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

Animas River at Durango
The peak seasonal /HCI relationships in this basin appear to behave in a manner
very similar to that of the San Juan River at Pagosa Springs. The physical orientation of
the basin is similar to the Animas and thus, there the similarities are not overwhelmingly
surprising. The reader is directed to the prior section for the San Juan River for details.
Dolores at Rico
This river produces a much lower amount of natural runoff than the San Juan and
Animas Rivers however; users in this basin rely on surface water in this location as well.
Unfortunately, it appears that there is no real notable relationship with the naturalized
flow and the HCI values, if anything it is far less notable than the neighboring basins. A
potential explanation is that the basin is oriented more north -south than the San
Juan /Animas basins therefore the influx of moisture into the region from a
south /southwesterly direction is far less orthogonal than earlier thought.
Table 6. Summary of Apr. -Sep. Naturalized Streamflow /HCI Relationships for the San Juan/Dolores
(dark `X' indicates a relatively strong relationship and light 'X' indicates a relatively weak
relationship).
F - Single Seasonal Runoff Timing
The timing aspect of the runoff in the basin was examined by looking at the
comparison of the Julian Date of the 50% point of the April -July peak seasonal flow
verses the HCI values. Before this was performed (period of available record 1975-
2003), it was necessary to determine the relationship of the date of 50 % flow and the
actual volume of that year. In the case of the flow of the Animas River at Durango, the
overall relationship between 50% flow and the volume was significant enough that we
examined the residual (or in effect taking out the effects of volume) to determine the
seasonal melting effect.
The net result in looking at this variable was that El Nino years did have a
tendency to have a delayed runoff in the basin (at least from reaching the 50% of total
flow while La Nina years were earlier). It is unsure what impact temperatures may have
on this tendency or if it relates to some extent, to the tendency of more precipitation in
the spring with El Nino, delaying the runoff.
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PDO
MEI
SOI
Nino 3.4
NAO
AMO
District 30
X
X
X
District 32
X
X
X
District 34
X
X
X
District 71
X
X
X
F - Single Seasonal Runoff Timing
The timing aspect of the runoff in the basin was examined by looking at the
comparison of the Julian Date of the 50% point of the April -July peak seasonal flow
verses the HCI values. Before this was performed (period of available record 1975-
2003), it was necessary to determine the relationship of the date of 50 % flow and the
actual volume of that year. In the case of the flow of the Animas River at Durango, the
overall relationship between 50% flow and the volume was significant enough that we
examined the residual (or in effect taking out the effects of volume) to determine the
seasonal melting effect.
The net result in looking at this variable was that El Nino years did have a
tendency to have a delayed runoff in the basin (at least from reaching the 50% of total
flow while La Nina years were earlier). It is unsure what impact temperatures may have
on this tendency or if it relates to some extent, to the tendency of more precipitation in
the spring with El Nino, delaying the runoff.
24