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El Niño Years (el + nino_year)
Selected AbstractsRainfall effects on rare annual plantsJOURNAL OF ECOLOGY, Issue 4 2008Jonathan M. Levine Summary 1Variation in climate is predicted to increase over much of the planet this century. Forecasting species persistence with climate change thus requires understanding of how populations respond to climate variability, and the mechanisms underlying this response. Variable rainfall is well known to drive fluctuations in annual plant populations, yet the degree to which population response is driven by between-year variation in germination cueing, water limitation or competitive suppression is poorly understood. 2We used demographic monitoring and population models to examine how three seed banking, rare annual plants of the California Channel Islands respond to natural variation in precipitation and their competitive environments. Island plants are particularly threatened by climate change because their current ranges are unlikely to overlap regions that are climatically favourable in the future. 3Species showed 9 to 100-fold between-year variation in plant density over the 5,12 years of censusing, including a severe drought and a wet El Niño year. During the drought, population sizes were low for all species. However, even in non-drought years, population sizes and per capita growth rates showed considerable temporal variation, variation that was uncorrelated with total rainfall. These population fluctuations were instead correlated with the temperature after the first major storm event of the season, a germination cue for annual plants. 4Temporal variation in the density of the focal species was uncorrelated with the total vegetative cover in the surrounding community, suggesting that variation in competitive environments does not strongly determine population fluctuations. At the same time, the uncorrelated responses of the focal species and their competitors to environmental variation may favour persistence via the storage effect. 5Population growth rate analyses suggested differential endangerment of the focal annuals. Elasticity analyses and life table response experiments indicated that variation in germination has the same potential as the seeds produced per germinant to drive variation in population growth rates, but only the former was clearly related to rainfall. 6Synthesis. Our work suggests that future changes in the timing and temperatures associated with the first major rains, acting through germination, may more strongly affect population persistence than changes in season-long rainfall. [source] Precipitation control over inorganic nitrogen import,export budgets across watersheds: a synthesis of long-term ecological researchECOHYDROLOGY, Issue 2 2008E. S. Kane Abstract We investigated long-term and seasonal patterns of N imports and exports, as well as patterns following climate perturbations, across biomes using data from 15 watersheds from nine Long-Term Ecological Research (LTER) sites in North America. Mean dissolved inorganic nitrogen (DIN) import,export budgets (N import via precipitation,N export via stream flow) for common years across all watersheds was highly variable, ranging from a net loss of , 0·17 ± 0·09 kg N ha,1mo,1 to net retention of 0·68 ± 0·08 kg N ha,1mo,1. The net retention of DIN decreased (smaller import,export budget) with increasing precipitation, as well as with increasing variation in precipitation during the winter, spring, and fall. Averaged across all seasons, net DIN retention decreased as the coefficient of variation (CV) in precipitation increased across all sites (r2 = 0·48, p = 0·005). This trend was made stronger when the disturbed watersheds were withheld from the analysis (r2 = 0·80, p < 0·001, n = 11). Thus, DIN exports were either similar to or exceeded imports in the tropical, boreal, and wet coniferous watersheds, whereas imports exceeded exports in temperate deciduous watersheds. In general, forest harvesting, hurricanes, or floods corresponded with periods of increased DIN exports relative to imports. Periods when water throughput within a watershed was likely to be lower (i.e. low snow pack or El Niño years) corresponded with decreased DIN exports relative to imports. These data provide a basis for ranking diverse sites in terms of their ability to retain DIN in the context of changing precipitation regimes likely to occur in the future. Copyright © 2008 John Wiley & Sons, Ltd. [source] El Niño Southern Oscillation link to the Blue Nile River Basin hydrologyHYDROLOGICAL PROCESSES, Issue 26 2009Wossenu Abtew Abstract The objective of this study is to evaluate the relationships of El Niño Southern Oscillation (ENSO) indices and the Blue Nile River Basin hydrology using a new approach that tracks cumulative ENSO indices. The results of this study can be applied for water resources management decision making to mitigate drought or flood impacts with a lead time of at least few months. ENSO tracking and forecasting is relatively easier than predicting hydrology. ENSO teleconnections to the Blue Nile River Basin hydrology were evaluated using spatial average basin rainfall and Blue Nile flows at Bahir Dar, Ethiopia. The ENSO indices were sea surface temperature (SST) anomalies in region Niño 3·4 and the Southern Oscillation Index (SOI). The analysis indicates that the Upper Blue Nile Basin rainfall and flows are teleconnected to the ENSO indices. Based on event correspondence and correlation analysis, high rainfall and high flows are likely to occur during La Niña years and dry years are likely to occur during El Niño years at a confidence level of 90%. Extreme dry and wet years are very likely to correspond with ENSO events as given above. The great Ethiopian famine of 1888,1892 corresponds to one of the strongest El Niño years, 1888. The recent drought years in Ethiopia correspond to strong El Niño years and wet years correspond to La Niña years. In this paper, a new approach is proposed on how to classify the strength of ENSO events by tracking consecutive monthly events through a year. A cumulative SST index value of ,5 and cumulative SOI value of , ,7 indicate strong El Niño. A cumulative SST index value of ,,5 and cumulative SOI index of ,7 indicate strong La Niña. Copyright © 2009 John Wiley & Sons, Ltd. [source] Effects of the El Niño,southern oscillation on temperature, precipitation, snow water equivalent and resulting streamflow in the Upper Rio Grande river basinHYDROLOGICAL PROCESSES, Issue 6 2004Songweon Lee Abstract Snowmelt runoff dominates streamflow in the Upper Rio Grande (URG) basin of New Mexico and Colorado. Annual variations in streamflow timing and volume at most stations in the region are strongly influenced by the El Niño,southern oscillation (ENSO) through its modulation of the seasonal cycles of temperature and precipitation, and hence on snow accumulation and melting. After removing long-term trends over the study period (water years 1952,99), the dependence of monthly temperature, precipitation, snow water equivalent (SWE) at snowcourse stations, and streamflow throughout the URG on ENSO was investigated using composite analyses of the detrended residuals and through dependence of the residuals on the Climate Prediction Center southern oscillation index during the preceding summer and fall. The climate of La Niña years was found to differ significantly from either El Niño or neutral years. Moreover, significant climatological ENSO-related effects are confined to certain months, predominantly at the beginning and end of the winter season. In particular, March of La Niña years is significantly warmer and drier than during either El Niño or neutral years, and November of El Niño years is significantly colder and wetter. Differences in temperature and precipitation lead to significant differences in SWE and streamflow in the URG between the three ENSO phases. Copyright © 2004 John Wiley & Sons, Ltd. [source] Basin-wide warming of the Indian Ocean during El Niño and Indian Ocean dipole yearsINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 11 2007J. S. Chowdary Abstract Basin-wide wintertime surface warming is observed in the Indian Ocean during El Niño years. The basin-wide warming is found to be stronger when El Niño and Indian Ocean Dipole (IOD) co-occur. The mechanisms responsible for the basin-wide warming are different for the years with El Niño only (El Niño without IOD) and for the co-occurrence (both El Niño and IOD) years. Strong westward propagation of downwelling Rossby waves is observed in the southern Indian Ocean during the IOD years. Such strong propagation is not seen in the case of the El Niño-only years. This indicates that the ocean dynamics play an important role in winter warming of the western Indian Ocean during the IOD years. The weak easterly wind anomalies in the El Niño-only years show no measurable impact on the Wyrtki Jets, but weakening or reversal of these jets is seen in the IOD years. This strongly suggests that the variability related to surface circulation is due to the local IOD forcing rather than El Niño induced wind anomaly. For the El Niño-only composites, surface heat fluxes (mainly latent heat flux and short wave radiation) play an important role in maintaining the basin-wide surface warming in the Indian Ocean. In the IOD-only composites (when there is no El Niño in the Pacific), such basin-wide warming is not seen because of the absence of ENSO (El Niño and Southern Oscillation) induced subsidence over the eastern Indian Ocean. For the years in which both El Niño in the Pacific and dipole in the Indian Ocean co-occur, warming in the western Indian Ocean is due to the ocean dynamics and that in the eastern Indian Ocean is due to the anomalous latent heat flux and solar radiation. Copyright © 2007 Royal Meteorological Society [source] Variability in the characteristics of cut-off low pressure systems over subtropical southern AfricaINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 3 2007A. T. Singleton Variability in the characteristics of cut-off low pressure systems over subtropical southern Africa is examined for the 1973,2002 period. These characteristics include their seasonality, frequency, duration, location and size. It is found that on average 11 cut-off lows occur over southern Africa south of 20°S per year and are most common in the March-May season. Potential relationships between the number of cut-off lows over southern Africa with the El Niño Southern Oscillation (ENSO), the Pacific South America pattern, the wave number 3 pattern and the semi-annual oscillation (SAO) are discussed. La Niña years appear to be associated with above average annual frequencies of cut-off lows but the reverse is generally not true for El Niño years. There was a shift in the preferred season for cut-off lows from March,May to June,August in the 1980s, which coincided with a weakening of the SAO and a shift in zonal wave number 3. This period also showed a change in the preferred location of these systems from southwestern subtropical southern Africa to the northeast of the region. The results suggest that there may be a relationship between cut-off lows over subtropical southern Africa, the wave number 3 pattern in the Southern Hemisphere and the SAO. Copyright © 2006 Royal Meteorological Society. [source] Identification of three dominant rainfall regions within Indonesia and their relationship to sea surface temperatureINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 12 2003Edvin Aldrian Abstract The characteristics of climatic rainfall variability in Indonesia are investigated using a double correlation method. The results are compared with empirical orthogonal function (EOF) and rotated EOF methods. In addition, local and remote responses to sea-surface temperature (SST) are discussed. The results suggest three climatic regions in Indonesia with their distinct characteristics. Region A is located in southern Indonesia from south Sumatera to Timor island, southern Kalimantan, Sulawesi and part of Irian Jaya. Region B is located in northwest Indonesia from northern Sumatra to northwestern Kalimantan. Region C encompasses Maluku and northern Sulawesi. All three regions show both strong annual and, except Region A, semi-annual variability. Region C shows the strongest El Niño,southern oscillation (ENSO) influence, followed by Region A. In Region B, the ENSO-related signal is suppressed. Except for Region B, there are significant correlations between SST and the rainfall variabilities, indicating a strong possibility for seasonal climate predictions. March to May is the most difficult season to predict the rainfall variability. From June to November, there are significant responses of the rainfall pattern to ENSO in Regions A and C. A strong ENSO influence during this normally dry season (June to September) is hazardous in El Niño years, because the negative response means that higher SST in the NIÑO3 of the Pacific region will lower the rainfall amount over the Indonesian region. Analyses of Indonesian rainfall variability reveal some sensitivities to SST variabilities in adjacent parts of the Indian and Pacific Oceans. Copyright © 2003 Royal Meteorological Society [source] Coral Cover Change Associated to El Niño, Eastern Pacific, Costa Rica, 1992,2001MARINE ECOLOGY, Issue 3 2003Carlos E. Jiménez Abstract., Changes in live and dead coral cover were documented at three localities off the Costa Rican central Pacific coast first in 1992 during the aftermath of the 1991,1992 El Niño; again in the period between 1994 and 1995, and last in January 2001. Recovery of coral communities after the 1991,1992 El Niño was expressed by a significant increase (,40 %) in 1994 of live coral cover at one locality (Manuel Antonio). A subsequent decrease (,50 %) in response to the very strong 1997,1998 episode was recorded at Manuel Antonio and Ballena, mainly due to partial tissue mortality of branching (Pocillopora spp.) and massive (Porites lobata) corals. Mortality of entire colonies associated to that event was scarce and confined to branching and nodular (Psammocora stellata) corals. This species was not found at one locality (Cambutal) in the 2001 survey and it is presumed locally extinct. The recovery of this coral and others will depend on recruits from surviving colonies in deeper waters and other coral communities in the vicinity. Within sites at a given locality, contrasting results in live coral cover variability were found. This is partially due to distinct coral assemblages, coral growth, physical exposure to tidal regime, and, related to the latter, variable duration and intensity of the warming event. In general, predominant meteorological conditions at the studied area are conducive to solar radiation (UV) stress during El Niño years and are related to changes in the atmosphere-ocean interactions in response to the warming events. [source] | |||||||||||||