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Understanding the groundwater storage and release (S-Q) process and its contribution to river flows is essential for different hydrological applications, especially in periods of water scarcity. The S-Q process can be characterized based on recession parameter b, which is the slope of the power–law relationship −dQ/dt = aQb of the recession flow analysis, where recession parameter b represents the linearity of the S-Q process. In various studies, it has been found that this parameter can present high variability, which has been associated with the approach or spatial variability of basin characteristics. However, the variability of parameter b and its relationship with geology and the behavior of groundwater storage over time (evolution over time) have not been sufficiently studied. The objective of this study is to analyze the variability of recession parameter b and its relationship with geological and morphological characteristics and climate variability at different time scales. To this end, 72 drainage basins located in south central Chile were examined via recession flow analysis, considering five different time scales (5 years, 10 years, 15 years, 20 years, and 25 years). In addition, to analyze spatial variability patterns and generate groups of basins with similar characteristics, a cluster analysis was carried out. Clusters were obtained using the principal component analysis (PCA) and K-means methods. The results show that in wet periods, the slope of recession parameter b tends to increase (fast drainage process), while in dry periods, the recession slope tends to decrease (slow drainage processes). In general, the results suggest that the variability of recession coefficient b indicates changes in S-Q behavior; therefore, it could be used as an indicator of the sensitivity of a basin to climate variability. [ABSTRACT FROM AUTHOR]

River flooding is one of the most widespread natural disasters. Projections indicate that climate change will increase flood hazard in many areas around the world. In this study, we investigate the individual and combined effects of sea level rise, flow increase and riparian vegetation encroachment on flood hazard in the lower Biobío River, Chile. Results show that each has the potential to individually increase flood hazard in certain areas, and that individual effects can compound. Encroachment of riparian vegetation onto previously sparsely vegetated areas of the floodplain, likely a result of the Chilean megadrought, causes higher flow resistance and increased flooding during large events. Somewhat counterintuitively, drought has therefore led to an increase in flood hazard in the study area. Drought risk for most land areas across the globe is expected to increase with climate change. Potential future vegetation encroachment should therefore be included as a key variable in riverine flood hazard studies. [ABSTRACT FROM AUTHOR]

Due to the climatic conditions in central-southern Chile, there are high heating energy consumption and PM2.5 emissions. Among the alternatives to mitigate it, the Chilean government has implemented subsidies to improve the housings envelope and to replace firewood stoves by pellet stoves and air-to-air heat pumps. Accordingly, for evaluating the effectivity of above-mentioned initiatives, this study proposes to identify the optimal solutions that minimize the energy demand, the environmental impacts, and the global costs, for social housing using different insulation materials and heating systems in four Chilean cities located in central-southern Chile. Results reveal pellet stoves with lower environmental impacts but higher global costs, while heat pumps offer an intermediate solution that can be enhanced with a greener electricity grid, but the global costs are still too high. Firewood stoves could be optimal solution depending on optimization weighting factors. The study emphasizes prioritizing housing envelope improvements in energy policies, followed by heating system enhancements. Although replacing firewood poses challenges due to costs, it is crucial for Chile's 2050 decarbonization goal. This research provides valuable insights into the complexities and potential solutions for transitioning away from firewood in Chilean social housing. • Woodstove replaced by pellet stove or heat pump reduce environmental impact by 34–45 %. • Heat pumps present global costs 34 %–88 % higher than wood stoves. • To improve the housing envelope is the first recommended public policy. • Public policies must simultaneously subsidy initial and operational cost. • Trade-off: global cost vs. environmental impacts determines optimal approach. [ABSTRACT FROM AUTHOR]

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Hydrological modelling has undergone constant growth with the increase in information processing capabilities. Hydrological models have traditionally been used to study the effects of climate change on management and land-use changes and for water resources planning, among other purposes. The aim of this study was to determine and analyse the advantages of the HBV and HYMOD models, which are commonly used in hydrology on daily and monthly time scales. A regional sensitivity analysis was used to compare the processes that take on greater importance at different time scales in the two models. As a result, it was found that quick precipitation-runoff processes prove to be better represented in the HBV model, while slow, time-aggregated processes are better represented by the HYMOD model. This study confirms that both models are adequate for rain-dominated basins, such as those of the study area. Additionally, the HBV model proved to be more robust in comparison to HYMOD. [ABSTRACT FROM AUTHOR]

Groundwater storage, drainage, and interbasin water exchange are common hydrological processes but often difficult to quantify due to a lack of local observations. We present a study of three volcanic mountainous watersheds located in south-central Chile (~36.9 ° S) in the Chillán volcanic complex (Chillán, Renegado, and Diguillín river basins). These are neighboring basins that are similar with respect to the metrics normally available for characterization everywhere (e.g., precipitation, temperature, and land cover). In a hydrological sense, similar (proportional) behavior would be expected if these catchments would be characterized with this general information. However, these watersheds show dissimilar behavior when analyzed in detail. The surface water balance does not fit for any of these watersheds individually; however, the water balance of the whole system can be explained by likely interbasin water exchanges. The Renegado river basin has an average annual runoff per unit of area on the order of 60-65% less than those of the Diguillín and Chillán rivers, which is contradictory to the hydrological similarity among the basins. To understand the main processes that control streamflow generation, two analyses were performed: (a) basin metrics (land cover, geologic, topographic, and climatological maps) and hydro-meteorological data analyses and (b) a water balance model approach. The analyses contribute to a plausible explanation for the hydrogeological processes in the system. The soils, topography, and geology of the Chillán-Renegado-Diguillín system favor the infiltration and groundwater movements from the Renegado river basin, mainly to the neighboring Diguillín basin. The interbasin water exchanges affect hydrological similarity and explain the differences observed in the hydrological processes of these three apparently similar volcanic basins. The results highlight the complexity of hydrological processes in volcanic mountainous systems and suggest that a simple watershed classification approach based on widely available data is insufficient. Simple local analyses such as specific flow analysis with a review of the geology and morphology can contribute to a better understanding of the hydrology of volcanic mountainous areas. [ABSTRACT FROM AUTHOR]

Three models for estimating the daily reference evapotranspiration ETo are evaluated in the agricultural zone of Chillán, Chile: Penman-Monteith FAO PMF, Prietsley-Taylor PT and Hargreaves-Samani HS. The daily ETo values estimated through these methodologies are compared with the daily values of ETo estimated from pan evaporation EToB data series obtained from meteorological stations of the Universidad de Concepción Campus Chillán and INIA Quilamapu, both located within Chillán's city limits. The comparison and analysis were performed with data covering a span of 13 years (1996 - 2008). Results indicate that the HS method systemically underestimates ETo values, particularly during dry periods. Moreover, differences between the three methods quantified with Root Mean Squared Error RMSE and Relative Differences RD computed for different time periods (1, 3, 7 and 30 days) suggest that the PT method fits better the observations, being more adequate for the agricultural area of Chillán - weekly averages yield RMSE of 1.01 mm/day and RD of 32.8%. [ABSTRACT FROM AUTHOR]

In Chile in recent years, changes in precipitation and temperatures have been reported that could affect water resource management and planning. One way of facing these changes is studying and understanding the behavior of hydrological processes at a regional scale and their different temporal scales. Therefore, the objective of this study is to analyze the importance of the hydrological processes of the HBV model at different temporal scales and for different hydrological regimes. To this end, 88 watersheds located in south-central Chile were analyzed using time-varying sensitivity analysis at five different temporal scales (1 month, 3 months, 6 months, 1 year, and 5 years). The results show that the model detects the temporality of the most important hydrological processes. In watersheds with a pluvial regime, the greater the temporal scale, the greater the importance of soil water accumulation processes and the lower the importance of surface runoff processes. By contrast, in watersheds with a nival regime, at greater temporal scales, groundwater accumulation and release processes take on greater importance, and soil water release processes are less important. [ABSTRACT FROM AUTHOR]

Chile is strongly impacted by climate variability driven by the El Niño southern oscillation and the Pacific decadal oscillation. These produce multi-year droughts that affect Chilean agriculture, which depends heavily on available water resources. This paper is based on the results of a 6-year study that was carried in the Peumo area of south central Chile, where there is intensive agriculture based on vineyards, orchards and annual crops. In the Peumo area, irrigation has a strong impact on groundwater recharge (22% from irrigation losses, 52% from canal seepage and 26% from rainfall). This research analysed how water management decisions can affect the groundwater system and how agricultural production within the valley would be affected. It was found that decisions such as intensive use of wells and the lining of canals will produce depletion of the water table, affecting low-income farmers who depend on shallow wells. [ABSTRACT FROM AUTHOR]

Muñoz, Enrique, José Luis Arumí, and José Vargas, 2012. A Design Peak Flow Estimation Method for Medium-Large and Data-Scarce Watersheds With Frontal Rainfall. Journal of the American Water Resources Association (JAWRA) 48(3): 439-448. DOI: 10.1111/j.1752-1688.2011.00622.x Abstract: We developed a reliable peak flow estimation method for the design of hydraulic structures. The method is valid in medium-large watersheds (100-5,000 km2) located in Chile between 32°45′ and 43°50′S, with scarcity of hydro-meteorological information, and where frontal rainfall prevails. The proposed method requires only rainfall data and geomorphologic descriptors as inputs, and relates the instant peak flow with the time of concentration rainfall flux (the contributing watershed area multiplied by the rainfall). The parameters of the model were defined with peak flows obtained from statistical analyses of historical fluviometric records from 25 watersheds. The quality of the proposed method is evaluated by applying it to three external watersheds different from those used to define model parameters, and comparing it with three other indirect methods and with peak flows obtained from statistical analyses, which were also used as the benchmark. The proposed method estimates peak flows with mean differences of less than 10%, which is two times less than other similar indirect methodologies, making it a recommendable option for estimating design peak flows. [ABSTRACT FROM AUTHOR]

Muñoz, Enrique, José Luis Arumí, and José Vargas, 2012. A Design Peak Flow Estimation Method for Medium-Large and Data-Scarce Watersheds With Frontal Rainfall. Journal of the American Water Resources Association (JAWRA) 48(3): 439-448. DOI: 10.1111/j.1752-1688.2011.00622.x Abstract: We developed a reliable peak flow estimation method for the design of hydraulic structures. The method is valid in medium-large watersheds (100-5,000 km2) located in Chile between 32°45′ and 43°50′S, with scarcity of hydro-meteorological information, and where frontal rainfall prevails. The proposed method requires only rainfall data and geomorphologic descriptors as inputs, and relates the instant peak flow with the time of concentration rainfall flux (the contributing watershed area multiplied by the rainfall). The parameters of the model were defined with peak flows obtained from statistical analyses of historical fluviometric records from 25 watersheds. The quality of the proposed method is evaluated by applying it to three external watersheds different from those used to define model parameters, and comparing it with three other indirect methods and with peak flows obtained from statistical analyses, which were also used as the benchmark. The proposed method estimates peak flows with mean differences of less than 10%, which is two times less than other similar indirect methodologies, making it a recommendable option for estimating design peak flows. [ABSTRACT FROM AUTHOR]

Data on historical extreme events provides information not only for water resources planning and management but also for the design of disaster-prevention measures. However, most basins around the globe lack long-term hydro-meteorological information to derive the trend of hydrological extremes. This study aims to investigate a method to estimate maximum and minimum flow trends in basins with limited streamflow records. To carry out this study, data from the Allipén River watershed (Chile), the Hydrologiska Byråns Vattenbalansavdelning (HBV) hydrological model at a daily time step, and an uncertainty analysis were used. Through a calibration using only five years of records, 21-year mean daily flow series were generated and the extreme values derived. To analyze the effect of the length of data availability, 2, 5, and 10 years of flows were eliminated from the analyses. The results show that in the case of 11 years of simulated flows, the annual maximum and minimum flow trends present greater uncertainty than in the cases of 16 and 19 years of simulated flows. Simulating 16 years, however, proved to properly simulate the observed long-term trends. Therefore, in data-scarce areas, the use of a hydrological model to simulate extreme mean daily flows and estimate long-term trends with at least 16 years of meteorological data could be a valid option. [ABSTRACT FROM AUTHOR]

Groundwater storage and discharge are important processes that have not yet been sufficiently studied in some parts of Chile. Additionally, in watersheds without snow cover or glaciers, groundwater storage and release are the main sources of minimum flow generation; therefore, improvements are required to characterize this process. This study aimed to use recession flow analysis to link groundwater storage depletion to the predominant geological characteristics of each watershed in order to improve our understanding of the groundwater storage-release process in 24 watersheds in south-central Chile. The results allowed different groundwater storage behaviors associated with different geological characteristics to be identified, making recession flow analysis a valuable tool for improving the representation and conceptualization of this process in order to advance toward better minimum flow predictions. [ABSTRACT FROM AUTHOR]

The gauging process can be very extensive and time-consuming due to the procedures involved. Since velocity measurement time (VMT) is one of the main variables that would allow gauging times to be reduced, this study seeks to determine the optimal point VMT and, thereby, reduce the overall gauging time. An uncertainty approach based on the USGS area-velocity method and the GLUE methodology applied to eight gauging samples taken in shallow rivers located in South-central Chile was used. The average point velocity was calculated as the average of 1 to 70 randomly selected instant velocity samples (taken every one second). The time at which the uncertainty bands reached a stability criterion (according to both width and slope stability) was considered to be the optimum VMT since the variations were negligible and it does not further contribute to a less uncertain solution. Based on the results, it is concluded that the optimum point VMT is 17 s. Therefore, a point velocity measurement of 20 s is recommended as the optimal time for gauging in shallow rivers. [ABSTRACT FROM AUTHOR]