Hydrological impacts of forest conversion to agriculture in a large river basin in northeast Thailand

Small‐scale experiments have demonstrated that forest clearance leads to an increase in water yield, but it is unclear if this result holds for larger river basins (>1000 km²). No widespread changes in rainfall totals and patterns were found in the 12 100 km² Nam Pong catchment in northeast Thailand between 1957 and 1995, despite a reduction in the area classified as forest from 80% to 27% in the last three decades. Neither were any detectable changes found in any other water balance terms nor in the dynamics of the recession at the end of the rainy season. When a hydrological model calibrated against data from the period before the deforestation was applied for the last years of the study period (1987–1995), runoff generation was however underestimated by approximately 15%, indicating increased runoff generation after the deforestation. However, this was mainly due to the hydrological response during one single year in the first period, when the Q/P ratio was very low. When excluding this year, neither analysis based on the hydrological model could reveal any significant change of the water balance due to the deforestation. More detailed land‐use analysis revealed that shade trees were left on agricultural plots as well as a number of abandoned areas where secondary growth can be expected, which is believed to account for the results. Copyright © 2001 John Wiley & Sons, Ltd.     

Postglacial relative sea-level change and stratigraphy of raised coastal basins on Kola Peninsula, northwest Russia

A relative sea-level curve for the Holocene is constructed for Polyarny on the Kola Peninsula, northwest Russia. The curve is based on 18 radiocarbon dates of isolation contacts, identified from lithological and diatomological criteria, in nine lake basins situated between 12 and 57 m a.s.l. Most of the lakes show a conformable, regressive I–II–III (marine–transitional–freshwater) facies succession, indicating a postglacial history comprising an early (10,000–9000 radiocarbon years BP) phase of rapid, glacio-isostatically induced emergence (5 cm year⁻¹) and a later phase (after 7000 years BP,) having a moderate rate of emergence (<0.5 cm year⁻¹). Three lakes together record a phase of very low rate of emergence or slight sea-level rise at a level of 27 m a.s.l., between 8500 and 7000 years BP, which correlates with the regional Tapes transgression. Pollen stratigraphy in the highest lake shows that the area was deglaciated before the Younger Dryas and that previously reconstructed Younger Dryas glacier margins along the north Kola coast lie too far north.     

In the wake of a counterclockwise rotating Adriatic microplate: Neogene paleomagnetic results from northern Croatia

In northern Croatia, the Neogene sediments cover complicated basement rocks which consist of Alpine and Dinaridic elements in the Zagorje area, and Variscan - Alpine formations of the Tisia (Tisza) megatectonic unit in the Slavonian Mountains (Mts.). The Neogene sediments were deposited in two separate basins before the Karpatian, but sedimentation became uniform from the Karpatian onwards (~17.5 Ma). Of the 24 localities that we have studied so far paleomagnetically from northern Croatia, 16 localities are of Karpatian or younger age, while the rest are pre-Karpatian. As a result of laboratory analysis, 16 localities yielded tectonically interpretable results. Our data suggests that northern Croatia shifted northwards, while rotating moderately counterclockwise, probably before the Karpatian. A second counterclockwise rotation occurred at the present latitude in post-Pontian times. There is no significant difference between localities situated above different basements, though Tisia is pictured as rotating clockwise in the Neogene. The paleomagnetic pattern of northern Croatia resembles that of areas situated north of the Periadriatic-Balaton line. Therefore, we conclude that northern Croatia is part of a larger block, dissected by several important tectonic lines, driven by the counterclockwise rotated Adriatic microplate.     

The Global Stratotype Section and Point （GSSP） for the base of the Holocene Series/Epoch （Quaternary System/Period） in the NGRIP ice core

The Greenland ice core from NorthGRIP （NGRIP） contains a proxy climate record across the Pleistocene-Holocene boundary of unprecedented clarity and resolution. Analysis of an array of physical and chemical parameters within the ice enables the base of the Holocene, as reflected in the first signs of climatic warming at the end of the Younger Dryas/Greenland Stadial 1 cold phase, to be located with a high degree of precision.     

Integrating uncertainty: Canyon Creek hyperconcentrated flows of November 1989 and 1990

Canyon Creek drains a 79 km² watershed in northwestern Washington State. Extensive logging occurred from the mid-1960s to 1980s, which resulted in numerous slope instabilities and a several order of magnitude increase in sediment supply to the creek. On November 9, 1989, a hyperconcentrated flow with a peak discharge of 450 m³/s destroyed one house on the fan. A forensic investigation of the event suggests that a temporary landslide dam may have formed at two coalescing earthflows about 4 km above the fan apex. The 1989 hyperconcentrated flow caused significant aggradation on the fan. One year later to the day, a significant flood occurred, which ran over the aggraded fan surface from the 1989 event. This latter event destroyed four more homes mostly through bank erosion and rendered a section of county road impassable. FLDWAV, a flood routing model capable of simulating unsteady flow conditions, was used to model landslide dam breaches for a number of different dam heights at the earthflows. Modeling results were then combined with historic air photograph interpretation, dendrochronology, and eyewitness accounts to construct a frequency–magnitude relationship for hyperconcentrated flows at Canyon Creek. FLDWAV results were combined with a hyperconcentrated flow runout model (FLO-2D) on the fan to estimate maximum flow depth and flow velocity for the design event, a 500-year return period with a predicted peak discharge of 710 m³/s. A large range of mitigation measures were reviewed, but it was concluded that buy-outs would be the most effective risk reduction measure. Property acquisition commenced in 2004.     

A new parallel PM code for very large-scale cosmological simulations

We have developed a parallel Particle–Particle, Particle–Mesh (P³M) simulation code for the Cray T3E parallel supercomputer that is well suited to studying the time evolution of systems of particles interacting via gravity and gas forces in cosmological contexts. The parallel code is based upon the public-domain serial Adaptive P³M-SPH (http://coho.astro.uwo.ca/pub/hydra/hydra.html) code of Couchman et al. (1995)[ApJ, 452, 797]. The algorithm resolves gravitational forces into a long-range component computed by discretizing the mass distribution and solving Poisson's equation on a grid using an FFT convolution method, and a short-range component computed by direct force summation for sufficiently close particle pairs. The code consists primarily of a particle–particle computation parallelized by domain decomposition over blocks of neighbour-cells, a more regular mesh calculation distributed in planes along one dimension, and several transformations between the two distributions. The load balancing of the P³M code is static, since this greatly aids the ongoing implementation of parallel adaptive refinements of the particle and mesh systems. Great care was taken throughout to make optimal use of the available memory, so that a version of the current implementation has been used to simulate systems of up to 10⁹ particles with a 1024³ mesh for the long-range force computation. These are the largest Cosmological N-body simulations of which we are aware. We discuss these memory optimizations as well as those motivated by computational performance. Performance results are very encouraging, and, even without refinements, the code has been used effectively for simulations in which the particle distribution becomes highly clustered as well as for other non-uniform systems of astrophysical interest.     

Namibia volcanic margin

Two end members of passive margin types are present on the Namibia margin: volcanic and non-volcanic. The central and southern parts of the Namibia margin feature characteristic volcanic margin elements such as thickened initial oceanic crust, seaward dipping reflectors, and high-velocity/density lower crust that extends beneath the rift zone that was formed during initial seafloor spreading in Early Cretaceous. The margin north of the Walvis FZ is non-volcanic in character and probably formed as a result of a ridge jump that occurred after cessation of the initial magmatic activity. The Walvis Ridge forms the boundary between the two margin types and resulted from the persistent magmatism associated with the Tristan plume. MCS data in conjunction with gravity modeling reveal a Paleozoic rift zone beneath the Namibia margin south of the Walvis FZ. The Paleozoic rift zone partly overlaps the Jurassic/Early Cretaceous rift zone which produced the breakup between Africa and South America. We calculate an average stretching value of =1.4 for the Paleozoic rift, based on subsidence modeling. The rift is partly bounded by low-angle faults, related to the orogenic collapse of the Pan-African fold belt, which provided a major Paleozoic sediment source. The offshore continuity of onshore ophiolitic complexes is suggested by the coast parallel high-amplitude magnetic anomaly G, and low-angle detachment faults along the southern part of the margin. The average stretching value for the Jurassic/Early Cretaceous rift is =1.7, which implies a syn-rift displacement on this margin of 70 km. The minimum igneous volume of the South Atlantic LIP was found to be in excess of 3.62×106 km³.