CHAPTER 3 : VULNERABILITY AND ADAPTATION

INTRODUCTION

An assessment of a country's vulnerability is an evaluation and analysis of the scope and severity of potential impacts of climate changes on the natural environment, main sectors of the economy, human health and social activities.

An assessment of a country's adaptation is an identification and evaluation of changes in technologies, practices, and policies that can be adopted to prepare for adaptation to climate change impacts.

It has been widely recognized that small island states are highly vulnerable to climate change and the resulting sea-level rise. Adaptation to these changes, on which countries should mainly focus during the next decade, is one of the environmental challenges to be taken into consideration for sustainable development. Anticipatory actions should be taken to mitigate the negative effects of these changes and priority should be given to the implementation of remedial measures. One possibility is to integrate climate change in the socio-economic development and management programmes at government and non-government levels.

In Mauritius, key socio-economic sectors which inter-alia are most likely to be affected by climate change and sea level rise are:

Sectoral impacts are identified and strategies are proposed to facilitate adaptation. These include revised management strategies to cope with the environmental stresses, contingency planning, research and development.
 

CLIMATE CHANGE SCENARIOS

Climate change scenarios are designed for use in identifying sectoral sensitivity to climate change and to show the potential magnitude of impacts but not to predict future climate.

Three basic options are available for creating climate change scenarios:

(i)      general circulation models (GCM)
(ii)     incremental
(iii)    analogue.
Climate Change Scenarios

General circulation models (GCMs) are mathematical representations of atmosphere, ocean, and land surface processes. The GCMs are run for current climate (1 x CO2) and for a doubling of carbon dioxide content (2 x CO2). Output from four GCMs, namely the Goddard Institute for Space Sciences (GISS) model, the Geophysical Fluid Dynamics Laboratory (GFDL) model, the Canadian Climate Centre Model (CCCM) and the British Meteorological Office Model (UK 89) have been analysed.

The current output from all the GCMs (1 x CO2) is compared with long-term observed climate data to determine which GCM resembles most the current climate.

GCM outputs and long-term observed climate data at Plaisance
 
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Mean/Total
Observed
Maximum temperature(oC)
29.4
29.2
28.9
28.0
26.4
24.9
24.0
23.8
24.6
25.9
27.6
28.9
26.8
Minimum temperature (oC)
22.5
22.6
22.4
21.2
19.6
18.2
17.7
17.3
17.6
18.5
19.9
21.5
19.9
Monthly rainfall (mm)
249
220
289
208
165
115
130
87
64
57
88
177
154
Monthly solarradiation(MJm-2)
657
572
540
455
423
346
367
423
494
618
634
664
6193
CCCM
Temperature difference
2.21
2.09
2.26
2.37
2.39
2.39
2.56
2.66
2.62
2.57
2.48
2.41
2.42
Rainfall ratio
1.13
1.11
1.05
0.87
1.72
0.94
1.32
1.06
0.82
1.05
1.09
0.96
1.09
Radiation ratio
0.96
0.94
0.99
0.98
0.96
1.00
0.97
1.02
1.02
0.96
1.00
0.99
0.98
GFD3
Temperature difference
2.65
2.92
2.94
2.83
2.68
2.65
2.99
2.62
2.11
2.34
2.74
2.73
2.68
Rainfall ratio
0.65
0.69
1.19
0.79
0.98
0.94
0.98
0.84
0.95
1.05
1.73
1.55
1.03
Radiation ratio
1.06
1.11
1.09
1.04
0.98
1.22
1.10
1.06
0.97
1.05
1.01
1.08
1.06
GISS
Temperature difference
3.62
3.64
3.80
4.03
3.41
3.78
3.06
3.73
3.47
3.39
3.48
3.67
3.59
Rainfall ratio
1.00
0.96
1.26
1.46
1.61
1.33
1.07
1.23
1.24
0.90
1.13
1.04
1.19
Radiation ratio
1.01
1.03
1.01
1.02
1.02
1.06
1.02
1.03
1.03
1.02
0.99
1.00
1.02
UK89
Temperature difference
1.96
2.01
2.30
2.44
2.57
2.48
2.34
2.08
1.88
1.76
1.73
1.94
2.12
Rainfall ratio
0.54
0.78
1.01
0.80
1.96
0.90
0.69
0.88
0.70
0.57
0.91
0.71
0.87
Radiation ratio
1.04
1.01
1.01
1.04
0.99
1.00
1.01
1.00
0.98
0.96
0.99
1.00
1.00

Incremental

Applying incremental changes to meteorological variables such as temperature and precipitation can also be used to construct climate change scenarios. Incremental changes have been combined with observed climate data to give an altered daily temperature and daily rainfall.

Incremental scenarios adopted
 
+ 2°C   and   20%   daily rainfall
+ 2°C   and   10%   daily rainfall
+ 2°C   and      0      daily rainfall
+ 2°C   and  -10%   daily rainfall
+ 2°C   and  -20%   daily rainfall
+ 4°C   and   20%   daily rainfall
+ 4°C   and   10%   daily rainfall
+ 4°C   and     0%   daily rainfall
+ 4°C   and  -10%  daily rainfall
+ 4°C   and  -20%  daily rainfall
Analogue

Historical warm periods can also be used to represent climate change.
 

VULNERABILITY

Coastal resources

The coastline of Mauritius is undergoing pronounced morphological changes as a result of natural causes and anthropogenic activities. The natural phenomena are:

The anthropogenic activities are: Accelerated sea-level rise (ASLR) would most likely worsen these problems. According to IPCC assessment, sea level is expected to rise between 15 to 95 cm with a best estimate of 50 cm by the year 2100. Sea- level rise projections of 0.5, 1.0, 1.5 and 2.0 m have also been used in case studies for Mauritius.

The major impacts of sea-level rise in Mauritius are land loss, erosion of beaches, damage to coastal infrastructure, degradation of coral reefs and loss of wetlands.

Land loss

Mauritius is surrounded by many low lying areas which will most likely be affected by ASLR and increased flooding from storm surges due to an expected increase in the number and intensity of tropical cyclones as a consequence of global warming.

Analysis of available 2m contour maps showed that the total coastal area under direct impact of sea-level rise will be of the order of 1030 ha representing about 0.5% of the island.

This land loss represents the most valuable land assets of the country, which are a source of recreation and the main attraction of the tourist industry. The areas most at risk are located in the South-West and North as well as, the estuary of the rivulet Terre Rouge, a sanctuary, which welcomes a large number of migratory birds.

Coastal Erosion

Beach erosion is a constant threat to many areas around the island, caused mainly by ill-designed jetties/groynes. These have caused alterations in current directions with the result that erosion has shifted to other places. A recent survey revealed that there are more than 200 jetties/groynes, which have been illegally constructed.

Coastal segments where marked erosion have been identified are in the region of Flic-en-Flac (West), Le Morne (South-West), Riambel (South), Pointe d'Esny (South-East), Cap-Malheureux and Grand Bay (North). It has been observed that the coastline is receding by almost 1 m per year in some places. Sea level rise will enhance the erosion problems of already threatened regions and increase the vulnerability of other areas.
 

Coastal Infrastructure

Coast roads representing 5% of the sea front are located mainly in the southern and eastern regions. It has been estimated that about 12 km of main coast road and 25 km of secondary coast road could be at risk with a rise in sea level.

More than 1000 houses will be totally under threat and 100 units partly. Based on the occupancy rate of 4.7 per unit, it is estimated that almost 6000 people (0.6% of the population) would be affected.

Coral reefs

Coral reefs are also susceptible to climate change as this would lead to higher water temperatures and rising sea level. In many parts of the world reefs have undergone episodes of bleaching. During the recent El-Nino episode when a temperature increase of 2 °C above the mean was observed in the water surrounding the Seychelles, widespread coral bleaching occurred.

In Mauritius, coral bleaching has occasionally been observed and has been attributed mostly to pollution.

Coastal Wetlands

Coastal wetlands are mostly found at elevations below the highest tide of the year and above mean sea level. They usually oscillate and move in response to changes in sediment supply and relative sea-level rise. The rate at which wetlands migrate is still unknown.

In Mauritius, some wetlands have been backfilled for development purposes and this has caused flooding in other places.

Agriculture

Sugar production, the main agricultural activity, is a key element of the Mauritian economy and is expected to continue for the forthcoming decades. The sugar industry together with other agricultural activities have a strong socio-economic bearing and need to be assessed for their vulnerability.

The impacts of climate change on agriculture were analysed using the following assumptions:

Direct effects of elevated CO2 and other greenhouse gases

The major effects of increased CO2 levels on productivity are through photosynthesis and respiration, as well as on water use, crop development and product quality. In most cases higher increases in productivity can be expected with the C3 plants compared to C4 plants (e.g., sugar cane). Total production of dry matter will increase, but not necessarily as sugar because of lower partitioning into sucrose. Sugar beet producers will benefit more than cane sugar producers. Weeds, mostly C3 plants, will grow more rapidly and hence compete more severely with sugar cane with possible negative effects on productivity.

Changes in the crop development and phenology can potentially cause shortening or lengthening of the crop cycle and may lead to decreases or increases in productivity. Structural changes especially in the carbohydrate status may affect the nutritional value, taste, storage quality and commercial value of some fruits and vegetables. Post-harvest losses may be higher in the case of flowers while the lower nitrogen content of fodder will mean reduced protein levels and hence diminished nutritional value for livestock.

Increases in atmospheric CO2 will lower crop water requirements by reducing transpiration per unit leaf area; its benefit cannot be quantified. Biological nitrogen fixation may increase or decrease and will result in different inputs of fertilizer.

Changes in climate parameters

Global warming is likely to lead to the following changes:

Temperature increases will change and extend the geographical range of some insect pests. The number of generations per year of some insects may increase with earlier establishment of the pest coinciding with vulnerable stages of crops and resulting in severe losses. Interspecific interactions between pests, their predators and parasites may change with integrated pest control becoming less effective.

Most agricultural diseases are expected to reach more severe levels under warmer conditions. Deseases caused by fungi and bacteria will become more recurrent in case warmer temperatures are accompanied with higher precipitation. The geographical range of the diseases also may change thus affecting susceptible cultivars grown in these areas.

The expected changes in rainfall amount, pattern and distribution make it difficult to assess its effect on agriculture. Relatively small changes in amount and seasonal distribution can have large effects on crop productivity in tropical areas. The magnitude and frequency of drought periods and heat stress could be of direct concern. There is a distinct possibility that sugarcane land in the sub-humid zone will become economically non-productive as a result of higher rates of evapotranspiration. Irrigation might have to be adopted in or extended to these areas.

Important indirect effects of climate change on agriculture come from concurrent effects on other physical systems. The most important is water resources and groundwater recharge.

The various impacts of climate change on crop and animal production could have higher order effects on income, employment, food production and exports. Production costs will change and may rise in terms of altered management requirements such as irrigation adoption or extension and reduction of pest and disease damages. Profitability at the national and farm level will change among other things because of changes in the production potential, in the costs of inputs and prices of outputs. The effect of climate change on a regional and international basis will also impede on profitability. This will in turn affect employment and the society.

Sea level rise

Agriculture and mangroves occupy about 45% of the coastal frontage. Agricultural activities will be under risk as a consequence of saline drift from sea-spray that will contribute to land degradation through salinisation of neighbouring soil. Mangroves are expected to retreat inland.

Concluding Remarks

The magnitude of change in the different climatic parameters will determine the vulnerability of our agricultural production and how many adaptive measures need be taken to maintain productivity. GCM outputs for Mauritius indicate that the increase in temperature will affect most of our agriculture. It is certain that all crops will not be affected to the same extent and that the same crop will respond differently in various regions. This will require different adaptive measures. Government may have to react to the effects of climate change at the regional and international levels even if effects at national level were negligible.

Water Resources

The fresh water supply of Mauritius comes from rivers, man-made lakes, natural lakes, and ground water basins. The 2100 mm mean annual rainfall is largely sufficient to replenish these water resources systems that have a total available storage capacity of the order of 460 Mm3. Both surface and underground water are utilized for domestic, industrial and agricultural purposes. There is still potential to exploit additional ground water to cater for increasing demands. Average per capita water consumption was about 190 l day-1 in 1995.

Water quality is closely tied up with the management of the coastal system. Water intrusion, pesticide use, agrochemicals and haphazard disposal of waste may cause toxic chemicals to penetrate into the water resource systems. Used water from sugar mills is discharged into the rivers and ends up in the lagoon. Government is well aware of potential water pollution and has embarked on an aggressive program including monitoring of surface, ground and lagoon water with special attention paid to effluents from industrial dying and washing.

Mauritius depends for 60% of its needs on underground water for domestic, industrial and agricultural purposes. Boreholes that are situated near the coast will be at risk due to salt-water intrusion.
 

Fisheries

Fisheries include coastal, banks and deep-sea fishing and aquaculture. Coastal fishery is the main source of fresh fish for the local markets. The annual production of fresh fish has stabilized at around 1600 t, peaking in the month of March. In August and September the catch usually decreases due to unfavourable weather.

Fish Aggregating Devices (FAD) installed by the Albion Fisheries Research Centre (AFRC) at various sites 1.5 to 12 km off the coast of Mauritius also play an important role in the supply of fresh pelagic fish to the local markets.

Fish obtained from sea banks represents 30% of the total fish consumption. The main banks exploited are the Nazareth and Saya de Malha along the Mauritius - Seychelles ridge and in the region of the Chagos, St Brandon and Albatros islands. The total annual catch from the banks was about 4400 t in 1995. Fishing on banks is mainly conducted when the weather is favourable.

The tuna-fishing zone lies between latitudes 4°N to 11°S and longitudes 50°E to 84°E and the regions around the Chagos are very productive. About 2800 t of tuna were landed in 1995: the main species being skipjack (67%), yellow fins (21%) and big-eye (10%).

Marine aquaculture focuses on shrimp farming and fresh aquaculture involves the fish "berri-rouge" and crayfish.
 

Climate change impacts on fish stocks and distribution can be assessed through variations in water properties or indirectly through fishing activities dependent on weather. Fish habitat and behaviour are directly related to climate.
 
 
 
 
 

Increased sea surface temperature

A rise in sea surface temperature causes:

Though General Circulation Models (GCMs) outputs only provide for expected changes in air temperature, multiple-regression analysis used in the development of models has indicated a significant rise in sea surface temperature also. The decrease in dissolved oxygen will affect fish population through:

·    increased mortality of adults and juveniles

·    reduction in growth

·    lower survival rates of eggs and larvae

Nutrients

Nitrates, phosphates and silicates are important nutrients. Their concentrations are higher in deep water and replenishment of upper layers comes through vertical diffusion, overturning and upwelling. Changes in wind regime and ocean circulation are expected to impact on the intensities and location of upwelling areas and hence on the distribution of nutrients leading to changes in fish population and migration behaviour.

Changes in climatic conditions on fish yield

More frequent changes in the wind and thermal stratification regime will be detrimental to the fish population since larval survival will be affected. Higher frequencies of weather extremes are expected to affect fishing operations.

Tuna fishery

Tuna is a migratory species and the choice of the route is strongly determined by sea surface temperature. The 28°C isotherm has been found to coincide with concentrations of tuna.

The vertical distribution of biomass and fish depends on the depth of the thermocline. A deeper thermocline necessitates more investments for exploitation.

The effects of El Nino

It is predicted that El Nino occurrence will become more frequent, intense and of longer duration with climate change. It has been observed that whenever a major El Nino occurs, warming also takes place in the other major ocean basins. Studies have also shown that El Nino will induce changes in ocean currents, upwelling and upper ocean heat content thus affecting size and location of fish stocks.

Health

Health is defined by the WHO as " a state of complete physical, mental and social well-being and not merely the absence of disease or infirmity." Climate has been found to act on human health through its effect on ecosystems, water resources, food species, disease agents and vectors. Available data show some correlation between number of malaria cases and heavy rainfall episodes unless appropriate precautionary measures are taken. Marked outbreaks of flu are also noted during some months of the year as a result of fluctuating temperatures. It is therefore important to consider human health and well-being under a climate-change scenario.

Climate change is expected to have a negative impact on human health in Mauritius. A 2°C increase in the average temperature when added to the already sultry conditions prevailing during summer in the capital city and the other coastal areas will be detrimental to the health of elderly persons, small children and chronic invalids. Furthermore, a combination of such temperatures with high values of relative humidity is bound to be catastrophic to human health.

Urbanization is relatively dense, as most people prefer individual dwellings to apartment buildings. Large areas are being covered by concrete structures with few parks and gardens being accommodated. Residential buildings have been erected to serve more as shelters from strong cyclonic winds than as efficient energy-consuming units. During summer these get heated up by solar radiation and emit the stored heat at night thus considerably increasing indoor temperatures.

Air conditioning facilities are becoming an important household item and as the lower income group will not be able to afford such facilities, excess heat will become a major health problem. A nation that cannot rest and recover will not be productive and is most likely to suffer from cumulative distress.
 

Land use change and forestry

Land use change

Deforestation has had a very strong influence on land as a resource and climate changes will in turn compound the damage. These impacts will be discussed in terms of the effects of increased CO2 level and changes in climate parameters.

Increased CO2 level

Elevated CO2 level will alter the composition of plants and will result in organic matter with a high carbon:nitrogen and carbon:phosphorus ratio. Such organic matter has a low rate of decomposition thereby slowing nutrient recycling. The activity of decomposer micro-organisms will be reduced by the poorer quality of the plant material while fungi may thrive as a result of the higher carbon content of the litter. Changes in the flora and fauna of the soil may affect its physical and chemical properties in the long-term and may necessitate changes in land use.

Climate parameters

Different rainfall patterns could affect distribution, tolerance, evolution and survival of animal and plant species resulting in a change in ecosystems. Rainfall of very high intensity may become more frequent. The resulting soil erosion may be severe thereby altering the uses made of land in certain areas. Leaching may increase on sloping land. Lower productivities may demand changes in land use and in extreme cases land may be simply abandoned.

Forestry

Increased CO2 level

The highest risk on existing natural forests may result from some species responding more positively to the temperature increase, CO2 fertilization, changing rainfall and solar radiation patterns. The devastating effects of extreme climate events such as tropical cyclones could render regeneration more difficult. They will result in changes that could alter the biodiversity in the long-term. Plantation forests may be affected in their productivity.

Climate parameters

Higher evapotranspiration demands of the forests used for grazing may cause this land to become less productive and result in lower carrying capacities.
 
 
 
 


 

ADAPTIVE MEASURES

Coastal resources

Of the three categories of responses required to protect human life and property, as recommended by the IPCC, the protection and accommodation options would be more appropriate as Mauritius is too small in size for the retreat or abandonment option.

Protection options

Hard structures to protect beaches are at times the only viable options. However studies should be conducted to identify the best orientation of these structures. The use of Gabion structures should be extended and improved on the basis of past experience.

Soft solutions such as vegetative cover should be adopted where appropriate. Walkways should be constructed to avoid further degradation of the already scarce vegetation of the beach.

Beach nourishment, a more popular form of erosion control, should be adopted. Future coastal protection should include beach restoration and maintenance as well as cyclone wave protection by dunes.
 
 

Accommodation options

The set back distance should be increased to beyond the present 15 m high-water mark. Steps should be taken to ensure that the removal of sand is completely banned as from the year 2001.

The existing passes through the reefs should not be enlarged and new passes should be avoided completely.

Agriculture, land use change and forestry

Agriculture

Agricultural systems have always adapted to changes and the magnitude and nature of the impacts will determine the degree of adjustment. It is certain that adaptation will depend on the degree of adoption of new technologies and management rules but will be constrained by economic and political factors. Expected adjustments will come through changes in land use, management and infrastructure. However, because of all the uncertainties linked with climate change it is very difficult to recommend specific options.

Changes in land use

The implementation of changes in land use does not seem to be a possible adaptive measure since land is a limited resource. A change in crop type also does not appear to be practicable. The cultivation of more drought resistant crop cultivars could be an interesting adaptive strategy for regions where soil moisture will become the limiting factor. A change in the harvest date can also be envisaged so as to make more efficient use of environmental resources.

Changes in management and infrastructure

As crop water requirements will increase under warmer conditions and with a possibility of poorer rainfall distributions, irrigation facilities will have to be extended.
 

Fertilizer use will change and increased amounts may be needed to counteract the effect of soil erosion and leaching. Farm infrastructure and practices may require changes to mitigate the effects of climate change.
 
 

Forestry

The best option appears to be closer monitoring for the prevention of further degradation. More adapted species can be introduced for exploitation in the plantation forests. The ecosystems need to be more closely monitored for prompt action in case the balance of species is affected. Tree plantation along river banks and motorways are to be envisaged.

Water resources

Adaptation options to maintain and ensure an adequate supply and quality of water are :


Concluding Remarks

The magnitude of change in the different climatic parameters will determine the vulnerability of the different sectors and the extent to which adaptive measures need to be adopted to limit their effects. Decision-makers may have to react promptly to counteract the possible impacts of climate change.