Comparing atmosphere-land surface feedbacks from models within the tropics (CALM)

Man-made transformations to the environment, and in particular the land surface, are having a large impact on the distribution (in both time and space) of rainfall, upon which all life is reliant. From global changes in the composition of the atmosphere, through the emission of greenhouse gases and aerosols, to more localised land use and land cover (LULC) changes due to an expanding population with an increasing ecological footprint, human activity has a considerable impact on the processes controlling rainfall. This is of particular importance for environmentally vulnerable regions such as many of those in the tropics. Here, widespread poverty, an extensive disease burden and pockets of political instability has resulted in a low resilience and limited adaptative capacity to climate related shocks and stresses. The CALM project has the overarching aims of: (i) furthering our understanding of how the interactions between tropical rainfall and the land surface are represented in the latest climate model simulations from the 5th Climate Modelling Intercomparison Project (CMIP5); and (ii) how these interactions relate to abrupt climate changes such as those which occurred over the Sahara thousands of years ago or, more recently, the prolonged Sahelian drought.

As recent climate disasters (such as flooding in Pakistan, heat waves in India and droughts in China) demonstrate, society is particularly vulnerable to extremes related to tropical rainfall. The overall objective of this project is to better understand both present day and future tropical rainfall variability and associated controlling processes. In particular, recent work has suggested that the atmosphere-land surface feedback is going to be increasing important for any possible abrupt climate changes, thus this project will focus on model simulations of this process over a location where such changes have already taken place. The research addresses the interconnected themes of water cycle drivers, the water cycle-human interface, society and the changing water cycle, and interactions between water at the land surface and in the sub-surface.

Land use (and related types of land cover) is rapidly changing, as an increasing population migrates to urban areas, large tracts of land are deforested, agriculture is intensified and increasing use is made of groundwater resources through irrigation. These changes influence the climate through the release of greenhouse gases and aerosols and by changing the flows of mass and energy from the surface to the atmosphere. Currently the climate influence of variations in concentrations of greenhouse gases and aerosols (induced by LULC change) is simulated for the past and projected into the future using bio-geochemical modelling, measurements of changes in atmospheric composition, or by building greenhouse gas emission scenarios driven by different future socio-economic changes. A recent project, CMIP5, has run a number of state-of-the-art climate models using various present-day and future emission scenarios of greenhouse gases, and therefore provides an unprecedented amount of simulated model data. This project aims to compare the data from all of these models, as well as observational, satellite-derived and blended observational-satellite data, to see how the interactions between rainfall and the land surface differs (or agrees) between the models and reality. By following a process-based methodology, which is already well established and widely used in other funded projects, the project will enable a better understanding of how present-day and future rainfall is associated with the surrounding environment.

The potential impact of this research is substantial, because many uncertainties remain over how the land surface influences tropical precipitation. The primary aim of this project is to improve our current level of understanding of how anthropogenic changes to the land surface contributes to trends and variability in tropical regions, which is crucial for society as this can have large economic, social and human impacts on individuals and society as a whole. Therefore the main beneficiaries will be intergovernmental, government, non-governmental stakeholders and policymakers and, eventually, individual farmers and people. The research outcomes will be of direct use in obtaining a better understanding of the impact of changes in precipitation patterns, and in particular the impact of changing the land surface, for the benefit of millions of people across the world. Ultimately, it will address the overall challenge of poverty reduction and continued development in the tropics.

The wider scientific community (including climate scientists, land use and land cover specialists, impact modellers and climate model developers), will all be beneficially impacted by the outcomes of the proposed research (see Academic beneficiaries for details). In addition to the academic community, this research will beneficially impact several institutions, including:

1. UK and International Governments - Both attribution and prediction of regional climate change over the tropics are relevant to a variety of governmental departments and ministries. In the UK, these include the Department for International Development (DFID), the Department for Energy and Climate Change (DECC), and the Department for Environment, Food and Rural Affairs (DEFRA). Thus this project will contribute to improvements in the science, that the above ministries and departments will in turn translate into impacts on the ground, through their regional partnerships.

2. Living with Environmental Change (LWEC) Partnership, which is a group of 22 UK public sector funders and users of environmental research within the UK, including the different research councils and central government departments. LWEC has the aim of providing decision makers with the best information for the management and protection of vital ecosystems, strengthening the evidence base for policy and addressing the uncertainties that remain about the impacts of climate change. In addressing the proposed objectives, this project will have direct relevance to the various policymakers included in this partnership.