Standard Precipitation Index (SPI) and, its variant, Standard Precipitation and Evapotranspiration Index (SPEI) are among the most commonly used drought assessment indices worldwide. SPI uses precipitation as its only input to assess drought. Unlike SPI, SPEI uses both precipitation and temperature, thereby considering the influence of global warming to some extent. Assessments of performance between SPI and SPEI is well addressed. However, no adequate literature was found on the assessment of the degree of agreement between SPI and SPEI at different time scales. Hence, this research focused on examining the level of agreement between SPI and SPEI as drought assessment tools at 1-month, 3-month, 6-month, 12-month and 24-month time scales. The test of agreement between SPI and SPEI was conducted using Cohen's Kappa statistics and the Bland-Altman method. Gridded monthly precipitation and temperature Climatic Research Unit time-series data version 4.01 were used to calculate SPI and SPEI for the period 1901 to 2016. The results of Cohen's Kappa statistics indicate that there existed a fair degree of agreement between SPI and SPEI at all time scales. A positive linear correlation (r > 0.7, p < 0.001) was also observed between SPI and SPEI ratings at all time scales. Small mean difference (bias) in the Bland and Altman analyses result indicated for the presence of agreement between the assessment tools. This study has found that there is an acceptable level of agreement between SPI and SPEI ratings in the study area, at all timescales.

Drought is controlled and enhanced by changes in the local and global climate factors. The changes in the global factors mainly occur on the vast oceanic surfaces, while the changes in the local factors occur in the area of drought influence. In order to skilfully forecast and monitor drought occurrences, it is crucial that the specific causal factors be identified and their links studied. Based on this concept, this study tried to establish a relationship between the drought occurrences in Tigray region and the climate factors at the local and global scale. Monthly gridded Climatic Research Unit (CRU) Time-series (TS) data version 4.01 was used to calculate the Standardized Precipitation and Evapotranspiration Index (SPEI). As potential global causal factors, SOI (Southern Oscillation Index), Sea Surface Temperature Anomalies (SSTAs) of the tropical oceanic surfaces, the Red Sea and Nino 3.4 regions were obtained from various sources. Vegetation cover and albedo data were also considered as local drought causal factors. The analyses results show that the zero-time-lag SSTA in the tropical Indian Ocean was identified as statistically significant (p < 0.01) drought influencing factor accounting for 5.8% and 8% of the variations in SPEI, at 1-month and 6-month time scales respectively. At 12-month time scale, however, the SSTAs in the tropical Indian Ocean, tropical Atlantic Ocean, tropical Pacific Ocean, the Red Sea and Nino 3.4 regions were designated as drought influencing factors. Differently, at 24-month time scale, SOI was also identified as drought influencing factor in addition to the SSTAs in the tropical Indian Ocean, tropical Pacific Ocean and the Red Sea region. In general, the findings revealed the variability in the number and type of causal factors based on time scale and time-lag. Nevertheless, the ability of the identified factors to explain the variation in SPEI remained small at all timescales investigated. This, therefore, indicates the need for further investigation on other drought causal factors in the study area.

SUMMARYTwelve non-pregnant female goats (West African Dwarf, WAD and Red Sokoto, RS) were used to investigate the effect of volumetric (0%, 33% and 67%) water restriction on feed intake and weight gain over a period of eight weeks. The goats are of 2 age groups: younger and older than 1 year. The experiment was arranged in a modified cross-over design with three treatment periods of 1 week each. In-between each treatment period was a 2-week wash-out period, when the effect of the previous was expected to have worn off. The average water intake (WI) was determined for the first 7 days of the experiment when all the animals were given water ad libitum. The 3 treatments were: (i) ad libitum supply of water every day; (ii) 33% reduction from average WI; and (iii) 67% reduction. Water drunk had positive and significant (p<0.001) correlation with feed intake in young and old WAD (r= 0.490 and 0.620 respectively) and RS (>1 year old; r= 0.615). All the four classes of goats showed positive highly significant (p<0.001) correlation between water drunk and daily weight gain (r= 0.408, 0.484, 0.555 and 0.422 respectively for WAD (<1 and >1 year old) and RS (<1 and >1 year old goats). RESUMEN Doce cabras no preñadas (West AfricanDwarf, WAD y Red Sokoto, RS) fueron empleadas para investigar el efecto de la restricción volumétrica (0%, 33% and 67%) del suministro de agua sobre la ingestión de alimento y ganancia de peso durante ocho semanas. Los animales se agruparon por edad en menores y mayores de un año. El experimento se dispuso según un diseño cruzado, modificado con tres periodos de tratamiento de una semana cada uno. Entre cada periodo se intercaló uno de lavado de dos semanas durante el que se eliminaba el efecto del experimento precedente. La ingestión media de agua (WI) fue determinada para los siete primeros dias del experimento durante los cuales a todos los animales se suministraba agua ad libitum. Los tratamientos fueron: (i) suministro de agua ad libitum, (ii) reducción del 33% sobre la ingestión media y (iii) 67% de reducción. El agua bebida mostró correlación positiva (p<0,001) con la ingestión de alimento en las cabras WAD jóvenes (r= 0,490) y mayores (r= 0,620) y para las RS de más de un año (r= 0,615). Todas las cabras mostraron correlación positiva (p<0,001) entre agua bebida y ganancia de peso (WAD:<1, r= 0,408 y >1, 0,484 y RS: <1, 0,555 y>1, 0,422).

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