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Rainfall Peaks (rainfall + peak)
Selected AbstractsSpawning and recruitment patterns of major fish species in Bontanga Reservoir, Ghana, West AfricaLAKES & RESERVOIRS: RESEARCH AND MANAGEMENT, Issue 1 2010Kwadwo Kwarfo-Apegyah Abstract The spawning and recruitment patterns of the major Cichlid fish species, including Hemichromis fasciatus, Oreochromis niloticus, Sarotherodon galilaeus, Tilapia zillii and other species, Auchenoglanis occidentalis, Brycinus nurse, Clarias gariepinus and Marcusenius senegalensis were studied for 24 months in Bontanga Reservoir, Ghana, using length-based fish stock assessment approaches. The species spawned throughout the year, with two spawning pulses described as major and minor spawning seasons. The major spawning season occurred from March to September for the Cichlids, and from May to September for the other species. The minor spawning season, indicative of extended spawning, occurred from October to March for all the fish stocks. Fish spawning began with the onset of the rains in April/May, peaking by June/July, before the rainfall peak in August for all the fish stocks studied. Recruitment was found to occur throughout the year, with major and minor pulses coinciding with the major and minor spawning seasons. Accordingly, the most appropriate time for a possible closed fishing period appears to be from June to August, 1 month after the start of, and before the end of, the rains. The estimated mean standard length (Lm) for first time spawners of A. occidentalis, B. nurse, C. gariepinus and H. faciatus were 11.7, 12.7, 2.7 and 7.5 cm respectively. The estimated maturity,length ratio of 0.4 and 0.2 for O. niloticus, S. galilaeus and T. zillii were lower than the known 0.7 for normal growth, suggesting the tilapias matured faster, and at a smaller size, in the reservoir. Apparent sexual precocity associated with early maturity, year-round spawning and recruitment were some important adaptations found to have sustained the reservoir fisheries, even during high fishing pressures. For conservation and sustainable exploitation of the fisheries, instituting a closed fishing season, mesh size regulations, withdrawal rights and a community-based fishery management system are recommended. [source] Hydrometeorological controls and erosive response of an extreme alpine debris flowHYDROLOGICAL PROCESSES, Issue 19 2009Lorenzo Marchi Abstract On 29 August, 2003, an intense convective storm system affected the Fella River basin, in the eastern Italian Alps, producing rainfall peaks of approximately 390 mm in 12 h. The storm triggered an unusually large debris flow in the ungauged Rio Cucco basin (0·65 km2), with a volume of approximately 78 000 m3. The analysis of the time evolution of the rainstorm over the basin has been based on rainfall estimates from radar observations and data recorded by a raingauge network. Detailed geomorphological field surveys, carried out both before and after the flood of August 2003, and the application of a distributed hydrological model have enabled assessment of flood response, estimation of erosion volumes and sediment supply to the channel network. The accounts of two eyewitnesses have provided useful elements for reconstructing the time evolution and the flow processes involved in the event. Liquid peak discharge estimates cluster around 20 m3 s,1 km,2, placing this event on the flood envelope curve for the eastern Italian Alps. The hydrological analysis has shown that the major controls of the flood response were the exceptional cumulated rainfall amount, required to exceed the large initial losses, and the large rainfall intensities at hourly temporal scales, required to generate high flood response at the considered basin scale. Observations on the deposits accumulated on the alluvial fan indicate that, although the dominant flow process was a debris flow, sheetflood also contributed to fan aggradation and fluvial reworking had an important role in winnowing debris-flow lobes and redistributing sediment on the fan surface. This points out to the large discharge values during the recession phase of the flood, implying an important role for subsurface flow on runoff generation of this extreme flash flood event. Copyright © 2009 John Wiley & Sons, Ltd. [source] Myths and facts on ratadas: Bamboo blooms, rainfall peaks and rodent outbreaks in South AmericaAUSTRAL ECOLOGY, Issue 3 2003FABIAN M. JAKSIC Abstract, ,Ratadas' are rodent irruptions or outbreaks that have been recorded in South America since the Spanish conquest in the 16th century. The notion that ratadas are associated with bamboo flowering and subsequent mast seeding at cycles of 30 years has appeared in the literature since the late 1800s. Based on 63 well-documented cases, we show that not only are ratadas associated with bamboo blooming, but also many are associated with rainfall peaks, and that these two outbreak types are geographically interspersed over South America. In addition, we dispel the notion that South American bamboo blooms occur every 30 years, which may only be the case for Merostachys fistulosa. For other species the modal cycles occur every 14 (Merostachys spp.), 12 (Chusquea quila and/or valdiviensis) or 14 years (Chusquea coleou). We also propose the hypothesis that rainfall-associated ratadas are ultimately caused by the occurrence of El Niño, and discuss the possible population dynamic mechanisms underlying rodent outbreaks in South America. Aiming at setting a standardized framework for spatial and temporal comparisons, we propose a trapping protocol and a threshold density for assigning the ,ratada' label. Several of the mice implicated in ratadas are reservoirs of emerging diseases, thus emphasizing the need for predictive power to forecast disease epidemics that affect human populations. Further, ratadas may be viewed as pulsed resources, thus enabling us to learn more of the ways communities respond to such intermittent inputs. [source] The role of growth stop as a morphogenetic factor in Mastomys natalensis (Rodentia: Muridae)BIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 4 2009CARLO FADDA The present study investigated growth patterns under three different environmental conditions in a single population of the rodent Mastomys natalensis (Rodentia, Muridae) in Morogoro, Tanzania. The study aimed to test whether and how post-weaning ontogenetic processes are affected by different environmental conditions. Morogoro is characterized by a bimodal rainfall pattern, with unreliable peaks occurring in November/December of some years and reliable ones in February to May. We recognized three different generation types. In the first one, the , generation, growth occurred during the dry second half of the year in years when the November/December rains were very poor. The second group (, generation) grew under conditions when these rains were abundant. Finally, the , generation, consisted of animals that were born in the middle of the rainy season in years when there was a continuity between both rainfall peaks. Analyses of size and shape following both Huxley,Jolicoeur and Gould,Mosimann approaches revealed that the three groups differ significantly both in size and shape. In both cases, the importance of the environment in assessing growth trajectories during post-natal ontogenetic processes is apparent. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 97, 791,800. [source] | ||||||||||