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Brazilian semi‐arid regions are characterized by water scarcity, vulnerability to desertification, and climate variability. The investigation of hydrological processes in this region is of major interest not only for water planning strategies but also to address the possible impact of future climate and land‐use changes on water resources. A hydrological distributed catchment‐scale model (DiCaSM) has been applied to simulate hydrological processes in a small representative catchment of the Brazilian northeast semi‐arid region, and also to investigate the impact of climate and land‐use changes, as well as changes associated with biofuel/energy crops production. The catchment is part of the Brazilian network for semi‐arid hydrology, established by the Brazilian Federal Government. Estimating and modelling streamflow (STF) and recharge in semi‐arid areas is a challenging task, mainly because of limitation in in situ measurements, and also due to the local nature of some processes. Direct recharge measurements are very difficult in semi‐arid catchments and contain a high level of uncertainty. The latter is usually addressed by short‐ and long‐time‐scale calibration and validation at catchment scale, as well as by examining the model sensitivity to the physical parameters responsible for the recharge. The DiCaSM model was run from 2000 to 2008, and streamflow was successfully simulated, with a Nash–Sutcliffe (NS) efficiency coefficient of 0·73, and R2 of 0·79. On the basis of a range of climate change scenarios for the region, the DiCaSM model forecasted a reduction by 35%, 68%, and 77%, in groundwater recharge (GWR), and by 34%, 65%, and 72%, in streamflow, for the time spans 2010–2039, 2040–2069, and 2070–2099, respectively, could take place for a dry future climate scenario. These reductions would produce severe impact on water availability in the region. Introducing castor beans to the catchment would increase the GWR and streamflow, mainly if the caatinga areas would be converted into castor beans production. Changing an area of 1000 ha from caatinga to castor beans would increase the GWR by 46% and streamflow by 3%. If the same area of pasture is converted into castor beans, there would be an increase in GWR and streamflow by 24% and 5%, respectively. Such results are expected to contribute towards environmental policies for north‐east Brazil (NEB), and to biofuel production perspectives in the region. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
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Experiments with a climate model were conducted under present day and last glacial maximum conditions in order to examine the model’s response to a vertical mixing scheme based on internal tide energy dissipation. The increase in internal tide energy flux caused by a 120 m reduction in sea level had the expected effect on diffusivity values, which were higher under lower sea level conditions. The impact of this vertical diffusivity change on the Atlantic meridional overturning is not straightforward and no clear relationship between diffusivity and overturning is found. There exists a weak positive correlation between overturning and changes to the power consumed by vertical mixing. Most of the climatic response generated by sea level change was not related to alterations in the internal tide energy flux but rather to the direct change in sea level itself. 相似文献
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Final disposal of high-level radioactive waste in deep repositories in clay formations is being considered by several countries. Repository safety assessment requires the use of numerical models of groundwater flow, solute transport and chemical processes. These models are being developed from data and knowledge gained from in situ experiments such as the CERBERUS experiment carried out at the HADES facility excavated in the Boom clay formation at Mol (Belgium). This long-term experiment is aimed at evaluating the effect of heating and radiation in Boom clay. The test was performed in a cased well drilled at 223 m depth and lasted from 1989 to 1994. A 60Co source of 400 TBq and two heaters were emplaced inside the well. Dose rate, temperature, porewater pressure and pH/Eh were measured in situ during the experiment and gas and porewater samples were taken for chemical analyses. Here a coupled thermo-hydro-geochemical (THC) model of the CERBERUS experiment is presented which accounts simultaneously for heating, radiation, solute diffusion and a suite of geochemical reactions including: aqueous complexation, acid–base, redox, mineral dissolution/precipitation, cation exchange and gas dissolution/ex-solution. Computed results indicate that heating and radiation causes a slight oxidation, a decrease in pH, slight changes in porewater chemistry and pyrite dissolution near the well. THC model results follow the general evolution of chemical data, but cannot fit SO4 data. Model discrepancies are partly overcome when microbially-mediated Fe and SO4 reduction are taken into account in a coupled thermo-hydro-bio-geochemical (THBC) model. This THBC model captures the trends of geochemical data, improves the fit to dissolved SO4 and predicts pyrite precipitation, a process observed near the CERBERUS well. The ability of the THBC numerical model to reproduce the overall trends of geochemical data of the CERBERUS experiment provides confidence in such a model as a suitable tool for the long-term prediction of geochemistry in the near field of a HLW repository in clay. However, the small number of available chemical data throughout the experiment and the lack of DOC and microbial data allow only a partial validation of the THBC model. 相似文献
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Vegetation response to rainfall seasonality and interannual variability in tropical dry forests 
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下载免费PDF全文 Rodolfo Souza Xue Feng Antonio Antonino Suzana Montenegro Eduardo Souza Amilcare Porporato 《水文研究》2016,30(20):3583-3595
Projected changes in rainfall seasonality and interannual variability are expected to have severe impacts on arid and semi‐arid tropical vegetation, which is characterized by a fine‐tuned adaptation to extreme rainfall seasonality. To study the response of these ecosystems and the related changes in hydrological processes to changes in the amount and seasonality of rainfall, we focused on the caatinga biome, the typical seasonally dry forest in semi‐arid Northeast Brazil. We selected four sites across a gradient of rainfall amount and seasonality and analysed daily rainfall and biweekly Normalized Difference Vegetation Index (NDVI) data for hydrological years 2000 to 2014. Rainfall seasonal and interannual statistics were characterized by recently proposed metrics describing duration, timing and intensity of the wet season and compared to similar metrics of NDVI time series. The results show that the caatinga tends to have a more stable response with longer and less variable growing seasons (3.1 ± 0.1 months) compared to the duration wet seasons (2.0 ± 0.5 months). The ecosystem ability to buffer the interannual variability of rainfall is also evidenced by the stability in the timing of the growing season compared to the wet season, which results in variable delays (ranging from 0 to 2 months) between the peak of the rainfall season and the production of leaves by the ecosystem. The analyses show that the shape and size of the related hysteresis loops in the rainfall–NDVI relations are linked to the buffering effects of soil moisture and plant growth dynamics. Finally, model projections of vegetation response to different rainfall scenarios reveal the existence of a maximum in ecosystem productivity at intermediate levels of rainfall seasonality, suggesting a possible trade‐off in the effects of intensity (i.e. amount) and duration of the wet season on vegetation growth and related soil moisture dynamics and transpiration rates. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
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Emilia Bocanegra Gerson Cardoso Da Silva Jr. Emilio Custodio Marisol Manzano Suzana Montenegro 《Hydrogeology Journal》2010,18(1):261-267
A comparative analysis of the existing hydrogeological and management information from 15 coastal aquifers in South America was performed in order to obtain insight into common features of the sub-continent coastal zones. Some knowledge from other areas has been incorporated. There is a very variable degree of knowledge and management practice, ranging from almost no data and no action (the most common case), to sound conceptual models about aquifer behaviour and comprehensive management actions such as relocation of abstractions, pumping brackish groundwater, and aquifer vulnerability mapping. Some common features are: intensive groundwater exploitation; lack of characterization studies to support resource planning and management; lack of monitoring networks; and the need for raising awareness within society and its involvement in resource planning and management action programmes. Quality and quantity problems arising in heavily populated areas associated with coastal aquifers in South America point to unsustainable groundwater development. The sustainable use of those aquifers must rely on adequate evaluation of aquifer characteristics and monitoring. 相似文献
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A numerical model of coupled saturated/unsaturated water flow, heat transfer and multi-component reactive solute transport
is presented to evaluate the long-term geochemical evolution in bentonite, concrete and clay formation for a potential geological
radioactive waste repository. Changes in formation porosity caused by mineral dissolution/precipitation reactions are taken
into account. Simulations were carried out with a general-purpose multicomponent reactive transport code, CORE2D V4. Numerical results show that pH in the bentonite porewater can vary from neutral to up to 13 over a time scale of 1 Ma
although dissolution of silica minerals and precipitation of secondary calcium silicate hydrate (CSH) minerals in bentonite
buffer the effect of the hyperalkaline plume. Mineral precipitation reduces the volume of pore space in bentonite close to
the bentonite–concrete interface due to the precipitation of CSH minerals. Model results indicate that bentonite porosity
decreases less than 25%. The hyperalkaline plume from the concrete only extends to a distance of 0.7 m in the clay formation
over the time range of 1 Ma. 相似文献