Thomas C. Piechota

El Nino/Southern Oscillation and Australian rainfall, streamflow and drought: Links and potential for forecasting

Abstract El Nino/Southern Oscillation (ENSO) has been linked to climate anomalies throughout the world. This paper presents an overview of the relationship between ENSO and rainfall, drought and streamflow in Australia. The teleconnection between ENSO and the hydroclimate of Australia is investigated using the empirical method of Ropelewski and Halpert and the potential for forecasting the hydroclimate variables are investigated by assessing the lag correlations between rainfall and streamflow and the indicators of ENSO several months earlier. The analyses show that dry conditions in Australia tend to be associated with El Nino. The link between rainfall and streamflow and ENSO is statistically significant in most parts of Australia, but it is not sufficiently strong to consistently predict rainfall and streamflow accurately. The teleconnection is stronger in the latter part of the year, and the analyses suggest that the indicators of ENSO can be used with some success to forecast spring rainfall in eastern Australia and summer rainfall in north-east Australia several months in advance. The ENSO indicators can also be used to help forecast spring runoff in south-east Australia and summer runoff in the north-east and east coasts of Australia. Unlike rainfall, the serial correlation in the streamflow data is generally similar or higher than the lag streamflow-ENSO correlation, and it must be used together with the ENSO indicators in developing streamflow forecast models. The seasonal forecasts of rainfall and streamflow are invaluable to the management of land and water resources, particularly in Australia, where the streamflow variability is higher than in most parts of the world.

Drought and Regional Hydrologic Variation in the United States: Associations with the El Niño‐Southern Oscillation

Using 94 years of monthly Palmer Drought Severity Index (PDSI) data for 344 climate divisions, this study investigates the hydroclimatic response in the United States to the extreme phases of the Southern Oscillation (El Nino and La Nina). Several regions of coherent response to El Nino-Southern Oscillation (ENSO) are identified. The strongest relationship between El Nino and extreme drought years is found in the Pacific Northwest. A strong relationship is also noticed in the southern United States, where dry conditions occur consistently during La Nina events. Next, the conditional response in PDSI is evaluated based on the extreme phases of the Southern Oscillation. The PDSI results were compared to similar analyses on 41 years of station temperature, precipitation, and streamflow data. A consistent response is seen in the other hydroclimatic variables, though the most filtered response is seen in PDSI data and streamflow data. The major contribution to the understanding of the ENSO–United States climate relationship is the evaluation of the general form of drought )nd comparison of these results to the fundamental hydrologic processes (precipitation, temperature, and streamflow).

Seasonal streamflow forecasting in eastern Australia and the El Niño–Southern Oscillation

Previous studies have identified a strong link between climate variability in Australia and the El Nino–Southern Oscillation (ENSO). This paper describes the development and use of a seasonal streamflow forecast model based on an optimal linear combination of forecasts derived from climatology, persistence, the Southern Oscillation index (SOI), and equatorial Pacific sea surface temperatures (SST). The model builds on the work of the Australian Bureau of Meteorology and that of other researchers who have investigated southeast Australian rivers. The model is tested using 66 years of unimpaired streamflow data from 10 eastern Australian catchments. Results from testing the model further support the ENSO-hydroclimate link, showing that eastern Australia generally receives below normal streamflow during El Nino conditions and above normal streamflow during La Nina conditions. In southeast Australia the SOI is a better predictor for July–September and October–December streamflow and the SST a better predictor of January–March and April–June streamflow. For many of the seasons and stations, the skill associated with the cross-validation forecast is better than that drawn from the baseline condition of climatology.

Western US streamflow and atmospheric circulation patterns during El Niño-Southern Oscillation

Abstract Using principal component analysis (PCA), cluster analysis, and jackknife analysis, we investigated the spatial and temporal modes that dominate streamflow variability in the western US in response to El Nino-Southern Oscillation (ENSO) events. Spatial variability was investigated with data only from ENSO years and with rotated PCA on 79 streamflow stations in the western United States. Eight regions, or clusters, were thus pinpointed as areas where streamflow tends to co-vary similarly following ENSO events; traditional cluster analysis confirmed the identification of these regions. The ENSO response in streamflow was then further evaluated by forming an aggregate ENSO composite for each region. Temporal variability of western US streamflow in the PCA-identified regions was evaluated with a ‘T-mode’ PCA that isolated the different responses in streamflow following ENSO events. The T-mode PCA breaks the 13 ENSO events that occurred from 1932 to 1993 into five subsets. It is interesting to note that the events in the dominant mode, PC1(+), occurred before 1976, and next mode, PC2(+), included events prior to 1976. Finally, we investigated the atmospheric circulation patterns over the North Pacific Ocean and much of North America that are associated with the various US streamflow responses. The circulation patterns vary according to the prescribed ENSO forcing. The results of this study contribute to a better understanding of the varied ENSO-streamflow relationship in the western US and the use of ENSO for long-range streamflow forecasting.

Coupled oceanic‐atmospheric variability and U.S. streamflow

Received 22 June 2005; revised 5 August 2005; accepted 23 September 2005; published 6 December 2005. (1) A study of the influence of interdecadal, decadal, and interannual oceanic- atmospheric 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 Nino-Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO)) and Atlantic Ocean (Atlantic Multidecadal Oscillation (AMO) and North Atlantic Oscillation (NAO)) oceanic- atmospheric 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 Nina impacts in the Southeast, while the NAO may influence La Nina 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.

Alternative principal components regression procedures for dendrohydrologic reconstructions

Streamflow reconstruction using tree ring information (dendrohydrology) has traditionally used principal components analysis (PCA) and stepwise regression to form a transfer function. However, PCA has several procedural choices that may result in very different reconstructions. This study assesses the different procedures in PCA-based regression and suggests alternative procedures for selection of variables and principal components. Cross-validation statistics are presented as an alternative for independently testing and identifying the optimal model. The objective is to use these statistics as a measure of the models performance to find a conceptually acceptable model with a low prediction error and the fewest number of variables. The results show that a parsimonious model with a low mean square error can be obtained by using strict rules for principal component selection and cross-validation statistics. Additionally, the procedure suggested in this study results in a model that is physically consistent with the relationship between the predictand and the predictor. The alternative PCA-based regression models presented here are applied to the reconstruction of the Upper Colorado River Basin streamflow and compared with results of a previous reconstruction using traditional procedures. The streamflow reconstruction proposed in this study shows more intense drought periods, which may influence the future allocation of water supply in the Colorado River Basin.

The western U.S. drought: How bad is it?

Historical stream flow records and the forecast for 2004 make the current (1999–2004) drought in the southwestern United States the worst one in the past 80 years for portions of the Upper Colorado River Basin (UCRB). For the Colorado River (near Cisco, Utah), the cumulative stream flow deficit (departure from long-term mean) for the current drought is almost 11 km8, or approximately 2 years of average stream flow Although the current drought is the most significant, based on historical stream flow records, is it the worst ever?

Climate variations, climate change, and water resources engineering

Prepared by the Surface Water Hydrology Technical Committee of the Environmental and Water Resources Institute of ASCE.

Water Management Decisions Using Multiple Hydrologic Models within the San Juan River Basin under Changing Climate Conditions

AbstractA modified version of the U.S. Bureau of Reclamation (Reclamation) long-term planning model, Colorado River Simulation System (CRSS), is used to evaluate whether hydrologic model choice has an impact on critical decision variables within the San Juan River Basin when evaluating potential effects of climate change through 2099. The distributed variable infiltration capacity (VIC) model and the lumped National Weather Service (NWS) River Forecast System (RFS) were each used to project future streamflow; these projections of streamflow were then used to force Reclamation’s CRSS model over the San Juan River Basin. Both hydrologic models were compared to evaluate whether or not uncertainty in climatic input generated from general circulation models outweighed differences between the hydrologic models. Differences in methodologies employed by each hydrologic model had a significant effect on projected streamflow within the basin. Both models project decreased water availability under changing climate c...

Quantitative Assessment of Climate Change Impacts on the Hydrology of the North Platte River Watershed, Wyoming

AbstractThe impact of climate change on water resources is a major issue for regions in the world. Climate parameters such as temperature and precipitation are expected to change in the future and could significantly impact available water resources. This paper assesses long-term water availability over the North Platte River watershed, Wyoming, by utilizing the variable infiltration capacity (VIC) hydrologic model and developing streamflow projections under anthropogenic climate change conditions. Uncertainties in the scenarios of climate change and global climate models are assessed by utilizing ensemble multiple models and multiple scenarios from the World Climate Research Programme’s database. The simulated streamflows are compared using an intermodel interscenario approach. Based on streamflow projections, there is a possibility of increased annual streamflow for this region through 2100, with maximum streamflow during 2085–2090. The simulated annual streamflows for future periods vary from −20 to 62...