WMOD00274 ‎(2)‎

• Title: Hydro-Climate Index Study - Final Report
• Prepared By: HDR Engineering
• Date: 2/14/2008
• County: Statewide
• State: CO
• Weather Modification - Doc Type: Report

Figure 4. Relationship of the Sept. - Nov. NAO vs. District 20 Dec.-Mar. Basin Avg. Precip.
(% of normal)
‘Neutral’ HCIvalue
for period (yellow)
Observed value for a
givenwater year vs.
HCI value for
Normal or mean value
corresponding period
(blue) with +/- 15-20%
range (green)
District 35
In District 35, the PDO appeared to be a prime leading indicator of precipitation
when compared to the other indices while the AMO and the MEI are reasonably modest
‘secondary’ indicators of note. An example of the PDO/Basin Avg. Relationship for this
Figure5
area can be seen in . There is a notable lack of ‘very dry’ years (< 80% of
normal) when the PDO value was greater than 0.25, while for very dry years there are
nearly 2 times the number of years when the BAP value was ‘very wet’ (> 120% of
normal) to occur in years that the PDO was greater than 0.50. A potential user of the data
would be keen to note what phase the AMO and/or the MEI maybe situated in as negative
AMO/El Nino years do have a bit of scatter (see Data Appendix for details). The one
item to note is that modest/strong positive AMO years are consistently dry across this
sub-basin with a lack of excessively wet years with a positive AMO mode in place.
Some preliminary conclusions are the following:
1)The ENSO indicators are important in portions of but, not in the entire reach of
Division 3 and,
2)The Atlantic index value is not trivial when considering the moderate winter-time
seasonal precipitation factors in the region.
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