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A - October to March Precipitation (single season) <br />This segment of precipitation was left in the October to March format vs. the <br />December to March format as existing datasets were readily available for this <br />information. Nevertheless, this analysis should still sufficiently cover the important <br />periods in the area and the precipitation /climate relationships. This basin was broken up <br />into three components, given the unique orientation of the basin. The first is the section <br />of the river upstream of Granite which could be best described as Lake County, the <br />second is from Granite to Salida, in southern Chafee County and the third is from Salida <br />to Pueblo Reservoir. For the purposes of this report these sections will be referred to as <br />the Upper, Middle, and Lower Arkansas sections respectively. <br />Upper Arkansas: <br />In this period, the PDO exhibited some correlation between HCI values and basin <br />average precipitation. For the PDO, in general, negative values of PDO corresponded <br />better with higher values of precipitation in the basin. However, this basin did exhibit a <br />modest signal with ENSO variables as well, more notably the MEI. From an ENSO <br />standpoint La Nina regimes tended to produce greater averages of precipitation while El <br />Nino's tended to be drier. <br />Middle Arkansas: <br />This portion of the basin also exhibited a similar and more steady relationship <br />with ENSO in that La Nina years tended to yield higher precipitation values while El <br />Nino years have drier tendencies. When examining the MEI, this relationship is <br />somewhat steady in the period leading up to and continuing into the winter. However, as <br />the seasons progresses into the winter months the relationship between the precipitation <br />and the NAO begins to rise in importance. In summary positive values of NAO <br />correlated to higher values of precipitation. Also on the "Atlantic" side of the equation, <br />early summer /fall values of the AMO exhibited a negative correlation between its value <br />and precipitation tendencies and unlike the NAO, this relationship actually weakened as <br />the late fall /early winter approached. <br />Lower Arkansas: <br />During this period, this sub -basin resulted in a number of relationships that was <br />stronger than most basins. However, the most robust relationships were with the NAO <br />and PDO, in which positive values correlated with higher precipitation values. For both <br />of these indexes, the relationship was stronger as the winter months approached. Also, <br />negative values of the NAO had some relationship with higher precipitation values. <br />Although ENSO was the relatively weakest component, there was some tendency for El <br />Nino's to experience above average precipitation, while La Nina exhibited some drier <br />tendencies. <br />27 <br />