El Niño & California

El Niño's impacts on California winter precipitation

First, we examined the dependence of the El Niño—California precipitation relationship on timing (early versus late winter), region (northern versus southern California), and the strength of the El Niño SSTA, based on 110-year observations.

Our results can be summarized by the following figure:

The probability of the anomalous statewide-wetness increases as El Niño intensity increases. (compare (c), (d) with (g), (h))
The relationship between ENSO and precipitation is stronger in the relatively dry southern California. (see (d))
The influences of El Niño on California winter precipitation are statistically significant in late winter (Feb-Apr, FMA), but not in early winter (Nov-Jan) even though that is when El Niño usually reaches its peak intensity. (compare (d) with (b), and (h) with (f))

Composites of (a), (c), (e) and (g) 200 hPa height anomalies (contour, interval: 10 m), SSTA (ocean) and (b), (d), (f), (h) precipitation anomalies (% of climatology) for (top) moderate-to-strong and (bottom) weak El Niños in (left) early and (right) late winters during 1900/01 to 2009/10. All the anomalies here are de-trended.

Stippling regions in (a), (c), (e), (g) indicate the 95% significance for 200 hPa height variations. Stippling regions in (b), (d), (f), (h) indicate the 95% significance for precipitation variations. The numbers ofEl Niño events for each case are indicated in the titles. (From Fig. 3 in Jong et al. 2016)

Details can be found in our publication on this work:

Jong, B.-T., M. Ting and R. Seager (2016): El Niño's impact on California precipitation: seasonality, regionality, and El Niño intensity. Environ. Res. Lett., 11. http://doi.org/10.1088/1748-9326/11/5/054021

2015/16 strong El Niño's & California dry winter

Based upon our previous study and seasonal forecast from North American Multimodel Ensemble (NMME), the 2015/16 strong El Niño was expected to bring above-average precipitation to drought-stricken California in the late winter, similar to the 1982/83 and 1997/98 strong El Niños. However, only normal to below-average precipitation fell across California in the late winter 2015/16.

We examine that whether the forecasts of California precipitation from NMME were too wet because sea surface temperature anomalies (SSTAs) forecasts were too warm in the equatorial eastern Pacific in the late winter. Our study shows that it is difficult to assert that the eastern tropical Pacific SSTAs caused the too-wet California precipitation forecast, especially in southern California. Interestingly, our work also suggests that internal variability alone could drive a normal to below-average winter in California, even in the presence of a strong El Niño.

FMA 2016 100-member ensemble mean precipitation anomalies over the US from AGCM observed SSTA runs, and forecast SSTA runs using (top) CCM3, (middle) CAM4, and (bottom) CAM5. (right) OBS minus FRCST differences. Stippling denotes 90% significance using a two-tailed Student’s t test. (unit: percent of climatology).
(From Fig. 7 in Jong et al. 2018)

Details can be found in our publication on this work:

Jong, B.-T., M. Ting, R. Seager, N. Henderson, and D.-E. Lee (2018): Role of equatorial Pacific SST forecast error in the late winter California precipitation forecast for the 2015/16 El Niño. J. Clim., 31, 839-852. http://doi.org/10.1175/JCLI-D-17-0145.1

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