Planning for El Niño: The Stages of Natural Hazard Mitigation and Preparation*

This study examines mitigation and preparation activities selected by four county and state governments in anticipation of the 1997–1998 El Niño. It expands the knowledge of how state and local governments plan short‐term projects and mitigate with longer‐term activities in anticipation of a natural hazard. It also provides a preliminary understanding of divergent responses and plans under similar disaster warnings. It outlines stages that governments follow in determining their natural hazard mitigation and preparedness activities. This model should provide hazard planners, particularly those planning for slower onset hazards, with insights into their own local circumstances, allowing them to choose appropriate strategies.     

2001—2018年印度尼西亚MODIS活跃火的发生特征与响应

基于印度尼西亚2001—2018年FIRMS MODIS活跃火（Active Fire）位置数据,通过GIS渔网（1 km×1 km）定量分析了该国活跃火的发生概率、强度及其对厄尔尼诺的响应。结果表明：① 印度尼西亚18年间至少发生过一次活跃火的区域（即“有火区”）占22.79%,五大岛屿“有火区”以加里曼丹岛最多,巴布亚岛最少。活跃火发生以低概率为主,集中在8—10月,加里曼丹岛和苏门答腊岛分布最多;中概率分布较少,苏门答腊岛东部低地平原和加里曼丹岛南部及西南沿岸最为集中;高概率零星分布,大部分集中在爪哇岛和苏拉威西岛。② 活跃火的发生强度以1级（1次/a）和2级（2~3次/a）为主,3级（4~7次/a）次之。1~5级（1~22次/a）活跃火主要集中在加里曼丹岛和苏门答腊岛,6级（23~165次/a）活跃火集中在爪哇岛、苏门答腊岛和苏拉威西岛,且强度从中心向四周递减。此外,不同概率组内活跃火的发生强度也不同,低、中、高概率活跃火分别以1次/a、1~3次/a、2~7次/a为主。③ 印度尼西亚8—10月活跃火对强、弱厄尔尼诺的敏感度不同,其响应表现在活跃火频次与影响面积显著增加,厄尔尼诺越强,活跃火响应程度越高。其中,苏门答腊岛响应程度最高,巴布亚岛最低。     

GEOGRAPHY AND THE LESSONS FROM EL NIÑO*

Recognized for years as a major environmental disruption, El Niño generated intense public interest in 1982–1983. During its last occurrence, this phenomenon, which develops in the tropical Pacific and usually affects rimlands of the Pacific basin, exceeded its boundaries and its effects were transmitted to continental North America, Europe, Africa and East Asia. Notwithstanding its vast areal extent, the interest of geographers in El Niño events, past and recent, has been comparatively less than that demonstrated by natural scientists and ecologists: little has been accomplished to place these climatic-ecological crises within global perspective. Lessons from El Niño include the acknowledgement of new concepts of climatic transitivity, ocean dynamics and energy exchanges that must find a place within the conceptual wealth of geography if this science intends to keep up with the rapid progress of other geosciences.     

Seasonal Response of Mean Monthly Streamflow to El Niño/Southern Oscillation in North Central Florida

The southeastern United States, including Florida, has been identified as a region of homogeneous response to the El Niño/Southern Oscillation (ENSO) climatic anomaly, in which mean monthly precipitation and discharge during winter is above or below normal following the onset of the warm (El Niño) or cold (La Niña) phase of ENSO, respectively. However, this understanding of the response is expanded through a study of the effects of the ENSO phenomenon on the probability distributions of mean monthly streamflows of the Santa Fe river. The Santa Fe river basin is situated between one region, which experiences the greatest proportion of annual streamflow during winter, and another where the largest percentage of annual flow occurs during late summer. The basin experiences both winter and summer peaks in precipitation and (subsequent) streamflow and may therefore display responses to ENSO during each season. A two-parameter lognormal distribution is employed to model these streamflows during warm and cold phases of ENSO. Increases in both the mean and the variance detected during warm phase winters are compatible with previous observations. Increases in variance apparent during cold phase summers have not been previously identified. These results, which have considerable bearing upon predictions of high and low flow probabilities during the year, suggest that the response in streamflow is not spatially homogeneous across the state.     

Sediment and Water Discharge Assessment on Santiago and Pánuco Rivers (Central Mexico): The Importance of Topographic and Climatic Factors

This study explores the main factors controlling sediment and water discharge in the Santiago and Pánuco Rivers, the two largest rivers of central Mexico. Both Santiago and Pánuco Rivers are sourced in the Central Plateau of Mexico and flow in an opposite direction. Santiago River flows over a tectonically active margin draining to the Pacific Ocean, and Pánuco River flows into the passive margin of the Gulf of Mexico. Mean annual and monthly values of suspended sediment load and water discharge spanning around 50 years were used to evaluate sediment load and water discharge in these two rivers. Our findings indicated that Santiago River delivers to the ocean around 45% more sediment than Pánuco River. However, we found that Santiago River has about half the water discharge of Pánuco River. The high river gradient along Santiago River is likely to enhance the net erosion and sediment transport capacity. Water discharge at Pánuco Basin is higher than in Santiago Basin because the annual rainfall is higher for the former. The difference in sediment and water discharge for both rivers are also related to El Niño Southern Oscillation events. Our results indicated that water discharge in Santiago River increases during El Niño and La Niña events. In contrast, Pánuco River is mostly affected by La Niña events.     

The influence of ENSO and PDO on tropical Andean glaciers and their impact on the hydrology of the Amazon Basin

Recent decades, particularly since the late 1970s, have witnessed a rapid retreat of glaciers in the tropical Andes. We compiled the changes in glacier surfaces along the eastern cordilleras of the tropical Andes of Peru and Bolivia since the early 1980s from the literature. Water levels from two Brazilian river basins in the Amazon basin (one (Madeira River) glacially fed by meltwater from the Andes and the other (Envira River) non‐glacially fed), were analysed for a 30‐year period between 1985?2014. Furthermore, precipitation data near these two basins were also analysed in order to understand the differential contributions of glacier melting and rainfall. Variations in the water levels from the glacially fed Madeira River showed that some years were associated with higher water levels even when the precipitation remained low during the corresponding season (May‐October). This observation was common when El Niño events occurred during the positive phase of Pacific Decadal Oscillation (PDO). Water levels in glacier‐fed Madeira River were slightly higher during the periods where El Niño and warm PDO co‐occurred. On the other hand, water levels in the Envira River were precipitation dependent; water levels were higher when the rainfall was high.     

The Coyote Brush Invasion of Southern California Grasslands and the Legacy of Mechanical Disturbance

This study investigates the recent invasion of exotic grasslands by coyote brush in La Jolla Valley, California. We test the “event dependent” hypothesis that mechanical disturbances during the past century were a key cause. To examine the relationship between past mechanical disturbances and vegetation dynamics we first conducted a review of the historical literature on practices of shrub removal and documented disturbance history using historical imagery. We next analyzed vegetation‐cover change over time using remotely sensed imagery and a vegetation map to document the history of native shrub advancement into exotic grassland by species association. Finally, we determined the topographic characteristics associated with different phases of shrub advancement. We found that mechanical disturbances historically varied by topography with upper and steeper slopes being least intensively disturbed. We found that shrub advancement rates, following release from grazing, varied by slope, elevation, and time period, and that Baccharis pilularis (coyote brush) was the main species to invade the more intensively disturbed sites at lower elevations. Our results indicate that mechanical disturbances played an important role in modifying the original vegetation cover with long‐lasting consequences, including a facilitating role for the subsequent Baccharis pilularis invasion. We concluded that the practice of grazing often included exotic mechanical disturbances that had long‐lasting impacts on native plants.     

Mesquite (Prosopis glandulosa) germination and survival in black-grama (Bouteloua eriopoda) grassland: relations between microsite and heteromyid rodent (Dipodomys spp.) impact

Prosopis pallida H.B.K. is one of the most economically and ecologically important tree species in the arid and semi-arid lands of the American continent. Sections of P. pallida were used to describe its wood anatomy and to determine whether annual rings were visible or not. Results showed that P. pallida has well-differentiated annual growth rings and is therefore suitable for dendrochronological studies. Tree ring chronologies correlate well with precipitation events related to El Niño Southern Oscillation phases. A master chronology for the northern area of Peru was built with these data, and some physiological derivations from the anatomy of P. pallida wood are discussed.     

Application of a statistical water-table model reveals connections between dunes and vegetation at Doñana

We present a simple statistical model of the water-table fluctuations based on a set of multiple regressions for a dune slack of the Doñana National Park, and its utility to understand some ecological processes. The variation in the coefficients of the regressions for different locations allows discrimination between different zones in the dune slack, and explains the spatial pattern of heath vegetation observed in the stabilized sands. Model simulations were compared with an existing sparse data set of water-table levels, and suggests possible mechanisms responsible for the catastrophic pine tree mortality, which happened during the drought of 1979–83.     

The Response of Aboriginal Burning Practices to Population Levels and El Niño–Southern Oscillation Events during the mid- to late-Holocene: a case study from the Sydney Basin using charcoal and pollen analysis

Pollen and macroscopic charcoal have been analysed from a sedimentary sequence representing approximately 6100 years from a site within Wollemi National Park. This is located to the north-west of Sydney and forms a part of the Greater Blue Mountains World Heritage Area. The overall aim of the work was to examine the prehistoric interrelationships between vegetation, fire and human activity. There were relatively minor changes in the vegetation over the last ～6000 years, perhaps reflecting the climate- and fire-resilient nature of the sclerophyllous vegetation found on Hawkesbury Sandstone throughout the Sydney Basin. Casuarinaceae declined in the late Holocene, a trend that has been detected in numerous palaeoecological studies throughout south-eastern Australia. This decline was unrelated to fire, which has been a persistent feature at the site over the entire analysed sequence. The fire regime at the site changed from 5.7 ka, which is interpreted as reflecting the onset of increased climatic variability associated with El Niño-Southern Oscillation (ENSO) events. Another dramatic change in the fire regime occurred at 3 ka, which was coeval with archaeological changes in the region. It is possible that the change in fire activity from 3 ka represented an alteration to Aboriginal management strategies associated with an increasing population and/or the increased risk of conflagrations in an ENSO-dominated climate.     

阿克苏河径流变化与北大西洋涛动的关系

使用小波、交叉小波多尺度分析、相关和突变检验以及线性趋势等方法研究了阿克苏河天然径流与北大西洋涛动的关系。结论如下：（1）对NAO与阿克苏河径流的年代际变化、周期、相关等分析表明两者关系密切;（2）交叉小波谱表明：阿克苏河径流与NAO在年、冬季和夏季各周期尺度上的20世纪90年代相关性高,相关显著区多集中在90年代;（3）阿克苏河径流与NAO年代趋势强弱变化具有一致性;（4）NAO突变影响阿克苏河径流突变;（5）NAO通过大气环流变化来影响阿克苏河流域温度和降水,进而影响其径流。