In the pavement industry, the majority of the materials used for construction, which are primarily composed of gravel, sand and crushed stone, are relatively local materials, unless there is access to water transport. An exception is specialized engineered materials/chemicals such as admixtures and additives. Figure 8 shows the order in which user input/selection is required before the tool outputs a comprehensive summary data of different commodities in tons, ton mile and/or dollar costs in tabular form. In this white paper, examples of domestic flow types are presented. Within the domestic flows, seven tables are presented that require user input. Each table has a drop-down list to select from. The CFS data is being collected every five-years since 1997. Data were also collected for the years 2013, 2014 and 2015. Additionally, users can extract future projection data based on macroeconomic forecasting model starting from 2020 to 2045 for every five-year interval . The origin and destination can be at the country, state or city level. The city and state boundaries in FAF4 are defined as FAF zone specific and the 132 domestic zones are a hybrid of core-based statistical areas that have been defined by the office of management and budget and state boundaries . As noted in the introduction, modeling of climate change indicates that the intensity of rainfall during extreme events will increase significantly, with the amounts depending on the extent of continued human contributions to greenhouse gases . Increased urbanization is one of the factors that has affected urban flooding and storm water runoff due to development in the flood plains and construction of impervious hardscapes. Figure 9 through Figure 11 show qualitatively how degrees of average perviousness of urban surfaces affect storm water runoff,vertical grow shelf infiltration and evapotranspiration.
The Environmental Protection Agency Storm Water Management Model is a simulation program which can perform dynamic rainfall-runoff modeling . The simulation can be conducted for both a single event or over a longer period of time and the program can analyze quantity and quality of runoff from different urban regions. The SWMM model works based on an assembly of sub catchment regions in which precipitation is received and runoff is generated. SWMM then uses simulation of a combination of pipes, storage devices, pumps and regulators, to model transport of this runoff. SWMM can record the quality and quantity of generated runoff in each of these sub catchments. It also can calculate the flow rate, flow depth and quality of water in pipes and channel sections for the duration of simulation. The hydrological processes that can be simulated in SWMM include evaporation, snow accumulation, infiltration, percolation of infiltrated water, water inter flow between groundwater and drainage system, etc. To overcome spatial variability in all these processes, the actual area of interest is divided into smaller sub catchment regions in which the hydrological properties are homogenous. Then, the overland flow can be dispelled between sub catchments, drainage systems or sub-areas. SWMM is also capable of analyzing runoff pollutant loads under different conditions such as dry-weather pollutant buildup, pollutant wash-off during storm incident, contribution of rainfall deposition, and reduction of concentration due to water treatment. The UM-LCA framework developed for this study aims to build a foundation for future assessments of alternative types of urban hardscape. Using materials such as pervious concrete, permeable pavers and porous asphalt and designs for construction of permeable pavements that allow the storm water to pass through the structure into the ground water table is one way to reduce storm water runoff through infiltration and detention, which also increases groundwater recharge and can help improve storm water quality. The water cycle can be quantified using the SWMM model.
SWMM provides additional capabilities relevant to urban hardscapes. There is an additional section called Low Impact Development which defines the properties of low impact technologies such as the permeable pavements. LID is an approach that manages storm water on-site by sustainable land planning and engineering design practices i.e., use of recyclable materials, permeable hardscape designs, and in-place recycling are some of the example practices. The LID module in SWMM includes the following technologies: bio-retention cell, porous pavement, infiltration trench, rain barrel, and vegetative swale. The Atmosphere Compartment contains climate information which determines how much precipitation LID will receive. The Land surface Compartment contains information about LID’s area.The Ground Water Compartment depends whether the LID allows storm water to recharge ground water. For example, the green roof conveys storm water into the drainage pipes and the water does not infiltrate into the ground directly. Therefore, in this case the Ground Water Compartment can be omitted. However, use of Ground Water Compartment is necessary if a structure, such as permeable pavements, allows water to infiltrate into the groundwater table. The climate information and rainfall are required for almost all the SWMM simulations. The data can be collected from National Climatic Data Center . The information about the modelled area is also one of the required inputs. As mentioned earlier, SWMM divides the defined area into several sub catchments according to the land usage . The properties of the subcatchment are: ’X-Coordinate’ and ’Y-Coordinate’ which defines the location of the sub catchment area on the map, ‘Area’ which shows the size of the sub catchment, and ’Rain Gauge’ which determines the duration and intensity of the rain.
The following are input parameters that are used in the LID module: surface layer, pavement layer, storage layer, under drain layer, and subgrade layer. After completion of the analysis, LID provides the following outputs: total inflow volume, total evaporation loss, total infiltration loss, total surface outflow, total under drain outflow, initial storage volume, and final storage volume. These outputs are available for any analyzed time step and can be viewed on the map in the program, tabulated or plotted for the further statistical analysis. Several data sources have been determined that can be used in the SWMM model as inputs. Data from cities in California was taken as an example to illustrate what type of information can be extracted from the sources reported in order to run the SWMM model. The following sources can be used to collect the information of the rainfall and climate for cities and regions in the U.S.Zimbabwe’s economy depends heavily on tobacco. There is concern that global efforts to reduce tobacco use may reduce demand for tobacco and significantly affect Zimbabwe’s economy and tobacco exports. Global tobacco demand has recently been stable or falling very gradually. However,vertical hydroponic public health efforts to reduce demand are offset by aggressive cigarette marketing, rising population and incomes, and the strongly addictive effects of nicotine. But tobacco prices have softened, and the long-term prospects are uncertain. Governments concerned about the future of tobacco are considering diversification options and strategies to develop other high-value crop substitutes . The world’s fourth largest flue-cured tobacco producer and the largest producer of tobacco leaf in Africa, Zimbabwe exports 90 percent of its raw tobacco and has typically earned around USD 600 million in foreign revenue annually, equal to almost 10 percent of GDP, 30 percent of total exports and 50 percent of agricultural exports. Moreover, 250,000 people or 5% of Zimbabwe’s total labor force are engaged in tobacco-related work including tobacco farming, manufacturing and retailing. Most tobacco in Zimbabwe is grown by large-scale commercial farmers, who account for about 87% of the land under tobacco and 95% of the total crop. This study compares the financial costs and returns to tobacco with twelve alternative crops, looking at profitability, costs, labor intensity, financial support, technical infrastructure, land-suitability, marketing difficulties, world demand, and production risks. The information may be useful to agriculturalists and government officials who are interested in exploring the potential for diversification by different sized farmers, as Zimbabwe considers options for the future. The study aims to provide an improved understanding of the trade-offs individual growers face in deciding what crops to grow. The analysis is based on an original set of 91 production budgets estimated in January 2001 specifically for this study, that estimated financial costs and returns in Natural Region II at the time. It should be noted that in 2000/2001, veterans of the independence war occupied several commercial farms and Government subsequently gazetted over 5,300 farms for compulsory acquisition and resettlement. This study took place before the impact of these events on agricultural output was evident, and does not address whether and how they might affect tobacco farming and its contribution to the economy of Zimbabwe. The study shows that tobacco is a highly profitable cash crop for both large and small farmers, generating direct income for large-scale farmers, and indirect income for smallholder farmers.
Dramatic changes in prices and yield are unlikely in the near future. And tobacco would remain relatively profitable, even if prices fell considerably. Farmers in Zimbabwe are aware of the risk of depending on one cash crop and have begun diversifying to lessen their tobacco dependence. Large scale commercial farmers have diversified into coffee and paprika, and horticultural crops – notably roses and supermarket vegetables- using their tobacco profits. These products can be grown in the same soil as tobacco, and generate high profits as well as employment opportunities. The study discusses the limitations of these alternatives, and notes that despite some rapid increases in some crops , they are still grown at a very limited scale compared with tobacco. Tobacco is one of the most profitable cash crops for both large-scale commercial and smallholder farmers. The study shows that tobacco would provide good financial returns even after a large drop in yield or price. Tobacco is likely to remain a very attractive crop for all categories of farmer even under progressively difficult market conditions. There are around 2,000 large-scale commercial tobacco growers, and 16,000 tobacco growing smallholder farmers – less than 1.5% of all smallholder households. Most smallholders grow only very small amounts of tobacco, in part because few smallholders have land that is suitable for intensive farming of tobacco. Even for farmers in suitable agro-ecological areas, however, tobacco is expensive to grow, with high up-front costs that smallholder farmers may not be able to cover. For example, high costs of production of flue-cured tobacco are a barrier to most cash-poor smallholders in tobacco areas. The financial incentives to smallholder farmers with the appropriate land to grow tobacco are, however, strong with the relative returns to cash and labor considerably higher than for most other crops. Most commercial farmers already have diversified sources of income, and have introduced various high-value crops including export roses, supermarket vegetables, paprika and coffee as part of their farm system, specifically to lessen their dependence on tobacco. As with all business decisions, the challenge for farmers is to find the right blend of crop enterprises that works best for them. Beyond the enterprises covered here, for example, the study indicates that, other than the crops discussed in the study, many other niche products also offer diversification potential for smallholder and LSC farmers including mushrooms, flower seeds, medical plants and spices. Citrus crops, including oranges, grapefruit and lemons are an important diversification option with more than 88,000 hectares of orchards planted on LSC farms as of 1999. Game ranching on LSC farms has been another popular diversification activity and can provide an important source of supplemental income. One of the main arguments against measures to reduce the demand for tobacco is the worry that falling demand will cause job losses in the farm sector. Tobacco is a good source of indirect income for smallholder farm households with family members who work as wage-laborers on large-scale commercial tobacco farms. Simple calculations suggest that the total wage bill for tobacco grown on LSC farms is around USD 47.3 million. To the extent that a share of this income is sent as remittance payments to family members in communal areas, tobacco can play a major role in helping to finance the inputs needed for improved management of major smallholder crops including maize and cotton. In countries where most of the tobacco crop is consumed domestically, expenditure switching will create demand for other goods and services, and employment gains in these other sectors are likely to offset the losses in the tobacco sector.