Simulating Groundwater-Streamflow Connections in the Upper Colorado River Basin

In mountain, snow driven catchments, snowmelt is supposed to be the primary contribution to river streamflows during spring. In these catchments the contribution of groundwater is not well documented because of the difficulty to monitor groundwater in such complex environment with deep aquifers. In this study we use an integrated hydrologic model to conduct numerical experiments that help quantify the effect of lateral groundwater flow on total annual and peak streamflow in predevelopment conditions. Our simulations focus on the Upper Colorado River Basin (UCRB; 2.8 × 10⁵ km²) a well-documented mountain catchment for which both streamflow and water table measurements are available for several important sub-basins. For the simulated water year, our results suggest an increase in peak flow of up to 57% when lateral groundwater flow processes are included—an unexpected result for flood conditions generally assumed independent of groundwater. Additionally, inclusion of lateral groundwater flow moderately improved the model match to observations. The correlation coefficient for mean annual flows improved from 0.84 for the no lateral groundwater flow simulation to 0.98 for the lateral groundwater flow one. Spatially we see more pronounced differences between lateral and no lateral groundwater flow cases in areas of the domain with steeper topography. We also found distinct differences in the magnitude and spatial distribution of streamflow changes with and without lateral groundwater flow between Upper Colorado River Sub-basins. A sensitivity test that scaled hydraulic conductivity over two orders of magnitude was conducted for the lateral groundwater flow simulations. These results show that the impact of lateral groundwater flow is as large or larger than an order of magnitude change in hydraulic conductivity. While our results focus on the UCRB, we feel that these simulations have relevance to other headwaters systems worldwide.     

Patuxent Landscape Model: 4. Model application

Using the LHEM/SME the Patuxent Landscape Model (PLM) was built to simulate fundamental ecological processes in the watershed scale driven by temporal (nutrient loadings, climatic conditions) and spatial (land use patterns) forcings. The model addresses the effects of both the magnitude and spatial patterns of land use change and agricultural practices on hydrology, plant productivity, and nutrient cycling in the landscape.     

The association of solar radio bursts with auroral streams

Slow drift (Type II) radio bursts from the sun are believed to be caused by a primary disturbance moving outward through the solar atmosphere with a velocity of about 1000 km/sec. Analysis of the 2 years, 1956 October 1 through 1958 September 30, over the sunspot maximum shows that 45 per cent of these bursts are associated with the subsequent occurrence of terrestrial auroræ and magnetic storms. The mean delay between the radio bursts and the terrestrial disturbances is 33 hr, which is in good accord with the velocity for the disturbing source as deduced from the radio data. Investigation of the properties of the individual slow drift bursts and their association with other solar radio and optical phenomena reveals no completely conclusive criteria to explain why only 45 per cent of the bursts are geomagnetically important. The geomagnetic effects are enhanced, however, if the bursts occur near the equinoxes and if they are accompanied by a flare o'f importance 2 or 3, or by continuum (Type IV) radiation.

In the reverse association, with radio data available for an average 14 hr daily, it is shown that at least 60 per cent of magnetic storms are preceded, within 4 days, by a slow drift burst.     

Quantifying the effects of subsurface heterogeneity on hillslope runoff using a stochastic approach

The role of heterogeneity and uncertainty in hydraulic conductivity on hillslope runoff production was evaluated using the fully integrated hydrologic model ParFlow. Simulations were generated using idealized high-resolution hillslopes configured both with a deep water table and a water table equal to the outlet to isolate surface and subsurface flow, respectively. Heterogeneous, correlated random fields were used to create spatial variability in the hydraulic conductivity. Ensembles, generated by multiple realizations of hydraulic conductivity, were used to evaluate how this uncertainty propagates to runoff. Ensemble averages were used to determine the effective runoff for a given hillslope as a function of rainfall rate and degree of subsurface heterogeneity. Cases where the water table is initialized at the outlet show runoff behavior with little sensitivity to variance in hydraulic conductivity. A technique is presented that explicitly interrogates individual realizations at every simulation timestep to partition overland and subsurface flow contributions. This hydrograph separation technique shows that the degree of heterogeneity can play a role in determining proportions of surface and subsurface flow, even when effective hillslope outflow is seen. This method is also used to evaluate current hydrograph separation techniques and demonstrates that recursive filters can accurately proportion overland and base-flow for certain cases.     

Combined inequality in wealth and risk leads to disaster in the climate change game

It is generally agreed that the risk of catastrophic climate change can only be reduced if agents cooperate to reduce greenhouse gas emissions over the course of the 21st Century. Previous economic experiments have suggested that sufficient cooperation can often be achieved providing individuals are adequately and convincingly informed of the consequences of their actions and the stakes involved. However, this previous work, has not allowed for the fact that in the real world agents vary in both: (1) their resources to mitigate climate change, and (2) the consequences that they face from climate change. We develop and expand the protocol of previous economic experiments to investigate the introduction of such combined asymmetries. We find that when inequality in resources is combined with a greater relative risk for poorer members, cooperation collapses, with tragic consequences. This is because the rich invest proportionally less into preventing climate change when they are less at risk. We also find, through the use of a post-game questionnaire, that those individuals who were more skeptical about climate change in the real world cooperated less in our games. Insofar as such experiments can be trusted as a guide to either people’s everyday behaviour or the interactions of nation states, these results suggest that voluntary cooperation to avoid climate catastrophe in the real world is likely to be hard to achieve.     

Magnetohydrodynamic simulation of the coronal transient associated with the solar limb flare of 1980, June 29, 18∶21 UT

Soft X-ray data from the XRP experiment on SMM are used to generate the temperature and density in the flaring region of the 1980, June 29 (18∶21 UT) solar flare. The temporal data (T _max ～- 20 × 10⁶ K and n _max ～- 4 × 10¹¹ cm^?3), together with an assumed velocity, are used to simulate mass injection as the input pulse for the MHD model of Wu et al. (1982a, 1983a). The spatial and temporal coronal response is compared with the ground-based, Mark III K-coronameter observations of the subsequent coronal transient. The simulation produces a spatially-wide, large amplitude, temporarily-steepened MHD wave for either of the two ‘canonical’ magnetic topologies (closed and open), but no shock wave. This result appears to be confirmed by the fact that a type II radio event was observed late in the event for only a few minutes, thereby indicating that a steepening wave with temporary, marginal shock formation, was indeed present. The density enhancements produced by the simulation move away from the Sun at the same velocity observed by the K-coronameter. However, the observation of the coronal transient included a rarefaction that does not appear in the simulation. A probable explanation for this discrepancy is the likelihood that the magnitude and temporal profile of the density of the soft X-ray emitting plasma should not have been used as part of the mass injection pulse. We believe that the temperature profile alone, as suggested by earlier simulations, might have been a necessary and sufficient condition to produce both the compression and rarefaction of the ambient corona as indicated by the K-coronameter data. Hence, the dense plasma observed by XRP was probably confined, for the most part, close to the Sun during the ～ 17 min duration of the observations.     

Regulation of peatland evaporation following wildfire; the complex control of soil tension under dynamic evaporation demand

The capability of peatland ecosystems to regulate evapotranspiration (ET) following wildfire is a key control on the resilience of their globally important carbon stocks under future climatic conditions. Evaporation dominates post-fire ET, with canopy and sub-canopy removal restricting transpiration and increasing evaporation potential. Therefore, in order to project the hydrology and associated stability of peatlands to a diverse range of post-fire weather conditions and future climates the regulation of evaporation must be accurately parameterised in peatland ecohydrological models. To achieve this, we measure the surface resistance (r_s) to evaporation over the growing season one year post-fire within four zones of a boreal peatland that burned to differing depths, relating r_s to near surface soil tensions. We show that the magnitude and temporal variability in r_s varies with burn severity. At the peatland scale, r_s and near-surface tension correlates non-linearly. However, at the point scale no relationship was evident between temporal variations in r_s and near-surface tension across all burn severities; in part due to the limited fluctuation in near-surface tensions and the precision of r_s measurements. Where automated measurements enabled averaging of errors, the relationship between near-surface tension and r_s switched between periods of strong and weak correlation within a burned peat hummock. This relationship, when strong, deviated from that obtained under steady state laboratory conditions; increases in r_s were more sensitive to fluctuations in near-surface tension under dynamic field conditions. Calculating soil vapour densities directly from near-surface tensions is shown to require calibration between peat types and provides little if any benefit beyond the derivation of empirical relationships between r_s and measured soil tension. Thus, we demonstrate important spatiotemporal fluctuations in post-fire r_s that will be key to regulating post-fire peatland hydrology, but highlight the complex challenges in effectively parameterising this important underlying control of near-surface tensions within hydrological simulations.     

An investigation of lead chromate (crocoite-PbCrO4) and other inorganic pigments in aged traffic paint samples from Hamilton,Ohio: implications for lead in the environment

Traffic paint samples collected from roads in the City of Hamilton, Butler County, OH, USA were investigated to determine whether or not pigments are hazardous and are of environmental concern. Powder X-ray diffraction (XRD) and scanning electron microscopy (SEM) indicate that white and gray paint samples are dominated by calcite, rutile, anatase and quartz and blue traffic paint samples are dominated by calcite and barite. XRD and SEM indicate that most yellow traffic paints have lead chromate (crocoite-PbCrO₄) with common particle sizes that are typically 125–350 nm in length and 75–200 nm in width. Larger aggregates of several micrometers in diameter are also observed. The solubility of PbCrO₄ (1.34 × 10^?7 mol/L at 25 °C) combined with an increase in solubility with exposure to 0.05–0.25 M NaCl and CaCl₂ road treatments solutions as demonstrated by basic batch experiments likely makes PbCrO₄ from traffic paint a potential source for lead pollution in surface water and groundwater that is not fully recognized.     

Hydrological shifts and tree growth responses to river modification along the Apalachicola River,Florida

Shifts in the hydrologic regime of Florida’s Apalachicola River have been attributed to anthropogenic changes throughout its watershed, including local dam construction. To assess impacts of those shifts on floodplain forests, we reconstructed tree growth using dendrochronology and compared these trends with hydrological and climatic variables. Comparisons of stream-gage data before and after dam construction on the Apalachicola River revealed statistically significant mean declines in annual average stage. Mean minimum annual stages, rise rates, and fall rates also decreased, while hydrograph reversals increased. Growth in four tree species correlated strongly with site-specific inundation parameters. A wetter climate in the two decades following dam construction and fine-scale fluctuation of the hydrograph may have set the stage for positive growth releases. Logging and hurricane wind throw events may have also contributed. However, drier conditions in the last two decades are now exacerbated by stage-discharge declines that had been masked previously. Tree growth rates and recruitment have decreased and, in the absence of a major disturbance, the forest canopy is composed of an older cohort of individuals. Our findings highlight how hydrograph variability, climate change, and vegetation disturbance are all relevant for gaging and anticipating the range of impacts of river modification on floodplain forests.