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

Table 7. Summary of single season Dec. -Mar. Precipitation/HCI Relationships for the Arkansas
basin (dark `X' indicates a relatively strong relationship and light 'X' indicates a relatively weak
relationship).
B - April -June Precipitation (single season)
Upper Arkansas:
During this period the PDO relationships earlier noted do experience a notable
reversal as spring approaches. The negative correlations between the PDO values and
precipitation tend to reverse with the three -month averages by the end of April, indicating
that what regime is important in one part of the year may be different in another period of
the year. Also a curious but, sharper reversal of the relationships between the ENSO
phase and precipitation takes place with El Nino's tendency to have higher precipitation
values and vice versa regarding La Nina.
Middle Arkansas:
During this period the PDO relationships noted do experience a notable reversal
as spring approaches. The negative correlations between PDO and precipitation values
tend to reverse with the three -month averages by the end of April, indicating that what is
regime is important in one period of the year may be different in another period of the
year. Also a curious but, sharper reversal of the relationships between the ENSO phase
and precipitation takes place with El Nino's tendency to have higher precipitation values
and vice versa regarding La Nina.
Lower Arkansas:
The modest trends of higher precipitation values in La Nina and drier El Nino
regimes continued in this region through this period and are fairly steady as spring
approaches. However, a curious relationship occurs with the NAO as the relatively
strong positive relationship between precipitation and NAO values quickly reverses from
early winter to late winter. (i.e. late - fall/early winter positive values of NAO would
generally portend greater precipitation values and vice versa however, as April
approaches it would be more favorable to have negative NAO values for greater
precipitation, ect.).
PDO
MEI
SOI
Nino 3.4
NAO
AMO
Upper Ark.
X
X
Middle Ark.
X
Lower Ark.
X
X
X
B - April -June Precipitation (single season)
Upper Arkansas:
During this period the PDO relationships earlier noted do experience a notable
reversal as spring approaches. The negative correlations between the PDO values and
precipitation tend to reverse with the three -month averages by the end of April, indicating
that what regime is important in one part of the year may be different in another period of
the year. Also a curious but, sharper reversal of the relationships between the ENSO
phase and precipitation takes place with El Nino's tendency to have higher precipitation
values and vice versa regarding La Nina.
Middle Arkansas:
During this period the PDO relationships noted do experience a notable reversal
as spring approaches. The negative correlations between PDO and precipitation values
tend to reverse with the three -month averages by the end of April, indicating that what is
regime is important in one period of the year may be different in another period of the
year. Also a curious but, sharper reversal of the relationships between the ENSO phase
and precipitation takes place with El Nino's tendency to have higher precipitation values
and vice versa regarding La Nina.
Lower Arkansas:
The modest trends of higher precipitation values in La Nina and drier El Nino
regimes continued in this region through this period and are fairly steady as spring
approaches. However, a curious relationship occurs with the NAO as the relatively
strong positive relationship between precipitation and NAO values quickly reverses from
early winter to late winter. (i.e. late - fall/early winter positive values of NAO would
generally portend greater precipitation values and vice versa however, as April
approaches it would be more favorable to have negative NAO values for greater
precipitation, ect.).