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Land-water linkages: A synopsis

MAN AND LANDSCAPE

Man depends on access to water in the landscape for several parallel functions. These include human and community health and well-being; biomass production; other forms of socioeconomic production; the maintenance of habitats for ecological protection; and the transport of soluble and solid materials such as nutrients, pollutants and sediments. The water passing through a landscape is influenced by human activities in that landscape, and may therefore present problems which must be anticipated and met by mitigating measures.

Water may sustain land use but may also be a constraint on land use and socio-economic and biomass production. At the same time, land use influences water characteristics by its partitioning of incoming rainfall between the vertical return flow to the atmosphere as evaporation and evapotranspiration, and the horizontal flow to aquifers and rivers (here classified as "blue water"). The various functions listed above, related to human activities, also affect both physical and chemical characteristics of water, as shown in Table 1.

For his use of natural resources, man must manipulate the landscape that contains them. Natural laws operating in that landscape produce side effects, often designated as "environmental impacts". For instance, changes in land use alter the two "joints", or boundaries in the soil profile that determine the partitioning of incoming water. The first of these boundaries, at the soil surface, serves as a division between flood flows and infiltration. The other, in the root zone, is a partition between the "green water" accessible in the root zone, later to be used in plant production, and the surplus water that flows on to recharge aquifers or other water bodies.

MAN'S INFLUENCE ON THE WATER CYCLE

The effects of human activities are propagated throughout the water cycle, from atmosphere to land, to groundwater and rivers, to lakes and coastal waters. Basically, man practices three types of disturbing activities. These relate to:

• waste handling, which results in sending pollutants to the atmosphere;

• manipulation of land and water systems to meet the needs of biomass dependence;

• manipulation of land and water systems to satisfy water dependence needs.

The influence of these interventions cascades through the water cycle, producing secondary effects on terrestrial, aquatic and marine ecosystems, and thus on the sustainability of the environment and of natural resources development and management. However, the resulting problem profiles are quite different in different hydroclimatic regions, both in the occurrence and the weight, or severity, of the problems generated (see Table 2).

TABLE 1. Effects of human action on physical and chemical water flow determinants

TABLE 2. Sustainability problems in different hydroclimates

Degree of problem severity: * higher, o lower.

Problems of water over-use and under-use can occur simultaneously, for example in different parts of the water cycle, e.g. "green" and "blue" waters.

LAND-WATER LINKAGES

To preclude unexpected problems through land-water linkages, there must be an integrated approach to land use and water. The integrity of the water cycle makes the river basin, or catchment the appropriate spatial unit for such integration, as decisions on upstream land use also effectively equate to decisions on downstream water resources, reflecting upstream-downstream interdependencies.

Conventionally, there is a dichotomy between land use and water resources. This is apparent even in UNCED Agenda 21, where land use and freshwater chapters show little appreciation of water related phenomena as determinants of land use, or of land use practices as determining water pathways, water flow and water quality.

This Workshop on Land and Water Integration and River Basin Management is therefore faced with the challenge of stimulating a shift from that conventional dichotomy toward acceptance of the concept that land is a system transitted by water, and thus the use of land is dependent on access to water, while at the same time the land use also influences the pathways, seasonality, yield and quality of the water during its passage.

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