Rainfall variability & change

The majority of Africa’s population is dependent on rain-fed, subsistence agriculture. Our understanding of what controls rainfall variability and change is worryingly poor. Research in the group aims to provide a more solid understanding of climate processes in key rainfall regions such as southern Africa, central Africa/Congo Basin, East Africa and the Sahel. We are also strongly motivated by analysing how the climate system is represented in climate models because these are the prime tools for prediction. In some of our projects such as IMPALA , DO4Models and CLARIFY we are working towards improving climate model performance over Africa.

Congo Basin

The Congo region in central Africa is one of the three main convective centres on the planet, and therefore one of the key drivers of the tropical circulation. Convection in this region is a significant contributor to global rainfall, particularly during transition seasons.  However, there is a lack of available observational data in the region due to inaccessibility and political tensions, and as a result there is a critical paucity of research on Congo climate dynamics. It follows that there is limited understanding of the region’s climate system, in particular the controls on rainfall and the extent to which numerical climate models are able to simulate its climate. Research will identify the major differences across climate model simulations of rainfall, and attempt to better understanding these differences in terms of mechanisms, model dynamics, and model parameterisations. Along with Richard Washington, two researchers in our group are actively working on this theme, namely Dr Neil Hart and Amy Creese.

East Africa

One of the most coherent increasing rainfall projections in the Coupled Model Intercomparison Project (CMIP) dataset is daily rainfall during the short rains (October to December) season over East Africa. This was analysed in detail by Helen Pearce for her DPhil. Coupled climate models are poor at replicating the daily rainfall field over the domain compared to satellite retrieval and reanalysis. They overestimate daily rainfall for days when dry conditions of suppressed convection should prevail. Detailed examination of the rainfall mechanisms – in particular moisture flux convergence – suggested that rainfall projections under a high emissions scenario at the end of the twenty-first century are overestimated and that an important part of the key increase in the projected rainfall may not be real. We will be taking this work forward over the period 2016-2018 with the DFID funded Reach project.

Sahel

Following large scale drought during the 1970s and early 1980s, the Sahel has received more research attention than any other African region. There are nevertheless many remaining questions regarding West African precipitation, and this is an important area of investigation in the Climate Research Lab, which also links nicely to the research into Saharan dust.

Of particular interest are the potential processes of change associated with global warming. Future projections for the Sahel diverge substantially with some models projecting wetter and some projecting drier conditions. We have analysed  drying projections in a group of Hadley Centre models and worked out whether the mechanism the model using to generate the drying is credible or not. We established that the drying mechanism is the same process that the model uses to generate dry years in the historical period but that this mechanism does not match out best estimate of what the observed atmosphere does in dry years. We have reason therefore not to believe the mechanism used by the model to produce future drying. This work points also to heating and upward motion in the Saharan Heat Low region, highlighting the need for further work about the relationship between the Saharan Heat Low and the West African monsoon.

southern Africa

Southern Africa has a remarkably complex climate system as it sits astride the tropical and mid-latitude climate systems with extreme events featuring the interaction between the two components of the large-scale circulation in the form of tropical-temperate cloud bands. As part of the NERC UMFULA project, we are currently actively researching these systems and their representation in coupled climate models.

Pan-African research

Aside from research that focuses on specific regions, we are also interested in climate variability and change across the African continent as a whole, and are working on a number of pan-African projects. This research focuses on comparison of data products including observations, reanalyses, and climate models, with a particular emphasis on the processes and mechanisms associated with precipitation change. The model analysis includes global and regional models, and large datasets including multi-model ensembles coordinated by CMIP, and perturbed physics ensembles. One approach we have used is to analyse the climate change associated with degrees of global warming.

We are currently leading the evaluation of the Met Office Unified Model over Africa, as part of the DFID-NERC funded IMPALA project. Historically, a great deal of effort to develop and evaluate models has focused on the representation of mid latitude climate, and IMPALA will instead highlight the key processes for Africa, in collaboration with experts from West, Central, East, and southern Africa. In evaluating the pan-African and regional climate systems in the UM, we hope to encourage other research groups to examine these dynamics in their own models, as well as generating metrics which can facilitate this work. The ideas and tools developed in IMPALA are designed to form the basis for a hub of metrics for African climate, which other scientists can access and contribute to.

Another area of interest is policy-relevant analysis of climate model projections. Model evaluation research is designed to support confidence assessments which can help adaptation planners understand which futures might be more or less credible. Projections have also been analysed in line with degrees of global warming including 2°C and 1.5°C, to support questions in international policy about the regional influence of global mitigation targets.

Contacts

Prof Richard Washington

Dr Neil Hart
Dr Rachel James
Callum Munday
Amy Creese

Advertisements