WEATHER AND WATER IN CITIES

The theme is indeed appropriate and timely, given the enormous pressure which the rapid rate of urban population growth is exerting on the environment and on the dwindling finite resources of our planet. The process of urbanization is illustrated by the fact that the total world population in 1950 was some 2.5 billion people, of whom about one-third lived in cities. By the year 2000, almost half the world's projected population of 6.2 billion will be living in towns and cities. The ratio is expected to increase to two-thirds by the year 2025. Alongside this increase is the emergence of mega-cities; these will be greatest in developing countries, where some 80 per cent of the world's urban residents will live. The implications of environmental changes for cities were addressed during Habitat II, whose Habitat Agenda reflects the priority issues to be addressed, such as natural disasters, availability of freshwater, environmental pollution and climate change.

One of the most serious threats to cities is the occurrence of natural disasters. In addition to natural catastrophes such as earthquakes, weather-related phenomena such as tropical cyclones, floods, droughts, landslides and locust infestations, result in loss of life and property and cause severe economic disruption. Statistics show that extreme meteorological and hydrological events account for about 70 per cent of all natural disasters. City dwellers are increasingly vulnerable to these extreme events, in view of the high population density and settlement in flood-prone marginal lands. When natural disasters strike a country, they can set the development of urban centres back several years. In the recent past, floods and tropical cyclones have caused enormous devastation and have inflicted considerable human suffering. For instance, in the USA, in 1993, the Mississippi floods caused damage estimated at more than US $10 billion and had serious repercussions on city dwellers along the river basin. The floods in Egypt in 1994 resulted in damage estimated at several hundreds of millions of US dollars. In the Philippines, in 1995, tropical cyclone Angela took 915 lives and caused some US $452 million of damage as it crossed populated areas, including the capital, Manila. It is worth noting that the construction of buildings and paved surfaces has a dramatic effect on the patterns of flooding following heavy rains. Most of the water remains on the surface to run off as minor and sometimes major floods. Even small streams can turn into raging torrents when they escape through old, inadequate drainage channels. What were once small, innocuous streams have been the origin of some of the most destructive floods of modern times in urban areas.

In order to mitigate the impacts of natural disasters, the International Decade for Natural Disaster Reduction (IDNDR) was launched by the United Nations in 1990. In the context of the Decade, WMO plays a key role by implementing its Plan of Action which places high priority on the enhancement of the capabilities of the national Meteorological and Hydrological Services(NMHSs) through programmes such as the World Weather Watch, the Education and Training Programme and the Technical Cooperation Programme. WMO supports the strengthening of disaster preparedness schemes through improved monitoring and warning systems, risk assessment, technology transfer, public information and training activities.

The effects of urbanization also have serious environmental impacts, including the availability of freshwater resources. The global demand for water has increased dramatically over the past century. Between 1900 and 1995, water withdrawal from existing sources has increased more than six-fold. This increase is more than double the rate of population growth during the same period. The demand is a result of increasing irrigation, urban agriculture, industrial growth and rising water consumption per capita for domestic and sanitation purposes.

In this regard, it should be noted that a significant proportion of urban dwellers, particularly in developing countries, have limited or no access to a safe, potable water supply. Estimates put this figure at 16 per cent worldwide, 21 per cent in South-East Asia, 22 per cent in the eastern Mediterranean and up to 48 per cent in Africa. Another problem is that, as cities expand, so do their water requirements, and it becomes more and more difficult and expensive to meet this demand, to the point that water rationing is being introduced in many cities. Furthermore, pressures of population growth require the transport of water from distant locations at high cost. Urban development is driven by socio-economic and strategic forces which often have little to do with the resources required. History has shown, however, that the provision of water resources can determine whether or not a city will flourish.

This is why cities which lack fresh water because of frequent droughts need to develop appropriate water monitoring and drought-relief capabilities. The impact of recent droughts on large urban areas in various parts of the world is further evidence that droughts are not just a rural problem. With continuous improvements in climate research and prediction, it is now possible to provide some warning in advance of the onset of such extreme weather events.

In cases where the available water supply is limited, competing demands sometimes lead to confrontations between individuals and among authorities within a country and between States. In recognition of this fact, it is incumbent on all nations to put in place an appropriate mechanism that will ensure the monitoring and effective management of water resources. The Rhine River Basin, which could be regarded as a kind of megacity, is an example of how water resources could be well managed for the benefit of millions of people.

Another factor which determines the sustainability of cities and poses an increasingly serious dilemma to urban planners, is the disposal of solid and liquid waste. In cases where cities dispose of their waste in rivers and lakes, some of it seeps into groundwater aquifers, resulting in disastrous pollution and health consequences for downstream communities.

Through its Hydrology and Water Resources Programme, WMO promotes the enhancement of the scientific and technological capabilities of NMHSs to monitor, assess and manage water resources. In this regard, a major initiative, jointly embarked upon by WMO and the World Bank, is the World Hydrological Cycle Observing System (WHYCOS). The system is being developed in several subregional components in order to improve our knowledge of the world's water resources. In response to a call by the UN Commission on Sustainable Development, a comprehensive assessment of global water resources aims to identify the availability of the resource, make projections of future needs, and propose appropriate solutions. WMO plays a key role in this endeavour and is one of the lead agencies in this exercise, which will be considered by a special session of the UN General Assembly in 1997.

In many ways, the well-being of city dwellers is also affected by the changing local climate generated by urban infrastructures. These infrastructures should be appropriately designed and energy-efficient in order to improve the urban climate. This includes the opening of urban corridors and the utilization of nocturnal downslope winds. Adapting buildings to the urban climate, using climatological information available from the national Meteorological Services, helps to provide the comfort needed by urban dwellers. It is well known that the weather in a city may be quite different from that in the surrounding countryside. This mainly man-made "local climate" might manifest itself in "urban heat islands", involving changes in wind, temperature, humidity, precipitation and radiation balance, together with various atmospheric pollutants, such as high levels of troposphericozone, chemical gases in the form of smoke from motorized traffic and effluents from industrial stacks. The resulting impacts include increased heat stress and other health hazards. In the context of its activities relating to the meteorological and climatological aspects of the urban environment, WMO places emphasis on the development and implementation of the Tropical Urban Climate Experiment (TRUCE), in cooperation with national and international organizations.

One aspect of urbanization which relates more closely to the linkages between cities and neighbouring rural areas is the problem of local pollution and acidification. Urban areas are major sources of various types of emissions, such as carbon dioxide, carbon monoxide, sulphur dioxide, nitrogen oxides and aerosols, and their environmental influence reaches far beyond the limits of the urban area itself. Various types of acidifying pollutants are transported downwind from conurbations and contribute to both dry and wet deposition on sometimes sensitive soils and waters. Their impact on lakes and on agricultural production in particular, may, in some cases, be disastrous. There may also be deleterious effects on forests. In turn, these effects will have an impact on water and food supply, and fuelwood needed by the urban population.

A major issue relating to atmospheric pollution is the intensive use of energy in urban areas. This contributes significantly to the emissions of greenhouse gases into the atmosphere. The Intergovernmental Panel on Climate Change warns that, if no measures are taken to reduce such emissions, an increase in global mean temperature of about 1°-3.5°C and a sea-level rise of 15-95 cm are expected before the end of the next century. For coastal cities and low-lying areas, such a rise will have serious consequences for human settlements, agriculture, biodiversity, coastal erosion and saltwater intrusion.

WMO, as the authoritative scientific voice in matters relating to the atmosphere, climate and water, is playing a leading role in international efforts to monitor and protect the environment through its scientific programmes such as the World Climate Programme, the Atmospheric Research and Environment Programme and the Hydrology and Water Resources Programme. Through its collaboration with other UN agencies and the NMHSs of Member countries, WMO continues to support relevant conventions such as the UN Framework Convention on Climate Change, the ongoing negotiations on the International Convention to Combat Desertification and the Vienna Convention on the Protection of the Ozone Layer and its protocols and amendments. These activities contribute towards ensuring the well-being of nations.

The theme "Weather and water in cities" for World Meteorological Day 1997 provides everyone with an excellent opportunity to consider the important contributions that are being made by WMO, in conjunction with the NMHSs of Member countries, towards sustainable urban development and towards the protection of life and property in cities, as well as in rural areas. On this auspicious day, I urge policy-makers, partner organizations and the general public to recognize the valuable services provided by the NMHSs to ensure the survival of the world's cities and of our planet Earth.