Ranger Station, Quincy, Sierraville Ranger Station, Blue Canyon and Pacific House. Additionally the seven NCDC climate division (see map) averages were compared to the ENSO events. These comparisons was done in terms of both average seasonal precipitation and also the number of occurrences within percent of normal categories. For ease of viewing, the moderate and strong events have been highlighted. Finally, anomaly maps, were constructed for each season showing the precipitation and 500-hPa anomalies for the primary "rainy" season of November through March.

Observations:

El Niño: The best "signal" associated with warm ENSO (El Niño) events is, as would be expected, with the "Strong" events, especially in Southern California. For the six seasons categorized as strong, all regions averaged above normal precipitation with the highest percentages of normal (PON) in Climate Divisions 6 and 7. Likewise, Divisions 6 (including Los Angeles) and 7 above normal and precipitation for all the Strong El Niño seasons. During weak and moderate warm events there is no such signal with the number of years of above and below normal being fairly evenly split statewide.

La Niña: During cool (La Niña) ENSO events the only real signal is during Strong events with below normal precipitation in Southern California (Division 6 and 7). The average rainfall during strong La Niñas in Southern California is about 68% with all seasons being below normal. Like the warm events there is no prevailing precipitation anomaly elsewhere during strong cool events or during weak or moderate events.

El Niño

Table 1. All El Niño Events - Average Percent of Normal Precipitation (18 events)

ENSO Type	Eureka	San Francisco	Sacramento	Fresno	Los Angeles	8SI	Div. 1	Div. 2	Div. 3	Div. 4	Div. 5	Div. 6	Div. 7	Anomaly Maps
All El Niño	103	117	108	116	132	106	106	104	97	112	107	122	125	Precip	500-hPa
Weak El Niño	99	102	100	114	130	102	98	94	96	102	104	118	129	Precip	500-hPa
Moderate El Niño	107	103	88	106	102	102	104	103	91	96	97	103	100	Precip	500-hPa
Strong El Niño	110	148	135	143	164	119	122	122	109	140	126	147	146	Precip	500-hPa

Table 2. All El Niño - Years by Percent of Normal Categories (18 events)

% of Normal	Eureka	San Francisco	Sacramento	Fresno	Los Angeles	8SI	Div. 1	Div. 2	Div. 3	Div. 4	Div. 5	Div. 6	Div. 7
<80%	3	5	7	5	4	7	6	8	6	6	7	4	3
80-100%	7	3	2	3	2	1	1	0	3	2	2	2	2
100-120%	1	2	0	1	1	3	4	3	4	1	1	4	3
120-140%	5	1	5	2	1	4	3	4	2	2	3	0	1
>140%	2	7	4	7	10	3	4	3	3	7	5	8	9

Table 3. Weak El Niño - Years by Percent of Normal Categories (8 events)

% of Normal	Eureka	San Francisco	Sacramento	Fresno	Los Angeles	8SI	Div. 1	Div. 2	Div. 3	Div. 4	Div. 5	Div. 6	Div. 7
<80%	1	3	3	3	3	3	3	4	2	3	3	3	2
80-100%	4	1	1	1	1	0	0	0	1	1	1	1	1
100-120%	1	1	0	0	0	2	2	1	3	0	0	0	1
120-140%	2	1	3	1	0	3	3	3	1	1	2	0	0
>140%	0	2	1	3	4	0	0	0	1	3	2	4	4

Table 4. Moderate El Niño - Years by Percent of Normal Categories (4 events)

% of Normal	Eureka	San Francisco	Sacramento	Fresno	Los Angeles	8SI	Div. 1	Div. 2	Div. 3	Div. 4	Div. 5	Div. 6	Div. 7
<80%	1	1	2	1	1	2	2	2	2	2	2	1	1
80-100%	1	1	1	2	1	0	0	0	1	0	1	1	1
100-120%	0	1	0	0	1	1	1	1	0	1	0	1	1
120-140%	2	0	1	0	0	0	0	0	0	0	0	0	0
>140%	0	1	0	1	1	1	1	1	1	1	1	1	1

Table 5. Strong El Niño - Years by Percent of Normal Categories (6 events)

	Eureka	San Francisco	Sacramento	Fresno	Los Angeles	8SI	Div. 1	Div. 2	Div. 3	Div. 4	Div. 5	Div. 6	Div. 7
<80%	1	1	2	1	0	2	1	2	2	1	2	0	0
80-100%	2	1	0	0	0	1	1	0	1	1	0	0	0
100-120%	0	0	0	1	0	0	1	1	1	0	1	3	1
120-140%	1	0	1	1	1	1	0	1	1	1	1	0	1
>140%	2	4	3	3	5	2	3	2	1	3	2	3	4

Table 6. All El Niño Events - Individual Years Percent of Normal Precipitation (18 events)

ENSO Type	Season	Eureka	San Francisco	Sacramento	Fresno	Los Angeles	8SI	Div. 1	Div. 2	Div. 3	Div. 4	Div. 5	Div. 6	Div. 7	Anomaly Maps
WE	1951-1952	122	150	133	127	177	137	124	135	120	141	133	158	160	Precip	500-hPa
SE	1957-1958	126	169	160	173	142	139	148	140	122	160	137	155	147	Precip	500-hPa
WE	1963-1964	97	57	70	62	53	69	77	70	81	61	66	74	87	Precip	500-hPa
SE	1965-1966	83	75	58	56	138	74	87	75	79	70	69	110	124	Precip	500-hPa
WE	1968-1969	122	116	134	210	185	131	125	132	141	137	160	163	180	Precip	500-hPa
WE	1969-1970	99	96	96	83	52	115	110	71	105	82	85	58	66	Precip	500-hPa
SE	1972-1973	90	159	140	127	143	100	101	110	94	139	116	118	110	Precip	500-hPa
WE	1976-1977	45	51	39	69	83	38	42	41	56	54	52	83	108	Precip	500-hPa
WE	1977-1978	93	124	147	166	225	137	128	132	101	145	150	200	204	Precip	500-hPa
SE	1982-1983	153	176	198	215	211	172	166	170	165	187	191	186	169	Precip	500-hPa
ME	1986-1987	72	64	58	85	52	64	73	63	59	61	64	57	67	Precip	500-hPa
ME	1987-1988	83	82	77	74	84	67	77	74	58	67	71	90	101	Precip	500-hPa
SE	1991-1992	57	89	74	101	142	70	71	73	75	87	76	114	142	Precip	500-hPa
ME	1994-1995	133	157	131	174	164	165	146	168	165	153	163	165	145	Precip	500-hPa
SE	1997-1998	151	218	179	184	209	159	156	161	117	196	167	198	185	Precip	500-hPa
ME	2002-2003	140	107	84	89	108	111	118	105	85	103	89	100	85	Precip	500-hPa
WE	2004-2005	117	143	123	141	246	114	103	110	106	140	132	184	204	Precip	500-hPa
WE	2006-2007	93	76	61	54	21	74	74	60	54	58	54	27	26	Precip	500-hPa

La Niña

Table 7. All La Niña Events - Average Percent of Normal Precipitation (19 events)

ENSO Type	Eureka	San Francisco	Sacramento	Fresno	Los Angeles	8SI	Div. 1	Div. 2	Div. 3	Div. 4	Div. 5	Div. 6	Div. 7	Anomaly Maps
All La Niña	101	90	89	86	80	96	98	93	94	87	85	70	72	Precip	500-hPa
Weak La Niña	96	86	85	81	80	91	94	90	92	86	84	70	74	Precip	500-hPa
Moderate La Niña	105	94	92	89	81	97	98	93	92	90	85	72	71	Precip	500-hPa
Strong La Niña	109	93	94	93	78	107	108	99	99	88	86	68	67	Precip	500-hPa

Table 8. All La Niña - Years by Percent of Normal Categories (19 events)

	Eureka	San Francisco	Sacramento	Fresno	Los Angeles	8SI	Div. 1	Div. 2	Div. 3	Div. 4	Div. 5	Div. 6	Div. 7
<80%	2	6	7	9	8	7	5	7	7	7	10	16	15
80-100%	7	5	6	6	7	3	5	4	3	6	5	3	3
100-120%	7	6	4	3	3	4	7	5	6	5	3	0	1
120-140%	3	2	1	1	1	3	1	3	3	1	1	0	0
>140%	0	0	1	0	0	2	1	0	0	0	0	0	0

Table 9. Weak La Niña - Years by Percent of Normal Categories (9 events)

	Eureka	San Francisco	Sacramento	Fresno	Los Angeles	8SI	Div. 1	Div. 2	Div. 3	Div. 4	Div. 5	Div. 6	Div. 7
<80%	2	3	4	5	4	4	2	4	4	4	5	7	6
80-100%	2	3	3	3	3	2	3	2	2	2	2	2	2
100-120%	5	3	1	1	1	1	4	2	1	3	2	0	1
120-140%	0	0	1	0	1	2	0	1	2	0	0	0	0
>140%	0	0	0	0	0	0	0	0	0	0	0	0	0

Table 10. Moderate La Niña - Years by Percent of Normal Categories (6 events)

	Eureka	San Francisco	Sacramento	Fresno	Los Angeles	8SI	Div. 1	Div. 2	Div. 3	Div. 4	Div. 5	Div. 6	Div. 7
<80%	0	2	2	3	2	2	2	2	2	1	3	6	5
80-100%	3	1	2	1	4	0	1	1	1	4	2	0	1
100-120%	1	3	2	2	0	3	3	3	3	1	1	0	0
120-140%	2	0	0	0	0	1	0	0	0	0	0	0	0
>140%	0	0	0	0	0	0	0	0	0	0	0	0	0

Table 11. Strong La Niña - Years by Percent of Normal Categories (4 events)

	Eureka	San Francisco	Sacramento	Fresno	Los Angeles	8SI	Div. 1	Div. 2	Div. 3	Div. 4	Div. 5	Div. 6	Div. 7
<80%	0	1	1	1	2	1	1	1	1	2	2	3	4
80-100%	2	1	1	2	0	1	1	1	0	0	1	1	0
100-120%	1	0	1	0	2	0	0	0	2	1	0	0	0
120-140%	1	2	0	1	0	0	1	2	1	1	1	0	0
>140%	0	0	1	0	0	2	1	0	0	0	0	0	0

Table 12. All La Niña Events - Individual Years Percent of Normal Precipitation (19 events)

ENSO Type	Season	Eureka	San Francisco	Sacramento	Fresno	Los Angeles	8SI	Div. 1	Div. 2	Div. 3	Div. 4	Div. 5	Div. 6	Div. 7	Anomaly Maps
WL	1950-1951	117	108	98	94	54	122	117	116	102	101	111	56	48	Precip	500-hPa
ML	1954-1955	86	73	83	94	81	70	73	70	59	76	77	74	76	Precip	500-hPa
SL	1955-1956	120	126	142	122	108	141	133	133	140	127	122	81	74	Precip	500-hPa
WL	1956-1957	94	69	77	75	64	86	84	81	89	76	77	75	76	Precip	500-hPa
WL	1962-1963	113	102	140	106	57	123	116	125	135	117	99	55	62	Precip	500-hPa
ML	1964-1965	105	103	102	102	92	121	113	118	119	95	105	80	81	Precip	500-hPa
WL	1967-1968	73	67	66	66	112	74	79	75	78	66	64	76	96	Precip	500-hPa
ML	1970-1971	124	87	91	78	83	108	119	101	108	85	82	75	76	Precip	500-hPa
WL	1971-1972	102	51	52	49	48	68	92	63	80	47	53	49	68	Precip	500-hPa
SL	1973-1974	137	128	115	95	101	148	152	130	105	119	99	79	70	Precip	500-hPa
WL	1974-1975	103	84	88	70	97	97	105	96	98	86	91	89	71	Precip	500-hPa
SL	1975-1976	87	37	37	75	49	50	65	45	52	39	53	59	70	Precip	500-hPa
WL	1984-1985	91	92	59	72	86	68	81	70	77	79	78	77	115	Precip	500-hPa
SL	1988-1989	90	81	80	80	54	89	84	88	101	67	70	55	55	Precip	500-hPa
WL	1995-1996	115	115	105	99	84	116	117	114	123	113	106	67	53	Precip	500-hPa
ML	1998-1999	129	109	78	64	61	107	109	95	103	91	80	56	56	Precip	500-hPa
ML	1999-2000	94	115	120	118	78	107	93	101	87	111	96	67	65	Precip	500-hPa
WL	2000-2001	59	90	83	96	121	65	60	66	50	86	77	89	80	Precip	500-hPa
ML	2007-2008	89	79	76	75	89	70	79	71	76	82	69	78	74	Precip	500-hPa