ENSO, Pacific Decadal Variability, and U.S. Summertime Precipitation, Drought, and Stream Flow

The investigation of fluctuations of wet and dry years has a long history in the climatology and hydrology literature. In this, the first of two papers investigating runs of consecutive dry years, the lengths (persistence) of dry runs are investigated. In the second paper the magnitude/intensity and severity (length × magnitude) of dry runs will be investigated. Consecutive dry years are associated with drought, which is a significant physical and economic phenomenon that imposes great stress on ecosystems and societies. Run lengths of consecutive years equal to or below the median were analysed for 3863 precipitation and 1236 runoff stations from around the world. Run lengths were found to be similar across all continents and Köppen climate zones, expect for tropical and arid North Africa (Sahel), which showed a distinct bias toward longer run lengths than any other region of the world. Generally, the run length observed in annual runoff was found to be similar to that observed in annual precipitation for the same location. Both annual precipitation and runoff data were found to be well described by the lag-one autoregressive (AR(1)) model or by white noise. The influence of the El Niño-southern oscillation on run lengths was not observed to be significant. The presence of decadal and multi-decadal oscillations was weakly observed in the results of the precipitation runs analysis. The faintness of the decadal and multi-decadal oscillation signal may be due to the sample sizes not being long enough and/or the runs analysis not being sensitive enough to detect their presence.

Section: Dmdos In Precipitation and Runoff Have Been Linked Tomentioning

confidence: 99%

“…• Australia (Warner, 1987;Power et al, 1999b); • North America (Cayan et al, 1998;Hamlet and Lettenmaier, 1999;Barlow et al, 2001;Neal et al, 2002);…”

Section: Introductionmentioning

confidence: 97%

Global analysis of runs of annual precipitation and runoff equal to or below the median: run length

Peel

Pegram

McMahon

2004

“…The third mode in the NH is a combination of these two modes. Barlow et al (2001) suggested that the NP mode dominated both in the JFM and JAS seasons. Actually, the second mode in the NP in the JAS season has a similar pattern to that in the JFM season.…”

Section: Dominant Variation Modes In the Global Sst Fieldmentioning

confidence: 99%

Regime shift in the global sea‐surface temperatures: its relation to El Niño–southern oscillation events and dominant variation modes

Yasunaka

Hanawa

2005

Significant changes of mean state appearing widely in the global sea-surface temperature (SST) anomaly field have happened five times from the 1910s to the 1990s : 1925, 1942, 1957, 1970 and 1976. Since the regions of change spread over both hemispheres and/or multiple oceanic basins, they can be considered as 'global regime shifts'. The years of regime shifts are consistent with those of the Northern Hemisphere regime shifts reported by previous studies.It is also shown that the regime shifts have happened concurrently with El Niño-southern oscillation (ENSO) events, which seems to suggest that the ENSO event acts as a trigger of the regime shift. At the regime shift, the tropical Pacific SSTs change from La Niña (El Niño) to El Niño (La Niña) conditions within 1 year. Further, the ENSO events occur just after the regime shifts begin in the July to September (JAS) season and reach the mature phase in the January to March (JFM) season as a typical evolution of the ENSO events. After that, they continue to at least the next year.The five regime shifts detected have similar features in their seasonal evolution and persistence of signals. First, the shifts start in the JAS season: an SST change occurs in the eastern and central tropical Pacific, and a change in the mid-latitudes of the North and South Pacific appears with the opposite sign. Then the shifts in the JFM season. The spatial patterns are similar to those of the JAS season, but signals in the North Pacific become remarkable. These features resemble those corresponding to a series of evolutions of ENSO events, but the signals in the North Pacific and the North Atlantic are much stronger than those of the typical ENSO events. After the shifts have happened, the changes in spatial patterns of SST that occurred at the regime shift persist until the next shift. The persistence of signals is more prominent in the JFM season than in the JAS season.From a review of the dominant variation modes in global SSTs using empirical orthogonal function (EOF) analyses, four modes are identified: the ENSO mode, the Southern Hemisphere trend mode, the North Pacific (NP) mode, and the Arctic oscillation (AO) mode. In the years when regime shifts occur, the ENSO mode, the NP mode, and the AO mode show significant concurrent phase reversals on the global scale as previously shown in the Northern Hemisphere. These findings provide a possible reason why SST changes in the regime shift are similar but not exactly the same pattern as that of ENSO. Furthermore, it can be considered that a simultaneous phase reversal of the NP mode would suppress the growth of anticyclonic (or cyclonic) circulation in the atmosphere over the western tropical Pacific. This suggests that an ENSO event, which begins with a regime shift, would not reverse its condition and last for the following several seasons.

“…Specifically, the El Niño-Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO) influence precipitation and streamflow patterns in the United States (Barlow et al, 2001;McCabe and Dettinger, 2002;McCabe et al, 2007). ENSO is a coupled oceanatmosphere phenomenon affecting the climate.…”

Section: Introductionmentioning

confidence: 99%

“…The warm phase of the PDO tends to coincide with anomalously cool temperatures and wet periods in the southern United States (Mantua and Hare, 2002). Barlow et al (2001) found that the three primary modes of Pacific variability (e.g., ENSO, PDO and the North Pacific mode) strongly influence US warm season precipitation and stream flow. McCabe and Dettinger (2002) demonstrated that the PDO is responsible for the majority of inter-annual variability in the April 1 snowpack in the western United States.…”

Section: Introductionmentioning

confidence: 99%

Discharge variability for an artesian spring of the Edwards Aquifer: Comal Springs (1933–2007)

Cox

Meng

Khedun

et al. 2009

Daily discharge volumes of Comal Springs, the largest artesian spring of the Edwards Aquifer (EA) in Central Texas, were utilized to characterize the flow of Comal Springs for the period of record spanning . The influence of water extraction (pumping) on discharge characteristics during the record was examined and found to be statistically significant for both volume and variability of spring discharge (p < 0.01). Pumping explains approximately a quarter of the variation in annual discharge (r 2 = 0.25) and nearly a third of the daily variability (r 2 = 0.32) within the Comal Springs discharge record.Statistically significant teleconnections to flow are demonstrated within the discharge record of Comal Springs. The El Niño-Southern Oscillation (ENSO, as measured by the Southern Oscillation Index) and the Pacific Decadal Oscillation (PDO) are shown to exhibit statistically significant correlations with annual mean flow from Comal Springs. PDO modulation of ENSO results in mean flow anomalies of 21.9% between extreme quintile years. The Atlantic Multi-decadal Oscillation (AMO) appears to exert influence based on the magnitude of the index value, irrespective of its positive or negative condition (p < 0.01), with the highest quintile (based on magnitude) years correlating with strong positive flow anomalies. A composite index was developed which combines the AMO, PDO and SOI. The extreme quintile years of this index demonstrate a 32.4% divergence in flow (p < 0.01) while demonstrating a stronger skill at capturing negative flow anomalies than positive anomalies.Precipitation data, at 4-km spatial resolution, were utilized to examine the temporal and spatial correlation of water input to the EA with rates of average monthly discharge from Comal Springs. The spatial dependence of the correlation between precipitation and Comal Springs discharge indicates significant seasonal variability. Overall, the correlation between precipitation and discharge is significant for spring, summer and fall seasons and not significant for winter.