HYDROLOGICAL RESPONSE OF SMALL WATERSHEDS FOLLOWING THE SOUTHERN CALIFORNIA PAINTED CAVE FIRE OF JUNE 1990

Following the Painted Cave Fire of 25 June 1990 in Santa Barbara, California which burned 1214 ha, an emergency watershed protection plan was implemented consisting of stream clearing, grade stabilizers and construction of debris basins. Research was initiated focusing on hydrological response and channel morphology changes on two branches of Maria Ygnacio Creek, the main drainage of the burned area. Research results support the hypothesis that the response of small drainage basins in chaparral ecosystems to wildfire is complex and flushing of sediment by fluvial processes is more likely than by high magnitude debris flows. During the winter of 1990–1991, 35–66 cm of rainfall and intensities up to 10 cm per hour for a five-minute period were recorded with a seasonal total of 100% of average (normal) rainfall (average=63 cm/year). During the winter of 1991–1992, 48–74 cm of rainfall and intensities up to 8 cm per hour were recorded with a seasonal total of 115% of normal. Even though there was moderate rainfall on barren, saturated soils, no major debris flows occurred in burned areas. The winter of 1992–1993 recorded total precipitation of about 170% of normal, annual average intensities were relatively low and again no debris flows were observed. The response to winter storms in the first three years following the fire was a moderate but spectacular flushing of sediment, most of which was derived from the hillslopes upstream of the debris basins. The first significant storm and stream flow of the 1990–1991 winter was transport-limited resulting in large volumes of sediment being deposited in the channel of Maria Ygnacio Creek; the second storm and stream flow was sediment-limited and the channel scoured. Debris basins trapped about 23 000 m³, the majority coming from the storm of 17–20 March 1991. Sediment transported downstream during the three winters following the fire and not trapped in the debris basins was eventually flushed to the estuarine reaches of the creeks below the burn area, where approximately 108 000 m³ accumulated. Changes in stream morphology following the fire were dramatic as pools filled with sediment which greatly smoothed longitudinal and cross-sectional profiles. Major changes in channel morphology occur following a fire as sediment derived from the hillslope is temporarily stored in channels within the burned area. However, this sediment may quickly move downstream of the burned region, where it may accumulate reducing channel capacity and increasing the flood hazard. Ecological consequences of wildfire to the riparian zone of streams in the chaparral environment are virtually unknown, but must be significant as the majority of sediment (particularly gravel necessary for fish and other aquatic organisms) entering the system does so in response to fires. © 1997 John Wiley & Sons, Ltd.     

Sulfur and nitrogen budgets for five forested appalachian plateau basins

Sulfur and nitrogen input–output budgets were estimated for five forested Appalachian Plateau basins in Pennsylvania for the period October 1988 to March 1990. Wet and dry deposition inputs were determined on a weekly basis from data collected at atmospheric deposition monitoring stations located near the study sites. Stream export was estimated from intensively sampled stream chemistry and continuous discharge data collected on all five basins. On four of the five basins, deposited sulfur was essentially in balance with stream flow export of sulfur (92–120% exported) for the 1989 water year. The fifth basin had net retention of deposited sulfur, with only 42% exported. All five basins retained the vast majority of deposited nitrogen (only 3–18% exported). The fraction of atmospherically deposited sulfur exported in stream flow was greater by a mean factor of 14 versus nitrogen, implying that sulfur dominates base cation leaching processes on these non-carbonate-based catchments. Although basins in the study were relatively homogeneous in terms of topography, climate, geology and land use, local basin conditions caused significant differences in input–output budgets, pointing to the need for replicated basin studies in a region. © 1997 John Wiley & Sons, Ltd.     

Current shortcomings of global mapping and the creation of a new geographical framework for the world

The vast bulk of topographic mapping - the geographical framework used to underpin many activities of the state and of business - has been created and is maintained to national standards. As a consequence, what is available differs greatly from country to country. Yet there is a range of needs for globally-consistent map information. Such needs have long been recognized: the International Map of the World was an attempt to meet them. A multiplicity of factors has constrained the National Mapping Organizations from meeting this aim. However, new technologies have enhanced our capacity to create a geographical framework almost anywhere in the world. Using such technologies, commercial and other non-commercial bodies (e.g. the US military and its counterparts within NATO) have begun to produce wide-area geographical information. This paper describes the nature of the need for global mapping, the players involved and the drivers and obstacles to progress. It proposes a rapid way to enhance the current situation through public/private sector partnerships based on a combination of skills, information assets and resources. If implemented, this could lead to global coverage of a framework derived from 1:25000 scale mapping within about two years.     

SPACE‐TIME MODELING OF GRIZZLY BEARS*

ABSTRACT. An appropriate conceptual leap can be made from human geography to physical geography by applying space‐time continuum modeling to zoogeomorphology—the alteration of the landscape by animals. Drawing on the work of Torsten Hägerstrand, we propose a space‐time continuum model of grizzly bears, a geomorphic agent. Through both data‐driven and conceptual applications, the model traces where and when grizzly bears are likely to wield a geomorphic impact. The model further demonstrates that geographers have much to gain by merging concepts from human and physical geography.     

BEYOND TWISTER: A GEOGRAPHY OF RECREATIONAL STORM CHASING ON THE SOUTHERN PLAINS*

ABSTRACT. Storm chasing is widely perceived as a new form of extreme sport or adventure travel. Each spring increasing numbers of tourists descend on the Southern Plains, the center of storm chasing in the United States, but little is known about their activities. According to longtime chasers, popular portrayals of storm pursuits are highly misleading, and growing participation in the sport is affecting storm chasing in the region. This study introduces the storm-chasing enterprise. Using route information and comments supplied by veteran chasers, I describe the spatial patterns of storm-chasing on the Southern Plains. Comparing the behavior and motivations of longtime enthusiasts with popular portrayals of the activity permits me to dispel many myths and to discuss the nature and future of this growing but little-understood recreational pursuit.     

强震前后广义地震应变释放过程的丛集特征

利用基于小波变换的多重分形奇异谱估计方法,研究了部分强震前后地震活动广义应变.释放过程的多重分形特征。结果表明,晨中区附近- -定范围内地展活动广义应变释放过程具有多重分形特征,但多重分形维数谱随7变化复杂,在强震发生前多重分形维数谱没有明显的变化。广义地震应变释放过程的多重分形奇异谱形态和Hausdorff奇异指数范围能提供更多关于地屣活动过程的信息,特别当η取较大值时Hausdorff奇异指数范围在强晨前明显变窄。研究还表明深源地展和浅源地晨发生前广义应变释放过程多重分形特征存在明显不同。