Most research into streamflow – ocean-atmospheric circulation teleconnections focuses initially on examining contemporary relationships, before moving on to examine lag relationships. Redmond and Koch (1991) correlated SOI and the Pacific-North American pattern (PNA) with contemporary surface hydro-climatic data. Split sample analyses were conducted to determine the climate response during the extreme phases of each index. October to March precipitation was shown to be most strongly correlated with SOI averaged over the July to November period. Correlations varied spatially. Especially strong associations were noted in the Pacific Northwest between PNA and streamflows, precipitation, and temperatures.
Barlow et al. (2001) used a covariance-based rotated PCA to extract the primary modes of SST from monthly data for the North Pacific basin. They then used these modes to examine concurrent relationships with U.S. precipitation, drought, and streamflows. They found a significant relationship between the three primary modes of Pacific variability (ENSO, PDO, and the North Pacific mode) and US warm season precipitation, drought, and streamflow. They also found that the relationship between these modes and streamflow and drought varies little throughout a season, but the relationship between these modes and precipitation varies substantially from month to month. However, their best example would only explain 25% of the variance. Something they say warrants further research is the identification of the factors that cause the general precursor relationships to greatly intensify during particular periods, eg. 1962-66, in their study. Nigam et al. (1999) also examine contemporary relationships between principal components of Pacific SSTs and US streamflows. They found that the two leading patterns in the SST data equate to the Pacific Decadal Oscillation and the North Pacific Mode, and that these “linkages” are statistically significant and could contribute to the development of warm season hydroclimate forecasts.
Studies on relationships between New Zealand inflows and ocean-atmosphere state variables include that by McKerchar and Pearson (1994), who studied contemporaneous relationships between New Zealand river flows and the SOI, with the aim of eventually
predicting season ahead river flows. They found that SOI and river flows are positively but weakly correlated for North Island rivers, and less significantly correlated for South Island rivers. They also found that the summer Clutha lake inflows correlation with lagged Spring SOI is r = -0.34. Hence they conclude that there is some scope for predicting lake inflows using SOI. They also note that negative SOI (El Nino) in spring results in enhanced spring snow accumulation in South Island catchments. They went on to use these relationships to predict summer inflows, by giving non-exceedence probabilities of summer inflows given a particular value of spring SOI. (McKerchar et al., 1996).
Studies of the low rainfalls that occurred in early 1992 (Basher et al. 1992, Fitzharris 1992) aid in developing a better understanding of processes affecting the Waitaki catchment’s rainfall and inflows. They reveal that rainfalls at the Hermitage (at 750masl in the Waitaki catchment) were only 30% of average in April and May 1992, and suggest that low inflows are mainly due to an absence of westerly airstreams and a predominance of cooler and drier southerly airstreams. Fitzharris (1992) notes that there was a higher than normal incidence of southwesterly to southerly airflows and colder than normal conditions in autumn 1992. This produced increased storage of precipitation as snow, but, abnormally for the increased south-westerly conditions of an El Nino pattern, there was lower than normal rainfall in the catchment. It was concluded that the presence of a moderately strong El Nino weather pattern enhanced the incidence of south-west winds over this period. Such low inflow periods are often associated with long-term or low frequency climatic fluctuations like the El Nino-Southern Oscillation phenomenon. The aerosols in the atmosphere from the eruption of Mt Pinatubo in the Phillipines in 1991-92 may also have contributed to lower temperatures in New Zealand, and these may have increased the proportion of precipitation falling as snow. An attempt was made to predict winter 1992 inflows, and the outcome was “uncertain” (Basher et al., 1992). These findings were reinforced by Fitzharris and Tait (1992), who examined surface pressure anomaly maps and their relationships to Hokitika (West Coast of the South Island) rainfall. They found that high spring to autumn inflows are associated with airflow from the west to south-west, but such conditions induce low inflows in winter because then much precipitation falls as snow. For inflows to be high in winter, higher than normal frequencies of northerly to north-westerly conditions are required, and low inflows in spring and summer are produced by anomalous easterly circulation conditions.
Oscillations in inflows were noted by Tomlinson (1981), who conducted time series analysis on several New Zealand rainfall and river flow records. Using filter analysis, he found that flow records include similar temporal oscillations to those found in rainfall series. Oscillations in the records of 8-12.5 years, and 12.5-35 years, were identified. The oscillations explained 15-40% of the variance in the series and were used to forecast an increased likelihood of generally lower rainfall and river flows over the country between 1983 and 1986. In retrospect, inflows and rainfall, though variable spatially, were not particularly low over this period.