Salerno, J., J.E. Diem, B.E Konecky, J. Hartter. 2019. Recent intensification of the seasonal rainfall cycle in equatorial Africa revealed by farmer perceptions, satellite-based estimates, and ground-based station measurements. Climatic Change, forthcoming.
Smallholder farmers and livestock keepers in sub-Saharan Africa are on the frontlines of climate variability and change. Yet, in many regions, a pau city of weather and climate data has prevented rigorous assessment of recent climate trends and their causes, thereby limiting the effectiveness of forecasts and other services for climate adaptation. In rainfed systems, farmer perceptions of changing rainfall and weather patterns are important precursors for annual cropping decisions. Here, we propose that combining such farmer perceptions of trends in seasonal rainfall with satellite-based rainfall estimates and climate station data can reduce uncertainties regarding regional climatic trends. In we stern Uganda, a rural and climatic ally complex transition zone between eastern and central equatorial Africa, data from 980 smallholder households suggest distinct changes in seasonal bimodal rainfall over recent decades, specifically wetter rainy seasons and drier dry seasons. Data from three satellite-based rainfall products beginning in 1983 largely corroborate respondent perceptions over the last 10–20 years, particularly in the southernmost sites near Queen Elizabeth National Park. In addition, combining all three information sources suggests an increasing trend in annual rainfall, most prominently in the north near Murchison Falls National Park over the past two decades; this runs counter to recent research asserting the presence of a drying trend in the region. Our study is unique in evaluating and cross-validating these multiple data sources to identify climatic change affecting people in a poorly understood region, while providing insights into region al-scale climate controls.
Diem, J.E., J. Hartter, J.D. Salerno, E. McIntyre, and A.S. Grandy. 2016. Comparison of measured multi-decadal rainfall variability with farmers’ perceptions of and responses to seasonal changes in western Uganda. Regional Environmental Change DOI:10.1007/s10113-016-0943-1.
Smallholder farmers in sub-Saharan Africa (SSA) are not only dealing with decreased production from land degradation, but are also impacted heavily by climate variability. Farmers perceive decreased rainfall or shortened rainy seasons throughout SSA; however, the link between perceptions and climate variability is complex, especially in areas with increasing land degradation. Moreover, little is known about climate variability and farmers’ perceptions in central equatorial Africa. The purpose of this study is to quantify inter-annual rainfall variability from 1983-2014 in western Uganda and to relate the rainfall variability and associated changes in soil moisture to perceptions and coping strategies of local farmers. Surveys of 308 farming households and 14 group interviews were conducted near Kibale National Park, and daily satellite-based rainfall data for the region were extracted from the African Rainfall Climatology version 2 database. Results indicate a decrease in the long rains by approximately three weeks throughout much of the region; thus, soil-water deficits have intensified. Farmers perceived later onsets of both the short rains and long rains, while also reporting decreasing soil fertility and crop yields. Therefore, farmers’ perceptions of rainfall variability in the Kibale region may reflect more the decrease in soil fertility than the shortened rainy seasons and decreased soil moisture. Expanding croplands has been the farmers’ most prevalent coping strategy to decreased yields; however, nearly all the unfarmed land in western Uganda is now in protected areas. Consequently, western Uganda is facing a crisis at the nexus of population growth, land use change, and climate change.
Diem, J.E., S.J. Ryan, J. Hartter, and M.W. Palace 2014. Satellite-based rainfall data reveal a recent drying trend in central equatorial Africa. Climatic Change 126:263–272.
West-central Uganda, a biodiversity hotspot on the eastern edge of central equatorial Africa (CEA), is a region coping with balancing food security needs of a rapidly growing human population dependent on subsistence agriculture with the conservation of critically endangered species. Documenting and understanding rainfall trends is thus of critical importance in west-central Uganda, but sparse information exists on rainfall trends in CEA during the past several decades. The recently created African Rainfall Climatology version 2 (ARC2) dataset has been shown to perform satisfactorily at identifying rainfall days and estimating seasonal rainfall totals in west-central Uganda. Therefore, we use ARC2 data to assess rainfall trends in west-central Uganda and other parts of equatorial Africa from 1983–2012. The core variables examined were three-month rainfall variables for west-central Uganda, and annual rainfall variables and seasonal rainfall totals for a transect that extended from northwestern Democratic Republic of the Congo to southern Somalia. Significant decreases in rainfall in west-central Uganda occurred for multiple three-month periods centered on boreal summer, and rainfall associated with the two growing seasons decreased by 20% from 1983–2012. The drying trend in west-central Uganda extended westward into the Congo rainforest. Rainfall in CEA was significantly correlated with the Atlantic Multidecadal Oscillation (AMO) at the annual scale and during boreal summer and autumn. Two other possible causes of the decreasing rainfall in CEA besides North Atlantic Ocean sea-surface temperatures (e.g., AMO), are the warming of the Indian Ocean and increasing concentrations of carbonaceous aerosols over tropical Africa from biomass burning.
Diem, J.E., J. Hartter, S.J. Ryan, and M.W. Palace 2014. Validation of satellite rainfall products for western Uganda. Journal of Hydrometeorology 15:2030–2038.
Central equatorial Africa is deficient in long-term, ground-based measurements of rainfall; therefore, the aim of this study is to assess the accuracy of three high-resolution, satellite-based rainfall products in western Uganda for the 2001–10 period. The three products are African Rainfall Climatology, version 2 (ARC2); African Rainfall Estimation Algorithm, version 2 (RFE2); and 3B42 from the Tropical Rainfall Measuring Mission, version 7 (i.e., 3B42v7). Daily rainfall totals from six gauges were used to assess the accuracy of satellite-based rainfall estimates of rainfall days, daily rainfall totals, 10-day rainfall totals, monthly rainfall totals, and seasonal rainfall totals. The northern stations had a mean annual rainfall total of 1390 mm, while the southern stations had a mean annual rainfall total of 900 mm. 3B42v7 was the only product that did not underestimate boreal-summer rainfall at the northern stations, which had ;3 times as much rainfall during boreal summer than did the southern stations. The three products tended to overestimate rainfall days at all stations and were borderline satisfactory at identifying rainfall days at the northern stations; the products did not perform satisfactorily at the southern stations. At the northern stations, 3B42v7 performed satisfactorily at estimating monthly and seasonal rainfall totals,ARC2 was only satisfactory at estimating seasonal rainfall totals, and RFE2 did not perform satisfactorily at any time step. The satellite products performed worst at the two stations located in rain shadows, and 3B42v7 had substantial overestimates at those stations.