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A GIS-based modeling of environmental health risks in populated areas of Port-au-prince, Haiti

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par Myrtho Joseph
University of Arizona - Master in Natural Resources Information System 1987
  

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4.4 Environmental Health Hazards

Table 18 in Appendix A and Figure 11 present a synopsis of the results by health hazard included in the model. As can be seen, waste pollution portrays the factor whose severity reaches the greatest physical extent, 53.4% of high and very high risks. Following this were pollution from streams (49.1%), high density housing (45.7%), and traffic (42.1%) (Table 18, Appendix A). The ranking of six factors coincides both for the percent of area covered and the proportion of area at high and very high risks. This would indicate a strong association between the physical extent of the factors and their perceived strength. Indeed the correlation coefficient between these two outputs exceeds 0.98. Correlation between EOW and Own weights over these two results was also tested. This yielded to a coefficient of regression (R2) of 41% (Table 20, Appendix A) and 33% (Table 21, Appendix A) when running successively single regressions of the EOW (column 2, Table 19) and the own weighting (column 3, Table 19) over the proportion of high/very high risk areas (column 6, Table 18). For both regressions the t-statistic was insignificant at 95% confidence limits and the p values significantly greater than zero. This result would suggest that the weight assigned by the experts had little to do with the perceived strength of these hazards. Similarly, when we ran a regression with the percent of study area covered by each factor (column 4, Table 19) as independent variable, correlations of 46% and 35% were found respectively for EOW and Own weighting with the t-statistic significant and p values acceptably low (close to zero) (see regression results in Tables 22 & 23, Appendix A). This would signify that the experts' judgment and our perception were more correlated to the physical extent of health hazards, which can be more easily quantified, than the perceived influence of those hazards. Although the participants in the expert opinion survey were not cautioned to provide their rankings based on the physical occurrence of these hazards, this result implies that this characteristic had to a certain extent influenced the weight the respondents attributed. Consequently, the experts did a better job than us in ranking the factors.

If we were to average the results obtained by individual factor, 52% of the study area would be at risk at all levels, of which 47% at high and very high risk. However, what these percentages did not unveil is the population exposed, though housing density is an unambiguous surrogate of population. Applying the 47% rate on the total population would be misleading since the areas at high risk are also the most populated. Not only are locations with high and very high housing density inherently exposed to high risks, the superimposition of low and moderate housing density areas to any other hazards where the vulnerability is high induces a high risk for the populations living in these areas. This was one of the issues the maximum approach attempted to address. Endless combinations could be done to put in evidence the severity of health risks in the study area. But for now, let's look at individual hazards and their associated risk levels.

Figure 11: Factors affecting environmental health in Port-au-Prince.

Percent of area by risk level

4.4.1 Traffic Pollution

Vehicle traffic forms a major source of indoor and outdoor air pollution in the study area. It is due to high population density that exposes both, to an increasing number of public and private vehicles using road surfaces not designed for this volume of traffic, and to the disorganized development of informal commercial activities which take over the streets. In addition to these environmental and physical settings, conditions of maintenance, regulation, and controls of the vehicle fleet exacerbates pollution. Nevertheless there is no obvious sign of concern either from the exposed population or from the entities in charge of the environment and traffic regulation and management, or again public and private organizations promoting health.

As displayed on Table 18 in Appendix A, about 76% percent of the area was found exposed to low to very high pollution risks. Neighborhoods with high and very high risks accounts for 42% of the study area while low and moderate risk amount to 13% and 21% respectively. The north-northeast section of the map displayed in Figure 12 makes abstraction of high traffic activities in some sections of Delmas Road adjacent to the border of Port-au-Prince. Only when Delmas Road intersects or crosses the border of the study area risks originated from this road appeared in the analysis. Nevertheless, most of this boundary section was found prone to high risk from traffic pollution.

Figure 12: Risks of traffic pollution in Port-au-Prince

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