Rafi Ahmad, Contributor
HISTORICALLY, recurrent natural disasters have overwhelmed the economy, infrastructure, and social fabric of Jamaica. The indirect costs are several orders of magnitudes higher than the direct costs. It is rather unfortunate that Jamaica's economy takes a step forward only to be pulled two steps backward by natural disasters.
Land resources in Jamaica are finite and quite often there are serious inherent constraints on land use. These, coupled with abundant active hazardous geological processes, profoundly affect the lives of Jamaicans both directly and indirectly. Yet we sometimes tend to proceed "as if fully confident of our ability to undo any damage that we inflict on land, secure in a mistaken belief that the land can meet all of our desires and remain all that it was". Natural active geological processes operating at the land surface both make human life possible and also pose a threat to that life.
Jamaica's mountainous terrain, its geology, being dominated by fractured, altered and deeply weathered bedrock, abundance of colluvium on hill slopes, high, often intense, precipitation due to tropical storms, its geophysical location astride seismically active plate boundary fault zone, all combine to make the island particularly susceptible to multiple hazards. Active geological processes, together with high urban population densities, many on marginal lands, make Jamaica one of the most environmentally sensitive regions in the world. Natural hazards and disasters have played a major role in shaping the communities which have suffered through them, particularly those in the low-income and rural groups.
Jamaica has a population density of 225 persons per square kilometres and 18,197 km of roads with a density of 1.6 km of road per sq. km. Anthropogenic activities have extensively interfered with the natural slopes during the last 400 years and the trend continues with new development encroaching on potentially unstable slopes. In rural Jamaica, population centres and agricultural farms are located along roads. Except for high hills, every human settlement is within a distance of some 1.5 km from a motorable road. The hub of the economic and social activities for the inhabitants is the road network. It is therefore important that the integrity of road networks be maintained. A number of maps and tables are included here to illustrate the effects of landslides on roads and also the seriousness of the problem. How road building affects stability of the adjacent slopes will be presented in a separate article.
Agriculture is a major economic activity utilising some 47 per cent of the land. However, over the last four decades the economy of Jamaica has expanded from an agricultural base to one that relies heavily on tourism, manufacturing, mining and diverse types of services. As a consequence, land use in Jamaica is changing rapidly in order to meet the economic and housing needs of the populace which must utilise hazard-prone geologically young landforms and steep slopes.
ROAD DEVELOPMENT
In order to meet the needs of the populace and to promote sustainable economic growth, Jamaica has embarked upon a major programme of building new roads, e.g. Highway 2000, and rehabilitation and maintenance of islands road network.
Human actions often increase the risk of landslides and flooding by modifying the landscape, building on unstable slopes, on small fans at the base of hill slopes formed by landslide debris, and in the path of debris generated by landslides. It appears, based on the reports in the news media in the wake of current disaster, that many of us are completely unaware of our exposure to landslide risks and debris fan flooding.
LANDSLIDES AND FLOODING
Natural hazards that affect Jamaica most frequently are landslides and flooding, which account for most of the natural disasters that have occurred on the island during the last two decades. These hazards are important because of their frequency, associated loss of life, disruption of socio-economic activities and their effect on the built and natural environment.
Our analysis of data on recurrent natural disasters in Jamaica unambiguously suggests a high landslide vulnerability and risk. Debris flows and mudflows along with alluvial fan flooding are the cause of most of our problems. Moreover, new development is constantly taking place on slopes prone to debris flows and on debris fans prone to flash flooding.
Landslides are a very costly hazard and are triggered by both rainfall and earthquakes. Earthquake-induced landslides pose a serious threat to citizenry and infrastructure.
Cumulative direct and indirect economic cost and social impact of Jamaican landslides cannot be quantified due to lack of information and also much of the damage remains undocumented. Since landslides and floods occur simultaneously, damage due to landslides is often misleadingly ascribed to damage from floods. Costs, however, are undoubtedly high.
During the period 1910-1965, some 7.3 per cent of the total expenditure of the Public Works Department accounted for damage repair costs related to landslides and flooding. This trend continues and present-day landslide costs are much higher as vulnerability has significantly increased. It has been estimated that throughout the Caribbean some US$15 million are spent annually to repair landslide damage to roads.
Hazards that affect the island most frequently, however, are debris flows and alluvial fan flooding and account for most of the disasters that have occurred on the island during the last decade and continue to present recurrent risks to life and property. Landslides preferentially occur along roads and are important because of their frequency, associated loss of life, disruption of socio-economic activities and their effect on the built and natural environment. Landslides amplify soil erosion in all of the watersheds that are regarded as severely to moderately degraded.
EXTENSIVE DAMAGE
Landslides and flooding in the parishes of Portland and St. Mary in the wake of the intense rainstorm of October 27- November 5, 2001 and the current May 2002 rainfall islandwide have caused land degradation in watersheds, extensive damage to road network, culverts, bridges, standing agricultural crops, poultry, electricity transmission lines, water pipelines and facilities, telecommunication lines, schools and more. Landslides and flooding in 2001 and 2002 occurred simultaneously, with landslides creating flood conditions. Landslides occurred both in the landscape modified for human use as well as on slopes under forest cover as is evidenced by spectacular brown scars that are clearly visible where vegetation has been disturbed. Hazard mapping for landslides, floods and earthquakes are the nuts and bolts to reduce recurrent losses and to formulate a land use policy. The good news is that a good number of such maps are readily available for Jamaica, some free of cost. Please contact us for further information.
Rafi Ahmad is affiliated with the Unit for Disaster Studies, Department of Geography and Geology, The University of the West Indies, Mona.
