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No. of bitstreams: 1 choqueconde_e_dr_bot.pdf: 12634736 bytes, checksum: d8da7485161968cf5d5723a8b589c057 (MD5) Previous issue date: 2017-06-14 / Item merged in doublecheck by Luiz Galeffi (luizgaleffi@gmail.com) on 2017-07-18T17:58:20Z Item was identical to item(s): 151818, 151941 at handle(s): http://hdl.handle.net/11449/151034, http://hdl.handle.net/11449/151112 / Asociación Universitaria Iberoamericana de Postgrado (AIUP) / O presente pesquisa teve por objetivo estudar a temperatura do ar e a evapotranspiração de referência (ETo) nas diferentes zonas agroecológicas da Bolívia (Lhanos, Vales e Andina) por meio de modelos estatísticos e geoestatísticos, com base de dados de temperatura do ar de 235 estações meteorológicas da Bolívia e 41 de países vizinhos. O estudo é apresentado em dois capítulos: O primeiro descreve a caracterização dos valores de temperatura média (Tmed) máxima (Tmax) e mínima (Tmin) do ar, mediante três distribuições espaciais: Departamentos, bacias hidrográficas e zonas agroecológicas, sendo esta última a melhor alternativa de análise. Uma análise de regressão linear permitiu a obtenção das equações de estimativa Tmed, Tmax e Tmin em função da altitude, com elevados coeficientes de determinação (R2). Os desvios resultantes das comparações entre os valores estimados das equações sazonais e mensais em relação à média anual sugerem, na maioria das altitudes, o uso das equações sazonais ou mensais, particularmente para Tmed e Tmin. Foram apresentados as variações espaciais da Tmed, Tmax e Tmin por meio de mapas isotérmicas. Os mapas comprovam a forte influência da altitude sobre valores de Tmed, Tmax e Tmin, colocando isotermas de valores mais altos na zona dos Lhanos (zonas baixas) e, de valores mais baixos na zona Andina (zonas altas). O segundo capítulo, descreve a caracterização da ETo nas três zonas agroecológicas da Bolívia, utilizando a temperatura como variável de entrada: McGuinness – Bordne, Hargreaves – Samani e Thornthwaite. Os três métodos, mostram que os aumentos da altitude e latitude determinam uma diminuição da ETo, no sentido da zona dos Lhanos para a zona Andina. O análise de regressão linear com os três métodos permitiu a obtenção das equações anuais de estimativas para a ETo em função da altitude, com melhor resultado para o modelo de McGuinness – Bordne, cujo R2 foi o mais elevado. Os desvios resultantes das comparações entre equações dos valores de ETo sazonais e mensais em relação à anual sugerem, na maioria das altitudes, o uso das equações sazonais ou mensais. As variações espaciais da ETo apresentadas por meio de mapas de isolinhas, corroboram a forte influência da altitude sobre valores de ETo, colocando isolinhas de valores mais altos na zona dos Lhanos, e de valores mais baixos nas zona Andina. / The objective of this research was to study air temperature and reference evapotranspiration (ETo) in the different agroecological zones of Bolivia (Plains, Valleys and Andean) using statistical and geostatistical models, with air temperature database of 235 meteorological stations in Bolivia and 41 of neighboring countries was used. The study is presented in two chapters: The first describes the characterization of the values of the medium (Tmed) maximum (Tmax) and minimum (Tmin) air temperature, through three spatial distributions: Departments, hydrographic basins and agroecological zones. Being the latter the best alternative of analysis. Linear regression analysis allowed to obtain the estimation equations for Tmed, Tmax and Tmin in function of altitude, with high determination coefficients (R2). The deviations resulting from comparisons between the seasonal and monthly equations estimated values in relation to the annual average suggest, in most altitudes, seasonal or monthly equations use, mainly for Tmed and Tmin. Were presented the spatial variations Tmed, Tmax and Tmin through isothermal maps. The maps show the strong influence of altitude on temperature values, placing higher isotherms in the Plains zone (lowlands) and lower in the Andean zone (highlands). The second chapter describes the characterization of ETo in the three agroecological zones of Bolivia, using temperature as the input variable: McGuinness - Bordne, Hargreaves - Samani and Thornthwaite. All three methods show that altitude and latitude increases determine an ETo decrease, in the direction of the Plains zone to the Andean zone. The three methods linear regression analysis helped obtaining the ETo annual estimation equations in function of altitude, with McGuinness - Bordne model showing the best result, as its R2 was the highest. The deviations resulting from comparisons between equations of seasonal and monthly ETo values in relation to the annual values suggest, at most altitudes, seasonal or monthly equations use. The ETo spatial variations are presented through isoline maps, corroborate the strong influence of altitude in ETo values by placing isolines of higher values in the Plains zone, and of lower values in the Andean zone. / La presente investigación tuvo por objetivo estudiar la temperatura del aire y la evapotranspiración de referencia (ETo) en las diferentes zonas agroecológicas de Bolivia (Llanos, Valles y Andina) a través de modelos estadísticos y geoestadísticos, con base de datos de temperaturas del aire de 235 estaciones meteorológicas de Bolivia y 41 de países vecinos. El estudio es presentado en dos capítulos: El primero describe la caracterización de valores de la temperatura media (Tmed) máxima (Tmax) y mínima (Tmin) del aire, mediante tres distribuciones espaciales: Departamentos, cuencas hidrográficas y zonas agroecológicas. Siendo esta última la mejor alternativa de análisis. Un análisis de regresión lineal logró obtener las ecuaciones anuales que estiman la Tmed, Tmax e Tmin en función de la altitud, con elevados coeficientes de determinación (R2). Las desviaciones resultantes de comparaciones entre las ecuaciones estacionales y mensuales en relación a la media anual sugieren, en la mayoría de las altitudes, el uso de ecuaciones estacionales o mensuales, particularmente para Tmed e Tmin. Fueron presentadas las variaciones espaciales de Tmed, Tmax e Tmin por medio de mapas isotérmicas, los mapas evidencian la fuerte influencia de la altitud sobre valores de Tmed, Tmax e Tmin, marcando isotermas de valores más altos en la zona de los Llanos (zonas bajas) y, de valores más bajos en la zona Andina (zonas altas). El segundo capítulo describe la caracterización de ETo en tres zonas agroecológicas de Bolivia, utilizando la temperatura del aire como variable de entrada: McGuinness - Bordne, Hargreaves - Samani y Thornthwaite. Los tres métodos demuestran que los aumentos de altitud y latitud determinan una disminución de ETo, en el sentido de la zona de los Llanos para la zona Andina. El análisis de regresión lineal con los tres métodos, facilitó la obtención de ecuaciones de ETo en función de la altitud, con mejor resultado para el método McGuinness - Bordne con R2 más alto. Las desviaciones resultantes de las comparaciones entre las ecuaciones de ETo estacionales y mensuales en relación a la anual sugieren, en la mayoría de las altitudes, el uso de ecuaciones estacionales o mensuales. Las variaciones espaciales de ETo presentados por medio de mapas de isolineas, corroboran la fuerte influencia de la altitud, colocando isolineas de valores más altos en la zona de los Llanos y, de valores más bajos en la zona Andina (zonas altas).

Recurring drought conditions have always been an endemic feature of climate in South Africa, limiting maize development and production. However, recent projections of the future climate by the Intergovernmental Panel on Climate Change suggest that due to an increase of atmospheric greenhouse gases, the frequency and severity of droughts will increase in drought-prone areas, mostly in subtropical climates. This has raised major concern for the agricultural sector, particularly the vulnerable small-scale farmers who merely rely on rain for crop production. Farmers in the Luvuvhu River catchment are not an exception, as this area is considered economically poor, whereby a significant number of people are dependent on rain-fed farming for subsistence. This study was therefore conducted in order to improve agricultural productivity in the area and thus help in the development of measures to secure livelihoods of those vulnerable small-scale farmers. Two drought indices viz. Standardized Precipitation Evapotranspiration Index (SPEI) and Water Requirement Satisfaction Index (WRSI) were used to quantify drought. A 120-day maturing maize crop was considered and three consecutive planting dates were staggered based on the average start of the rainy season. Frequencies and probabilities during each growing stage of maize were calculated based on the results of the two indices. Temporal variations of drought severity from 1975 to 2015 were evaluated and trends were analyzed using the non-parametric Spearman’s Rank Correlation test at α (0.05) significance level. For assessing climate change impact on droughts, SPEI and WRSI were computed using an output from downscaled projections of CSIRO Mark3.5 under the SRES A2 emission scenario for the period 1980/81 – 2099/100. The frequency of drought was calculated and the difference of SPEI and WRSI means between future climate periods and the base period were assessed using the independent t-test at α (0.10) significance level in STATISTICA software. The study revealed that planting a 120-day maturing maize crop in December would pose a high risk of frequent severe-extreme droughts during the flowering to the grain-filling stage at Levubu, Lwamondo, Thohoyandou, and Tshiombo; while planting in October could place crops at a lower risk of reduced yield and even total crop failure. In contrast, stations located in the low-lying plains of the catchment (Punda Maria, Sigonde, and Pafuri) were exposed to frequent moderate droughts following planting in October, with favorable conditions noted following the December planting date. Further analysis on the performance of the crop under various drought conditions revealed that WRSI values corresponding to more intense drought conditions were detected during the December planting date for all stations. Moreover, at Punda Maria, Sigonde and Pafuri, it was observed that extreme drought (WRSI <50) occurred once in five seasons, regardless of the planting date. Temporal analysis on historical droughts in the area indicated that there had been eight agricultural seasons subjected to extreme widespread droughts resulting in total crop failure i.e. 1983/84, 1988/89, 1991/92, 1993/94, 2001/02, 2002/03, 2004/05 and 2014/15. Results of Spearman’s rank correlation test revealed weak increasing drought trends at Thohoyandou (ρ = of 0.5 for WRSI) and at Levubu and Lwamondo (ρ = of 0.4 for SPEI), with no significant trends at the other stations. The study further revealed that climate change would enhance the severity of drought across the catchment. This was statistically significant (at 10% significance level) for the near-future and intermediate-future climates, relative to the base period. Drought remains a threat to rain-fed maize production in the Luvuvhu River catchment area of South Africa. In order to mitigate the possible effects of droughts under climate change, optimal planting dates were recommended for each region. The use of seasonal forecasts during drought seasons would also be useful for local rain-fed maize growers especially in regions where moisture is available for a short period during the growing season. It was further recommended that the Government ensure proper support such as effective early warning systems and inputs to the farmers. Moreover, essential communication between scientists, decision makers, and the farmers can help in planning and decision making ahead of and during the occurrence of droughts. / Agriculture, Animal Health and Human Ecology / M. Sc. (Agriculture)