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The Yukon River Basin, underlain by discontinuous permafrost, has experienced a warming climate over the last century that has altered air temperature, precipitation, and permafrost. We investigated a water chemistry database from 1982 to 2014 for the Yukon River and its major tributary, the Tanana River. Significant increases of Ca, Mg, and Na annual flux were found in both rivers. Additionally, SO4 and P annual flux increased in the Yukon River. No annual trends were observed for dissolved organic carbon (DOC) from 2001 to 2014. In the Yukon River, Mg and SO4 flux increased throughout the year, while some of the most positive trends for Ca, Mg, Na, SO4, and P flux occurred during the fall and winter months. Both...
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This study provides a fast and easy-to-apply method to estimate threshold friction velocity (TFV) of wind erosion in the field. Wind tunnel experiments and a variety of ground measurements including air gun, pocket penetrometer, torvane, and roughness chain were conducted in Moab, Utah and cross-validated in the Mojave Desert, California. Patterns between TFV and ground measurements were examined to identify the optimum method for estimating TFV. The results show that TFVs were best predicted using the air gun and penetrometer measurements in the Moab sites. This empirical method, however, systematically underestimated TFVs in the Mojave Desert sites. Further analysis showed that TFVs in the Mojave sites can be...
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Snow cover duration in a seasonally snow covered mountain range (San Juan Mountains, USA) was found to be shortened by 18 to 35 days during ablation through surface shortwave radiative forcing by deposition of disturbed desert dust. Frequency of dust deposition and radiative forcing doubled when the Colorado Plateau, the dust source region, experienced intense drought (8 events and 39?59 Watts per square meter in 2006) versus a year with near normal precipitation (4 events and 17?34 Watts per square meter in 2005). It is likely that the current duration of snow cover and surface radiation budget represent a dramatic change from those before the widespread soil disturbance of the western US in the late 1800s that...
Glacial flour dust storms in the Gulf of AK: hydrologic and meteorological controls and their importance as a source of bioavailable iron (In revision), credited to Schroth, A.W., published in 2010. Published in Geophysical Research Letters, in 2010.
Tree-ring records spanning the past seven centuries from the central and southern Rocky Mountains were studied using wavelet analysis to examine multidecadal (>30?70 yr) patterns of drought variation. Fifteen tree-ring series were grouped into five regional composite chronologies based on shared low-frequency behavior. Strong multidecadal phasing of moisture variation was present in all regions during the late 16th century megadrought. Oscillatory modes in the 30?70 yr domain persisted until the mid-19th century in two regions, and wet-dry cycles were apparently synchronous at some sites until the 1950s drought. The 16th/17th century pattern of severe multidecadal drought followed by decades of wet conditions resembles...
The changing hydrologic regime of the Upper Colorado River Basin presents a daunting challenge for water resources management. A major source of concern is that of ascertaining the nature of runoff variability and re-calibrating the systemic management and planning based on a more reliable envelope of water supply variations to meet societal needs. In this letter, we examine the long-term variability and change in the Upper Colorado annual runoff volume—quantified as shifts in the mean, interannual variability, and persistence—in a recent tree-ring based reconstruction extending back to 762AD. A simple model for reservoir storage requirement shows sensitivity to the changing hydrologic regime, with episodes...
We used a simulated data set of hydro-climatological variables to examine for 20th century trends in soil moisture, runoff, and drought characteristics over the conterminous United States (U.S.). An increasing trend is apparent in both model soil moisture and runoff over much of the U.S., with a few decreasing trends in parts of the Southwest. The trend patterns were qualitatively similar to those found in streamflow records observed at a station network minimally affected by anthropogenic activities. This wetting trend is consistent with the general increase in precipitation in the latter half of the 20th century. Droughts have, for the most part, become shorter, less frequent, and cover a smaller portion of the...
Topographic depressions serve as the key spatial control on large global dust sources. In contrast, the temporal control on these hotspots has remained elusive. We provide the first global observational evidence that the annual cycle of emissions from dust hotspots is determined by an erosivity feature in the form of wind gustiness. We use TOMS AI and an aridity index to define 131 global dust hotspots. The correlation between the annual cycle of hotspot dust and the annual cycle of gustiness is 70% stronger than the corresponding correlation with wind. The mean significant correlation with wind (n = 106 hotspots) is 0.37 (? = 0.24) and the mean of significant correlation (n = 118 hotspots) with gustiness is 0.63...
The wind-forced detachment and movement of soil particles, is known for having important regional and global implications on climate change and biogeochemical cycles. The wind erosion process occurs when wind speed exceeds a certain threshold value, which depends on a number of factors, including surface soil moisture. In arid regions changes in atmospheric humidity contribute to most of the variability in surface soil moisture, which, in turn, has a significant influence on wind erosion threshold. This paper investigates the dependence of wind erosion threshold on air humidity in two arid regions in North America, the Mojave Desert (CA) and Canyonlands (UT). Field data are used to test existing models relating...
Here we show that there is a significant relationship between Nino 3.4 ENSO anomaly (Dec?Jan average) and precipitation in the southwestern United States. This contributes to increased frequency of dust events in the years following strong La Ni�a and El Ni�o years. High probabilities (60%?100%) exist for an elevated frequency of dust events in years when the ENSO anomaly, annual precipitation, or annual P/PE falls below the 10th percentile. This analysis provides a quantitative framework in which to evaluate the expected effects of climate change on this and other arid regions. Published in Geophysical Research Letters, volume 29, issue 9, on pages 1332 - 1332, in 2002.
The high demand for water, the recent multiyear drought (19992007), and projections of global warming have raised questions about the long-term sustainability of water supply in the southwestern United States. In this study, the potential effects of specific levels of atmospheric warming on water-year streamflow in the Colorado River basin are evaluated using a water-balance model, and the results are analyzed within the context of a multi-century tree-ring reconstruction (14901998) of streamflow for the basin. The results indicate that if future warming occurs in the basin and is not accompanied by increased precipitation, then the basin is likely to experience periods of water supply shortages more severe than...
New tree-ring records of ring-width from remnant preserved wood are analyzed to extend the record of reconstructed annual flows of the Colorado River at Lee Ferry into the Medieval Climate Anomaly, when epic droughts are hypothesized from other paleoclimatic evidence to have affected various parts of western North America. The most extreme low-frequency feature of the new reconstruction, covering A. D. 762-2005, is a hydrologic drought in the mid-1100s. The drought is characterized by a decrease of more than 15% in mean annual flow averaged over 25 years, and by the absence of high annual flows over a longer period of about six decades. The drought is consistent in timing with dry conditions inferred from tree-ring...
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Transport of dissolved organic carbon (DOC) from land to water is an important but poorly known component of northern carbon cycles. We examined seasonal patterns of arctic river DOC flux, focusing on the largely uncharacterized snowmelt period. High-intensity sampling of the Kolyma River showed rapid increases in DOC concentration during peak discharge, yielding unique DOC-water flux relationships compared to summer, fall and winter. Our annual DOC flux estimates were 31% higher than previous estimates for the basin based on few or no snowmelt samples. Synthesis of the sparse literature show that 55% of arctic river DOC flux occurs during snowmelt. Biogeochemical characterizations of DOC in large rivers are usually...
    map background search result map search result map Impact of disturbed desert soils on duration of mountain snow cover A simple method to estimate threshold friction velocity of wind erosion in the field Snowmelt dominance of dissolved organic carbon in high-latitude watersheds: Implications for characterization and flux of river DOC Multidecadal increases in the Yukon River Basin of chemical fluxes as indicators of changing flowpaths, groundwater, and permafrost Impact of disturbed desert soils on duration of mountain snow cover A simple method to estimate threshold friction velocity of wind erosion in the field Snowmelt dominance of dissolved organic carbon in high-latitude watersheds: Implications for characterization and flux of river DOC Multidecadal increases in the Yukon River Basin of chemical fluxes as indicators of changing flowpaths, groundwater, and permafrost