Final.HCI.Report.HDR

• Title: Hydro-Climate Index Study
• Prepared For: CWCB & Colorado River WCD
• Prepared By: HDR Engineering Inc.
• Date: 12/28/2007
• County: Statewide
• State: CO
• Country: USA
• Weather Modification - Doc Type: Scientific Study

Figure 4. Relationship of the Sept. - Nov. NAO vs. District 20 Dec. -Mar. Basin Avg. Precip.
(% of normal)
Sep. -Nov. NAO vs. Dec. -Mar. Precipitation for District 20 (% of normal precipitation)
+
♦
c
`o ♦
c
o =-
a +
CL
a'
c
co
+
+
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-2.00 -1.75 -1.50 -1.25 -1.00 -0.75 -0.50 -0.25 0.00 0.25 0.50 0.75 1.00 1.25 1.50 1.75 2.00
Sep -Nov North Atlantic Oscillation Value
Some `secondary' but, weaker relationships exist with the Pacific Decadal
Oscillation (PDO) and minimal constructive relationships show up with the ENSO
indicators.
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
area can be seen in Figure 5. 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,
10
+
+
Some `secondary' but, weaker relationships exist with the Pacific Decadal
Oscillation (PDO) and minimal constructive relationships show up with the ENSO
indicators.
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
area can be seen in Figure 5. 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,
10