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Both historical information on sub-Saharan droughts/famines and measured rainfall data from northern Nigeria were analysed. Their parallel existence since 1905 allows famine chronologies to be quantified from the rainfall series. It is found that the most disruptive historical famines occurred when the cumulative deficit of rainfall fell below 1.3 times the standard deviation of long-term mean annual rainfall for a particular place. Thus defined, rainfall droughts matched approximately 90% of the famine events chronicled for northern Nigeria. An attempt is made to utilise information obtained from this matching of events to interpret droughts which occurred before scientific measurements. Difficulties inherent in such interpretation are discussed. 相似文献
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Visual MODFLOW, a numerical groundwater flow model, was used to evaluate the impacts of groundwater exploitation on streamflow
depletion in the Alluvium and Terrace aquifer of the Beaver-North Canadian River (BNCR) in northwestern Oklahoma, USA. Water
demand in semi-arid northwestern Oklahoma is projected to increase by 53% during the next five decades, driven primarily by
irrigation, public water supply, and agricultural demand. Using MODFLOW’s streamflow routing package, pumping-induced changes
in baseflow and stream leakage were analyzed to estimate streamflow depletion in the BNCR system. Simulation results indicate
groundwater pumping has reduced baseflow to streams by approximately 29% and has also increased stream leakage into the aquifer
by 18% for a net streamflow loss of 47%. The magnitude and intensity of streamflow depletion, however, varies for different
stream segments, ranging from 0 to 20,804 m3/d. The method provides a framework for isolating and quantifying impacts of aquifer pumping on stream function in semiarid
alluvial environments.
Résumé Visual MODFLOW, un modèle numérique d’écoulement des eaux souterraines, a été utilisé pour évaluer les impacts de l’exploitation de l’eau souterraine sur la réduction du régime de la rivière dans un aquifère d’alluvions et de terrasse de la Rivière canadienne Beaver-North (BNCR) au nord-ouest de l’Oklahoma, aux USA. La demande d’eau dans le nord-ouest semi-aride de l’Oklahoma devrait augmenter de 53% durant les cinq prochaines décennies, essentiellement du fait de l’irrigation, la demande en eau potable et la demande agricole. En utilisant le module numérique traitant les rivières dans MODFLOW, les changements sur le régime de base des cours d’eau induits par le pompage et la recharge par la rivière ont été analysés pour estimer la réduction du régime de la rivière du système BNCR. Les résultats de la simulation indiquent que le pompage de l’eau souterraine réduit le débit de base de la rivière de 18% pour une perte nette du débit de la rivière de 47%. L’importance et l’intensité de la réduction du débit de base, toutefois, varie selon le bief, de 0 à 20,840 m3/d. La méthode apporte un cadre pour isoler et quantifier les impacts sur le pompage de l’aquifère sur le fonctionnement de la rivière dans un environnement alluvial semi-aride.
Resumen El Visual MODFLOW, que es un modelo numérico de flujo de agua subterránea, fue usado para evaluar los impactos de la explotación del agua subterránea, en la disminución de la cantidad de flujo de una corriente superficial, relacionada al acuífero del aluvión y de la terraza del Río canadiense Beaver-North (BNCR) en Oklahoma del noroeste, EUA. Se proyecta que la demanda de agua aumentará en un 53%, en el sector semiárido de Oklahoma del noroeste, durante las próximas cinco décadas, principalmente debido a la irrigación, suministro de agua público, y la demanda agrícola. Mediante el uso del paquete especial para relaciones corriente superficial- acuífero (SFR) de MODFLOW, se analizaron cambios inducidos por el bombeo, tanto en el flujo base, como en el goteo del río, para estimar la disminución del flujo de la corriente en el sistema de BNCR. Los resultados de la simulación indican, que el bombeo de agua subterránea ha reducido el flujo base a los arroyos aproximadamente en un 29% y también ha aumentado el goteo del arroyo hacia el acuífero en 18%, resultando una pérdida neta del flujo del río de un 47%. La magnitud e intensidad de la disminución del flujo del río, sin embargo, varía en sus diferentes segmentos, oscilando de 0 a 20,804 m3/d. El método suministra un marco, para aislar y cuantificar los impactos del bombeo del acuífero, sobre el funcionamiento de una corriente superficial en los ambientes aluviales semiáridos.相似文献
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Sequential application of the single shift Normal Homogeneity Test (NHT) to the time series of Sahel rainfall revealed three clusters of discontinuities or breakpoints separating climatically stationary periods: 1933–1944, 1955–1974, and 1980–1989. At least one breakpoint was detected in 33 of the 55 series analyzed, while two breakpoints occurred in 12. The breakpoints of 1933–1944 marked the termination of spatially localized droughts in western Burkina Faso and southern Mali. Generally speaking, the Sahel drought that began in the late 1960s, persisted into 1998. However, abrupt positive shifts that occurred during the late 1980s restored mean annual rainfall to pre-drought levels at isolated locations. The stationarity of the periods between breakpoints suggests that the abrupt shifts are the dominant source of inhomogeneity in Sahel rainfall. Unlike the widely used climatic normal periods (CNPs), stationary periods are suitable for calculating various empirical indices for application in agriculture and rural water-resources planning in the area. The large number of breakpoints detected at different time periods suggests that Sahel rainfall series are prone to sudden transitions between quasi-stable climatic regimes; much like the onset, drought may terminate abruptly through a sudden shift in the mean annual rainfall. [Key words: Sahel, West Africa, drought, rainfall.] 相似文献
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Jason P. Julian Richard E. Thomas Sayed Moursi Bruce W. Hoagland Aondover Tarhule 《地球表面变化过程与地形》2012,37(4):449-458
In 1820, the lower Canadian River meandered through a densely forested floodplain. By 1898, most of the floodplain had been cleared for agriculture and changes in channel geometry and specific stream power followed, particularly channel widening and straightening with a lower potential specific stream power. In 1964, a large upstream hydropower dam was constructed, which changed the flow regime in the lower Canadian River and consequently the channel geometry. Without destructive overbank floods, the channel narrowed rapidly and considerably due to encroachment by floodplain vegetation. The lower Canadian River, which was once a highly dynamic floodplain‐river system, has now been transformed into a relatively static river channel. These changes over the past 200 years have not been linear or independent. In this article, we use a variety of data sources to assess these historical changes along the lower Canadian River floodplain and identify feedbacks among floodplain cultivation, dam construction, specific stream power, and channel width, slope, and sinuosity. Finally, we combine the results of our study with others in the region to present a biogeomorphic response model for large Great Plains rivers that characterizes channel width changes in response to climate variability and anthropogenic disturbances. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
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Climate and land use changes greatly modify hydrologic regimes. In this paper, we modelled the impacts of biofuel cultivation in the US Great Plains on a 1061‐km2 watershed using the Soil and Water Assessment Tool (SWAT) hydrologic model. The model was calibrated to monthly discharges spanning 2002–2010 and for the winter, spring, and summer seasons. SWAT was then run for a climate‐change‐only scenario using downscaled precipitation and a projected temperature for 16 general circulation model (GCM) runs associated with the Intergovernmental Panel on Climate Change Special Report on Emission Scenarios A2 scenario spanning 2040–2050. SWAT was also run on a climate change plus land use change scenario in which Alamo switchgrass (Panicum virgatum L.) replaced native range grasses, winter wheat, and rye (89% of the basin). For the climate‐change‐only scenario, the GCMs agreed on a monthly temperature increase of 1–2 °C by the 2042–2050 period, but they disagreed on the direction of change in precipitation. For this scenario, decreases in surface runoff during all three seasons and increases in spring and summer evapotranspiration (eT) were driven predominantly by precipitation. Increased summer temperatures also significantly contributed to changes in eT. With the addition of switchgrass, changes in surface runoff are amplified during the winter and summer, and changes in eT are amplified during all three seasons. Depending on the GCM utilized, either climate change or land use change (switchgrass cultivation) was the dominant driver of change in surface runoff while switchgrass cultivation was the major driver of changes in eT. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
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Damaging rainfall and rain-induced flooding occur from time to time in the drought-prone Sahel savanna zone of Niger in West
Africa but official records of these events and their socioeconomic impacts do not exist. This paper utilized newspaper accounts
between 1970 and 2000 to survey and illustrate the range of these flood hazards in the Sahel. During the study interval, 53
newspaper articles reported 79 damaging rainfall and flood events in 47 different communities in the Sahel of Niger. Collectively,
these events destroyed 5,580 houses and rendered 27,289 people homeless. Cash losses and damage to infrastructure in only
three events exceeded $4 million. Sahel residents attribute these floods to five major causes including both natural and anthropogenic,
but they view the flood problem as driven primarily by land use patterns. Despite such awareness, traditional coping strategies
appear inadequate for dealing with the problems in part because of significant climatic variability. Analysis of several rainfall
measures indicates that the cumulative rainfall in the days prior to a heavy rain event is an important factor influencing
whether or not heavy rainfall results in flooding. Thus, despite some limitations, newspaper accounts of historical flooding
are largely consistent with measured climatic variables. The study demonstrates that concerted effort is needed to improve
the status of knowledge concerning flood impacts and indeed other natural and human hazards in the Sahel. 相似文献
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