Sea level rise (SLR) is one of the major consequences of ongoing climate change. Over the past century, global sea level has been rising, and the rate has been found accelerating in recent decades (Fig. 1). Since 1970, the global mean SLR is partly attributed to the anthropogenic (human-induced) forcing. SLR will pose a major threat particularly to the maritime and island countries around the world.

Malaysia is a maritime country, with a shoreline totals approximately 4809 km, comprising 1972 km in Peninsular Malaysia and 2837 km in East Malaysia (Sabah and Sarawak). This does not include nearly 1000 islands and coral reefs belonging to the country in the Straits of Malacca, the South China Sea, the Celebes Sea and the Sulu Sea. Most of the major cities are located in the coastal zones such as Penang, Klang, Johor Bahru, Kuantan, Kuching and Kota Kinabalu. Thus, SLR will cause severe impacts on the large growing populations and economic importance of the coastal zones in Malaysia.

Understanding characteristics of sea level change over different spatial and temporal scales will provide better insight particularly for coastal risk assessment and sea level projection. In Malaysia, mean sea level (MSL) variation in the west coast of Peninsular Malaysia and the East Malaysia (Sabah and Sarawak) are primarily driven by the interannual climate variability of El Niño Southern Oscillation. The increase (decrease) of interannual MSL can be linked to La Niña (El Niño) event up to 5 cm. In the east coast of Peninsular Malaysia, the sea level variation is mainly dominated by the seasonal MSL cycle with maximum sea level about 30 cm higher during the Northeast Monsoon period. The long-term trends of MSL rise for 1993-2018 around Malaysia were approximately about ~4 mm/yr (within range of uncertainties). Over the same period, the rates of MSL rise in this region were larger than the global average (~3.3 mm/yr). Note that the MSL rise is not globally homogeneous as regional patterns are partly driven by non-uniform steric (density) changes and ocean dynamics (Fig. 2). The MSL rise also primarily contributes to the increase of extreme sea level events and coastal flooding.

SLR projections are predicted based on how greenhouse gas concentration in the atmosphere will change in the future due to human activities, the term known as Representative Concentration Pathway (RCP). Considering the scenario of very high future concentration (upper range of RCP 8.5), the mid-range projections for coastal sea level rise in Malaysia are 0.67 - 0.74 m with upper range projections is in the range of 0.94 – 1.02 m by the end of the 21st century (Table 1). SLR projections are slightly higher by few centimetres in the East Malaysia as compared to Peninsular Malaysia. This future MSL rise can be attributed to the global factors such as thermal expansion and melting of glaciers and ice sheets as well as regional contributions from ocean dynamics (e.g. ocean circulation). Furthermore, several factors that are not considered in this projection such as local and regional geological changes could also affect the future SLR in Malaysia.

The combination of a strong La Niña event, the peak of the mean seasonal cycle, and the higher spring tides will lead to a greater risk of coastal flooding especially in the low-lying coastal areas. Furthermore, together with the heavy rainfall typically during the Northeast Monsoon season and particularly along the east coast of the Peninsular Malaysia, these combined factors will contribute to the larger and immediate impacts of compound coastal flooding in Malaysia. With the sea level projected to increase in the future, more intense and frequent coastal flooding will likely to happen. Moreover, the MSL rise will cause a variety of long-term physical impacts to the coastal zones including (i) the permanent submergence of coastal low-lying regions by higher MSL or mean high tides; (ii) exacerbate coastal erosion; (iii) degradation of coastal ecosystems and habitats; and (iv) saltwater intrusion to surface and ground water. These in turn will affect the economic and coastal communities in Malaysia.

Understanding spatial and temporal variation of sea level change will provide vital information to relevant authorities in making well-informed decision regarding coastal planning, development and management. In responding to SLR, response options available includes (i) physical protection such as building a seawall, (ii) advance by coastal reclamation project that should be able to greatly support natural accretion of land, (iii) accommodation of the risk such as raising building; and (iv) retreat by moving coastal community and assets out from the vulnerable areas. The response selection must be chosen with the objectives to reduce hazards, exposure and vulnerability using integrated approach that also consider public participation and conflict resolution practices. This will lead to better implementation of adaptation strategies and avoid future conflict.


References

Amiruddin, A. M., Haigh, I. D., Tsimplis, M. N., Calafat, F. M., & Dangendorf, S. (2015). The seasonal cycle and variability of sea level in the South China Sea. Journal of Geophysical Research: Oceans, 120(8), 5490–5513.

Frederikse, T. et al. (2020). The causes of sea-level rise since 1900. Nature, 584(7821), 393–397.

McInnes, KL, Church, JA, Zhang, X, Monselesan,D, and Legresy B. (2017). Sea-Level Rise Projections for Malaysia. Final Report for NAHRIM, Malaysia.

Oppenheimer, M. et al. (2019). Sea Level Rise and Implications for Low-Lying Islands, Coasts and Communities. IPCC Special Report on the Ocean and Cryosphere in a Changing Climate. Intergovernmental Panel on Climate Change.

Woodworth, P. L. et al. (2019). Forcing Factors Affecting Sea Level Changes at the Coast. In Surveys in Geophysics (Vol. 40).