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We have examined the evidence presented by Labat et al. and found that (1) their claims for a 4% increase in global runoff arising from a 1 °C increase in air temperature and (2) that their article provides the “first experimental data-based evidence demonstrating the link between the global warming and the intensification of the global hydrological cycle” are not supported by the data presented. Our conclusions are based on the facts that (1) their discharge records exhibit non-climatic influences and trends, (2) their work cannot refute previous studies finding no relation between air temperature and runoff, (3) their conclusions cannot explain relations before 1925, and (4) the statistical significance of their...
Categories: Publication; Types: Citation
Previous research has suggested that a general inverse relation exists between winter precipitation in the southwestern United States (US) and summer monsoon precipitation. In addition, it has been suggested that this inverse relation between winter precipitation and the magnitude of the southwestern US monsoon breaks down under certain climatic conditions that override the regional winter/monsoon precipitation relations. Results from this new study indicate that the winter/monsoon precipitation relations do not break down, but rather shift location through time. The strength of winter/monsoon precipitation relations, as indexed by 20-year moving correlations between winter precipitation and monsoon precipitation,...
Detrended, modelled first leaf dates for 856 sites across North America for the period 1900–2008 are used to examine how the El Niño Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO) separately and together might influence the timing of spring. Although spring (mean March through April) ENSO and PDO signals are apparent in first leaf dates, the signals are not statistically significant (at a 95% confidence level (p < 0.05)) for most sites. The most significant ENSO/PDO signal in first leaf dates occurs for El Niño and positive PDO conditions. An analysis of the spatial distributions of first leaf dates for separate and combined ENSO/PDO conditions features a northwest–southeast dipole that is...
Categories: Publication; Types: Citation; Tags: ENSO, PDO, phenology, spring
The relations of decadal to multidecadal (D2M) variability in global sea-surface temperatures (SSTs) with D2M variability in the flow of the Upper Colorado River Basin (UCRB) are examined for the years 1906-2003. Results indicate that D2M variability of SSTs in the North Atlantic, North Pacific, tropical Pacific, and Indian Oceans is associated with D2M variability of the UCRB. A principal components analysis (with varimax rotation) of detrended and 11-year smoothed global SSTs indicates that the two leading rotated principal components (RPCs) explain 56% of the variability in the transformed SST data. The first RPC (RPC1) strongly reflects variability associated with the Atlantic Multidecadal Oscillation and the...
The timing of snowmelt runoff (SMR) for 84 rivers in the western United States is examined to understand the character of SMR variability and the climate processes that may be driving changes in SMR timing. Results indicate that the timing of SMR for many rivers in the western United States has shifted to earlier in the snowmelt season. This shift occurred as a step change during the mid-1980s in conjunction with a step increase in spring and early-summer atmospheric pressures and temperatures over the western United States. The cause of the step change has not yet been determined. Published in Journal of Hydrometeorology, volume 6, issue 4, on pages 476 - 482, in 2009.
A monthly snow accumulation and melt model was used with monthly Precipitation-elevation Regressions on Independent Slopes Model (PRISM) temperature and precipitation data to generate time series of 1 April snow water equivalent (SWE) for 1900 through 2008 in the western United States. Averaged across the western United States, SWE generally was higher than long-term (1900?2008) average conditions during the periods 1900?25, 1944?55, and 1966?82; SWE was lower than long-term average conditions during the periods 1926?43, 1957?65, and 1984?2008. During the period 1900?2008, the temporal pattern in winter precipitation exhibited wetter-than-average and drier-than-average decadal-scale periods with no long-term increasing...
Rain-on-snow events pose a significant flood hazard in the western United States. This study provides a description of the spatial and temporal variability of the frequency of rain-on-snow events for 4318 sites in the western United States during water years (October through September) 1949–2003. Rain-on-snow events are found to be most common during the months of October through May; however, at sites in the interior western United States, rain-on-snow events can occur in substantial numbers as late as June and as early as September. An examination of the temporal variability of October through May rain-on-snow events indicates a mixture of increasing and decreasing trends in rain-on-snow events across the western...
Categories: Publication; Types: Citation
Recent research suggests a link between drought occurrence in the conterminous United States (US) and sea surface temperature (SST) variability in both the tropical Pacific and North Atlantic Oceans on decadal to multidecadal (D2M) time scales. Results show that the Atlantic Multidecadal Oscillation (AMO) is the most consistent indicator of D2M drought variability in the conterminous US during the 20th century, but during the 19th century the tropical Pacific is a more consistent indicator of D2 M drought. The interaction between El Niño-Southern Oscillation (ENSO) and the AMO explain a large part of the D2M drought variability in the conterminous US. More modeling studies are needed to reveal possible mechanisms...
Categories: Publication; Types: Citation
In this study, winter mean 700 mbar height anomalies over the eastern North Pacific Ocean and the western USA are related to variability in snowpack accumulations measured on or about 1 April at 21 snowcourse stations within and near the Gunnison River basin in Colorado. Results indicate that lower than normal snowpack accumulations are primarily associated with positive 700 mbar height anomalies (anomalous anticyclonic circulation) over the western USA. Moist air from the Pacific Ocean is moved to the north of the western USA along the western margin of the anomalous anticyclonic circulation. In contrast, higher than normal snowpack accumulations are associated with negative 700 mbar height anomalies (anomalous...
Recent research suggests a link between drought occurrence in the conterminous United States (US) and sea surface temperature (SST) variability in both the tropical Pacific and North Atlantic Oceans on decadal to multidecadal (D2M) time scales. Results show that the Atlantic Multidecadal Oscillation (AMO) is the most consistent indicator of D2M drought variability in the conterminous US during the 20th century, but during the 19th century the tropical Pacific is a more consistent indicator of D2 M drought. The interaction between El Niño-Southern Oscillation (ENSO) and the AMO explain a large part of the D2M drought variability in the conterminous US. More modeling studies are needed to reveal possible mechanisms...
Categories: Publication; Types: Citation
Detrended, modelled first leaf dates for 856 sites across North America for the period 1900–2008 are used to examine how the El Niño Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO) separately and together might influence the timing of spring. Although spring (mean March through April) ENSO and PDO signals are apparent in first leaf dates, the signals are not statistically significant (at a 95% confidence level (p < 0.05)) for most sites. The most significant ENSO/PDO signal in first leaf dates occurs for El Niño and positive PDO conditions. An analysis of the spatial distributions of first leaf dates for separate and combined ENSO/PDO conditions features a northwest–southeast dipole that is...
Categories: Publication; Types: Citation; Tags: ENSO, PDO, phenology, spring
Snow-water equivalent (SWE) data measured at several hundred montane sites in the western United States are used to examine the historic effects of El Nino and La Nina events on seasonal snowpack evolution in the major subbasins in the Columbia and Colorado River systems. Results are used to predict annual runoff. In the Columbia River Basin, there is a general tendency for decreased SWE during El Nino years and increased SWE in La Nina years. However, the SWE anomalies for El Nino years are much less pronounced. This occurs in part because midlatitude circulation anomalies in El Nino years are located 35� east of those in La Nina years. This eastward shift is most evident in midwinter, at which time, SWE anomalies...
More than half (52%) of the spatial and temporal variance in multidecadal drought frequency over the conterminous United States is attributable to the Pacific Decadal Oscillation (PDO) and the Atlantic Multidecadal Oscillation (AMO). An additional 22% of the variance in drought frequency is related to a complex spatial pattern of positive and negative trends in drought occurrence possibly related to increasing Northern Hemisphere temperatures or some other unidirectional climate trend. Recent droughts with broad impacts over the conterminous U.S. (1996, 1999–2002) were associated with North Atlantic warming (positive AMO) and northeastern and tropical Pacific cooling (negative PDO). Much of the long-term predictability...
Categories: Publication; Types: Citation
This paper describes a data assimilation method that uses observations of snow covered area (SCA) to update hydrologic model states in a mountainous catchment in Colorado. The assimilation method uses SCA information as part of an ensemble Kalman filter to alter the sub-basin distribution of snow as well as the basin water balance. This method permits an optimal combination of model simulations and observations, as well as propagation of information across model states. Sensitivity experiments are conducted with a fairly simple snowpack/water-balance model to evaluate effects of the data assimilation scheme on simulations of streamflow. The assimilation of SCA information results in minor improvements in the accuracy...
A water-balance model is used to simulate time series of water-year runoff for 4 km × 4 km grid cells for the conterminous United States during the 1900–2008 period. Model outputs are used to examine the separate effects of precipitation and temperature on runoff variability. Overall, water-year runoff has increased in the conterminous United States and precipitation has accounted for almost all of the variability in water-year runoff during the past century. In contrast, temperature effects on runoff have been small for most locations in the United States even during periods when temperatures for most of the United States increased significantly.
Categories: Publication; Types: Citation
The effects of continued global warming on water resources are a concern for water managers and stake holders. In the western United States, where the combined climatic demand and consumptive use of water is equal to or greater than the natural supply of water for some locations, there is growing concern regarding the sustainability of future water supplies. In addition to the adverse effects of warming on water supply, another issue for water managers is accounting for, and managing, the effects of natural climatic variability, particularly persistently dry and wet periods. Analyses of paleo-reconstructions of Upper Colorado River basin (UCRB) flow demonstrate that severe sustained droughts, and persistent pluvial...
Categories: Publication; Types: Citation
Abstract: The relations of decadal to multidecadal (D2M) variability in global sea-surface temperatures (SSTs) with D2M variability in the flow of the Upper Colorado River Basin (UCRB) are examined for the years 1906-2003. Results indicate that D2M variability of SSTs in the North Atlantic, North Pacific, tropical Pacific, and Indian Oceans is associated with D2M variability of the UCRB. A principal components analysis (with varimax rotation) of detrended and 11-year smoothed global SSTs indicates that the two leading rotated principal components (RPCs) explain 56% of the variability in the transformed SST data. The first RPC (RPC1) strongly reflects variability associated with the Atlantic Multidecadal Oscillation...
Models suggest that average temperatures in the central Rocky Mountains will increase by >3°C over the next century, while precipitation may remain within late Holocene boundaries. This study investigates the potential hydrologic effects of such warming when combined with the full range of precipitation variability experienced over the past millennium. Using the upper Yellowstone drainage as a test case, a water balance model is constructed to estimate river discharge from precipitation and temperature inputs (r = 0.85 versus observed). The model then was run using tree ring precipitation estimates for 1177–1910 and 1911–1995 A.D. combined with (1) average observed temperatures 1896–1995; (2) reconstructed Northern...
Categories: Publication; Types: Citation