Question

How does population density act as a function of distance to water? How does climate influence how close people live to water?

Answer 1

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.

Access to freshwater is of crucial importance to humans. Traditionally, people have inhabited places close to rivers or lakes to ensure water supply for several purposes, including household water supply and water for agriculture and livestock . Human population has increased rapidly during the past century, from 1.6 billion in 1900  to 6.9 billion in 2010.Over the same period, the percentage of the global population living in urban areas has increased from around 16% in 1900 (i.e. 0.3 billion people)  to over 50% in 2010 (i.e. 3.5 billion. Over time, the relationship between human populations and freshwater bodies – and the direct dependence of humans on them – has changed, due to physical (e.g. pollution of water bodies), socioeconomic (e.g. increased population, urbanisation, and economic development), and cultural (e.g. aesthetic preferences and traditional habits) factors .

It could therefore be argued that today, in many parts of the world, the geographical distance to a freshwater source is not as vital for everyday survival as it was in the past. Recent technological developments have made it possible to pump groundwater from hundreds of metres below the ground and to convey it over long distances at reasonable cost through pipes and canals. In addition, water can be purified efficiently and desalinisation is increasingly carried out in variou.s arid area.

However, despite these technological developments, which have ensured clean water supply for large numbers of the world's population, over 800 million people still live without improved sources (as in the WHO definition) of drinking water  This development deficit is in part due to lack of investments required to implement such measures  either due to a lack of financial resources or other factors such as lack of institutional capacity, political will, and war. Hence, almost one billion people collect their water from distant, unprotected source; for these people the geographic distance to water bodies is still of vital importance. For many others, who are supplied with clean water, the proximity to rivers and lakes remains an important issue for aesthetic, cultural, and other reasons  A short distance to water is, however, not always a positive factor. For example, in flood-prone agricultural areas (such as the Lower Mekong floodplains and large parts of Bangladesh), annual flooding may be essential for agriculture and fisheries, but living too close to the river can make populations vulnerable in the event of an extreme flood .

Many of the key factors that enable a good supply of water are unevenly distributed among the global population, such as: wealth  human population and water resource availability  Densely populated areas often do not overlap with areas that are water-rich  This population pressure is projected to increase further in most countries and the changing climate is also expected to increase the pressure on water resources in the future . Hence, there is an increasing recognition of the need to adapt to these changes in both socioeconomic and physical drivers  Global studies on climate adaptation and development would benefit from an improved understanding of the relationship between human populations and the distance to freshwater.

However, to the best of our knowledge there are no such comprehensive assessments of relationships between human populations and the distance that they live from freshwater bodies. This is despite the availability of high resolution population density datasets which have, in recent years, led to advances in studies examining other factors responsible for the geographical distribution of people around the globe. Examples of such factors include: urban centres sea coast, volcanism and biodiversity .

Major factors influencing distance to water

We found clear regional differences in the distance to which human populations live from water, with people living closest to water in high northern latitudes and parts of the tropics, due to the abundance of many rivers and lakes. Interestingly, whilst the population distance to water is generally highest in arid regions, the relative distance to water (i.e.dwrpop/land) is lowest in these regions.

There are also large differences between the different types of population groups (urban, peri-urban, and rural). Our results clearly show that, on a global scale, population density is not greatly affected by dwland in urban and peri-urban areas, whilst in rural areas there is a clear decrease in population density as thedwland to freshwater increases ). These global findings mask important differences between regions. We have shown that in most regions, the dwpop for urban populations tends to be rather similar to the dwpop for rural populations. However, interesting differences are found in the Middle East and North Africa, where urban populations live significantly closer to water than rural populations, and in the Americas, where urban populations live further from water than rural populations. This could be related to the fact that large cities of the Americas developed much later than many of the major cities in the old world, by which time means of transporting water from source to consumption point were more advanced.

The most distinct difference in median between population classes can be seen for North Africa, where the  in rural areas is more than the double that in urban and peri-urban areas This may be because in this (mainly) arid region, water bodies are more limited, thus increasing their attractiveness for human settlement, and resulting in urban areas close to them. In addition, the region contains many ancient cities where proximity to fresh water was essential for the founding of large settlements. Also, in the present day the GDP of many countries in this region is relatively low meaning that high costs of water transport may make it financially prohibitive to locate cities far from freshwater bodies. On the other hand, rural populations in this region appear to live relatively far from freshwater bodies; this could have several causes. For example, in response to the arid conditions of the region, agricultural practices may have evolved to be able to make use of rainwater harvesting techniques and ground- or soil-water sources. Moreover, there are large numbers of ephemeral streams and wetlands in the region, which may be essential for rural communities. However, ephemeral water bodies and ground- or soil-water sources are not included in our analysis.

Implications for adaptation and management

Global studies on climate adaptation and development can benefit from an improved understanding of the relationship between human populations and the distance to freshwater. For example, global estimates of the costs of adapting to climate change in the water supply sector  have so far used decision rules on preferred adaptation options based on water availability and cost. However, such rules could be improved by incorporating spatial patterns of the distance of human populations from water. For example, in regions where people live far from surface water bodies, adaptation based on water transport may become prohibitively expensive, and groundwater use or rainwater harvesting may be more effective and/or efficient.

In this study, we have shown that populations in arid zones tend to live the furthest from freshwater bodies in absolute terms. On average, people in Northern Africa and the Middle East live furthest from water, and this is especially the case for rural populations in North Africa. Hence, when estimating global adaptation requirements and costs one must consider that long-distance transport of water from reservoirs may not be feasible in the latter. Also, between similar regions, the ability to adapt is related to financial means; in more affluent arid regions those means may be more readily available for implementing such systems, whilst in less-affluent regions a focus on smaller scale activities such as rainwater harvesting may be preferential.

Our results also show large regional differences in distance to water between urban and rural populations. Again, this is important to consider in planning integrated water management and adaptation measures as water requirements differ between urban and rural areas; globally aggregated estimates may mask these important differences.

Several studies have also shown that in many parts of the world, river runoffs, and thus water availability, are significantly related to different forms of interannual climate variability This should also be considered when designing measures for water supply; especially those people directly dependent on a distant freshwater body can be severely impacted if water availability is decreased in a given year (or several years) due to such variability.

With our analysis, we hoped to provide additional information related to ‘access to safe drinking water’, which is one of the assessment measures used by WHO (World Health Organisation). The definition of WHO changed, however, after year 2000 from ‘access to clean water’ to ‘access to improved drinking-water source’ Thus, rivers and streams are excluded from the new definition. We do believe, however, that rivers and streams are important in many ways for those 13% of the global population without access to improved drinking-water sources and also to people who obtain their drinking water from secured sources but do use unimproved water sources for activities such as the washing of laundry. Thus, our results and methodology could be useful for further analysing the situation of populations in countries with poor access to water. Our results also identify regions where extra attention may already be needed to supply water given the physical shortage and relatively long distance to surface freshwater sources.

Future research needs

The limitations of this study, discussed in the materials and methods section, give a pathway for future research needs in distance to water calculations.

The inclusion of small streams, local surface waters, springs, ground water sources, and ephemeral water bodies (including wetlands) in the calculations could better reflect the relationships between populations and fresh water, particularly in rural areas. In the present study, those water sources were excluded from the analysis due to poor data availability, but they should be included in future global analyses as soon as appropriate global datasets become available.

Water quality is also an important factor in the relationship between population and water. Poor water quality may decrease the usefulness of water, even if water would be at a close proximity, for example in many densely populated or industrialised areas. A global dataset of water quality could allow us to exclude polluted freshwater bodies from the analysis.

In this study we were not aiming to separate cultural or economic factors from physical factors when analysing distance to water. Naturally, in some parts of the world the distance to water is much more crucial for survival in everyday life, while elsewhere it may have a more aesthetic, cultural, or recreational value. More detailed analysis of these different ‘values’ of water would be an interesting addition to the work presented here. Furthermore, rapid population (and economic) growth and urbanisation have probably changed the relationship between water and human populations. Thus, an historical analysis of how the distance to water has evolved could reveal interesting regional trends. If you are not satisfied with my answer then plzz comment plzz don't down vote plzz comment my CF score is not good.