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Calvin W. Rose Bofu Yu William L. Hogarth Augustine E. A. Okom Hossein Ghadiri 《Journal of Hydrology》2003,280(1-4):33-51
The spatial and size distribution of sediment deposited from short periods of overland flow due to the effect of a simulated grass buffer strip was measured for low slopes of 1.6, 3.4 and 5.1%. These data were analysed so as to critically evaluate two alternative models of the process of re-entrainment of recently deposited sediment. A model of re-entrainment, previously thought to be appropriate only for a steady-state or equilibrium situation, was found to give better agreement with experiments than did a model previously used in the literature on this subject. 相似文献
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Herbert Ssegane Devendra M. Amatya Augustine Muwamba George M. Chescheir Tim Appelboom E.W. Tollner Jami E. Nettles Mohamed A. Youssef François Birgand R.W. Skaggs 《水文研究》2017,31(20):3458-3471
Historically, paired watershed studies have been used to quantify the hydrological effects of land use and management practices by concurrently monitoring 2 similar watersheds during calibration (pretreatment) and post‐treatment periods. This study characterizes seasonal water table and flow response to rainfall during the calibration period and tests a change detection technique of moving sums of recursive residuals (MOSUM) to select calibration periods for each control–treatment watershed pair when the regression coefficients for daily water table elevation were most stable to minimize regression model uncertainty. The control and treatment watersheds were 1 watershed of 3–4‐year‐old intensely managed loblolly pine (Pinus taeda L.) with natural understory, 1 watershed of 3–4‐year‐old loblolly pine intercropped with switchgrass (Panicum virgatum), 1 watershed of 14–15‐year‐old thinned loblolly pine with natural understory (control), and 1 watershed of switchgrass only. The study period spanned from 2009 to 2012. Silvicultural operational practices during this period acted as external factors, potentially shifting hydrologic calibration relationships between control and treatment watersheds. MOSUM results indicated significant changes in regression parameters due to silvicultural operations and were used to identify stable relationships for water table elevation. None of the calibration relationships developed using this method were significantly different from the classical calibration relationship based on published historical data. We attribute that to the similarity of historical and 2010–2012 leaf area index on control and treatment watersheds as moderated by the emergent vegetation. Although the MOSUM approach does not eliminate the need for true calibration data or replace the classic paired watershed approach, our results show that it may be an effective alternative approach when true data are unavailable, as it minimizes the impacts of external disturbances other than the treatment of interest. 相似文献
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Philip G. Oguntunde Babatunde J. Abiodun Gunnar Lischeid 《Meteorology and Atmospheric Physics》2012,118(1-2):95-105
Trends and periodicity analyses can provide information on climate variability inherent in a particular variable. In this study, trend tests and spectral analysis are used to examine the existence of trends and cycles in temperature series (1901–2000) of Nigeria. Periods 1901–1929 and 1942–1980 exhibited cooling trends while 1930–1941 and 1981–2000 showed warming trends. The warmest years in Nigeria were 1941, 1935, 1931 and 1987. The coldest years were 1929, 1975, 1925 and 1974. Whereas no significant trends were detected for 1901–1930 period, the standard period 1931–1960 was marked by significant cooling while 1961–1990 was marked with significant warming. Annual temperature has risen by 0.03?°C/decade during the last century. The overall warming was mostly confined to the south of 12°N especially during April and June. Changes in minimum temperature are higher than that of maximum temperature. The quasi-biennial oscillation was found in annual data for all the six zones with periods of about 2–4?years. Nigeria landscape is under strong North Atlantic Oscillation influence in dry season and under ENSO influence during wet season. Annual temperature series was also found to exhibit significant negative correlation with SOI. 相似文献
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We report on our implementation of EULAG as a dynamical core in the Community Atmospheric Model (CAM). EULAG is a non-hydrostatic, parallel computational model for all-scale geophysical flows. EULAG’s name derives from its two computational options: EULerian (flux form) or semi-LAGrangian (advective form). The model combines nonoscillatory forward-in-time (NFT) numerical algorithms with a robust elliptic Krylov solver. A signature feature of EULAG is that it is formulated in generalized coordinates. In particular, this enables grid adaptivity. In total, these features give EULAG novel advantages over the existing dynamical cores in CAM. This paper uses a series of aqua-planet simulations to demonstrate that CAM-EULAG results compare favorably with those from CAM simulations at standard CAM resolution that use current finite volume or Eulerian-spectral dynamical core options. We also show that the grid adaptivity implemented in CAM3-EULAG allows higher resolution in selected regions without causing anomalous behavior such as spurious wave reflection. 相似文献
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The relationship between the F2-layer critical frequency and solar wind parameters during magnetic storm sudden commencement (SSC) and main phase periods for intense (IS) and very intense (VIS) class of storms is investigated. The analysis covers low- and mid-latitude stations. The effects of ionospheric storm during SSC period is insignificant compared to the main phase, but can trigger the latter. The main phase is characterized by severe negative storm effect at both latitudes during VIS periods while it is latitudinal symmetric for IS observations. The IS reveal positive/negative storm phase in the low-/mid-latitudes, respectively. Ionization density effect is more prominent during VIS events, and is attributed to large energetic particle and solar activity input into the earth magnetosphere. However, ionospheric effect is more significant at the low-latitude than at the mid-latitude. Lastly, ionospheric storm effect during a geomagnetic storm may be related to the combinational effect of interplanetary and geomagnetic parameters and internal ionospheric effect, not necessarily the solar wind alone. 相似文献
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Musa Olufemi Awoyemi Ojudoo Darius Ajama Olayide Sakirudeen Hammed Augustine Babatunde Arogundade Sesan Cornelius Falade 《Geophysical Prospecting》2018,66(Z1):40-54
High‐resolution aeromagnetic data over the Bida Basin, North Central Nigeria has been analysed to investigate the possible continuity of Ifewara fault zone, through the Bida Basin, to Zungeru fault zone. Analytic signal magnitude, horizontal gradient magnitude, and Euler deconvolution methods were applied to the aeromagnetic data to delineate the subsurface structures. The results showed that a prominent NNE–SSW trending fault associated with the Ifewara fault zone extends through the study area. Other faults trending in the ENE–WSW, NE–SW, NW–SE, E–W, and WNW–ESE directions were also mapped. Interpreted models revealed the presence of intrusives and a possible mineralised zone within the study area. We therefore concluded that the inferred fault zones within the basin have affinity with the trend of the Ifewara fault zone, which is an indication of possible extension and linkage with Zungeru fault zone through the Bida Basin. 相似文献
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Ulrich?DiassoEmail authorView author&#;s OrcID profile Babatunde?J?Abiodun 《Theoretical and Applied Climatology》2018,133(3-4):647-662
This study investigates how a large-scale reforestation in Savanna (8–12°N, 20°W–20°E) could affect drought patterns over West Africa in the future (2031–2060) under the RCP4.5 scenario. Simulations from two regional climate models (RegCM4 and WRF) were analyzed for the study. The study first evaluated the performance of both RCMs in simulating the present-day climate and then applied the models to investigate the future impacts of global warming and reforestation on the drought patterns. The simulated and observed droughts were characterized with the Standardized Precipitation and Evapotranspiration Index (SPEI), and the drought patterns were classified using a Self-organizing Map (SOM) technique. The models capture essential features in the seasonal rainfall and temperature fields (including the Saharan Heat Low), but struggle to reproduce the onset and retreat of the West African Monsoon as observed. Both RCMs project a warmer climate (about 1–2 °C) over West Africa in the future. They do not reach a consensus on future change in rainfall, but they agree on a future increase in frequency of severe droughts (by about 2 to 9 events per decade) over the region. They show that reforestation over the Savanna could reduce the future warming by 0.1 to 0.8 °C and increase the precipitation by 0.8 to 1.2 mm per day. However, the impact of reforestation on the frequency of severe droughts is twofold. While reforestation decreases the droughts frequency (by about 1–2 events per decade) over the Savanna and Guinea coast, it increases droughts frequency (by 1 event per decade) over the Sahel, especially in July to September. The results of this study have application in using reforestation to mitigate impacts of climate change in West Africa. 相似文献
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