Climatology of El Niño Events
and California Precipitation

by Jan Null, CCM
Updated October 2017


 Summary:   With the periodic reoccurrence of El Niņo 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 warm ENSO events across California.

Overview:  El Niņo events have are defined from the Oceanic Niņo Index (ONI) into Weak, Moderate, Strong and Very Strong events.   Then the seasonal (July 1 through June 30) percent of normal precipitation for each category, plus a collective category of "all" warm events, was collated for a number of cities and geographic areas. These include three major watersheds, the Northern Sierra Nevada Eight Station Index (8SI, map), the Southern Sierra Nevada Five Station Index (5SI, map) and the Tulare Basin Six Station Index (6SI, map). Additionally the seven NCDC climate division (see map) and the entire state of California (CA) 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.

Observations:  The best "signal" associated with warm ENSO (El Niņo) events is, as would be expected, with the "Very Strong" events all at least 140% of normal except for Climate Divison 3 which was between 120% and 140%.  In the "Strong"category Southern California showed a significant positive signature with the three seasons categorized as strong, all  averaged above normal precipitation with the highest percentages of normal (PON) in Los Angeles, Climate Divisions 6 and 7.  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.

Also:  United States El Niņo Winter Preciptation & Temperature Climatology for a graphical display of warm ENSO events for the entire United States from 1950-51 through 2016-17.

Important Caveat:  The data presented here is a climatology of past events and is made up of a broad range of events from a small sample that are averaged together.  Consequently, like all averages, this type of data should not be used as a forecast


California El Niņo Precipitation Climatology
Table 1.  All El NIņo Events - Average Percent of Normal Seasonal Precipitation (24 events)
ENSO Type Div. 1 Div. 2 Div. 3 Div. 4 Div. 5 Div. 6 Div. 7 CA 8SI 5SI 6SI SF SJC EKA RDD SAC FAT LAX SAN
All El Niņo 105% 103% 103% 107% 106% 119% 118% 107% 100% 100% 105% 100% 103% 100% 114% 101% 108% 121% 127%
Weak El Niņo 95% 91% 94% 86% 90% 100% 106% 94% 90% 87% 87% 83% 89% 91% 104% 88% 88% 105% 110%
Moderate El Niņo 109% 109% 115% 113% 116% 126% 115% 114% 109% 112% 120% 100% 97% 110% 111% 100% 119% 123% 129%
Strong El Niņo 96% 93% 88% 109% 98% 122% 124% 100% 87% 84% 93% 105% 107% 84% 111% 99% 101% 129% 139%
Very Strong El Niņo 142% 144% 137% 160% 152% 159% 152% 147% 140% 146% 154% 153% 159% 137% 160% 151% 170% 161% 163%
All Table 2.  All El NIņo - Years by Percent of Normal Categories (24 events)
% of Normal Div. 1 Div. 2 Div. 3 Div. 4 Div. 5 Div. 6 Div. 7 CA 8SI 5SI 6SI SF SJC EKA RDD SAC FAT LAX SAN
<80% 7 9 8 10 9 9 6 7 9 10 10 9 10 3 7 9 9 8 5
80-100% 3 1 4 4 4 3 5 6 3 5 3 4 3 10 3 5 4 3 3
100-120% 7 7 4 0 1 1 3 2 5 0 1 4 1 6 4 1 1 1 4
120-140% 3 3 5 2 4 2 1 3 4 4 4 2 3 3 3 5 4 1 3
>140% 4 4 3 8 6 9 9 6 3 5 6 5 7 2 7 4 6 11 9
Weak Table 3.  Weak El NIņo - Years by Percent of Normal Categories (10 events)
% of Normal Div. 1 Div. 2 Div. 3 Div. 4 Div. 5 Div. 6 Div. 7 CA 8SI 5SI 6SI SF SJC EKA RDD SAC FAT LAX SAN
<80% 3 4 4 6 4 6 5 4 4 5 5 5 6 1 4 4 6 5 4
80-100% 1 1 2 1 3 1 2 3 1 2 2 2 1 6 0 3 1 2 3
100-120% 5 4 2 0 0 0 0 0 4 0 0 2 0 3 3 1 1 0 0
120-140% 1 1 2 1 2 0 0 2 1 2 2 1 1 0 1 1 1 0 0
>140% 0 0 0 2 1 3 3 1 0 1 1 0 2 0 2 1 1 3 3
Moderate Table 4.  Moderate El NIņo - Years by Percent of Normal Categories (6 events)
% of Normal Div. 1 Div. 2 Div. 3 Div. 4 Div. 5 Div. 6 Div. 7 CA 8SI 5SI 6SI SF SJC EKA RDD SAC FAT LAX SAN
<80% 2 2 1 2 2 2 1 2 2 2 2 2 2 1 2 2 1 2 1
80-100% 0 0 2 1 1 0 2 0 0 1 0 0 1 1 1 1 2 0 0
100-120% 1 1 0 0 0 1 0 1 1 0 1 2 0 2 0 0 0 1 2
120-140% 2 2 1 1 1 0 0 1 2 1 0 1 2 2 1 3 1 0 1
>140% 1 1 2 2 2 3 3 2 1 2 3 1 1 0 2 0 2 3 2
Strong Table 5.  Strong El NIņo - Years by Percent of Normal Categories (5 events)
% of Normal Div. 1 Div. 2 Div. 3 Div. 4 Div. 5 Div. 6 Div. 7 CA 8SI 5SI 6SI SF SJC EKA RDD SAC FAT LAX SAN
<80% 2 3 3 2 3 0 0 1 3 3 3 2 2 1 1 3 2 0 0
80-100% 2 0 0 1 0 2 0 2 1 1 0 1 0 3 2 0 1 1 0
100-120% 0 1 1 0 0 0 3 1 0 0 0 0 1 0 0 0 0 0 1
120-140% 0 0 1 0 1 2 1 0 1 1 2 0 0 1 1 1 1 1 2
>140% 1 1 0 2 1 1 1 1 0 0 0 2 2 0 1 1 1 3 2
Very Strong Table 6.  Very Strong El NIņo - Years by Percent of Normal Categories (3 events)
% of Normal Div. 1 Div. 2 Div. 3 Div. 4 Div. 5 Div. 6 Div. 7 CA 8SI 5SI 6SI SF SJC EKA RDD SAC FAT LAX SAN
<80% 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
80-100% 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
100-120% 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
120-140% 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
>140% 2 2 1 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2
Table 7. Percent of Normal (1981-2010) Rainfall for All Years
  Normal 49.77" 36.69" 20.46" 22.03" 20.70" 17.80" 6.35" 24.10" 54.52 42.57 30.50 23.65" 18.42 40.33" 34.62 18.52" 11.50" 14.93" 10.34
ENSO Type Rainfall Season 1 2 3 4 5 6 7 Calif 8SI 5SI 6SI SF SJC EKA RDD SAC FAT LAX SAN
* 1950-1951 111% 109% 117% 86% 106% 57% 62% 99% 119% 119% 118% 101% 88% 115% 116% 95% 90% 55% 62%
Mod. El Niņo* 1951-1952 123% 129% 133% 135% 135% 162% 147% 134% 132% 123% 148% 138% 127% 118% 140% 129% 121% 176% 189%
Weak El Niņo 1952-1953 118% 102% 98% 80% 82% 75% 75% 96% 100% 75% 88% 89% 62% 118% 127% 88% 84% 63% 68%
Weak El Niņo 1953-1954 107% 89% 78% 78% 82% 91% 77% 89% 92% 81% 86% 60% 65% 105% 106% 73% 77% 80% 95%
Weak La Niņa 1954-1955 68% 69% 62% 80% 77% 79% 71% 71% 68% 67% 77% 67% 76% 83% 75% 81% 89% 80% 75%
Mod. La Niņa 1955-1956 139% 134% 142% 120% 125% 84% 76% 125% 136% 136% 125% 115% 116% 115% 143% 138% 117% 107% 47%
  1956-1957 90% 81% 93% 74% 79% 77% 65% 83% 83% 78% 75% 64% 65% 91% 81% 74% 71% 64% 93%
Stg. El Niņo 1957-1958 153% 142% 128% 161% 143% 160% 126% 147% 134% 124% 137% 154% 141% 121% 179% 155% 165% 142% 145%
Weak El Niņo 1958-1959 77% 68% 73% 61% 59% 53% 59% 67% 71% 61% 48% 44% 63% 81% 66% 59% 60% 37% 55%
  1959-1960 86% 78% 70% 66% 68% 69% 82% 75% 81% 70% 70% 65% 67% 86% 104% 71% 70% 55% 78%
  1960-1961 97% 78% 73% 59% 61% 42% 52% 72% 72% 56% 50% 59% 64% 110% 93% 68% 60% 32% 36%
  1961-1962 82% 86% 100% 97% 101% 121% 89% 95% 84% 97% 97% 75% 80% 72% 99% 94% 99% 126% 100%
  1962-1963 116% 116% 131% 110% 105% 61% 58% 108% 118% 105% 98% 94% 130% 109% 114% 136% 101% 56% 41%
Mod. El Niņo 1963-1964 78% 68% 85% 62% 71% 71% 79% 73% 67% 71% 70% 52% 18% 93% 57% 67% 59% 53% 73%
Weak La Niņa 1964-1965 117% 112% 120% 96% 108% 82% 70% 107% 117% 123% 104% 94% 97% 101% 115% 99% 97% 92% 89%
Stg. El Niņo 1965-1966 88% 71% 79% 75% 73% 97% 109% 81% 71% 75% 63% 69% 68% 80% 90% 57% 53% 137% 157%
  1966-1967 109% 123% 140% 135% 138% 129% 90% 125% 117% 134% 163% 124% 129% 110% 131% 142% 130% 147% 111%
  1967-1968 79% 76% 78% 63% 67% 77% 96% 75% 71% 59% 60% 61% 84% 70% 69% 64% 63% 111% 83%
Mod. El Niņo* 1968-1969 120% 128% 147% 161% 169% 175% 142% 145% 127% 163% 186% 106% 136% 118% 151% 130% 200% 184% 121%
Weak El Niņo 1969-1970 111% 113% 115% 80% 86% 63% 69% 97% 111% 97% 79% 88% 73% 95% 154% 93% 79% 52% 66%
Mod. La Niņa 1970-1971 119% 106% 125% 85% 85% 80% 64% 102% 104% 76% 76% 79% 95% 119% 133% 88% 74% 83% 83%
Weak La Niņa 1971-1972 93% 68% 82% 48% 57% 51% 49% 69% 66% 67% 54% 47% 41% 98% 75% 50% 46% 48% 59%
Stg. El Niņo 1972-1973 95% 110% 104% 144% 122% 129% 113% 114% 96% 95% 128% 145% 150% 86% 123% 136% 121% 142% 119%
Stg. La Niņa 1973-1974 149% 132% 108% 116% 105% 87% 74% 120% 143% 110% 101% 117% 104% 132% 161% 112% 91% 100% 69%
Weak La Niņa 1974-1975 104% 92% 102% 92% 94% 93% 74% 96% 93% 105% 95% 77% 87% 99% 129% 86% 67% 96% 111%
Stg. La Niņa 1975-1976 67% 49% 56% 39% 54% 63% 78% 56% 48% 55% 54% 34% 37% 83% 63% 36% 71% 48% 95%
Weak El Niņo 1976-1977 41% 41% 68% 50% 50% 66% 84% 52% 37% 45% 54% 47% 58% 44% 58% 38% 66% 82% 84%
Weak El Niņo 1977-1978 127% 131% 124% 157% 157% 207% 200% 147% 132% 148% 155% 114% 141% 90% 179% 142% 158% 224% 195%
  1978-1979 74% 80% 80% 91% 99% 131% 129% 90% 77% 101% 90% 79% 78% 62% 95% 97% 93% 132% 162%
Weak El Niņo 1979-1980 110% 118% 133% 121% 128% 165% 180% 128% 111% 134% 136% 104% 121% 94% 109% 128% 104% 181% 164%
  1980-1981 73% 74% 79% 70% 73% 69% 71% 73% 69% 64% 67% 65% 71% 73% 95% 68% 72% 60% 84%
  1981-1982 142% 145% 148% 132% 140% 100% 103% 135% 153% 152% 126% 157% 98% 120% 156% 164% 97% 72% 120%
V. Stg. El Niņo 1982-1983 162% 166% 164% 193% 186% 199% 191% 176% 166% 187% 194% 161% 194% 147% 184% 192% 205% 209% 190%
Weak La Niņa 1983-1984 111% 108% 120% 78% 94% 64% 88% 99% 110% 109% 95% 95% 86% 120% 105% 78% 66% 70% 60%
Weak La Niņa 1984-1985 78% 71% 78% 75% 77% 78% 125% 78% 66% 72% 86% 85% 81% 87% 75% 58% 69% 86% 100%
  1985-1986 114% 126% 139% 122% 133% 116% 111% 124% 131% 139% 142% 121% 120% 97% 133% 128% 129% 120% 147%
Mod. El Niņo 1986-1987 72% 62% 67% 60% 63% 61% 82% 65% 61% 56% 61% 59% 50% 69% 63% 56% 81% 51% 100%
Stg. El Niņo* 1987-1988 77% 73% 64% 73% 73% 99% 115% 77% 65% 63% 73% 75% 72% 80% 84% 75% 70% 84% 137%
Stg. La Niņa 1988-1989 88% 86% 97% 60% 71% 57% 64% 79% 86% 71% 79% 74% 53% 86% 93% 77% 76% 54% 59%
  1989-1990 74% 74% 78% 58% 68% 52% 43% 68% 72% 72% 66% 61% 64% 67% 83% 96% 82% 49% 82%
  1990-1991 64% 69% 80% 80% 79% 99% 107% 77% 61% 76% 78% 60% 76% 62% 61% 69% 85% 77% 123%
Stg. El Niņo* 1991-1992 68% 71% 63% 92% 78% 124% 155% 82% 67% 64% 65% 81% 104% 54% 79% 71% 96% 141% 135%
  1992-1993 120% 128% 127% 139% 134% 188% 185% 137% 121% 134% 132% 113% 137% 108% 146% 138% 144% 183% 191%
  1993-1994 63% 64% 67% 70% 67% 78% 57% 67% 59% 55% 68% 64% 79% 73% 65% 65% 74% 54% 103%
Mod. El Niņo* 1994-1995 143% 163% 166% 161% 164% 182% 149% 161% 159% 169% 153% 144% 152% 128% 158% 127% 165% 163% 178%
Mod. La Niņa* 1995-1996 118% 115% 129% 105% 106% 76% 51% 109% 112% 104% 102% 105% 112% 111% 107% 102% 95% 83% 53%
  1996-1997 118% 115% 135% 112% 119% 87% 66% 114% 126% 129% 114% 96% 99% 125% 76% 107% 104% 83% 73%
V. Stg. El Niņo 1997-1998 154% 160% 132% 191% 168% 211% 177% 167% 154% 154% 179% 200% 186% 145% 181% 174% 175% 208% 185%
Stg. La Niņa* 1998-1999 109% 96% 101% 81% 85% 65% 64% 92% 103% 92% 79% 99% 88% 124% 85% 75% 61% 61% 70%
Stg. La Niņa* 1999-2000 95% 98% 86% 101% 97% 78% 64% 92% 103% 99% 92% 105% 80% 90% 95% 116% 112% 77% 60%
Weak La Niņa 2000-2001 59% 66% 58% 90% 81% 100% 93% 74% 63% 71% 75% 82% 88% 57% 83% 81% 92% 120% 89%
  2001-2002 93% 87% 76% 73% 77% 36% 32% 76% 87% 81% 84% 106% 72% 101% 80% 97% 61% 30% 31%
Mod. El Niņo 2002-2003 117% 105% 91% 99% 94% 105% 90% 103% 108% 91% 104% 101% 99% 132% 97% 90% 85% 110% 111%
  2003-2004 94% 91% 83% 76% 74% 60% 93% 83% 90% 71% 69% 87% 88% 95% 100% 71% 66% 62% 54%
Weak El Niņo 2004-2005 101% 110% 115% 144% 139% 192% 206% 130% 107% 129% 127% 135% 161% 110% 107% 118% 138% 249% 234%
Weak La Niņa* 2005-2006 139% 141% 135% 121% 127% 93% 84% 127% 150% 132% 119% 146% 147% 146% 125% 127% 127% 88% 56%
Weak El Niņo 2006-2007 75% 62% 56% 50% 53% 31% 32% 57% 67% 59% 56% 71% 58% 88% 63% 59% 52% 22% 40%
Stg. La Niņa* 2007-2008 81% 72% 75% 79% 72% 88% 82% 78% 67% 69% 85% 73% 71% 85% 66% 74% 73% 91% 76%
Weak La Niņa 2008-2009 70% 78% 76% 70% 76% 68% 78% 73% 86% 94% 85% 77% 74% 74% 66% 88% 68% 61% 95%
Mod. El Niņo 2009-2010 99% 97% 93% 115% 105% 114% 113% 103% 99% 107% 113% 102% 110% 110% 84% 112% 107% 110% 110%
Stg. La Niņa* 2010-2011 112% 123% 143% 125% 141% 139% 109% 127% 135% 154% 149% 122% 100% 112% 101% 129% 152% 135% 131%
Mod. La Niņa* 2011-2012 82% 73% 60% 68% 63% 64% 59% 70% 78% 61% 73% 66% 46% 101% 65% 66% 71% 58% 84%
Mod. La Niņa 2012-2013 77% 78% 79% 60% 61% 47% 65% 69% 80% 63% 51% 70% 61% 80% 79% 82% 49% 39% 68%
  2013-2014 55% 58% 66% 44% 48% 43% 63% 54% 56% 47% 49% 0.5302 41% 52% 49% 53% 42% 41% 53%
Weak El Niņo* 2014-2015 82% 78% 83% 35% 59% 60% 83% 75% 71% 45% 43% 0.7691 88% 84% 73% 86% 57% 57% 94%
V. Stg. El Niņo 2015-2016 111% 106% 116% 97% 102% 67% 89% 98% 99% 99% 89% 0.9797 96% 120% 114% 88% 129% 65% 113%
Weak La Niņa 2016-2017 141% 157% 178% 150% 155% 131% 122% 141% 175% 171% 154% 1.3687 118% 157% 130% 179% 150% 127% 135%

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