This report, which encompasses the findings of a Regional Diagnostic Study (RDS) for West Africa, was undertaken in 2014-15 to advance understanding of climate change in semi-arid regions of Africa and Asia. The RDS represents the first phase of a research effort under the Adaptation at Scale in Semi-Arid Regions (ASSAR) project. ASSAR is one of four consortia generating new knowledge of climate change hotspots under the Collaborative Adaptation Research Initiative in Africa and Asia (CARIAA1). The ASSAR project operates in Western, Eastern and Southern Africa and Western India. The ASSAR focal countries in Africa are Ghana, Mali, Ethiopia, Kenya, Botswana, and Namibia, and in India the focal states are Tamil Nadu, Maharashtra, and Karnataka. The project spans a five-year period from 2014-2018, and has a three-phase research program: a regional diagnostic phase, a regional research program phase, and a synthesis phase. ASSAR aims to generate new stakeholder-driven knowledge on vulnerability and adaptation to climate change in semi-arid regions, develop innovative communication approaches for effective knowledge sharing on climate change vulnerability and adaptation, and stengthen capacity for adaptation in research, policy and practice domains. The RDS for West Africa was undertaken through a partnership between START, the Institute for Environment and Sanitation Studies at the University of Ghana, and the International Centre for Research in the Semi-Arid Tropics (ICRISAT) in Bamako, Mali. This RDS aims to develop a systematic understanding of existing knowledge of climate change trends, impacts, vulnerabilities, and adaptation strategies, as well as to identify important barriers to and enablers of effective adaptation in semi-arid regions. Secondly, the RDS serves to identify gaps in research, policy and practice related to climate change adaptation. The RDS provides a foundation for developing an integrated regional research program (RRP) on climate change vulnerability and adaptation centered around advancing knowledge on socio-economic and biophysical systems, governance and institutions, gender, and wellbeing. The RDS thus provides a broad regional-scale context into which the RRP can be designed to focus on achieving deeper understanding of the multi-faceted nature of vulnerability, adaptation enablers and adaptation barriers. There are multiple target audiences for the findings generated through this RDS. They include academics and researchers, stakeholders from government, civil society, and the international donor community. The findings of this report will be used to inform a communication strategy that will allow for broader dissemination of key findings from this RDS. This RDS report represents the initial step in ASSAR West Africa’s efforts to understand and unpack the complexities of vulnerability and adaptation within a dynamic development context that includes population and demographic change, urbanization, land-use change, and advancing communication technologies. The approach taken by the West Africa team in developing the RDS will allow for information produced through the RDS to set the stage for indepth research to begin in mid-2015. Specifically, this is accomplished through: Description of the major socio-economic, governmental and environmental characteristics as they relate to the region’s extensive dryland2 areas (Chapter 2). Regional analysis for climate trends and projections that provide key messages about climate change (Chapter 3). Exploration of how important development dynamics in the region interact with climate variability and change to amplify vulnerabilities (Chapters 2 and 4). Examination of gender and governance dimensions of vulnerability and adaptation (Chapter 5). Elaboration of how current risk management practices in agriculture link to climate change adaptation (Chapter 5). Synthesizing of important barriers and enablers of adaptation and key knowledge gaps and needs (Chapter 5). Gender and governance are prominent themes that cut across Chapters 4 and 5. In compiling this report, it was difficult to draw clear lines delineating content for each of these topics that would fit cleanly into vulnerability and adaptation spheres. Thus vulnerability and adaptation dimensions of gender are combined into a single sub-section within Chapter 5, and aspects of governance described in Chapter 5 partially reiterate issues raised in Chapter 4 but with a deeper analysis. The ASSAR project in West Africa focuses on the dry sub-humid band that extends from the Upper West Region of northern Ghana through southern Mali, referred to as the Wa-Bobo-Sikasso (WBS) transect. This transect features diverse socio-economic conditions set against fairly homogenous biophysical conditions. The region experiences high exposure to dry spells, and has medium-high to high drought risk and strong multi-decadal fluctuations in climate. The region is also experiencing significant land degradation and processes that can lead to desertification. This region is characterized by very high rates of poverty, comparable to those of the Sahel (as described in Chapter 2). The selection of this transect allows the ASSAR projectto link directly with the CCAFS project within the Dryland Systems Collaborative Research Programme (CRP) of the CGIAR, also described in Chapter 2.