Climate change projections
The temperature projection for Asia is for warming to accelerate. The rate of warming in the South Asia is projected to be significantly faster than that seen in the 20th century, and more rapid than the global mean rate of warming. However, rainfall and temperature changes will be seasonal. Throughout South Asia, warming during December, January and February is expected to be at its greatest and associated with a decrease in precipitation, whilst the consensus of regional models is that summer rainfall will increase. Extreme weather events are also projected to increase in frequency throughout the region, including heatwaves and unusually heavy rainfall. Tropical cyclone intensity is expected to rise by 10 - 20% for sea surface temperature rises of 2 - 4°C.
National level modelling, undertaken by the Sri Lankan Centre for Climate Change Studies, suggest that the changes in Sri Lanka broadly - but not completely - follow the regional expectations:
- The regional temperature trends are played out in Sri Lanka. By 2100, the temperature during the southwest monsoon season (May to September) is anticipated to be 2.5 °C, whilst the northeast monsoon season (December to February) is expected to yield a temperature increase of 2.9 °C.
- Rainfall is slightly different to the regional trend, with Sri Lanka's increases in rainfall levels anticipated in both summer and winter seasons. However, the rainfall change is expected to be greater during the southwest monsoons (May to September) than northeast monsoons (December to February).
- In both seasons, rainfall and temperature is projected to increase with time, from 2025, 2050 to 2100.
- Rainfall changes are also uneven across Sri Lanka - much greater increases are expected on the windward side of the central hills.
The projections quoted above assume 'medium' levels of greenhouse emissions continue throughout the next century. However, it is important to understand that the results of climate projections vary significantly depending on whether high or low future global greenhouse gas emissions are assumed. High emissions scenarios, in which rapid, fossil fuel-intensive global economic growth is achieved over the coming century, produce anticipated temperature increases of greater than 5-°C in South Asian during December, January and February by the end of the century. On the other hand, low emissions scenarios, in which the use of natural resources is assumed to reduce and clean, resource-efficient technologies are introduced, yield a temperature increase of less than 3°C. The implication is clear - large cuts in carbon emissions and radical changes in global patterns of consumption, particularly in the West, will be required to prevent climate change from bringing catastrophic changes across South Asia.
Future impacts and vulnerabilities
• The most profound impacts of climate change in Sri Lanka will be in agriculture and food security, water and coastal resources, biodiversity changes, and human health.
The IPCC offer the following summary of the vulnerability of key sectors in the South Asia region. In keeping with the IPCC approach, the summary reports both the degree of vulnerability and the level of confidence. The South Asia region has the highest proportion of 'highly vulnerable' sectors of all the Asia sub-regions.
Agriculture and food security: Overall crop yield (wheat, maize and rice) could decrease in South Asia by up to 30% by the end of this century (compared with an increase of up to 20% in East and South East Asia). Most Sri Lankan crops, and particularly rice, are produced at the top end of the optimum temperature range for cultivation, meaning that the anticipated increases in temperature could have a profound effect on yields. Estimates suggest that rice yield could be reduced by nearly 6% for a 0.5°C temperature rise - equating to a reduction in GDP of 0.2%. Areas affected by salt water intrusion - an increasing problem as the sea level continues to rise - will experience much greater losses as paddy salinity increases. Higher temperatures will also increase the evaporation of water content from soils, leading to water stressing in upland crops in particular. Higher night time temperatures are likely to impair tuber crop development (particularly potato) and decrease the sugar content of harvestable fruits. Even small reductions in rainfall are anticipated to cause a several fold decrease in ground water replenishment, with severe implications for intensive, lift-irrigation dependant agricultural production in Sri Lanka's sandy soil regions (Kalptiya and Jaffna Peninsula). Soil erosion, and in particular the loss of productive topsoil is also likely during high rainfall (greater than 25mm per hour) events. Global climate change and the increased frequency of ENSO events affect the migration routes and numbers of fish larvae currently present in South Asian waters and as a result a general decline in fishery production is anticipated across the region. However, predicting fish stocks is complex: changes in ocean current, sea level and salinity, wind speed and direction, strength of upwelling, mixing layer thickness, and the response of predators to these multiple factors will all contribute to future availability of fish supply.
Water resources: All future emissions scenarios predict increasing water stress in South Asia, with the effects being felt as early as 2020. In Sri Lanka, overall rainfall volumes are greater than the total demand for water - however, the demand is unevenly spread with areas in which water supply is already insufficient to meet needs. As temperature increases, increased evaporation will drive up the demand for irrigation water, contributing to water scarcity. Increases in high rainfall events will increase soil erosion, which in turn accelerates the silting up of existing reservoirs, further contributing to water stress.
Coastal/ low lying areas: All coastal areas in Asia are currently facing increasing stress with threats to human and environmental resilience. However, rising sea levels will have further, major impact on costal and low lying communities in South Asia. The most conservative climate change scenarios predict a rise in sea level of 40cm by the end of this century, which will increase the annual number of people affected by flooding in Asia from 12 million to 94 million, with almost 60% of these people living in South Asia (including the coastlines of Pakistan, Sri Lanka and Bangladesh). Sea level rise scenarios for Sri Lanka suggest a shoreline retreat of 10m by 2050. Ecosystems and biodiversity: Up to 50% of biodiversity it a risk from climate change across Asia. In South Asia, grasslands are particularly under threat and large decreases are likely as temperatures rise and evaporation increases. Sea level rise and surface temperature rise threatens coastal ecosystems, rich in biodiversity, whilst coral reefs are at risk of bleaching from higher temperatures. Sea level rise also leads to salt water intrusion into estuary and lagoon systems, threatening these habitats.
Human health and migration: Increasing temperatures are likely to yield a spread in insect borne diseases, whilst warmer sea-surface temperatures support phytoplankton blooms that are the breading ground for bacterial diseases such as cholera. Flooding, precipitation rise and sea level rise will all pollute surface water, leading to an increase in cholera, diarrhoeal and skin diseases, whilst increases in the epidemic potential for malaria (12-27%) and dengue fever (21-47%) are anticipated. Migration following extreme weather events is also to be anticipated.