# Presentation: 051932

## Did the El Niño of 2002-03 break the drought in Colorado or elsewhere in the West? 

- Klaus Wolter
- NOAA-CIRES Climate Diagnostics Center
- klaus.wolter@noaa.gov

**•****  ****Drought in the Western U.S.: 1999 - 2003**
**• **** ****Expected precipitation anomalies in 2002-03**
**• **** ****Observed precipitation anomalies in 2002-03**
**• **** ****Role of individual precipitation events **
**• **** ****Preliminary Conclusions**

- With Kudos to Jon Eischeid, Roger Pielke, Sr., and Robin Webb

## Western U.S. Drought from 1999-2002

**Notes:**
One of the original motivations for the drought monitor was the severe drought that developed in much of the western U.S. after the 97-98 El Nino. The severe fire seasons of 2000 and 2002 were preceded/accompanied by particularly dry and hot conditions.

## Where did the West recover from drought conditions in 2002-03?

- During the winter of 2002-03, the West Coast got “wet” first; followed by interior states from Arizona to Montana that recovered at least partially from a severe multi-year drought. This fall, drought has reaffirmed its grip on states like New Mexico and Montana.

**Notes:**
A PHDI of -2 is considered a good drought threshold. Every western state carried drought conditions at this threshold or higher at the beginning of the WY 03. Compared to the eastern U.S., recovery has been much less decisive, but much welcome nevertheless

## Stateof ENSO mid-2002 into early 2003 based on MEI: a moderately strong El Niño event

- MEI ranks in JA’02: **11**, SO: 13, ND: **10**, JF’03: **9**, MA: 20

**Notes:**
Starting with Vern’s legendary call for El Niño conditions in early 2002, there was much hope for the El Nino of 2002-3 to deliver some much needed moisture in the southwestern quadrant of the U.S. By about August it was clear that we would have a decent sized event, although much weaker than five years earlier.

## Percentage of Significant Departures  During

**Percentage of Significant Departures  During**
**El Ni****ñ****o: 18.0%**
**10 cases:**
**1957, 63, 65, 72, 82,  86, 87, 91, 94, 97**
**If the MEI were used, 1977 would replace 1963.**

**Notes:**
Solid circles = 95% significant compared to neutral years.  Note that many interior stations are quite wet this time of year. Note also how few stations have a significant dry signal.

## Percentage of Significant Departures  During

**Percentage of Significant Departures  During**
**El Ni****ñ****o: 20.5%**
**10 cases:**
**1957-58, 65-66,         68-69, 72-73, 82-83,  86-87, 87-88, 91-92, 94-95, 97-98**
**If the MEI were used, 1977-78 would replace 1968-9.**

**Notes:**
Mid-winter hits the hardest in CA and AZ/NM. Stormtrack shifts south, somewhat. Dry conditions are common from the mountains of CO to most of Montana west to the PNW.

## Percentage of Significant Departures  During

**Percentage of Significant Departures  During**
**El Ni****ñ****o: 6.1%**
**10 cases:**
**1958, 66, 69, 73, 83,  87, 88, 92, 95, 98**
**If the MEI were used, 1978 would replace 1964.**

**Notes:**
With a nod to delayed impacts, this map shows the spring AFTER an El Nino winter - the spring of 1978 was a lot wetter than 64... Note the little bull’s eye over NE CO.

## Percentage of significant composite precipitation anomalies in the Western U.S. vs. three different ENSO indices: Niño 3.4, Southern Oscillation Index (SOI), and Multivariate ENSO Index (MEI).  Highest values in each season are underlined. Niño 3.4, the “official” measure of ENSO, is not optimal for anticipating regional impacts.

| ENSO INDEX | Niño 3.4 SST |  | SOI |  | MEI |  |
| --- | --- | --- | --- | --- | --- | --- |
|  | El Niño | La Niña | El Niño | La Niña | El Niño | La Niña |
| SON | 18.0 | 3.7 | 5.6 | 2.9 | 14.7 | 3.7 |
| DJF | 20.5 | 1.4 | 20.5 | 14.0 | 25.4 | 4.1 |
| MAM | 4.6 | 4.3 | 4.1 | 12.7 | 13.3 | 3.8 |
| JJA | 13.5 | 5.0 | 12.0 | 2.8 | 15.4 | 6.2 |
| MAM (from NDJF) | 6.1 | 4.7 | 10.0 | 8.6 | 9.4 | 8.3 |

**Percentage of significant composite precipitation anomalies in the Western U.S. vs. three different ENSO indices: Ni****ñ****o 3.4, Southern Oscillation Index (SOI), and Multivariate ENSO Index (MEI).  Highest values in each season are underlined. Niño 3.4, the “official” measure of ENSO, is not optimal for anticipating regional impacts.**

**Notes:**
Could not resist: Using 10 cases each, with four-month seasons folded into three (SON really is ASON), this table shows that both the SOI and the MEI do “better” than Nino 3.4 (except for SON!). Also, except for La Nina springs with the SOI, every scenario shows more percentage points with the delayed than with the zero-lag scenario. Food for thought!

## Recent precipitation trends for the U.S.: (left) SON, (bottom left) DJF, and (bottom right) MAM.  Correlations above 0.3 can be considered significant. According to this analysis, Montana has had the most pervasive drying trend in the West over the last 30 years. This comes on top of the expected El Niño signal, or does it express the preference for El Niño conditions during that period?  Compared to recent temperature trends, most of the precipitation trends appear insignificant.

**Notes:**
Context of using OCN and the importance of trends: not so wild for precip trends -  yet!

## How representative are climate divisions?

**How representative are climate divisions?**

- Biggest problems exist with precipitation in the interior West,
- and Climate Divisions do NOT include SNOTEL data.

**Notes:**
Apropos, Climate Divisions: major problems in the West, especially the interior!

## New Climate Divisions

- Official CDs for Colorado (left) and Experimental CDs (right) based on multivariate statistical analysis of climate data that also include **SNOTEL** data. Such new CDs are being derived for the entire U.S.A.
- Let us focus on 1 (red), 3 (black), 6 (purple), and 8 (green) for this El Niño “impact study”.

**Notes:**
The old chestnut - check out region 2: from WY to NM - I don’t think so!  As can be seen on the right, only old 5 - the San Luis valley - survives more or less intact.

## El Niño in Colorado

- Seasonal precipitation amounts (in percentiles from 1950-99) for 10 El Niño cases: 1957-8, 65-6, 72-3, 77-8, 82-3, 86-7, 87-8, 91-2, 94-5, and 97-8, based on the MEI. If 8 or more cases out of 10 reside above or below the median, the distribution is shifted significantly.  If 4 or more cases reside in the upper (80%) or lower (20%) quintile,  there is only a 10% chance that this result is by accident. The 2002-3 El Niño event ended up ranked 10th, pushing 1977-78 into 11th place.

- Wet

- Wet

- WET

- Wet

- Dry

**Notes:**
One figure says it all: this is what I showed the public starting last October, it sums up the impacts of El Niño in Colorado for the most important regions, and still allows for probabilistic information to be included.  Although only the significant pdf-shifts are highlighted, every region shows better chances for wetness in the fall and spring, and lower chances for that in the winter (except for the Arkansas valley). If I point out only one region, it would be my neck of the woods, where 9 of 10 cases were wetter than the median during... (65-66 was the “bad” boy!).

## Observed precipitation rankings in 2002-3

- During the fall season of 2002, increased western U.S. precipitation matches expectations quite well, in particular over Utah, western Colorado and northern New Mexico. During the following winter, the overall El Niño foot print remains visible, with Washington receiving more than expected and AZ/NM less. Dry conditions over the central high plains are the least consistent with El Niño expectations.

**Notes:**
Grinding through stuff - SON was a decent match, DJF still quite good. PNW starts out with a dry bang, but then gets lucky during the winter. S CA starts out wet and continues for the next three seasons.

## Observed precipitation rankings in 2002-3

- During the spring of 2003, California continues to receive good moisture consistent with lingering El Niño conditions. The Pacific Northwest into Montana appear lucky to receive more moisture than expected. Over the interior southwest, northeast Colorado ‘hit the jackpot’ due to its March snowstorm, while AZ/NM continue to ‘under perform’. A more detailed look at Colorado follows below, revealing that the spring moisture bonanza is actually very consistent with MEI-based expectations.

**Notes:**
A wet spring in NE CO means that the wettest season of the year is wet. Given that we are in Reno, I had to use at least one gambling phrase!

## What a difference a year makes, The Big Picture

- September 2001 through August 2002 maximizes the impact of the 12-month running drought in the southwestern U.S. Compared to the record-setting recovery in the eastern U.S., our return to near-normal in 2002-03 appears rather bland. It was most welcome nevertheless, and, together with prudent water management, it allowed for at least a modest recovery in the western water supply situation.

**Notes:**
Mention that northern CO reservoirs are mostly back to normal, after dire warnings that it would take three years to recover, and that the soil moisture deficit would ‘eat’ into the water ‘harvest’.

## What a difference a year makes, Colorado-style

- WY 2002 was the driest on record in much of southern Colorado, and close to that in the north. WY 2003 ended up close to or wetter than normal along the Front Range and in most of northern Colorado. Dry pockets persist in the southeastern plains and the San Luis Valley. The biggest positive anomaly (around Summit County) overlaps with massive cloud-seeding efforts last winter...

**Notes:**
Sorry about the first slide - could not get the matching ones. All you need to know is that every station in WY 2002 was below normal (showed this last year?), something you never see in CO. Note the bull’s eye over Winter Park and Vail.

## Impact of the 2002-3 El Niño in Colorado

**Notes:**
A lot of information on one page: 1. Mountains on the left, estern plains on the right. Open circles are old CD data, solid circles are new ones. Hit WDW in north without fail, while the south was true to form only in fall and winter. Note that a wet June rectified the situation in the Arkansas valley. 
 Note the contrast between CD 2 and the San Juans in the spring in terms of observations - some of this is probably because of preliminary data.
3. Most extreme result: spring in FR, where most people live: 90%-tile, was much appreciated, especially after 20% winter. Ironically, the dryness in the winter often precedes good spring (MARCH) moisture, so my comments in this direction were duly noted...

## Did the 2002-3 seasonal totals in Colorado match expectations (high hopes)?

- Using the simplest possible classification of the data (above or below the median), let’s compare the expected WET/DRY/WET sequence in most of Colorado (expect for the Arkansas Valley that tends to get WET in all 3 seasons from fall to spring) with preliminary observations:
- The northern two “climate divisions” (1 and 8) received WET/DRY/WET, while the south (3 and 6) ended up DRY during the spring. This means that 10 out of 12 “forecasts” were correct in their sign, and two were not. How unusual is that?
- If you classify each season since 1950 into above and below median precipitation totals, and compare against the WET/DRY/WET scenario (WWW for region 6), there are only two cases (out of 42) in which there is a match this good (10 out of 12) during non-El Niño years (1984-5 and 98-99), while there are three such cases (out of 10) during El Niño years. IOW, the a priori odds for such a good match were 30%, given the El Niño setup, and only 5% during the other years.
- Another way of quantifying this: the median number of matches of this type is  only FIVE out of 12 during non-El Niño years, and between EIGHT and NINE during El Niño years. IOW, 2002-3 did not only match, but exceed expectations in Colorado.

**Notes:**
Something to add here?

## The importance of individual events

- Big storms battered California on and off during the winter and spring of 2002-3. One can argue that the siege of storms in mid-December made all the difference for the Sierra Nevada snowpack, while the biggest rain in L.A. came right in the middle of the annual AMS meeting.  Higher odds for big storms are typical of El Niño, but this one broke some records!

**Notes:**
Note that half the annual fell in SFO during mid-December! 20% in one day in LA was nothing to sneeze at either!

## Snowstorm of the century?!

- Speaking of records, the mid-March 2003 storm was easily one of the biggest three snowstorms of the last century in Colorado, rivaling or exceeding totals last seen in April 1921 (24h U.S. record at Silver Lake, Boulder County), and December 1913 (the ‘analog’ case in terms of the synoptic set-up?). Liquid totals reached 7-9” H2O at numerous COOP and SNOTEL sites along the Front Range, or 20-30% of the average annual precipitation at these locales.

**Notes:**
George Grell’s wife shoveling snow while her husband takes pictures... She is about 5’10”!
Mention the interesting meso-scale effect of lower toals from Weld County through Boulder... I almost got ‘screwed’!

## The role of individual storms in Colorado

- The March 17-20 snow storm turned a lackluster winter around, and refilled Front Range reservoirs. It is easily the biggest single snow storm (in terms of SWE) in Front Range SNOTEL history (since 1978).
- A near-record breaking snow storm in late April hit West Slope ski resorts right after many of them had closed down for the season. As can be seen in this SNOTEL diagram for Vail, this one contributed only about 10% to the annual total, while the March storm added 25% to Lake Eldora’s totals.

**Notes:**
Anything to add? Sierra Nevada would have been impressive...
Also: we get occasional dumps in the Front Range foothills, but the mountains typically spread out their bounty - too high in elevation!

## Preliminary Conclusions

- As discussed last year, multi-year drought conditions in the West reached record proportions by late summer 2002, matching or exceeding the severity of one of the worst droughts on record along the eastern seaboard.
- Recovery since then has been not nearly as decisive for the West as it has been for the East. In fact, if it had not been for a few key events (that did not “produce” for everyone), the drought would have continued virtually unabated.
- The El Niño of 2002-03 provided for a rare opportunity to combine the typically skilful forecasts during such events with increased public interest in the West.  Much was riding on this one!

**Notes:**
People actually paid attention, due to the drought! A repeat of 2001-2 would have spelled disaster for much of the interior southwest!

## Preliminary Conclusions

- Probably not unrelated to its only moderate size, the El Niño of 2002-3 did not provide for universal relief in the southwestern U.S. Nevertheless, beneficial moisture during the fall and late winter season in particular helped turn things around from California to Colorado.
- Of course, this preliminary assessment does not prove that the observed precipitation anomalies were related to El Niño. However, I hope I was able to point out areas of agreement and disagreement.
- While the tier of states from Washington to Montana fared better than expected, unchanged or worsened drought conditions in New Mexico and parts of Arizona attest to the worst disappointments of this El Niño year in the West.

**Notes:**
Nah!