A number of models have been suggested •or hydrologic time series in general and streamflow series in particular. Most of them are normal autoregressive (AR) of order 1 with either constant or periodic parameters. Since generally hydrologic time series are nonnormal (skewed), transformations have been suggested to make the series approximately normal. A new class of univariate models is proposed herein which incorporates skewed and correlation properties within the model structure without the necessity of transformations. Such models assume a gamma marginal distribution and a constant or periodic aut0regressive structure. The models may be additive gamma, multiplicative. gamma, or a mixed model which incorporates properties of both additive and multiplicative models. The gamma models were tested and compared in relation to (transformed) normal AR models by computer simulation studies based on five weekly streamflow series with samples varying from 35 to 40 years of record. The results show that the new class of gamma models compares favorably with respect to the normal models in reproducing the basic statistics usually analyzed for streambow simulation. It is expected that the proposed gamma models will be of interest to other researchers for further developments and applications to hydrologic and geophysical time series. INTRODUCTION Synthetic generation of streamflow sequence_s is commonly utilized in planning and operational studieg of water resources systems. Such synthetic sequences are generated so as to rep•roduce a set of statistical properties which are found in the historical streamflow data. For such purpose, a number of time series models have been suggested since Hennan [1955] and Thomas and Fiering [1962] applied G•tussian auto•egressire (AR) models to seasonal hydrologic series. In modeling these series it is usually assumed that they are seasonally stationary and that seasonality is reflected in the mean, variance, covariance, and the skewness. However, in general, one may assume seasonality in the marginal distribution. Annual streamflow series may be considered approximately normal' however, for shorter time interval series such as monthly, weekly, and daily series, departures from normality become important. The problem of skewed streamflows has been handled by a number of methods. A Widely used technique is to use transformations to render a series close to normal [Box and Cox, 1965]. Examples of this approach are given by Matalas [1967], Mejia and Rodri•iuez-lturbe [1974], Lettenrnaier and Burqes [1977], Hirsch [1979], and Stedinqer [1981]. Another approach is to find the statistical properties of the noise in such a way as to reproduce the skew of the series. See, for instance, the Wilson-Hilferty (W-H) transformations used by Thomas and Fierinq [1962], Beard [1965], Payne et al. [1969], McGinnis and Sammens [1970], McMahon and Miller [1971], and O'Connell [1974]. Although the coefficient of skewness can be reproduced by this approach, the underlying variable is not gamma. A related problem ...

The Silala River basin is located in a remote area in the Andes Mountain range, where hydro‐meteorological and hydrogeological data are scarce. Consequently, the hydrological functioning of this river system was not well understood. Due to a dispute between Chile and Bolivia over the status and use of the waters of the Silala River, Chile requested the International Court of Justice to adjudge the Silala River system to be an international watercourse. To support the case, scientific studies were carried out in both countries to fill hydrological and hydrogeological knowledge gaps. This article reviews the Silala River basin topographic characterization, historical water use, and the dominant hydrological processes, and briefly summarizes an enhanced monitoring programme, reported in more detail elsewhere in this Special Issue. The longitudinal topographic profile and river slope show that Silala fluvial system is an exorheic watershed; waters from the Cajones and Orientals wetlands in Bolivia, the two headwater sources of the Silala fluvial system, naturally flow from Bolivia to Chile, demonstrating that the Silala River system is indeed an international watercourse. New hydro‐meteorological, hydrological and hydrogeological measurement stations were installed in both countries and provided improved process insights and spatiotemporal coverage within the basin. These new observations helped to populate hydraulic, hydrological, and hydrogeological models, aimed to improve understanding of the functioning of the system, including the effects of historical disturbance due to channelization of the Bolivian wetlands.This article is categorized under: Science of Water > Hydrological Processes Human Water > Rights to Water

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Population and industry growth in dry climates are fully tied to significant increase in water and energy demands. Because water affects many economic, social and environmental aspects, an interdisciplinary approach is needed to solve current and future water scarcity problems, and to minimize energy requirements in water production. Such a task requires integrated water modeling tools able to couple surface water and groundwater, which allow for managing complex basins where multiple stakeholders and water users face an intense competition for limited freshwater resources. This work develops an integrated water resource management model to investigate the water-energy nexus in reducing water stress in the Copiapó River basin, an arid, highly vulnerable basin in OPEN ACCESSWater 2014, 6 2591 northern Chile. The model was utilized to characterize groundwater and surface water resources, and water demand and uses. Different management scenarios were evaluated to estimate future resource availability, and compared in terms of energy requirements and costs for desalinating seawater to eliminate the corresponding water deficit. Results show a basin facing a very complex future unless measures are adopted. When a 30% uniform reduction of water consumption is achieved, 70 GWh over the next 30 years are required to provide the energy needed to increase the available water through seawater desalination. In arid basins, this energy could be supplied by solar energy, thus addressing water shortage problems through integrated water resource management combined with new technologies of water production driven by renewable energy sources.

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