Annual stream flow variability over the western United States [abstract] (original) (raw)
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Coupled oceanic-atmospheric variability and U.S. streamflow
Water Resources Research, 2005
1] A study of the influence of interdecadal, decadal, and interannual oceanicatmospheric influences on streamflow in the United States is presented. Unimpaired streamflow was identified for 639 stations in the United States for the period 1951-2002. The phases (cold/negative or warm/positive) of Pacific Ocean (El Niño-Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO)) and Atlantic Ocean (Atlantic Multidecadal Oscillation (AMO) and North Atlantic Oscillation (NAO)) oceanicatmospheric influences were identified for the year prior to the streamflow year (i.e., long lead time). Statistical significance testing of streamflow, based on the interdecadal, decadal, and interannual oceanic-atmospheric phase (warm/positive or cold/negative), was performed by applying the nonparametric rank-sum test. The results show that in addition to the well-established ENSO signal the PDO, AMO, and NAO influence streamflow variability in the United States. The warm phase of the PDO is associated with increased streamflow in the central and southwest United States, while the warm phase of the AMO is associated with reduced streamflow in these regions. The positive phase of the NAO and the cold phase of the AMO are associated with increased streamflow in the central United States. Additionally, the coupled effects of the oceanic-atmospheric influences were evaluated on the basis of the long-term phase (cold/negative or warm/ positive) of the interdecadal (PDO and AMO) and decadal (NAO) influences and ENSO. Streamflow regions in the United States were identified that respond to these climatic couplings. The results show that the AMO may influence La Niña impacts in the Southeast, while the NAO may influence La Niña impacts in the Midwest. By utilizing the streamflow water year and the long lead time for the oceanic-atmospheric variables, useful information can be provided to streamflow forecasters and water managers.
Water Resources Research, 1991
A statistical analysis was undertaken to determine the nature and magnitude of the relationship of precipitation, temperature and streamflow in the western United States to large-scale atmospheric circulation patterns. The Southern Oscillation Index (SOB was used as an indicator of the El Nifio/Southern Oscillation (ENSO) and the PNA index as an indicator of the Pacific#North America pattern. These indices were correlated with surface climate data and split sample analyses were conducted to determine climate response during the extreme phases of each index. October-March precipitation was shown to be most strongly correlated with SOI averaged over the July-November period. The analysis showed that there are two centers of opposite association with the SOI. During low values of the SOI (ENSO events) precipitation is low in the Pacific northwest and high in the desert southwest. Correlations between SOI and temperature were greatest in the Pacific northwest. The split sample analysis also revealed statistically significant differences in precipitation occurring during extremes of the SOI. The PNA pattern was related to precipitation and temperature over a concurrent time period. Especially strong associations were noted in the Pacific northwest for both precipitation and temperature. Streamflow showed associations with SO I similar to precipitation.
Interdecadal and Interannual Oceanic / Atmospheric Variability and United States Seasonal Streamflow
Impacts of Global Climate Change, 2005
A study of the influence of interdecadal and interannual oceanic / atmospheric influences on seasonal streamflow in the U.S. is presented. Unimpaired streamflow was identified for 639 stations in the U.S. for the period 1951-2002. Pacific Ocean [El Niño-Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO)] and Atlantic Ocean [Atlantic Multidecadal Oscillation (AMO)] oceanic / atmospheric phases (e.g., warm or cold) were identified for the year (or season) prior to the year of the winter-spring season streamflow (i.e., long lead-time). Statistical significance testing of the difference in means (and medians) of streamflow, based on the interdecadal and interannual oceanic / atmospheric phase (warm or cold), was performed applying the two-sample t-test and the rank-sum test. Additionally, the coupled effects of the oceanic / atmospheric influences were evaluated, based on the long-term phase (warm or cold) of the interdecadal variables (PDO and AMO) and ENSO, and streamflow regions in the U.S. were identified that respond to these climatic couplings. The results show that, in addition to the well-established ENSO signal, the PDO and AMO influence streamflow variability in the United States. Additionally, the phase (warm or cold) of the PDO and AMO enhance (or dampen) the ENSO signal in several streamflow regions in the United States. By utilizing the winter-spring streamflow season (e.g., typical period of peak runoff) and the long lead-time for the oceanic / atmospheric variables, useful information can be provided to streamflow forecasters and water managers.
The regional persistence and variability of annual streamflow in the United States
Water Resources Research, 1998
Inference from individual streamflow records can be extremely misleading, even for large samples. One is often tempted to trust information available from a streamflow record rather than to exploit regional average statistics of those records. This study documents that regional average streamflow statistics usually contain much more information about the variability and persistence of streamflow at a particular site than does the individual streamflow record for that site. Experiments are performed using time series of annual streamflow at 1544 gauging stations across the continental United States. We document that 18 broad water resource regions of the United States are homogeneous in terms of the year-to-year persistence of streamflow, whereas much smaller regions are required to obtain homogeneity in terms of the variability of streamflow. Classical homogeneity measures ignore the serial correlation of streamflow. Instead, homogeneity is quantified using the sampling properties of at-site estimates of the coefficient of variation C v and lag-one correlation 1 of annual streamflows. Additional experiments using the Hurst coefficient reveal that the long-term persistence structure of historical annual streamflow series is indistinguishable from the long-term persistence structure of either an AR(1) or ARMA(1,1) process. If historical flow series are generated from either an AR(1) or ARMA(1,1) process, then even given 1544 observed time series, we are unable to distinguish between those two processes.
Annual Cycle Variability of Precipitation, Temperature and Streamflow in the Western United States
Journal of Climate, 2004
There is a growing body of scientific literature, which shows that low frequency components of the climate system such as ENSO (El Niño-Southern Oscillation) have significant influence on some regional annual cycle variability of climate variables. In this paper we analyze the influence of such low frequency modulations, and other possible mechanisms on the annual cycles of precipitation, temperature and streamflow in the western United States. We consider two periods, 1950-1975 and 1976-2000 to compare ...
Hydrology
The spatiotemporal hydrologic variability over different regions of the contiguous United States poses the risk of droughts and floods. Understanding the historic variations in streamflow can help in accessing future hydrologic conditions. The current study investigates the historic changes in the streamflow within the climate regions of the continental United States. The streamflow records of 419 unimpaired streamflow stations were grouped into seven climate regions based on the National Climate Assessment, to evaluate the regional changes in both seasonal streamflow and yearly streamflow percentiles. The non-parametric Mann–Kendall test and Pettitt’s test were utilized to evaluate the streamflow variability as a gradual trend and abrupt shift, respectively. The Walker test was performed to test the global significance of the streamflow variability within each climate region based on local trend and shift significance of each streamflow station. The study also evaluated the presenc...
Assessing the climate‐scale variability of atmospheric rivers affecting western North America
Geophysical Research Letters, 2017
A new method for automatic detection of atmospheric rivers (ARs) is developed and applied to an atmospheric reanalysis, yielding an extensive catalog of ARs land-falling along the west coast of North America during 1948-2017. This catalog provides a large array of variables that can be used to examine AR cases and their climate-scale variability in exceptional detail. The new record of AR activity, as presented, validated and examined here, provides a perspective on the seasonal cycle and the interannual-interdecadal variability of AR activity affecting the hydroclimate of western North America. Importantly, AR intensity does not exactly follow the climatological pattern of AR frequency. Strong links to hydroclimate are demonstrated using a high-resolution precipitation data set. We describe the seasonal progression of AR activity and diagnose linkages with climate variability expressed in Pacific sea surface temperatures, revealing links to Pacific decadal variability, recent regional anomalies, as well as a generally rising trend in land-falling AR activity. The latter trend is consistent with a long-term increase in vapor transport from the warming North Pacific onto the North American continent. The new catalog provides unprecedented opportunities to study the climate-scale behavior and predictability of ARs affecting western North America. Plain Language Summary We have created a new seven-decade-long catalog of atmospheric river behavior land-falling upon the west coast of North America. The catalog has been validated against independent precipitation observations to ensure that the atmospheric rivers represented therein are associated with extreme orographic precipitation. Our results clearly delineate a prominent role for atmospheric rivers in California's hydroclimate. Atmospheric river variability has been particularly important in the recent California drought as well as its most recent lapse. We also detect a long-term increasing trend in water vapor transport impinging on the west coast of North America associated with atmospheric rivers and overall wintertime water vapor transport associated with climate warming. Our results, moreover, suggest that potential predictability of seasonal behavior of atmospheric rivers may hinge on sources of climatic variability somewhat different from that of total water vapor transport.
Hydrology, 2016
The study focused on investigating the presence of change patterns in 600 unimpaired streamflow stations across the continental U.S. at different time intervals to understand the change patterns that can provide significant insight regarding climate variability and change. Each station had continuous streamflow data of at least 30 years (the entire dataset covered a range of 109 years). Presence of trends and shifts were detected in water year and the four seasons (fall, winter, spring, and summer) analyzing the water year and seasonal mean flows. Two non-parametric tests, namely, the Mann-Kendall test and the Pettitt's test were used to identify the trends and the shifts, respectively. The results showed an increasing trend in the northeast and upper-mid regions, whereas southeast and northwest regions underwent a decrease. Shifts followed similar patterns as trends with higher number of stations with significant change. Fall and spring showed the highest number of stations with increasing and decreasing change, respectively, in the seasonal analyses. Results of this study may assist water managers to understand the streamflow change patterns across the continental U.S., especially at the regional scale since this study covers a long range of years with a large number of stations in each region.
Water Resources Research, 1990
Differences in runoff and rainfall variability between southeastern Australia and southeastern United States have been examined, using various standard techniques such as principal component and spectral analyses, and examination of the quick and base flow components of runoff. It is shown that the higher runoff variability in Australia can be partly explained by the large‐scale circulation and rainfall patterns associated with the Southern Oscillation which are unlike those in the southeastern United States. Whereas the Southern Oscillation signal is easily detectible in the southeast Australian rainfall and runoff data, it is, with the exception of several small areas, absent in the southeastern United States data. In the case of this particular comparison, the differences in runoff variability between the two selected regions were found to be largest in winter and spring months and smallest in summer.
Hydrology
Understanding the interconnections between oceanic-atmospheric climate variables and regional streamflow of the conterminous United States may aid in improving regional long lead-time streamflow forecasting. The current research evaluates the time-lagged relationship between streamflow of six geographical regions defined from National Climate Assessment and sea surface temperature (SST), 500-mbar geopotential height (Z 500), 500-mbar specific humidity (SH 500), and 500-mbar east-west wind (U 500) of the Pacific and the Atlantic Ocean using singular value decomposition (SVD). The spatio-temporal correlation between streamflow and SST was developed first from SVD and thus obtained correlation was later associated with Z 500 , SH 500 , and U 500 separately to evaluate the coupled interconnections between the climate variables. Furthermore, the associations between regional streamflow and the El Niño Southern Oscillation (ENSO), Pacific Decadal Oscillation, and Atlantic Multidecadal Oscillation were evaluated using the derivatives of continuous wavelet transform. Regional SVD analysis revealed significant teleconnection between several regions and climate variables. The warm phase of equatorial SST had shown a stronger correlation with the majority of streamflow. Both SVD and wavelet analyses concluded that the streamflow variability of the regions in close proximity to the Pacific Ocean was strongly associated with the ENSO. Improved knowledge of teleconnection of climate variables with regional streamflow variability may help in regional water management and streamflow prediction studies.