The rainfall specifics characteristics vary from one region to another. The knowledge of the rainfall potential to cause erosion is necessary to plan agricultural and civil engineering activities. For Quarai and Rio Grande (RS, Brazil), were determined the rainfall erosivity and its relationship with precipitation and rainfall coefficient, rainfall patterns and rainfall return period. Were used rainfall data charts of 38 years of Quarai (1966-2003) and 23 years of Rio Grande (1957, 1959-1978 e 1980-1981). For each erosive rainfall were separated the segments of the rainfall chart with the same intensity and the data registered in worksheet. With the software Chuveros were estimated the mean monthly and annual rainfall erosivity, the EI30 index in the International System of Units and the rainfall patterns. The mean monthly values of precipitation and erosivity index were expressed as percentages of the mean annual values of precipitation and erosivity index, respectively, to obtain the curve of accumulated distribution of precipitation and erosivity index in function of time. The rainfall coefficient (Rc) was calculated. Were performed Pearson correlations and linear regressions between the erosivity index EI30 and the mean annual values of precipitation and rainfall coefficient.. The rainfall return period were calculated for 2, 5, 10, 20, 50 e 100 years. The mean annual values of EI30 for Quarai and Rio Grande were 9292.1 e 5135.0 MJ mm ha-1 h-1 ano-1, respectively. Were obtained the equations EI30 = -754.37 + 13.50 p (r2 = 0.85) e EI30 = - 47.35 + 82.72 Rc (r2 = 0.84) for Quarai. For Rio Grande the equations were not significant. In relation to the total of the rainfalls studied for each place, 44.3% of the number and 90.4% of the volume were erosive in Quarai, and 32.6% of the number and 99.3% of the volume were erosive in Rio Grande. The method of extreme distribution type I was adequate for obtaining the curves of intensity-duration-frequency. The rainfall return periods may be calculated by the equations using the values of the parameters found, or by the figures of intensity-durationfrequency. / As características específicas das chuvas variam de uma região a outra. O conhecimento da potencialidade das chuvas em causar erosão é necessário para planejar atividades agrícolas e de engenharia civil. Para as localidades de Quarai e Rio Grande (RS), foram determinados a erosividade da chuva e a relação com a precipitação e o coeficiente de chuva, os padrões da chuva e o período de retorno da chuva. Utilizaram-se dados pluviográficos de 38 anos de Quarai (1966-2003) e 23 anos de Rio Grande (1957, 1959-1978 e 1980-1981). Para cada chuva erosiva foram separados os segmentos do pluviograma com a mesma intensidade e registrados os dados em planilha. Com o programa Chuveros foram calculadas a erosividade mensal, anual e média das chuvas pelo índice EI30 no Sistema Internacional de Unidades e os padrões de chuva. Os valores médios mensais da precipitação e do índice de erosividade foram expressos como percentagens do valor médio anual da precipitação e do índice de erosividade respectivamente, para obter a curva de distribuição acumulada da precipitação e do índice de erosividade em função do tempo. O coeficiente de chuva (Rc) foi calculado. Foram realizadas correlações de Pearson e regressões lineares simples entre o índice de erosividade EI30 e os valores médios anuais de precipitação e de coeficiente de chuva. O período de retorno foi calculado para 2, 5, 10, 20, 50 e 100 anos. Os valores médios anuais de EI30 para Quarai e Rio Grande foram 9292,1 e 5135,0 MJ mm ha-1 h-1 ano-1, respectivamente. Para Quarai, obtiveram-se as equações EI30 = -754,37 + 13,50 p (r2 = 0,85) e EI30 = -47,35 + 82,72 Rc (r2 = 0,84). Para Rio Grande as equações não foram significativas. Em relação ao total das chuvas estudadas em cada localidade, 44,3% do número e 90,4% do volume foram erosivas em Quarai, e 32,6% do número e 99,3% do volume foram erosivas em Rio Grande. O método da distribuição extrema tipo I foi adequado para obter as curvas de intensidade duração-freqüência. Os períodos de retorno da chuva podem ser calculados através das equações utilizando os valores dos parâmetros achados, ou pelos gráficos das curvas de intensidade-duração-freqüência.

MESHWR / Department of Hydrology and Water Resources / This study was aimed at investigating the long term seasonal and annual changes in rainfall duration and magnitude at Luvuvhu River Catchment (LRC). Rainfall in this catchment is highly variable and is characterised of extreme events which shift runoff process, affect the timing and magnitude of floods and drought, and alter groundwater recharge. This study was motivated by the year to year changes of rainfall which have some effects on the availability of water resources. Computed long term total seasonal, annual rainfall and total number of seasonal rainy days were used to identify trends for the period of 51 years (1965- 2015), using Mann Kendal (MK), linear regression (LR) and quantile regression methods. The MK, LR and quantile regression methods have indicated dominance of decreasing trends of the annual, seasonal rainfall and duration of seasonal rainfall although they were not statistically significant. However, statistical significant decreasing trends in duration of seasonal rainfall were identified by MK and LR at Matiwa, Palmaryville, Levubu, and Entabeni Bos stations only. Quantile regression identified the statistically significant decreasing trends on 0.2, 0.5 and 0.7 quantiles only in the Palmaryville, Levubu and Entabeni Bos, respectively. Stations with non-statistically significant decreasing trends of annual and seasonal rainfall had magnitude of change ranging from 0.12 to 12.31 and 0.54 to 6.72 mm, respectively. Stations with non-statistically increasing trends of annual and seasonal rainfall magnitude had positive magnitude of change ranging from 1.51 to 6.78 and 2.05 to 6.51 mm, respectively. The Study recommended further studies using other approaches to determine the duration of rainfall to improve, update and compare the results obtained in the current study. Continuous monitoring and installation of rain gauges are recommended on the lower reaches of the catchment for the findings to be of complete picture for the whole catchment and to also minimize the rainfall gaps in the stations. Water resources should be used in a sustainable way to avoid water crisis risk in the next generations. / NRF