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Climate models are useful tools for monthly to decadal prediction of the evolution of climate. This study assesses how CMIP6 models represent soil moisture-latent heat regimes and coupling processes between the land and atmosphere. Metrics considered are terrestrial and atmospheric coupling indices to show the nature and strength of the coupling over Africa, focusing on the March to May (MAM) and June to August (JJA) seasons over East, Central, and West Africa. Characterization of the annual cycle indicates that model biases are highest during the peak of the rainfall season and least during the dry season, while soil moisture biases correspond with rainfall. Models show appreciable sensitivity to regional characteristics; there was model consensus in representing East Africa and the Sahel as regions of limited soil moisture, while major differences were noted in the wet regime over Central Africa. Most CMIP6 models tend to overestimate the strength of the terrestrial and atmospheric coupling pathways over East and Southern Africa. Inter-model differences in coupling indices could be traced to their inter-annual variability rather than the mean biases of the variables considered. These results encourage further advancement of land surface schemes in the next generation of climate models for a better representation of climate over Africa. [ABSTRACT FROM AUTHOR]

As one of three global hot spots of tropical convection, potential future changes to the Congo Basin climate system will have regional and tropics‐wide implications. However, the latest generation of climate models from the Coupled Model Intercomparison Project 5 disagree on the sign and magnitude of future change and diverge in their estimation of the historical rainfall climatology. This study assesses the plausibility of different signals of future rainfall change by examining the processes relating to rainfall projections in samples of historically wet or dry models during the September–November rainy season. In the west Congo Basin, there are no significant differences in rainfall change projections in models that are historically wet or dry. Both composites feature wetting in the north (up to 1.8 mm/day) and drying in the south, associated with enhanced tropical Atlantic sea surface temperatures, increased evaporation, and enhanced low‐level moisture flux into the basin. In the east Congo Basin, there is greater evidence that differences in model historical climatologies has an influence on the magnitude of future rainfall change. Historically wet models project significant wetting in the northeast (1.19 mm/day) associated with a weakened northern component of the African Easterly Jet (AEJ) and enhanced moisture convergence. Dry models do not capture the structure of the AEJs in the historical period, and so changes to the AEJs under warming do not produce the same wetting pattern. The analysis therefore casts doubt on the plausibility of the driest rainfall change signals in the east Congo Basin. Key Points: The magnitude and distribution of Congo Basin future rainfall change varies across coupled modelsProcess‐based model evaluation can help to identify the plausibility of rainfall projections in the absence of observational dataHistorical model biases in the African Easterly Jets affect the magnitude of future rainfall change in the east Congo Basin [ABSTRACT FROM AUTHOR]

An important challenge for climate science is to understand the regional circulation and rainfall response to global warming. Unfortunately, the climate models used to project future changes struggle to represent present-day rainfall and circulation, especially at a regional scale. This is the case in southern Africa, where models from phase 5 of the Coupled Model Intercomparison Project (CMIP5) overestimate summer rainfall by as much as 300% compared to observations and tend to underestimate rainfall in Madagascar and the southwest Indian Ocean. In this paper, we explore the climate processes associated with the rainfall bias, with the aim of assessing the reliability of the CMIP5 ensemble and highlighting important areas for model development. We find that the high precipitation rates in models that are wet over southern Africa are associated with an anomalous northeasterly moisture transport (~10-30 g kg-1 s-1) that penetrates across the high topography of Tanzania and Malawi and into subtropical southern Africa. This transport occurs in preference to a southeasterly recurvature toward Madagascar that is seen in drier models and reanalysis data. We demonstrate that topographically related model biases in low-level flow are important for explaining the intermodel spread in rainfall; wetter models have a reduced tendency to block the oncoming northeasterly flow compared to dry models. The differences in low-level flow among models are related to upstream wind speed and model representation of topography, both of which should be foci for model development. [ABSTRACT FROM AUTHOR]

Congo basin September-November rainfall varies by up to a factor of 3 across CMIP5 coupled models. The severe lack of observational data in this region makes model evaluation difficult using standard techniques. This study uses a process-based assessment to evaluate the plausibility of mechanisms related to coupled model rainfall in September-November. Models tend to simulate a rainfallmaximumin either the west or east of the basin. In most months, western Congo rainfall is positively correlated with eastern Congo rainfall across models, as relatively wet models are often wetter everywhere; however, in August-November this correlation becomes insignificant, suggesting that processes relating to rainfall differences in each subdomain are distinct. Composite analysis of wet and dry models in each subdomain suggests that the tropical eastern Atlantic SST bias helps differentiate between models in the west: wetter models tend to have a larger (~1°-2°C) and more equatorward SST bias, higher evaporation over the ocean, and higher local convection. In the east, rainfall differences between models are related to more remote SST differences, including cold South Atlantic and warm eastern Indian Ocean SSTs. Wetter models exhibit stronger westerly flow across the tropical eastern Atlantic, as part of an enhanced equatorial zonal overturning cell. Dry models in the east feature a stronger and more equatorward northerly component of the midlevel African easterly jet, which may contribute to suppressed convection over the domain. This assessment casts doubt on the credibility of models that are very wet in the west of the Congo basin and have a large Atlantic SST bias. [ABSTRACT FROM AUTHOR]

Purpose – The purpose of this paper is to identify, analyse and document local traditional indicators used in drought forecasting in the Mzingwane Catchment and to assess the possibility of integrating traditional rainfall forecasting, using the local traditional indicators, with meteorological forecasting methods. Design/methodology/approach – Self-administered structured questionnaires were conducted on 101 respondents in four districts of the Mzingwane Catchment area, namely, Beitbridge, Mangwe, Esighodini and Mwenezi from February to August 2012. In addition, key informant interviews and focus group discussions were also used in data collection and the collected data were analysed for drought history and demographics; drought adaptation and the use of drought forecasting methods in the catchment using Statistical Package for Social Science. Findings – The paper reveals the growing importance of precipitation forecasts among Mzingwane communities, particularly the amount, timing, duration and distribution of rainfall. Rainfall was cited as the major cause of drought by 98 per cent of the respondents in the catchment. Whilst meteorological rainfall forecasts are available through various channels, they are not readily accessible to rural communities. Furthermore, they are not very reliable at local level. The paper shows that communities in the Mzingwane Catchment still regard local traditional knowledge forecasting as their primary source of weather forecasts. The paper finds that plant phenology is widely used by the local communities in the four districts for drought forecasting. Early and significant flowering of Mopane trees (Colophospermum mopane) from September to December has been identified to be one of the signals of poor rainfall season in respect to quantity and distribution and subsequent drought. Late and less significant flowering of Umtopi trees (Boscia albitrunca) from September to December also signals a poor rainfall season. Originality/value – The paper fulfils an identified need to study and document useful traditional drought indicators. Furthermore, the paper provides a platform for possible integration of traditional drought forecasting and meteorological forecasting and ensure sustainable rural livelihood development. The paper is useful to both meteorological researchers and resource-constrained communities in Mzingwane Catchment. [ABSTRACT FROM AUTHOR]

This paper presents an objective analysis of the structure of daily rainfall variability over the South American/South Atlantic region (15°-60° Wand 0°-40° S) during individual austral summer months of November to March. From EOF analysis of satellite derived daily rainfall we find that the leading mode of variability is represented by a highly coherent meridional dipole structure, organised into 2 extensive bands, oriented northwest to southeast across the continent and Atlantic Ocean. We argue that this dipole structure represents variability in the meridional position of the South Atlantic Convergence Zone (SACZ). During early and later summer, in the positive (negative) phase of the dipole, enhanced (suppressed) rainfall over eastern tropical Brazil links with that over the subtropical and extra-tropical Atlantic and is associated with suppressed (enhanced) rainfall over the sub-tropical plains and adjacent Atlantic Ocean. This structure is indicative of interaction between the tropical, subtropical and temperate zones. Composite fields from NCEP reanalysis products (associated with the major positive and negative events) show that in early and late summer the position of the SACZ is associated with variability in: (a) the midlatitude wave structure, (b) the position of the continental low, and (c) the zonal position of the South Atlantic Subtropical High. Harmonic analysis of the 200 hPa geopotential anomaly structure in the midlatitudes indicates that reversals in the rainfall dipole structure are associated primarily with variability in zonal wave 4. There is evidence of a wave train extending throughout the midlatitudes from the western Pacific into the SACZ region. During positive (negative) events the largest anomalous moisture advection occurs within westerlies (easterlies) primarily from Amazonia (the South Atlantic). In both phases a convergent poleward flow results along the leading edge of the low-level trough extending from the tropics into temperate latitudes. High summer events differ from those in early and late summer in that the rainfall dipole is primarily associated with variability in the phase of zonal wave 3, and that tropical-temperate link is not clearly evident in positive events. [ABSTRACT FROM AUTHOR]