Volcanic ash layers from the Last Glacial Termination in the NGRIP ice core

The tephrochronological record of the 1400–1640 m depth (～10 000–16 000 calendar ice core years before present) of the NGRIP ice core has been established by particle screening of selected samples. Ash was identified in 20 samples. Correlation with ice, marine and terrestrial records from volcanic source regions in the northern hemisphere positively identifies the Saksunarvatn Ash and the Vedde Ash (Ash Zone 1). Major element chemistry of the remaining identified ash layers mainly points towards an Icelandic origin. This tephrochronological record provides new important marker horizons for correlating the timing of the climatic changes associated with the Last Glacial Termination within the North Atlantic region, as well as outlining more details concerning the frequency and composition of volcanic eruptions occurring at this deglaciation. Copyright © 2005 John Wiley & Sons, Ltd.     

Subsurface storm flow formation at different hillslopes and implications for the ‘old water paradox’

Although many studies over the past several decades have documented the importance of subsurface stormflow (SSF) in hillslopes, its formation is still not well understood. Therefore, we studied SSF formation in the vadose soil zone at four different hillslopes during controlled sprinkling experiments and natural rainfall events. Event and pre‐event water fractions were determined using artificially traced sprinkling water and ²²²Rn as natural tracer. SSF formation and the fraction of pre‐event water varied substantially at different hillslopes. Both intensity of SSF and fraction of pre‐event water depended on whether SSF in preferential flow paths was fed directly from precipitation or was fed indirectly from saturated parts of the soil. Soil water was rapidly mobilized from saturated patches in the soil matrix and was subsequently released into larger pores, where it mixed with event water. Substantial amounts of pre‐event water, therefore, were contained in fast flow components like subsurface storm flow and also in overland flow. This finding has consequences for commonly used hydrograph separation methods and might explain part of the ‘old water paradox’. Copyright © 2007 John Wiley & Sons, Ltd.     

Reaching a climate agreement: compensating for energy market effects of climate policy

Because of large economic and environmental asymmetries among world regions and the incentive to free ride, an international climate regime with broad participation is hard to reach. Most of the proposed regimes are based on an allocation of emissions rights that is perceived as fair. Yet, there are also arguments to focus more on the actual welfare implications of different regimes and to focus on a ‘fair’ distribution of resulting costs. In this article, the computable general equilibrium model DART is used to analyse the driving forces of welfare implications in different scenarios in line with the 2?°C target. These include two regimes that are often presumed to be ‘fair’, namely a harmonized international carbon tax and a cap and trade system based on the convergence of per capita emissions rights, and also an ‘equal loss’ scenario where welfare losses relative to a business-as-usual scenario are equal for all major world regions. The main finding is that indirect energy market effects are a major driver of welfare effects and that the ‘equal loss’ scenario would thus require large transfer payments to energy exporters to compensate for welfare losses from lower world energy demand and prices.

Policy relevance

A successful future climate regime requires ‘fair’ burden sharing. Many proposed regimes start from ethical considerations to derive an allocation of emissions reduction requirements or emissions allowances within an international emissions trading scheme. Yet, countries also consider the expected economic costs of a regime that are also driven by other factors besides allowance allocation. Indeed, in simplified lab experiments, successful groups are characterized by sharing costs proportional to wealth. This article shows that the major drivers of welfare effects are reduced demand for fossil energy and reduced fossil fuel prices, which implies that (1) what is often presumed to be a fair allocation of emissions allowances within an international emissions trading scheme leads to a very uneven distribution of economic costs and (2) aiming for equal relative losses for all regions requires large compensation to fossil fuel exporters, as argued, for example, by the Organization of Petroleum Exporting Countries (OPEC).     

ASSURE: a model for the simulation of urban expansion and intra-urban social segregation

Numerous cities in developing regions worldwide are expanding at a tremendous rate. This requires adequate strategies to address the needs of these growing cities with diverse populations. Nonetheless, the development of urban policies is often hampered by the lack of reliable data or insight in the socio-spatial dynamics of this urban expansion. This paper therefore presents ASSURE, a spatially and temporally explicit model that can simulate urban growth and intra-urban social segregation, taking into account alternative policy strategies and expected social dynamics. The model has a flexible structure that allows incorporating specific city conditions that influence residential decision-making and adapting the simulation to the data available. This, in combination with the transparent model structure, makes ASSURE a potentially valuable decision support tool for urban planning. The potential is demonstrated with an example where the urban growth of and social segregation in Kampala (Uganda) is simulated based on (semi-)quantitative and qualitative data for ca. 800 households collected through interviews. The results of the simulations show that depending on the scenario, the spatial segregation and accessibility problems will evolve highly differently.     

Ambiguity in the altitude effect of precipitation isotopes for estimating groundwater recharge elevation and paleoelevation reconstruction in the leeward side of a mountain

The altitude effect of isotopes in precipitation is not as significant on the leeward side of a mountain as it is on the windward side, which makes it difficult to use isotopes at leeward sites, especially if estimating elevation of groundwater recharge or reconstructing paleoelevations. Samples of precipitation were taken at three stations with different elevations—2,306–3,243 m above mean sea level (asl)—on the leeward side of the Meili Snow Mountains on the southeastern Tibetan Plateau from August 2017 to July 2018. The isotope vs. altitude gradients were calculated based on two adjacent stations at the daily, monthly, and annual scales. Most of the gradients are beyond the global ranges of –0.5 to –0.1‰ per 100 m for δ¹⁸O and –5 to –1‰ per 100 m for δ²H, and some of the gradients are even positive. Local processes of sub-cloud evaporation and mixing with recycled moisture are identified for the ambiguous altitude effect, while regional atmospheric circulation processes dominate the major patterns of stable isotope variation at the three stations. The groundwater recharge elevation is estimated to be in a very large range, 2,562–6,321 m asl, which could be caused by the differences in isotope vs. altitude gradient in the studied catchments. Considering the complex atmospheric processes affecting precipitation isotopes, sampling of event-based/monthly precipitation at more than two altitudes for at least one complete hydrological year is a minimum requirement to establish a reasonable isotope vs. altitude gradient.