Evaluation and application of multi-source satellite rainfall product CHIRPS to assess spatio-temporal rainfall variability on data-sparse Western margins of Ethiopian Highlands

The spatio-temporal characteristic of rainfall in the Beles Basin of Ethiopia is poorly understood, mainly due to lack of data. With recent advances in remote sensing, satellite derived rainfall products have become alternative sources of rainfall data for such poorly gauged areas. The objectives of this study were: (i) to evaluate a multi-source rainfall product (Climate Hazards Group Infrared Precipitation with Stations: CHIRPS) for the Beles Basin using gauge measurements and (ii) to assess the spatial and temporal variability of rainfall across the basin using validated CHIRPS data for the period 1981-2017. Categorical and continuous validation statistics were used to evaluate the performance, and time-space variability of rainfall was analyzed using GIS operations and statistical methods. Results showed a slight overestimation of rainfall occurrence by CHIRPS for the lowland region and underestimation for the highland region. CHIRPS underestimated the proportion of light daily rainfall events and overestimated the proportion of high intensity daily rainfall events. CHIRPS rainfall amount estimates were better in highland regions than in lowland regions, and became more accurate as the duration of the integration time increases from days to months. The annual spatio-temporal analysis result using CHIRPS revealed: a mean annual rainfall of the basin is 1490 mm (1050-2090 mm), a 50 mm increase of mean annual rainfall per 100 m elevation rise, periodical and persistent drought occurrence every 8 to 10 years, a significant increasing trend of rainfall (similar to 5 mm year(-1)), high rainfall variability observed at the lowland and drier parts of the basin and high coefficient of variation of monthly rainfall in March and April (revealing occurrence of bimodal rainfall characteristics). This study shows that the performance of CHIRPS product can vary spatially within a small basin level, and CHIRPS can help for better decision making in poorly gauged areas by giving an option to understand the space-time variability of rainfall characteristics

Effect of integrated soil fertility management on hydrophysical soil properties and irrigated wheat production in the upper Blue Nile Basin, Ethiopia

In Ethiopia, soil fertility problem caused by acidity substantially limits agricultural productivity, necessitating sustainable integrated nutrient management. This study assessed the effect of combined application of lime, manure and inorganic fertilizer on selected hydrophysical properties of an acid clay Nitisols in the Koga irrigation scheme, Ethiopia. Five levels of integrated soil fertility management treatments were tested for four consecutive cropping seasons: (i) 0.86 t ha(-1) lime combined with 3 t ha(-1) manure and full-dose inorganic (urea and NPS-B) fertilizer (L3); (ii) 1.15 t ha(-1) lime combined with 3 t ha(-1) manure and full-dose inorganic fertilizer (L2); (iii) 1.43 t ha(-1) lime combined with 3 t ha(-1) manure and full-dose inorganic fertilizer (L1); (iv) 3 t ha(-1) manure combined with full-dose inorganic fertilizer (M); and (v) full-dose inorganic fertilizer alone (C) as a control. Undisturbed soil samples were collected at 0-10 and 10-20 cm soil depths and analyzed to determine saturated hydraulic conductivity (Ks), soil-water retention characteristics, total porosity and bulk density. Disturbed soil samples were collected at the same depths to analyze soil organic carbon and texture. Infiltration capacity measurements and visual evaluation of soil structural quality were done in the field. Significantly higher (P L2 > M > L3 > and C for both soil depths 0-10 and 10-20 cm. The Ks under plots treated with L1 was 64% and 37% higher than that of C for the 0-10 and 10-20 soil depths, respectively. Significantly (P < 0.05) higher infiltration capacity was found at L1 (0.007 cm min(-1)) followed by L2, L3 and M (0.006 cm min(-1), 0.006 cm min(-1), and 0.005 cm min(-1)) compared with C (0.004 cm min(-1)), respectively. Good soil structural quality (Sq) score was identified in L1, L2, L3 and M, whereas in C poor Sq score was found. As compared with C, grain yield was improved by 69% at L1, 59% at L2, 53% at L3, and 44% at M during 2018 and by 70% at L1, 58% at L2, 55% at L3 and 46% at M in 2019. In conclusion, the application of organic manure combined with lime and inorganic fertilizer enhanced the infiltration rate, water holding capacity and grain yield more than the inorganic fertilizer application alone. There was also a significant effect of liming as such, with the highest doses showing the best results