Embedding isochronous cells overland flow module into MODFLOW

This study integrates a simple overland flow module (isochronous cells model) with the river module of MODFLOW such that temporal and spatial interactions between stream flow and groundwater can be simulated using net rainfall data of a watershed. The isochronous cells model is an efficient travel time runoff approach based on geographic information system (GIS) that considers both spatial and temporal variations of net rainfall through hill slope of the watershed. This overland module is easily coupled with MODFLOW river routing module. Specifically, the stream flow from the isochronous cells model is directly assigned to both sides of river cells of the MODFLOW model. Such an integration of MODFLOW and isochronous cells model is especially useful in watersheds where river flow data are limited. The feasibility of this integrated model was demonstrated using a case study in the middle and downstream regions of the Yitong River watershed, China. Copyright © 2012 John Wiley & Sons, Ltd.     

Removal of dissolved selenium by siderite,pyrite, and sphalerite: Implications to selenium sequestration in water-saturated,anoxic coal waste rock

The mechanisms of abiotic sequestration of Se(VI) and Se(IV) on a sample of coal waste rock collected from the Elk Valley, Canada and on three pure mineral species (i.e., siderite, pyrite, and sphalerite) present in coal waste rock were assessed using sterile batch testing under water-saturated, anoxic conditions. Only siderite removed measurable Se(VI) from the test solutions with ~90% removal after 100 d attributed to initial adsorption to the siderite surface as Se(VI) and subsequent reduction to Se(IV) and Se(0). In contrast to Se(VI), all samples removed Se(IV) from the aqueous solutions. The rate of Se(IV) removal was pyrite > siderite > waste rock > sphalerite. The waste rock sample removed Se(IV) from solution in two stages: up to ~40% of the aqueous Se(IV) was rapidly removed (by day 1) followed by slower removal of Se(IV) with up to ~97% removal after 99 d. Se(IV) removal is attributed to the adsorption of Se(IV) and subsequent reduction to Se(0) onto the siderite and pyrite phases of the waste rock. The initial (1 d) removal of Se(IV) by waste rock was characterized using a distribution coefficient (K_d) of 15.5 L/kg. Longer-term Se(IV) removal was fitted with zero and first order removal rates. The removal of Se(IV) by sphalerite was minor and deemed to have a minimal effect on Se sequestration in the waste rock. Desorption tests on waste rock showed that the fraction of sequestered Se susceptible to desorption decreased with time as adsorbed Se(IV) was reduced to insoluble Se(0). These findings show that abiotic Se sequestration can occur in saturated, anoxic zones in coal waste rock dumps.     

Nationally Determined Contributions under the Paris Agreement and the costs of delayed action

Current country-level commitments under the Paris Agreement fall short of putting the world on a required trajectory to stay below a 2°C temperature increase compared to pre-industrial levels by the end of the century. Therefore, the timing of increased ambition is hugely important and as such this paper analyses the impact of both the short and long-term goals of the Paris Agreement on global emissions and economic growth. Using the hybrid TIAM-UCL-MSA model we consider the achievement of a 2°C target against a baseline of the Nationally Determined Contributions (NDCs) while also considering the timing of increased ambition of the NDCs by 2030 and the impacts of cost reductions of key low-carbon technologies. We find that the rate of emissions reduction ambition required between 2030 and 2050 is almost double when the NDCs are achieved but not ratcheted up until 2030, and leads to lower levels of economic growth throughout the rest of the century. However, if action is taken immediately and is accompanied by increasingly rapid low-carbon technology cost reductions, then there is almost no difference in GDP compared to the path suggested by the current NDC commitments.

Key policy insights

• Delaying the additional action needed to achieve the 2°C target until 2030 is shown to require twice the rate of emissions reductions between 2030 and 2050.

• Total cumulative GDP over the century is lower when additional action is delayed to 2030 and therefore has an overall negative impact on the economy, even without including climate change damages.

• Increased ratcheting of the NDC commitments should therefore be undertaken sooner rather than later, starting in conjunction with the 2023 Global Stocktake.

• Early action combined with cost reductions in key renewable energy technologies can reduce GDP losses to minimal levels (<1%).

• A 2°C future with technological advancements is clearly possible for a similar cost as a 3.3°C world without these advances, but with lower damages and losses from climate change.

     

Simulation and detection of tsunami signatures in ocean surface currents measured by HF radar

High-frequency (HF) surface wave radars provide the unique capability to continuously monitor the coastal environment far beyond the range of conventional microwave radars. Bragg-resonant backscattering by ocean waves with half the electromagnetic radar wavelength allows ocean surface currents to be measured at distances up to 200 km. When a tsunami propagates from the deep ocean to shallow water, a specific ocean current signature is generated throughout the water column. Due to the long range of an HF radar, it is possible to detect this current signature at the shelf edge. When the shelf edge is about 100 km in front of the coastline, the radar can detect the tsunami about 45 min before it hits the coast, leaving enough time to issue an early warning. As up to now no HF radar measurements of an approaching tsunami exist, a simulation study has been done to fix parameters like the required spatial resolution or the maximum coherent integration time allowed. The simulation involves several steps, starting with the Hamburg Shelf Ocean Model (HAMSOM) which is used to estimate the tsunami-induced current velocity at 1 km spatial resolution and 1 s time step. This ocean current signal is then superimposed to modelled and measured HF radar backscatter signals using a new modulation technique. After applying conventional HF radar signal processing techniques, the surface current maps contain the rapidly changing tsunami-induced current features, which can be compared to the HAMSOM data. The specific radial tsunami current signatures can clearly be observed in these maps, if appropriate spatial and temporal resolution is used. Based on the entropy of the ocean current maps, a tsunami detection algorithm is described which can be used to issue an automated tsunami warning message.     

Joint multifractal description of the relationship between wind patterns and land surface air temperature

Land surface air temperature (SAT), registered at 1.25–2 m above the ground, is influenced by wind patterns. As a consequence, some phenomena such as urban heat islands and the formation of ground-level air pollutants are affected. Detailed understanding of the effects of wind circulations on SAT is convenient to improve the knowledge of these phenomena. Thus, the joint multifractal analysis has been applied to describe time series recorded at Cordoba (southern Spain) from 2001 to 2008 revealing the presence of seasonal patterns related with warm and cold winds blowing from the SW (later spring and summer) and NE (later autumn and winter), respectively, that provoke different heterogeneity in SAT values. In addition, the extreme high SAT values seem to be related with summer SW winds. However, the presence of rare low SAT values produced by NE winds is less relevant.