Food insecurity in urban Tanzania

The urban food security challenge in Tanzania is both distinct and pressing. With an urban population that is set to more than double by 2030, so will its food requirements. Many food security challenges exist, including weak rural-urban food supply linkages, an inadequate food import budget and production constraints on the smallholder farming sector. In light of this, Tanzanian policy is aiming to improve the capacity of rural areas to meet the growing urban food demand

Strengthening the contribution of cities to growth

Strengthening the role of Africa’s urban areas as engines of growth remains a major challenge; while research can make a contribution, the focus needs increasingly to be on appropriate policies and the mobilisation of resources in support of those policie

Economies of scale, distribution costs and density effects in urban water supply: a spatial analysis of the role of infrastructure in urban agglomeration

Economies of scale in infrastructure are a recognised factor in urban agglomeration. Less recognised is the effect of distribution or access costs. Infrastructure can be classified as: (a) Area-type (e.g. utilities); or (b) Point-type (e.g. hospitals). The former involves distribution costs, the latter access costs. Taking water supply as an example of Area-type infrastructure, the interaction between production costs and distribution costs at settlement level is investigated using data from England & Wales and the USA. Plant level economies of scale in water production are confirmed, and quantified. Water distribution costs are analysed using a new measure of water distribution output (which combines volume and distance), and modelling distribution areas as monocentric settlements. Unit distribution costs are shown to be characterised by scale economies with respect to volume but diseconomies with respect to average distance to properties. It follows that higher settlement densities reduce unit distribution costs, while lower densities raise them. The interaction with production costs then means that (a) higher urban density (“Densification”) is characterised by economies of scale in both production and distribution; (b) more spread out settlement (“Dispersion”) leads to diseconomies in distribution; (c) “Suburbanisation” (expansion into lower density peripheral areas) lies in between, with roughly constant returns to scale, taking production and distribution together; and (d) “Constant density” expansion leads to small economies of scale. Keeping (per capita) water supply costs low thus appears to depend as much on density as size. Tentative generalisation suggests similar effects with other Area-type infrastructure (sewerage, electricity supply, telecommunications); and with Point-type infrastructure (such as hospitals), viewing access costs as distribution costs in reverse. It follows that the presumption in urban economics that such services are always characterised by economies of scale and therefore conducive to agglomeration may not be correct

Spatial costs in a monocentric city (and implications for agglomeration)

Using water supply as a model for a wider range of infrastructure services, the effect of a negative exponential density gradient on distribution costs is investigated for four monocentric urban development scenarios: (a) Densification; (b) Dispersion; (c) Suburbanisation; and (d) Constant density. It is shown that economies of scale in production can be outweighed by diseconomies in distribution in cases (b) and (c), suggesting that the agglomeration benefits of infrastructure cannot be taken for granted. They depend as much on the effect of density on distribution costs as the effect of size on production costs

The influence of urban form on spatial costs

There is a general presumption in urban economics that average commuting costs are increasing in city size. By analogy, it might be supposed that other spatial costs, such as distribution costs for utility services or access costs to schools and hospitals, will have the same characteristic. However, the basic commuting result derives from an urban model in which population density is uniform out to the city boundary and commuters travel individually and radially to the central business district. It is more realistic to suppose that population density declines away from the centre, as in the standard monocentric urban model and that there are likely to be scale economies in both commuting (e.g. from use of buses or metros) and distribution (e.g. larger diameter water mains). The aim of this paper is to explore the implications of such factors for spatial costs, using data on water distribution costs for 35 ?urban districts? in the supply area of one of the water companies in England & Wales. Distribution cost elasticities are quantified for two contrasting urban development scenarios, confirming that in the case of Suburbanization average distribution costs are increasing in city size, as generally assumed; however, in the case of Densification these costs are decreasing in city size. The interaction with water production costs is also considered, showing that, in the case of Densification, scale economies in production are reinforced by density economies in distribution, whereas in the case of Suburbanisation they are offset to a greater or lesser extent by diseconomies in distribution, i.e. higher spatial costs. A final section relates these findings to the literature on commuting costs, urban agglomeration and sprawl. It is concluded that high density settlement has the potential to reduce average costs in distribution (including commuting) as well as production, so that both favour agglomeration. Accordingly, urban modelers should be cautious about assuming that commuting (and other spatial costs) are always increasing in city size. JEL classification: R12, R32, D24, L95urbanisation, spatial analysis, returns to scale, water utilities