Farmers’ perceptions of climate variability is compared with the sensitivity of observed yields for wheat, maize, soybean, and sunflower crops to interannual and intra-annual climate variability in two districts (Junín and San Justo) in central Argentina from the 1970s. A recent transition occurred here between mixed crop and livestock farming to a more specialized system, dominated by transgenic soybean combined with glyphosate. According to the ethnographic fieldwork, farmers ranked drought first and flood second as the main adverse climate factors in both districts. Overall, the farmers’ representations fit rather well with the observed relationships between interannual variability of yields and rainfall, especially in Junín. The adverse impact of long-lasting dry spells, especially during the first half of the crop cycle, is usually combined with the more linear impact of large rainfall amounts (anomalously positive/negative rainfall amounts associated with anomalously positive/negative yields) during the second half of the crop cycle. This relationship is strong for soybeans, similarly large for maize, far weaker for wheat, and reversed for sunflower, which is the only crop that benefits, on average, from anomalously low rainfall amounts at a specific stage of the crop cycle. The adverse effect of flood on soybeans and maize seems less phase-locked and more diluted across the crop cycle. This paper presents the argument that climate and society have a complex relationship, requiring an integrated analysis of the social context, people’s perceptions of climate, and scientific climate knowledge. The concept of “climate social significance” is proposed in order to highlight the strategies implemented by different socioproductive groups to address adverse climate events.

a b s t r a c tAccurate seasonal predictions of rainfall may reduce climatic risks that farmers are usually faced with across the tropical and subtropical zones. However, although regional-scale seasonal amounts have regularly been forecasted since 1997/98, the practical use of these seasonal predictions is still limited by myriad factors. This paper synthesizes the main results of a multi-disciplinary ethnographic and climatic project (PICREVAT). Its main objective was to seek the climatic information -beyond the seasonal amounts -critical for crops, both as an actual constraint to crop yields and as identified by the current and past practices and perceptions of farmers. A second goal was to confront the relevance and significance of this climatic information with its spatial coherence, which gives an upper bound of its potential predictability. The ethnographic and climatic analyses were carried out on three very different fields: North Cameroon (mixed food crops associated with a cash crop -cotton -integrated into a national program); Eastern slopes of Mt Kenya (mixed food crops, with a recent development of maize at the expense of sorghum and pearl millet); and Central Argentina (mixed crops and livestock recently converting to monoculture of transgenic soybean, referred to as soybeanization).The ethnographic surveys, as well as yield-climate functions, emphasized the role played by various intra-seasonal characteristics of the rainy seasons beyond the seasonal rainfall amounts, in both actual yields and people's representations and/or crop management strategies. For instance, the onset of the rainy season in East Africa and North Cameroon, the season duration in the driest district of the eastern slopes of Mount Kenya, or rains at the core (August) and at the end of the rainy season in North Cameroon have been highlighted. The dynamics of farming systems (i.e. soybeanization in Central Argentina, increasing popularity of maize in East Africa, recent decline of cotton in North Cameroon) were also emphasized as active drivers; these slow changes could increase climatic vulnerability (i.e. soybean is far more sensitive to rainfall variations than wheat, maize is less droughthttp://dx.