3 research outputs found
Flow-duration curve integration into digital filtering algorithms for simulating climate variability based on river baseflow
A baseflow separation methodology combining the outcomes of the flow–duration curve and the digital filtering algorithms to cope with the restrictions of the traditional procedures has been assessed. Using this methodology as well as the monitored and simulated hydro-climatologic data, the baseflow annual variations due to climate change and human-induced activities were determined. The outcomes show that the long-term baseflow index at the upstream sub-basin is nearly half of that at the downstream from October to April, whereas, they are close to each other for the remaining months. Some of the groundwater reacts to precipitation and an evident rise in the groundwater contribution has been detected for the hydrological years 1998–2001 and 2006–2008. The contrary has been recorded for 1987. The water released from the reservoir in the dry periods lead to distinctions in the detected baseflow index between the pre-damming and post-damming periods of the river
The Relationship between the Mean Surface Air Temperature in Egypt and NAO Index and ENSO
Changes in the frequency and severity of hydrological droughts over Ethiopia from 1960 to 2013
Here we present an analysis of drought occurrence and variability in Ethiopia, based on the monthly precipitation data from the Climate Research Unit (CRU-v3.22) over the period from 1960 to 2013. The drought events were characterized by means of the Standardized Precipitation Index (SPI) applied to precipitation data at a temporal scale of 12 months. At the national scale, the results reveal a statistically significant decrease in the severity of droughts over the 54-year period, a pattern that is mostly attributed to a statistically significant decrease in the frequency of high intensity drought episodes (i.e., extreme and very extreme droughts), compared to moderate droughts. To assess the general patterns of drought evolution, a principal component analysis (PCA) was applied to the SPI series. PCA results indicate a high spatial heterogeneity in the SPI variations over the investigated period, with ten different spatially well-defined regions identified. These PCA components accounted for 72.9% of the total variance of drought in the region. These regions also showed considerable differences in the temporal variability of drought, as most of the regions exhibited an increase in wetness conditions in recent decades. In contrast, the regions that receive less than 400 mm of annual precipitation showed a declining trend, with the largest changes occurring over Afar region. Generally, the highly elevated regions over the central Ethiopian Highlands showed the weakest changes, compared to the lowlands. This study confirms the local character of drought evolution over Ethiopia, providing evidence for policy makers to adopt appropriate local policies to cope with the risks of drought. Over Ethiopia, the detailed spatial assessment of drought evolution is required for a better understanding of the possible impacts of recurrent drought on agriculture, food production, soil degradation, human settlements and migrations, as well as energy production and water resources management across Ethiopia.Se presenta un análisis de la ocurrencia y variabilidad de sequías en Etiopía, basado en datos de precipitación mensual de la Climate Research Unit (CRU-v3.22) para el periodo entre 1960 y 2013. Los eventos de sequía se caracterizaron por medio del Índice de Precipitación Estandarizada (SPI) aplicado a los datos de precipitación para una escala temporal de 12 meses. A escala nacional, los resultados revelan un descenso estadísticamente significativo en la severidad de las sequías en un periodo de 54 años, un patrón que se atribuye principalmente al descenso en la frecuencia de episodios de sequía de elevada intensidad. Para comprobar los patrones generals de evolución de sequías se aplicó un análisis de components principals (PCA) a las series de SPI. Los resultados del PCA indican una alta heterogeneidad espacial en las variaciones del SPI durante el period investigado, habiéndose identificado diez regiones espacialmente diferentes. Los components del PCA representaron el 72.9% de la varianza total de sequías en la region. Estas regiones también mostraron un aumento en las condiciones de humedad en décadas recientes. En contraste, las regiones que reciben menos de 400 mm de precipitación annual mostraron una tendencia decreciente, siendo la region de Afar la que presenta los mayores cambios. En general, las regiones más elevadas de las tierras altas del centro de Etiopía son las que mostraron menores cambios en comparación con las tierras bajas. Este estudio confirma el carácter local de la evolución de las sequías en Etiopía, proporcionando evidencias para los políticos y técnicos con el fin de adoptar políticas locales apropiadas para enfrentarse a los riesgos de sequías. En Etiopía, se require un studio especial detallado de la evolución de las sequías para una major comprensión de los posibles impactos de sequías recurrentes sobre la agricultura, la producción de alimento, la degradación del suelo, los asentamientos humanos y las migraciones, así como la producción de energía y las gestión de los recursos hídricos en Etiopía