Global warming levels of 1.5oC and 2oC: impacts over Madagascar

Summary

Building efficient climate change adaptation and mitigation plans require an understanding of the impacts of these changes at regional and national scales. This work examines the potential impacts of different global warming levels over Madagascar. Overall, the island is projected to experience a robust increase in annual mean temperature and more frequent heat wave days when the temperature is 1.5oC - 2oC above pre-industrial levels. Deficits in early summer mean rainfall, a decrease in the number of consecutive wet days and an increase in dry spells will likely occur in the central and eastern parts of the country.

Background

At the 2015 Paris climate summit, 195 countries agreed to make efforts to keep the global temperature increase below 2oC over pre-industrial levels and attempt to limit the increase to 1.5oC. Such a goal requires countries to build national adaptation plans, which create an urgent need to understand the possible impacts of global warming levels (GWLs) in different areas. Previous studies show that these impacts are neither spatially nor temporally uniform. For instance, land areas warm faster than the oceans, while frequent and/or intense extreme events may increase in some regions more than others.

Over the past decades, sub-Saharan Africa has already experienced more frequent and intense extreme events than before. At 1.5oC and 2oC GWLs, the temperature increases over the subcontinent are projected to be higher than that of the global mean, accompanied by frequent heat waves, drought and flood periods. These impacts have been evident in Madagascar. However, few studies have been done on changes in temperature and rainfall over the island.

Description of the study

Our work investigated, for the first time, the potential impacts of 1.5oC and 2oC GWLs on mean and extreme temperature and rainfall over Madagascar. Such understanding is crucial to create an adaptation and mitigation plan of the island consistent with the Paris agreement.

Simulated daily temperature and rainfall from the CORDEX-Africa (Coordinated Regional Downscaling Experiment) multi-model ensemble mean were used in this study. The analyses focused on simulations from the present period (1970-2015) and future projections under Representative Concentration Pathway 8.5 (RCP 8.5), which is considered to be the most realistic business-as-usual scenario, given the current trajectory of greenhouse gas emissions.

This study recognises the particular importance of climate information on the development and well-being of Madagascar; the effects of adverse weather events are compounded by its low adaptive capacity. In addition to loss of life, damage from intense tropical cyclones cost the island an average of USD 87 million annually. Moreover, despite the flooding caused by the number of tropical cyclones hitting the island, water stress remains a major concern in most areas, with Madagascar classified as one of most stricken countries for water shortages. The southern part of the country has been experiencing a prolonged drought, leading to famine and mass migration. One-third of the world's incidence of human plague is reported to occur in Madagascar, facilitated by the island’s warm and wet conditions. The island is also one of the world’s top conservation priorities due to its exceptional biodiversity and high rates of endemism. These factors could be highly impacted by any changes in temperature and rainfall.

Outcome

At both 1.5oC and 2oC warming levels, Madagascar experiences a robust increase in annual mean surface temperature, ranging from 0.9oC to 1.2oC (1.3oC to 1.8oC) at 1.5oC GWL. The greatest rises in temperature are mostly confined to over the West and Southern parts of the island, with these areas registering a significant increase of up to 100% in the frequency of heat wave days at 1.5oC GWL and up to 200% at 2oC GWL.

At the same time, a dipole-like pattern of rainfall changes is projected over the island from October to November. The regions of Melaky, Menabe and Atsimo-Andrefana (over the west and southwest) are characterised by rainfall increases (up to 10% of the current average amount), with more wet spell days and excessive amounts of extreme rainfall. In contrast, the central, eastern and northern parts of the island show a decrease in both total rainfall and wet spell days, with an increase in dry spell days. From January to April, the island experiences an overall increase in total and extreme rainfall, with the greatest variation (up to 12% of the present average amount) in the north, northeast and eastern regions (mainly over Diana, Sava, Sofia, Analanjirofo and Atsinanana). It is noted however that these projections reflect significant uncertainty in rainfall change models.

Lessons

No change in rainfall is projected over the island when the summer months (October to April), are averaged with early (October to December) and late (January to April) summer. Such findings highlight the need for Madagascar (as could be the case for other regions) to obtain climate information on a shorter time scale than the annual mean, in which changes during different times of a season cancel each other out. Climate researchers, policy makers and stakeholders must collaborate to generate data that most effectively contributes to the development of the country.

Impact

These findings have the potential to contribute directly to the national adaptation, mitigation and development plans of Madagascar. It is known that the rises in temperature and heat wave days projected at 1.5oC and 2oC GWLs over the island will lead to more heat-related deaths and an increase in vector-borne diseases. Moreover, the planting season in Madagascar generally occurs during the months of October, November and December. The overall rainfall deficit, the increase in dry spell days and changes in extreme rainfall during these months could have significant implications for the start of the planting season, as well as impacts on agriculture and food production over the country. The decrease in mean rainfall could also impact hydroelectricity production, with most of the hydropower plants installed in the eastern part of the island.

Bio

Rondrotiana Barimalala is Malagasy climate scientist, based at the Department of Oceanography, University of Cape Town, South Africa. She is currently a Future Leader African Independent Researcher (FLAIR) fellow and was supported by the Climate Research for Development (CR4D) program to conduct this study. CR4D is a joint program supported by the African Academy of Sciences (The AAS), the United Kingdom Foreign, Commonwealth & Development Office (FCDO, formerly DFID) Weather and Climate information SERvices for Africa (WISER) programme and the Africa Climate Policy Centre (ACPC) of the United Nations Economic Commission for Africa, which aims to strengthen the links between climate science research and climate information in order to support development planning in Africa.