Impacts and Solutions

Professor James C.I. Dooge
Centre for Water Resources Research
University College Dublin

The advances in simulating future climate change by global climate models over the past two decades has reduced many of the original uncertainties in relation to this problem. The problems of estimating the impact of such change on the hydrological cycle present even greater difficulties. Only when these are overcome can we tackle with hope of success the still greater problems of reducing these impacts.

Our planet is unique because of the abundance of liquid water which provided the environment for the emergence of life and the development and maintenance of human society. If the earth were five per cent closer to the sun, water could only exist in its hydrosphere as water vapour; if the earth were five per cent further from the sun, water could only exist in its hydrosphere in frozen form. The fact that the average global values of temperature (15^o Celsius) and pressure plot close to the triple point of water on the phase diagram of water together with the natural variation of temperature with latitude, ensure the existence of a vigorous hydrological cycle involving water vapour, liquid water, and frozen water.

This behavior of water has been observed and studied over the past three millennia. The early Greek philosophers discussed the question of the balance between the net evaporation (evaporation minus precipitation) over the ocean and the net precipitation (precipitation minus evaporation) over the land. They were firmly of the opinion that the net precipitation on land was insufficient to supply springs and rivers and concluded that water must pass through the ocean floor and be raised within the hills and mountains by some mechanism to provide water for springs. Leonardo da Vinci a thousand years later compared this process to the rising of sap in plants and the circulation of blood in the human body. The fact that precipitation over land was sufficient to provide the runoff of springs and rivers was established gradually only in the 17th and 18th centuries.

The hydrological cycle of rainfall, runoff and evaporation does not exist in isolation. The interaction at various time scales between the hydrological cycle and the cycle of erosion and sedimentation has long been recognised. More recently the study of the geo-chemical cycles of carbon, nitrogen and sulphur has revealed the importance of their linkage to the hydrological cycle. These three cycles (hydrological, erosional, geo-chemical) can be considered as part of a general geosystem which interacts in turn with the regional socio-economic system. Population growth and economic development combine to increase the demand for water of good quality. At the same time, these two factors also combine to impact the geosystem in such a way as to reduce the supply of unpolluted water. The continuation of these two tendencies in the future will produce water crises of unprecedented magnitude.

There have been a number of important international conferences and statements on climate impacts and water resources over the past ten years or so. In 1989 the Helsinki University of Technology organised the First International Conference on Climate and Water and in 1990 the First Assessment Report of the IPCC contained some comments on the impacts of climate change on the hydrological cycle. In January 1991 the International Conference on Water and the Environment (ICWE) organised by the specialised agencies of the UN concerned with water was organised in Dublin and provided the input on water to the UN Conference on Environment and Development (UNCED) held in Rio later that year. The ICWE agreed a statement on Water and Sustainable Development based on four guiding principles:

(a) the need for a holistic approach to the development and management of water resources;

(b) the need to base such development and management on a fully participatory basis;

(c) the need to recognise the pivotal role of women as providers and users of water; and

(d) the recognition of water resources development as an economic good subject to the basic right of all to access clean water at an affordable price.

The impact of climate change on water resources was dealt with in more detail in the Second Assessment Report of the IPCC issued in 1995 and in the Report of the Second International Conference on Climate and Water held at Espoo in 1998. The latter Conference made a number of recommendations concerning:

(a) research priorities (data networks, problems of scale, need for interdisciplinary dialogue);

(b) research management (large scale land-surface experiments, advanced planning for remote sensing, communication with decision makers and the public);

(c) project design and management (effect of climate change, broad dialogue on practical operational problems, conflict resolution on water issues); and

(d) policy formulation (national planning based on up-to-date information, respect for local culture and level of development, involvement of all stakeholders at an early stage).

Though water as a colourless and odourless liquid appears to our senses to be the simplest of substances, many of its properties are quite strange. Its anomolously high boiling point ensure the presence on our planet of huge masses of liquid water; its anomolously high surface tension prolongs the retention of soil moisture during droughts; its anomolously high dielectric constant makes it an almost universal solvent of both nutrients and toxins; the anomolously high values of latent heat, thermal conductivity and specific heat all combine to enhance greatly the role of water as a climate modifier through the atmospheric circulation of water vapour and the oceanic circulation of liquid water.

To understand the role of water in climate completely would require exact knowledge of its behaviour over a range of 15 orders of magnitude from the water molecule (10⁷ millimetres) to the grid scale of a general circulation model (10² kilometres). This covers the domains of physical chemistry (10^-7 to 10^-2 millimetres), fluid mechanics (10^-2 millimetres to 10^-2 metres), physical hydrology (10^-2 metres to 10² metres), regional and global hydrometeorology (10² metres to 10² kilometres). Certainty has not been achieved in the study of water at these diverse scales and hence certainty in predicting the precise nature of climate change and its impacts is not at present possible. But common sense tells us that certainty is not necessary in many important decisions. Suppose our doctor tells us that he strongly recommends us to give up smoking and hard drinking. If we ask "can you guarantee that if I don’t give them up I will be dead within a year?", his reply would be "I cannot guarantee that but it will shorten your life and if I were you I would give them up immediately". We use the precautionary principle in many personal decisions. We should not hesitate to use it in the case of climate change.