ABSTRACT:The present study attempts to explore changes in rainfall pattern in the Indian Himalayas during 20th century using 80-year data from 30 rain gauge stations maintained by the India Meteorological Department (IMD). Modified Mann-Kendall test (MMK) was applied to detect trend, and Pettitt-Mann-Whitney (PMW) test was employed to detect possible shift. Implication of the change is discussed in terms of percentage change over mean. The results show that the most probable year of change in annual as well as monsoon rainfall in the region is 1964. There was an increasing trend upto 1964 (corroborating with all India and nearby plains), followed by a decreasing trend in 1965-1980 (exclusive to this region). In the entire region, changes are most conspicuous over the Shivaliks and the southern part of the Lesser Himalayas.

A new technique is developed for identifying groups for regional flood frequency analysis. The technique uses a clustering algorithm as a starting point for partitioning the collection of catchments. The groups formed using the clustering algorithm are subsequently revised to improve the regional characteristics based on three requirements that are defined for effective groups. The result is overlapping groups that can be used to estimate extreme flow quantiles for gauged or ungauged catchments. The technique is applied to a collection of catchments from India and the results indicate that regions with the desired characteristics can be identified using the technique. The use of the groups for estimating extreme flow quantiles is demonstrated for three example sites. La formation de groupes pour l'estimation régionale de la fréquence des cruesRésumé Nous avons développé une nouvelle technique afin de déterminer des groupes de bassins pour estimer la fréquence des crues à l'échelle régionale. Le point de départ de cette technique est un algorithme d'agrégation permettant de réaliser une partition de l'ensemble des bassins considérés. Afin d'améliorer la régionalisation les groupes ainsi formés sont ensuite modifiés en s'appuyant sur trois exigences définies de telle sorte que les groupes soient utilisables avec efficacité. Le résultat consiste en groupes pouvant se recouvrir qui peuvent être utilisés pour estimer les quantiles de crues extrêmes de stations jaugées ou non. Cette technique a été appliquée à un ensemble de bassins versants de l'Inde et les résultats montrent qu'elle permet d'estimer les caractéristiques désirées. Trois sites de démonstration ont fait l'objet de l'utilisation des groupes pour l'estimation des quantiles des crues extrêmes.

Characterization of the seasonal and inter-annual spatial and temporal variability of rainfall in a changing climate is vital to assess climate-induced changes and suggest adequate future water resources management strategies. Trends in annual, seasonal and maximum 30-day extreme rainfall over Ethiopia are investigated using 0.5• latitude × 0.5• longitude gridded monthly precipitation data. The spatial coherence of annual rainfall among contiguous rainfall grid points is also assessed for possible spatial similarity across the country. The correlation between temporally coinciding North Atlantic Multidecadal Oscillation (AMO) index and annual rainfall variability is examined to understand the underlying coherence. In total 381 precipitation grid points covering the whole of Ethiopia with five decades of precipitation data are analysed using the Mann-Kendall test and Moran spatial autocorrelation method. Summer (July-September) seasonal and annual rainfall data exhibit significant decreasing trends in northern, northwestern and western parts of the country, whereas a few grid points in eastern areas show increasing annual rainfall trends. Most other parts of the country exhibit statistically insignificant trends. Regions with high annual and seasonal rainfall distribution exhibit high temporal and spatial correlation indices. Finally, the country is sub-divided into four zones based on annual rainfall similarity. The association of the AMO index with annual rainfall is modestly good for northern and northeastern parts of the country; however, it is weak over the southern region.Key words trend analysis; annual rainfall; seasonal rainfall; spatial autocorrelation; Ethiopia Variabilité temporelle et spatiale des précipitations annuelles et saisonnières sur l'EthiopieRésumé La caractérisation de la variabilité saisonnière et interannuelle spatiale et temporelle des précipitations dans un climat changeant est essentielle pour évaluer les modifications induites par le climat et proposer des stratégies adéquates de gestion future des ressources hydriques. Les tendances des séries de pluies annuelles, saisonnières et les maximums sur 30 jours ont été étudiées sur l'Ethiopie à l'aide d'une grille de données de 0,5• × 0 5• degré carré. La cohérence spatiale des précipitations annuelles entre les points de grille de précip-itations adjacents a également été évaluée pour apprécier une possible similarité spatiale à travers le pays. La corrélation entre l'indice de l'oscillation multidécennale de l'Atlantique Nord (OMA) et l'indice de la variabilité pluviométrique a été examinée afin de comprendre la cohérence sous-jacente. Un total de 381 points de la grille de précipitation couvrant cinq décennies on été comptabilisés sur l'ensemble de l'Ethiopie. Les données sur les précipitations ont été analysées en utilisant le test de Mann-Kendall et la méthode d'autocorrélation spatiale de Moran. Les séries de la baisse dans le Nord, le Nord-Ouest et l'Ouest du pays, alors que quelques points de grille dans l'Est montrent ...

Continuous rainfall data in grid format are required to run models for hydrological and agricultural research as well as water resources planning and management. The present work attempts to prepare a normal annual rainfall map in Himalayan region of India lying in Uttarakhand state at 1 km spatial resolution which currently is not available. In the region, India Meteorological Department maintains observatories/raingauge stations and data from 44 stations were used in this study. A comparative analysis of interpolation techniques like Inverse Distance Weighted, Polynomial, Splines, Ordinary Kriging and Universal Kriging shows that Universal Kriging with hole-effect model and natural logarithmic transformation with constant trend having Root Mean Square Error (RMSE) of 328.7 is the best choice. This is followed by Ordinary Kriging (RMSE 329.1), Splines (RMSE 392.4), Inverse Distance Weighted (RMSE 409.8) and Polynomial Interpolation (RMSE 418.5).Cross validation of the results shows the largest over prediction at Tehri rainfall station (62.5%) and largest under prediction at Nainital station (−36.5%). Physiographic zone wise, the least errors occur in the plains and the largest in the Great Himalayas. The spatial average rainfalls are 1,472 mm for Terai/Bhabar, 1,782 mm for the Shivalik ranges, 1,591 mm for the Lesser Himalayas and 1,635 mm for the Great Himalayan region. The mean areal rainfall in the region is 1,608 mm.

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