California El Nino and La Nina Precipitation Climnatology

This is a catalog of California precipitation anomalies for previous Strong and Very Strong El Niño events based upon their strength for the 10 state hydrologic regions and the 3 Sierra Nevada Precipitation Indices. It has the average for all strong and very strong events and the wide range of the individual seasons that went into making up each of the averages.

This is a climatological analysis of past events and NOT a forecasting tool. This is especially true for the averages of different strength events which are made up of what are a very broad range of conditions; some that are decidedly atypical.

The Relative Oceanic Niño Index (RONI) is used to identify El Niño (warm) and La Niña (cool) events in the tropical Pacific. The RONI is the running 3-month mean SST anomaly for the Niño 3.4 region (i.e., 5°N-5°S, 120°-170°W) minus the overall average tropical 3-month sea surface temperature anomaly (SSTA). Events are defined as 5 consecutive overlapping 3-month periods at or above the +0.5^o anomaly for warm (El Niño) events and at or below the -0.5 anomaly for cool (La Niña) events. The threshold is further broken down into Weak (with a 0.5 to 0.9 SST anomaly), Moderate (1.0 to 1.4), Strong (1.5 to 1.9) and Very Strong (≥ 2.0) events. For the purpose of this report, an event is categorized as weak, moderate, strong or very strong it must have equaled or exceeded the threshold of the highest category for at least 3 consecutive overlapping 3-month periods.

El Niño Events:
Strong: 1957-1958, 1965-1966, 1972-1973
Very Strong: 1982-1983, 1991-1992, 1997-1998, 2015-2016


		Table 1. ALL STRONG & VERY STRONG El NIño - Years by Percent of Normal Categories (7 events)
% of Normal	N Coast	Sacramento	N Lahontan	SF Bay	S Joaquin	C Coast	Tulare Lk	S Lahontan	S Coast	Colo River	Calif	8SI	5SI	6SI
<50%	0	0	0	0	0	0	0	0	0	0	0	0	0	0
50-70%	1	0	1	0	0	0	0	0	0	0	0	1	1	2
70-90%	0	2	1	2	2	2	2	0	1	1	2	1	1	0
90-110%	2	1	1	1	1	1	1	1	0	0	1	1	2	1
110-130%	1	1	2	0	1	0	0	3	2	2	1	1	0	0
130-150%	0	1	1	1	1	1	1	1	1	1	1	1	1	2
>150%	3	2	1	3	2	3	3	2	3	3	2	2	2	2
Average All	119%	122%	112%	135%	124%	144%	136%	145%	151%	150%	125%	116%	121%	131%
Max % Normal	161%	170%	161%	197%	190%	215%	201%	204%	213%	208%	177%	170%	199%	209%
Min % Normal	70%	74%	63%	77%	74%	82%	78%	103%	78%	82%	83%	69%	68%	68%

		Table 2. Catalog of Strong & Very Strong El Niño Years (1950-1951 to 2024-2025)
Strong El Niño	N Coast	Sacramento	N Lahontan	SF Bay	S Joaquin	C Coast	Tulare Lk	S Lahontan	S Coast	Colo River	Calif	8SI	5SI	6SI
1957-1958	151%	146%	128%	159%	139%	169%	154%	130%	168%	141%	146%	137%	131%	147%
1965-1966	91%	77%	79%	77%	77%	82%	78%	112%	127%	128%	86%	73%	80%	68%
1972-1973	94%	112%	99%	143%	118%	147%	139%	127%	130%	123%	112%	98%	101%	138%

V Strong El Niño	N Coast	Sacramento	N Lahontan	SF Bay	S Joaquin	C Coast	Tulare Lk	S Lahontan	S Coast	Colo River	Calif	8SI	5SI	6SI
1982-1983	161%	170%	161%	197%	190%	208%	201%	204%	211%	208%	177%	170%	199%	209%
1991-1992	70%	74%	63%	85%	74%	103%	83%	142%	133%	182%	83%	69%	68%	69%
1997-1998	151%	165%	130%	182%	160%	215%	193%	194%	213%	187%	167%	157%	162%	192%
2015-2016	116%	109%	123%	100%	108%	87%	106%	103%	78%	82%	105%	112%	105%	96%

AVERAGE	1957-1958	1965-1966	1972-1973

1982-1983	1991-1992	1997-1998	2015-2016