How close do we live to water? A global analysis of population distance to freshwater bodies

Abstract

Traditionally, people have inhabited places with ready access to fresh water. Today, over 50% of the global population lives in urban areas, and water can be directed via tens of kilometres of pipelines. Still, however, a large part of the world's population is directly dependent on access to natural freshwater sources. So how are inhabited places related to the location of freshwater bodies today? We present a high-resolution global analysis of how close present-day populations live to surface freshwater. We aim to increase the understanding of the relationship between inhabited places, distance to surface freshwater bodies, and climatic characteristics in different climate zones and administrative regions. Our results show that over 50% of the world's population lives closer than 3 km to a surface freshwater body, and only 10% of the population lives further than 10 km away. There are, however, remarkable differences between administrative regions and climatic zones. Populations in Australia, Asia, and Europe live closest to water. Although populations in arid zones live furthest away from freshwater bodies in absolute terms, relatively speaking they live closest to water considering the limited number of freshwater bodies in those areas. Population distributions in arid zones show statistically significant relationships with a combination of climatic factors and distance to water, whilst in other zones there is no statistically significant relationship with distance to water. Global studies on development and climate adaptation can benefit from an improved understanding of these relationships between human populations and the distance to fresh water.

Figure 1. Distance to water.

A: Average land distance to fresh water for each square kilometre of land (dw_land). B: Median distance of population to water (dw_pop) at FPU (Food Production Unit) scale.

Figure 2. Relationship between land distance to water (dw_land) and population density.

The population densities for urban, peri-urban, and rural populations are presented as lines while the total average population density is presented as bars. Note: y-axis has a logarithmic scale; global average population densities are presented with a linear scale in Figure 3.

Figure 3. Population density vs. land distance to water (dw_land) (bars) and the percentage of total population vs. distance to water (lines, differentiated between climate zones).

Figure 4. Regional results for population distance to fresh water (dw_pop) with subdivision of population groups.

Columns show the results per population class (urban, peri-urban, rural) while the total average distance to water is presented below the abbreviation of the region. The abbreviations for the regions are as follows: Au&Oc-Australia and Oceania; CAm-Central America; EA-Eastern Asia; EE&CA-Eastern Europe and Central Asia; SA-South Asia; LAm-Latin America; ME-Middle East; M&SAf-Middle and Southern Africa; NAf-North Africa; NAm-North America; SEA-Southeast Asia; and WE-Western Europe.

Figure 5. Ratio (dwr_pop/land) of ‘population distance to water’ (dw_pop) over the ‘land distance to water’ (dw_land) by FPUs (for regional results see Table 4 ; Supporting Information S2).

In areas where the ratio is smaller than 1, people live relatively close to water as the average dw_pop is lower than the average dw_land in that FPU. For areas with a ratio greater than 1, on the other hand, the opposite is the case and people live relatively far from freshwater sources. The thresholds are derived from the statistical analysis as follows: dwr_{pop /land} is between 0.5–1.3 for 95% of the cases, and between 0.8 and 1.0 in 50% of the cases (i.e. the grey values represent FPUs within this 50% interval).

Figure 6. Scatter plot of population distance to water and water availability per person.

Analysis scale is the FPU level. Total population in the matrix's nine areas is presented in the top right corner of the plot, the percentage of the world's total population is in brackets. The lines represent population distributions for the distance to water (lower x-axis, right y-axis) and for water availability (left y-axis and upper x-axis). These lines represent where large concentrations of people are present. Note: the left and lower axes have a logarithmic scale.