Wednesday - U.S. Drought Monitor Forum

1. California Climate
Outcome Likelihood Tool
Nina Oakley, Kelly Redmond, Grant Kelly, Britta Daudert
Western Regional Climate Center
USDM Forum
April 22 2015 – Reno, NV

2. Motivations
 How might this year turn out?
 NCDC “Amelioration” tool (PHDI) 1
 M. Dettinger “ESP” analysis
 P. Iñiguez PRISM simulations
 What water managers want:
 Better seasonal forecasts, monitoring, communication2
 Constrain decision-making
 Tool that is customizable, daily resolution
 Tool that is graphical, explains caveats3
1ncdc.noaa.gov/temp-and-precip/drought/recovery/
2Steinemann 2014, BAMS
3Pulwarty 2003, Water Resources

3. Data Source
 NWS COOP via ACIS
 Daily, long record
 Decision makers often state climate forecasts unreliable1
 Suggest stations with record 1920 or better-present
 Any station, any record
in US
 Provisions for how
much missing data
acceptable
COOP at Manzanita Lake, CA1Pulwarty 2003, Water Resources

6. 3 Data Options
 “Observed” data in station record
 Distribution built from all past periods equal to “recovery period”
in station record
 “Analog” Periods
 Identify periods in station record of date range equal to
observed period that are within +/- 1, 2, or 3 deciles of current
observed total
 Take their corresponding future “recovery” periods and create
distribution
 Random sampling of station record
 Sample each day of “recovery period” from station record, build
“synthetic accumulations”, repeat 1000x
 Apr 13 2001 + Apr 14 1934 + Apr 15 1901 + ... Sept 30 1996
 Doesn’t account for multiple day precipitation streaks

7. 2 “Analysis” Options
 Amelioration
 Likelihood of reaching normal, recovering deficit by end of
“recovery period”
 Custom Threshold
 Likelihood of receiving a user-specified amount of
precipitation by end of “recovery period”

9. At RENO
2014-10-01 to
2015-04-12
2.93 in accum.
0 missing days
2.43 in deficit
11.87 in needed
by 09-30-2016
to recover deficit,
reach normal
15.6% chance
of recovering
based on 77 of
78 possible
periods in record
1937-03-01 to
2015-04-12
“Observed”
option
Deciles
Amount needed
Normal
for period
Probability of
occurrence

11. “Analog”
option
At RENO
2014-10-01 to
2015-04-12
2.93 in accum.,
falls between
10th - 20th
percentile
2.43 in deficit
11.87 in needed
by 09-30-2016 to
recover deficit,
reach normal
13% chance
of recovering
using +/- 1
decile analog
(10th-30th
percentile),
23 periods
Probability of
occurrence
Amount needed
Normal
for period

12. Example graph + table for Sacramento, CA
Likelihood of exceeding threshold of 3 inches
by end of WY 2015 (20% chance)

13. Spaghetti Plot (coming soon)
Observed Precipitation
10-01-2014 through
04-12-2015
+
Selected precipitation
traces 04-13-2015
through 09-30-2016
=
Range of outcomes
based on climatology
Hypothetical Station
Observed period 10-01-2014 to 04-12-2015,
Future period ending 09-30-2016 10 traces shown
precipitation
time

14. Limitations and Future Work
 Using historic record, does not account for future trends
 Point rather than areal data
 Test on target audience, implement feedback
http://wrcc.dri.edu/col/
 Expand to other accumulating quantities
 snowfall, HDD, CDD, GDD

15. Thank you!
South Yuba River, Sierra Nevada, CA
Feb 7/8 2015 Atmospheric River event
Bad for skiing, good for kayaking
Photo credit: Ben Hatchett nina.oakley@dri.edu
@WRCCclimate
Connect with WRCC!

17. Random
Sampling
2014-10-01 to
2015-03-18
3.09 in
0 missing
0.15 in deficit
6.65 in needed
to recover deficit
by 09-30
28.6% chance
of recovering
based on 1000
random daily
samples from
record
1892-01-01 to
2015-03-19