Studies simulating the large-scale afforestation of the African Sahel constantly find warning signals of increased risk of extreme temperatures and heatwaves resulting from changes in albedo and latent heat flow. We r...Studies simulating the large-scale afforestation of the African Sahel constantly find warning signals of increased risk of extreme temperatures and heatwaves resulting from changes in albedo and latent heat flow. We review the afforestation measures underlying three simulation studies, together with a restoration model in which compartments are formed by greenbelts to enable succession of savanna vegetation, protected from hot wind and drought. Savanna-like vegetation (around 20% woody plants) will show bright reflective surface and drying of leaves during dry season rather than constant green color, with very different impact on albedo and temperatures. We derive that the simulated risks of extreme heat and flooding from rain will strongly depend on species, shape and density of the new vegetation. Ecological restoration concepts are expected to mitigate or prevent such restoration related climatic risks. Compact afforestation of the Sahel does not appear to be necessary or feasible. A restoration model based on compartmentalization and the protected succession of diverse, climatically adaptable vegetation could also be used in populated drylands, as a sustainable and temperature balancing solution to desertification.展开更多
Many parameters have been indicated crucial for the selection of a saline aquifer as a carbon dioxide(CO_(2))storage site.However,less attention has been given to the impact of heterogeneity on the performance of thes...Many parameters have been indicated crucial for the selection of a saline aquifer as a carbon dioxide(CO_(2))storage site.However,less attention has been given to the impact of heterogeneity on the performance of these storage media.Thus,the heterogeneity effect was evaluated in this paper by adopting a numerical modeling approach and the existing screening criterion developed for the aquifers was updated.The updated criterion for CO_(2)storage purpose would enhance the confidence level during the selection of deep saline aquifer and thus,help to address the climate change issue.The numerical modeling was carried out via CO_(2)STORE module of Eclipse300 Simulator to evaluate the effect of different levels of heterogeneity on CO_(2)storage potential.Different degrees of heterogeneity from homogenous systems to highly heterogeneous systems in the model were incorporated through the Lorenz coefficient.In this way,simulation of nine cases was carried out for three different aquifers with different porosity values.A comparison of these results showed that heterogeneity causes the aquifer to have lower storage capacity.On the trapping potential,dissolution trapping was significant and the amount of free gas in all cases was minimum.In addition,the aquifer with the highest level of heterogeneity(HLH)had a minimum fraction of residual trapping regardless of porosity.It was also found that final pressure at the end of 30 years is the same and high for low-level heterogeneity(LLH)and medium level heterogeneity(MLH)cases and low for HLH,while the injection rate stability duration is least for HLH and maximum for LLH.Based on the results obtained,it can be concluded that low to medium level heterogeneous aquifers with a good porosity can be a suitable choice for CO_(2)storage.展开更多
文摘Studies simulating the large-scale afforestation of the African Sahel constantly find warning signals of increased risk of extreme temperatures and heatwaves resulting from changes in albedo and latent heat flow. We review the afforestation measures underlying three simulation studies, together with a restoration model in which compartments are formed by greenbelts to enable succession of savanna vegetation, protected from hot wind and drought. Savanna-like vegetation (around 20% woody plants) will show bright reflective surface and drying of leaves during dry season rather than constant green color, with very different impact on albedo and temperatures. We derive that the simulated risks of extreme heat and flooding from rain will strongly depend on species, shape and density of the new vegetation. Ecological restoration concepts are expected to mitigate or prevent such restoration related climatic risks. Compact afforestation of the Sahel does not appear to be necessary or feasible. A restoration model based on compartmentalization and the protected succession of diverse, climatically adaptable vegetation could also be used in populated drylands, as a sustainable and temperature balancing solution to desertification.
文摘Many parameters have been indicated crucial for the selection of a saline aquifer as a carbon dioxide(CO_(2))storage site.However,less attention has been given to the impact of heterogeneity on the performance of these storage media.Thus,the heterogeneity effect was evaluated in this paper by adopting a numerical modeling approach and the existing screening criterion developed for the aquifers was updated.The updated criterion for CO_(2)storage purpose would enhance the confidence level during the selection of deep saline aquifer and thus,help to address the climate change issue.The numerical modeling was carried out via CO_(2)STORE module of Eclipse300 Simulator to evaluate the effect of different levels of heterogeneity on CO_(2)storage potential.Different degrees of heterogeneity from homogenous systems to highly heterogeneous systems in the model were incorporated through the Lorenz coefficient.In this way,simulation of nine cases was carried out for three different aquifers with different porosity values.A comparison of these results showed that heterogeneity causes the aquifer to have lower storage capacity.On the trapping potential,dissolution trapping was significant and the amount of free gas in all cases was minimum.In addition,the aquifer with the highest level of heterogeneity(HLH)had a minimum fraction of residual trapping regardless of porosity.It was also found that final pressure at the end of 30 years is the same and high for low-level heterogeneity(LLH)and medium level heterogeneity(MLH)cases and low for HLH,while the injection rate stability duration is least for HLH and maximum for LLH.Based on the results obtained,it can be concluded that low to medium level heterogeneous aquifers with a good porosity can be a suitable choice for CO_(2)storage.
