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Long‐term time series of climatological data measured at meteorological stations provide one of the most authentic annals of climate in the past. However, there are a host of factors that affect measurements of climate parameters and make the data unsuitable for direct use and analysis. Serial completion and homogenization thus have to be undertaken in order to draw valid conclusions about the climate, or to apply the time series in impact studies. This study reports on gap filling and homogenization results of climatological elements in the headwater region of the Upper Blue Nile Basin from 1980 to 2013. Firstly, approaches for reconstruction of the time series from neighboring stations using different techniques were compared and selected. Neighboring stations were selected based on horizontal distance and coefficient of correlation. Secondly, the reconstructed time series were homogenized using Multiple Analysis of Series for Homogenization (MASH). The results show improved spatial coherence of the final data series. Higher spatial coherence was revealed for maximum temperature than for minimum temperature and rainfall. For rainfall and minimum and maximum temperatures, the coefficient of correlation weighting method outperforms other candidate methods, such as the normal ratio method (NRM), the modified NRM, and the inverse distance weighting method. Rainfall series for half of the stations considered were found to be homogeneous, and thus inhomogeneity corrections were not applied. Inhomogeneity in the remaining stations either underestimates or overestimates annual rainfall series. All stations revealed inhomogeneity in the mean annual maximum and minimum temperature series. These serially complete and homogenized data on rainfall, and minimum and maximum temperatures of the present study can be used for climate change and hydrological studies in the basin.

Changes in hydro-meteorological historical records are of considerable importance for future planning. This study analyses trends of hydro-climatological indices of annual and seasonal precipitation, temperature and discharge in the "Norte Chico" region of Chile (29)(30)(31)(32) • S), located in the Central Andes. It addresses how these trends possibly impacted on the water resources in a nival regime, typical for arid mountainous regions. Homogenous records were tested against monotonic trends using the non-parametric rank-based Mann-Kendall test. The results suggested, at a very high confidence level, a strong warming signal trend over recent decades, consistent at the annual and seasonal levels. Furthermore, warmer days are observed in summer, especially at higher elevations. The region also experienced a shift in the rainy season over the last 42 years. However, an increase in precipitation was observed over recent decades, whereas an annual decrease was the general tendency when the whole century was considered. Changes in discharge were not unequivocal and glacier retreat has been compensated for possibly by an increase in snowmelt in recent years. Hence, in an under-studied area, from the hydrological perspective, this work provides some insights for a better understanding of changing hydrological processes in the mid-latitude Andes Cordillera. • S), située dans les Andes centrales. Elle aborde la façon dont ces tendances ont peut-être influencé les ressources en eau dans un régime nival, typique dans les régions montagneuses arides. Des enregistrements homogènes ont été comparés à des tendances monotones en utilisant le test non-paramétriques de rang de MannKendall. Les résultats ont suggéré, avec un niveau de confiance très élevé, une forte tendance au réchauffement durant ces dernières décennies, cohérente à l'échelle annuelle et saisonnière. Par ailleurs, des jours plus chauds sont observés en été, surtout en altitude. La région a également connu un changement dans la saison des pluies au cours des 42 dernières années. Toutefois, une augmentation des précipitations a été observée au cours des dernières décennies, alors que la tendance générale sur le siècle est à la baisse. Les changements de débits ne sont pas univoques, et le recul des glaciers a probablement été compensé par une augmentation de la fonte des neiges dans les dernières années. Ainsi, dans une zone sous-étudiée, du point de vue hydrologique, ce travail apporte un éclairage pour une meilleure compréhension de l'évolution des processus hydrologiques dans la Cordillère des Andes de moyenne latitude.