Sahel Seasonal to Decadal Climate Variability and Atmosphere/Surface Two-Way Interactions

University Of California-Los Angeles, Los Angeles CA

Investigators

Abstract

Dramatic change over the Sahel from wet conditions in the 1950s to much drier conditions in the 1970s and the 1980s and then to partial recovery since the 1990s, represents one of the strongest interdecadal signals on Earth in the twentieth century. Studies suggest that Sahel climate variability is strongly influenced by external forcings: sea surface temperature (SST), land surface processes, and aerosols. However, general circulation model (GCM) studies with a single external forcing (for example, SST) have not been able to reproduce full seasonal, interannual, and decadal variability and anomalies (SIDVA) of Sahel climate. In most of these studies, SST, land, and aerosol conditions were specified, i.e., there was only one way interaction. The relative roles of the external forcings and their two-way interactions in the Sahel climate SIDVA have never been quantitatively and comprehensively examined. This project will conduct a set of 60-year simulations with a coupled Atmospheric GCM/biophysical model/dynamic vegetation model as well as preliminary tests with Atmospheric-Ocean GCM/ biophysical model/dynamic vegetation model, incorporating two way feedback processes, to explore the causes of Sahel climate SIDVA and to assess the relative contribution of ocean and land, including human-induced land use and land cover (LULC) change. Recently available data will be used to specify LULC change. In addition, a regional climate model (RCM) using Atmospheric GCM simulations from selected years as lateral boundary conditions will be applied to assess the regional details of surface-atmosphere interactions in the Sahel climate SIDVA. This work will test whether the RCMs will provide additional subseasonal to decadal prediction skill and if they are able to provide supplementary skillful regional information not available in coarse scale GCM predictions. This interdisciplinary research will test the hypothesis that a comprehensive understanding of West African Monsoon (WAM) SIDVA and its mechanisms requires synthesized investigation, including multi-major external forcings and their full feedbacks in the climate model. Data from satellite and field measurements, especially from African Monsoon Multidisciplinary Analyses (AMMA) project, and other sources will be applied for evaluation and specification of model simulations/predictions. Model-simulated major features and components relevant to the Sahel climate SIDVA, such as precipitation, soil moisture, vegetation condition, SST, as well as their relationship to each other will be comprehensively analyzed and compared with data from different sources. This project intends to provide a comprehensive understanding of how different earth processes and human activities have contributed to the Sahel climate variability and anomalies over much of the last century through the representation of key non-linear feedback processes in WAM climate simulations. This project has broader impacts. Understanding Sahelian climate seasonal, interannual, and decadal variability and anomaly has been recognized as a critical component in global climate studies by international programs. The distinct climate features, the strong coupling between Sahel climate and external forcings, the controversy on the causes of the Sahel climate anomalies, especially the drought, and significant social and economic implications of Sahel climate SIDVA make this region extremely important for the scientific community. This project will address some of the key scientific issues in the study of Sahelian climate and will contribute to identification of the attribution of Sahel rainfall changes to anthropogenic and natural drivers and the effect of climate variability on ecosystems and water resources. The results from this study will not only further our understanding of the Sahelian climate, but also provide useful information through regional downscaling for social planning, which is crucial for the fragile Sahelian economy. They will be distributed through the Global Energy and Water Cycle Experiment Hydroclimatology Panel (GEWEX GHP) database and the African Centre of Meteorological Application for Development (ACMAD).