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The arid and semi-arid regions account for approximately 30% of the world total area and are inhabited by approximately 20% of the total world population. Issues of present and future climate variability and change on agriculture and forestry in the arid and semi-arid tropics of the world were examined and discussion under each of these issues had been presented separately for Asia, Africa and Latin America.

The 1997–1998 El-Nino caused an extreme drought in the northeastern region with considerable losses for agriculture, livestock, water resources and society. Regionally, the impact of these anomalies can be striking. In the southeastern region, for example, in the State of Sao Paulo in the El Nino period, the effects caused by this phenomenon were quite different with above average rainfall in months like May and June. This situation can be observed, as indicated by the rainfall anomalies represented by the monthly Standardized Precipitation Index (SPI) for the month of May in 1998 (Figure 17.1). The occurrence of these anomalies lead the State Government to create a task force involving the various sectors of society, such as, research institutes, universities and the civil defense, to propose mitigation measures.

Foi comparada a eficiência do uso da água pelos cultivares de arroz IR-665-4-5-5, de porte baixo, folhas eretas, e IAC-1246, de porte alto e folhas pendentes, cultivados em duas densidades de plantio (0,30 e 0,60m entre linhas), em Latossolo Roxo de textura argilosa, no Centro Experimental de Campinas. A evapotranspiração real foi determinada através do método do balanço hídrico em condições de campo. Os resultados mostraram que o cultivar de arroz IR-665-4-5-5, semeado a 0,30m entre linhas, teve maior evapotranspiração, enquanto a variedade IAC-1246, sob o mesmo espaçamento, apresentou maior eficiência de uso da água. Estreita relação foi observada entre evapotranspiração real e índice de área foliar para os tratamentos de maior densidade de plantio.This paper describes the water use efficiency for two rice cultivars IR-665-4-5-5 and IAC-1246, tilled in an Oxisol under two planting densities (0.30 and 0.60m between rows) at the Central Experimental Farm of Campinas. Actual evapotranspiration was determined by the field water balance (BRUNINI, GROHMANN; SANTOS, 4). The results indicated that the cultivar IR-665-4-5-5 with 0.30m between rows had the highest water consumption (about 616mm); but the cultivar IAC-1246 with 0.30m between rows had the highest water use efficiency followed by the cultivar IR-665-4-5-5 with 0.30m between rows. A close relationship was found between actual evapotranspiration and leaf area index for the higher density treatments.

Estudou-se o efeito da temperatura do solo sobre a produtividade de cenoura (var. nantes) cultivada em latossolo roxo sob quatro condições: com cobertura de plástico sobre a cultura, e solo nu; sem cobertura de plástico sobre a cultura, e solo com cobertura morta; com cobertura de plástico sobre a cultura, e solo com cobertura morta; e sem cobertura de plástico sobre a cultura, e solo nu. Observou-se que o tratamento com cobertura de plástico e solo com cobertura morta foi o que apresentou menor amplitude térmica no perfil, seguido do tratamento sem cobertura de plástico e com cobertura morta, e por último o tratamento sem cobertura de plástico e solo nu. A produtividade de raízes está intimamente relacionada com as variações térmicas no perfil de solo, decorrentes dos tipos de cobertura, sendo maior no tratamento que apresentou menor amplitude térmica.The effect of soil temperature on the development of carrots (Daucus carota L.) was analysed under four conditions: with polyethylene cover over the crop and bare soil; without polyethylene cover over the crop and soil with mulch; with polyethylene cover over the crop and soil with mulch; and without polyethylene cover over the crop and bare soil. A close relationship between type of mulch, soil temperature, and root yields was observed. The treatment with plastic covering the crop and the soil with mulch had the greatest yield, and the treatment with neither plastic covering the crop nor mulch on the soil had the lowest yield.

Através de um sistema de unidades térmicas, estudou-se o efeito da temperatura média do ar sobre o desenvolvimento de alface (Lactuca sativa L.), cultivar "white boston". Os resultados evidenciaram que a temperatura-base de desenvolvimento dessa hortaliça varia com o estádio de desenvolvimento da cultura, sendo igual a 6°C para a fase germinação-transplante, e 10ºC para a fase transplante-colheita. Observou-se que o desenvolvimento da planta em função da temperatura média do ar não é linear, pois atinge um máximo em torno de 22°C e após isso a taxa do desenvolvimento é decrescente.The effect of mean air temperature on the development of lettuce (Lactuca sativa L.) variety White Boston was determined in a heat-unit system. The results showed that the base temperature is function of the stage of development of the crop. The base temperature for the phase: emergence-transplant was 6°C and for the phase transplant-harvest was 10°C. It was observed that there is not a linear relationship between crop development and mean air temperature because the growth rate had a maximum at 22°C and it decreased after this value.

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