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Classification of natural flow regimes of non‐perennial rivers and streams (NPRS) is an incipient field of research. NPRS represent approximately 70% of the total Mediterranean rivers and are expected to increase in the next decades as a result of climate change. Due to the ecological importance of NPRS and the need to improve national ecological assessment methods within the scope of the Water Framework Directive (WFD), this paper aims to classify the hydrological regime of 69 non‐regulated streams, testing several hydrological indices related to the magnitude, frequency, duration, timing, and rate of change in periods of flow cessation. Using daily flow records, a total of 315 indices were calculated and their relationships were examined with Principal Component Analysis (PCA) for different thresholds used to define zero‐flow condition (0, 1, 2, and 5 L/s). Redundancy analysis identified five indices that better describe the patterns of hydrological variability in Mediterranean NPRS: number of days per year without flow, annual percentage of months without flow, mean daily annual flow, coefficient of variation of Julian date of the annual start of zero‐flow and annual rise rate. Using these indices, a self‐organizing map (SOM) was trained in order to categorize the NPRS into three groups with similar hydrological features. The results of this study provide a statistically‐based hydrological classification of NPRS in Mediterranean environments. We expect that this classification will provide useful insights to water authorities to improve the assessments of the ecological status in this type of water bodies. [ABSTRACT FROM AUTHOR]

Streamflow is the runoff response integrated in space and time over a complex system involving climatic and catchment physiographic factors. In the Andes, accelerating runoff process understanding is hampered by the inability to quantify heterogeneity of surface and subsurface catchment properties. Here, we present a statistical approach based on regression models and correlation analysis that links hydrological signatures and catchment properties to unveil processes in a set of volcanic mountain catchments (latitude 0°30'N) in Ecuador. The catchments represent form and function diversity in the same hydrological unit. We found that despite of similar atmospheric‐water inputs the water yield in the north‐east region is about 5× larger than in the south‐west region and their flow regimes are asymmetric. The soil‐bedrock interface and lithology exert a first‐order control on hydrologic partitioning, and this allowed us to hypothesize two hydrological mechanisms. Firstly, in the north‐east region, the perennial streamflow is associated with seasonal rainfall patterns, and subsequent drainage processes taking place at the surface and subsurface level. The amount of streamflow is related to landform characteristics, high canopy density and root development of forest as well as water holding capacity of organic soils. From a mechanistic standpoint, the low concentration time, steep slopes and shallow infiltration limited by high‐consolidated deposits of sedimentary and volcanics suggest a lateral movement of the flow. Secondly, in the south‐west region the streamflow regime is mostly groundwater‐dependent and it becomes seasonally enhanced by rainfall. Larger seasonal variations of precipitation and temperature result into enhanced evapotranspiration in the drier months, limiting shallow soil infiltration. Under the soil layers, highly permeable pyroclastic deposits and andesitic lavas promote deep percolation. The results highlight the degree of dissimilarity of hydrological processes in Andean settings, but unravelling their complexity seems plausible using streamflow signatures and causal explanatory models. [ABSTRACT FROM AUTHOR]

We aimed to quantify the delayed effects of flows on aquatic ecosystems using 33 years of monitoring data on macroinvertebrates and water quality and 51 years of hydrological data, spanning 2,300 km of the Murray River, Australia. By incorporating the delayed effects of hydrological indices, along with physicochemical variables, into generalized additive models to form distributed lag nonlinear models for macroinvertebrate richness and abundance, we found that the effects of floods on macroinvertebrates could last up to 32 years, depending on their magnitude. The models indicated that a large flood can cause an initial depression in macroinvertebrate abundance and richness, followed by a sustained increase persisting for over 25 years before returning to preflood levels. Twelve hydrological indices representing the magnitude of flow events were evaluated, with the q90/med (the 6‐monthly flow exceeded 10% of time, divided by the long‐term median) performing (slightly) better than other indices. Competing hypotheses for the mechanisms underlying the apparent long‐term effect of floods were considered, with the most plausible explanation being the flood‐mediated influx of allochthonous organic matter, especially coarse and large woody debris, that might drive the persistent change in the aquatic community. It is generally believed that macroinvertebrate communities recover quickly after floods, but our findings suggest that we may need to reconceptualize the effects that floods can have on aquatic macroinvertebrates and the communities they support, especially in the context of flow restoration and climate change. Plain Language Summary: Research is being done around the world to understand how much water is required to sustain river ecosystems, and therefore, how much can be extracted for consumptive uses such as irrigated agriculture. We used long‐term monitoring data (1980–2012) on aquatic macroinvertebrates—which includes insects, crustaceans, mussels, snails, and worms that spend all or part of their life in water—collected along 2,300 km of the Murray River, Australia, to investigate the relationship between river flow and the health of aquatic ecosystems. These data indicate that small to medium flows might have an immediate effect through improvements in water quality, but large floods may have sizeable delayed impacts on macroinvertebrates lasting more than three decades. The number of species and overall abundance of macroinvertebrates initially decreased, due to washout, but then increased for a period of about 25 years after the historic flood of 1993, persisting throughout the Millennium drought (1996–2010). The positive legacy of floods might be due to an influx of woody debris during the event, which can provide habitat and food for macroinvertebrates until decomposition of the woody material is complete. Key Points: Long‐term data on macroinvertebrates, water quality, and hydrology in the Murray River enabled quantifying the flow‐ecology relationshipFlood impacts on macroinvertebrate abundance and richness may persist for decades, while small to medium flows have indiscernible effectsA flood‐induced influx of organic matter might underlie the apparent long‐term effect of floods [ABSTRACT FROM AUTHOR]

As a consequence of the remote location of the Andean páramo, knowledge on their hydrologic functioning is limited; notwithstanding, these alpine tundra ecosystems act as water towers for a large fraction of the society. Given the harsh environmental conditions in this region, year-round monitoring is cumbersome, and it would be beneficial if the monitoring needed for the understanding of the rainfall-runoff response could be limited in time. To identify the hydrological response and the effect of temporal monitoring, a nested ( n = 7) hydrological monitoring network was set up in the Zhurucay catchment (7.53 km2), south Ecuador. The research questions were as follows: (1) Can event sampling provide similar information in comparison with continuous monitoring, and (2) if so, how many events are needed to achieve a similar degree of information? A subset of 34 rainfall-runoff events was compared with monthly values derived from a continuous monitoring scheme from December 2010 to November 2013. Land cover and physiographic characteristics were correlated with 11 hydrological indices. Results show that despite some distinct differences between event and continuous sampling, both data sets reveal similar information; more in particular, the monitoring of a single event in the rainy season provides the same information as continuous monitoring, while during the dry season, ten events ought to be monitored. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Quantifying the impact of land use and cover (LUC) change on catchment hydrological response is essential for land-use planning and management. Yet hydrologists are often not able to present consistent and reliable evidence to support such decision-making. The issue tends to be twofold: a scarcity of relevant observations, and the difficulty of regionalizing any existing observations. This study explores the potential of a paired catchment monitoring network to provide statistically robust, regionalized predictions of LUC change impact in an environment of high hydrological variability. We test the importance of LUC variables to explain hydrological responses and to improve regionalized predictions using 24 catchments distributed along the Tropical Andes. For this, we calculate first 50 physical catchment properties, and then select a subset based on correlation analysis. The reduced set is subsequently used to regionalize a selection of hydrological indices using multiple linear regression. Contrary to earlier studies, we find that incorporating LUC variables in the regional model structures increases significantly regression performance and predictive capacity for 66% of the indices. For the runoff ratio, baseflow index, and slope of the flow duration curve, the mean absolute error reduces by 53% and the variance of the residuals by 79%, on average. We attribute the explanatory capacity of LUC in the regional model to the pairwise monitoring setup, which increases the contrast of the land-use signal in the data set. As such, it may be a useful strategy to optimize data collection to support watershed management practices and improve decision-making in data-scarce regions. [ABSTRACT FROM AUTHOR]

Larned, Scott T., David B. Arscott, Jochen Schmidt, and Jan C. Diettrich, 2010. A Framework for Analyzing Longitudinal and Temporal Variation in River Flow and Developing Flow-Ecology Relationships. Journal of the American Water Resources Association (JAWRA) 46(3):541-553. DOI: 10.1111/j.1752-1688.2010.00433.x We propose a framework for analyzing longitudinal flow variation and exploring its ecological consequences in four steps: (1) generating longitudinally continuous flow estimates; (2) computing indices that describe site-specific and longitudinal flow variation, including intermittence; (3) quantifying and visualizing longitudinal dynamics; (4) developing quantitative relationships between hydrological indices and ecological variables (flow-ecology relationships). We give examples of each step, using data from a New Zealand river and an empirical longitudinal flow model, ELFMOD. ELFMOD uses spot-gauging data and flow or proxy variable time series to estimate flow magnitude and state (flowing or dry) at user-defined intervals along river sections. Analyses of flow-ecology relationships for the New Zealand river indicated that fish and benthic and hyporheic invertebrate communities responded strongly to variation in mean annual flow permanence, flow duration, dry duration, drying frequency, inter-flood duration, and distances to flowing reaches. To put longitudinal flow variation into a broader context and guide future research, we propose a conceptual model that combines elements of two contrasting perspectives: rivers as longitudinal continua, and rivers as patch mosaics. In this conceptual model, hydrologically complex rivers are composed of linear sequences of nested hydrological gradients, which are bordered by hydrogeomorphic discontinuities, and which collectively generate hydrological dynamics at river-section scales. [ABSTRACT FROM AUTHOR]

The relationship between river flows, summarized by hydrological indices, and catches of Australian bassMacquaria novemaculeatafrom recreational fishing competitions were examined in the Hawkesbury-Nepean River system. Between 55 and 198 fishermen took part in six monthly fishing competitions. The number of hours fished increased from 570 to 1800 h between 1998 and 2001. A total of 11 275 Australian bass were caught over the study period. The percentage of young-of-the-year(YOY) Australian bass and the catch of fish per unit effort was influenced by either the flow regime occurring in the same year and flow in the previous year. The number of Australian bass caught per unit effort was positively associated with the median volume of water and the number and duration of high flow events occurring in the previous year. The percentage of YOY Australian bass caught in any one year was positively associated with the median flow in the same year of capture and the maximum, mean and variation of daily flows, the number and duration of high flow events and the greatest rise and fall of daily flows in the previous year. [ABSTRACT FROM AUTHOR]

This study assessed the effects of hydrological events on aquatic communities at the mesohabitat scale (pool, run, and riffle) in the high Andean region. Four headwater sites located in the Zhurucay microcatchment (southern Ecuador), with elevations higher than 3,500 m, were selected and monitored considering in each site a 50‐m‐long reach and within each reach five cross sections. In each of these reaches, 19 sampling campaigns were conducted in the period December 2011–October 2013, collecting macroinvertebrates and physical characteristics. A total of 27 hydrological indices were calculated using the daily flow rate as input. Large peak flow, small peak flow, and low flow (LF) events were defined based on discharge thresholds. Multivariate statistics showed that 14 hydrological indices were significantly related to the aquatic community. Further, the study revealed that (a) peak events produced stronger effects on communities than LF events, (b) the observed effects of LF events were weaker than those encountered in other latitudes, and (c) local benthic communities have more resilience than similar communities studied in other latitudes. [ABSTRACT FROM AUTHOR]