Low Streamflow Events Research Articles

Streamflow in the United States: Characteristics, trends, regime shifts, and extremes

Long-term streamflow observations contain essential information for understanding hydrological changes and managing water resources. A continental-scale dataset or analysis of temporal streamflow change is still lacking across hydrologic gauges in the Conterminous United States (CONUS). Here, we compiled 70 years of streamflow records from 1951 to 2021 at ~ 8000 hydrologic stations across the CONUS and characterized temporal trends, regime shifts, and extreme events using a Bayesian time series analysis algorithm. We found that the occurrences of sudden streamflow changes (e.g., regime shifts and extreme events) have been increasing with time across the CONUS. In addition, we derived 181 streamflow indicators that are valuable for hydrological and biological applications, such as the duration and frequency of high or low streamflow events. The Mississippi River Basin, especially the middle and lower parts, was a hot spot of high-frequency high-flow events. Overall, we anticipate the dataset generated here offers valuable information for understanding and quantifying changes in water resources across the CONUS.

A high-resolution perspective of extreme rainfall and river flow under extreme climate change in Southeast Asia

Abstract. This article provides high-resolution information on the projected changes in annual extreme rainfall and high- and low-streamflow events over Southeast Asia under extreme climate change. The analysis was performed using the bias-corrected result of the High-Resolution Model Intercomparison Project (HighResMIP) multi-model experiment for the period 1971–2050. Eleven rainfall indices were calculated, along with streamflow simulation using the PCR-GLOBWB hydrological model. The historical period 1981–2010 and the near-future period 2021–2050 were considered for this analysis. Results indicate that, over former mainland Southeast Asia, Myanmar will face more challenges in the near future. The east coast of Myanmar will experience more extreme high-rainfall conditions, while northern Myanmar will have longer dry spells. Over the Indonesian maritime continent, Sumatra and Java will suffer from an increase in dry-spell length of up to 40 %, while the increase in extreme high rainfall will occur over Borneo and mountainous areas in Papua. Based on the streamflow analysis, the impact of climate change is more prominent in a low-flow event than in a high-flow event. The majority of rivers in the central Mekong catchment, Sumatra, Peninsular Malaysia, Borneo, and Java will experience more extreme low-flow events. More extreme dry conditions in the near future are also seen from the increasing probability of future low-flow occurrences, which reaches 101 % and 90 %, on average, over Sumatra and Java, respectively. In addition, based on our results over Java and Sumatra, we found that the changes in extreme high- and low-streamflow events are more pronounced in rivers with steep hydrographs (rivers where flash floods are easily triggered), while rivers with flat hydrographs have a higher risk in terms of the probability of low-flow change.

Non‐Stationary Influences of Large‐Scale Climate Drivers on Low Flow Extremes in Southeast Australia

AbstractThe intensity, duration, and frequency (IDF) of low streamflow events are often considered stationary in time. Given droughts are likely to become more frequent and extreme, here those IDFs are analyzed for their non‐stationarity in relation to three climate drivers, namely, the El Niño‐Southern Oscillation, the Indian Ocean Dipole, and the Southern Annular Mode. For this, low flow events were identified for 161 unregulated catchments in Victoria, Australia. The relationship between the climate drivers and the IDFs were developed using covariate‐based non‐stationary statistical models. We found that several of these catchments exhibit strong non‐stationary influences from the climate modes. Such catchments have a higher probability of experiencing more intense, prolonged, and/or frequent low flows when a dry phase of these climate drivers occurs. We found that catchments having strong evidence of non‐stationary frequency (n = 77) were more compared to those having non‐stationary intensity (n = 19) or duration (n = 34). Further, we derived projected indices of these climate drivers from CMIP5 models for the RCP8.5 scenario. These indicate an intensification in the dry phase of the climate drivers. Using information of the projected indices in the IDF models, we found that future dry phases of these climate drivers are likely to further increase the probability of experiencing higher magnitudes of low flow IDFs in catchments non‐stationary in these characteristics in relation to one or more of these climate drivers. Frequency shows greater response to future dry phases of these drivers than intensity or duration of low flows.

Development of flow-duration-frequency curves for episodic low streamflow

In water resources management and practices, the time-connected duration and frequency of episodic low streamflow events (and droughts) are often needed for a range of purposes such as water supply planning, low flow management, and drought planning. However, the existing graphical tools commonly used in hydrology such as flow duration curves (FDC), discharge-duration-frequency (QdF), and severity-duration-frequency (SDF) curves, often do not provide this information. In this study, we contribute an approach to develop a flow-duration-frequency (FDF) curve by fitting the exponential function to graphically show the time-connected duration and frequency of episodic low streamflow events. The FDF fitting is comprehensively tested with a bootstrap resampling experiment using long-term continuous streamflow records for 92 USGS gages located in the state of Illinois, U.S.A. The experiment results reveal that the proposed methodology can reasonably develop FDF curves for episodic low streamflow events. The results demonstrate that the FDF fitting is improved by using longer streamflow record though the improvement appears to level off with 30 years or longer streamflow records. The results also confirm that the FDF fitting is more reliable for higher streamflow threshold to define episodic low streamflow events.

Future hydrological constraints of the Montseny brook newt (Calotriton arnoldi) under changing climate and vegetation cover.

The Montseny brook newt (Calotriton arnoldi) is a critically endangered amphibian species which inhabits a small 20 km2 holm oak and beech forest area in NE Spain. Calotriton arnoldi strictly lives in running waters and might be highly vulnerable to hydrological perturbations expected to occur under climate and vegetation cover changes. Knowledge about the potential response of the species habitat to environmental changes can help assessing the actions needed for its conservation. Based on knowledge of the species and supported by observations, we proposed daily low and high streamflow event thresholds for the viability of C. arnoldi. We used the rainfall–runoff model PERSiST to simulate changes in the frequency and duration of these events, which were predicted under two climate and four vegetation cover scenarios for near‐future (2031–2050) and far‐future (2081–2100) periods in a reference catchment. All future scenarios projected a significant decrease in annual streamflow (from 21% to as much as 67%) with respect to the reference period. The frequency and length of low streamflow events will dramatically increase. In contrast, the risk of catastrophic drift linked to high streamflow events was predicted to decrease. The potential change in vegetation toward an expansion of holm oak forests will be more important than climate changes in determining threshold low flow conditions. We thus demonstrated that consideration of potential changes in vegetation and not only changes in climate variables is essential in simulating future streamflows. This study shows that future low streamflow conditions will pose a severe threat for the survival of C. arnoldi and may help taking management actions, including limiting the expansion of holm oak forest, for ameliorating the species habitat and help its conservation.

Effects of climate change on streamflow extremes and implications for reservoir inflow in the United States

The magnitude and frequency of hydrometeorological extremes are expected to increase in the conterminous United States (CONUS) over the rest of this century, and their increase will significantly impact water resource management. In this study, we evaluated the large-scale climate change effects on extreme hydrological events and their implications for reservoir inflows in 138 headwater subbasins located upstream of reservoirs across CONUS using the Variable Infiltration Capacity (VIC) hydrologic model. The VIC model was forced with a 10-member ensemble of global circulation models under the Representative Concentration Pathway 8.5 that were dynamically downscaled using a regional climate model (RegCM4) and bias-corrected to 1/24° grid cell resolution. Four commonly used indices, including mean annual flow, annual center timing, 100-year daily high streamflow, and 10-year 7-day average low streamflow were used for evaluation. The results projected an increase in the high streamflow by 44% for a majority of subbasins upstream of flood control reservoirs in the central United States (US) and a decrease in the low streamflow by 11% for subbasins upstream of hydropower reservoirs across the western US. In the eastern US, frequencies of both high and low streamflow were projected to increase in the majority of subbasins upstream of both hydropower and flood control reservoirs. Increased frequencies of both high and low streamflow events can potentially make reservoirs across CONUS more vulnerable to future climate conditions. This study estimates reservoir inflow changes over the next several decades, which can be used to optimize water supply management downstream.

Performance of ensemble streamflow forecasts under varied hydrometeorological conditions

Abstract. The paper presents a methodology that gives insight into the performance of ensemble streamflow-forecasting systems. We have developed an ensemble forecasting system for the Biała Tarnowska, a mountainous river catchment in southern Poland, and analysed the performance for lead times ranging from 1 to 10 days for low, medium and high streamflow and different hydrometeorological conditions. Precipitation and temperature forecasts from the European Centre for Medium-Range Weather Forecasts served as inputs to a deterministic lumped hydrological (HBV) model. Due to a non-homogeneous bias in time, pre- and post-processing of the meteorological and streamflow forecasts are not effective. The best forecast skill, relative to alternative forecasts based on meteorological climatology, is shown for high streamflow and snow accumulation low-streamflow events. Forecasts of medium-streamflow events and low-streamflow events under precipitation deficit conditions show less skill. To improve performance of the forecasting system for high-streamflow events, the meteorological forecasts are most important. Besides, it is recommended that the hydrological model be calibrated specifically on low-streamflow conditions and high-streamflow conditions. Further, it is recommended that the dispersion (reliability) of the ensemble streamflow forecasts is enlarged by including the uncertainties in the hydrological model parameters and the initial conditions, and by enlarging the dispersion of the meteorological input forecasts.

A 200-year reconstruction of Kocasu River (Sakarya River Basin, Turkey) streamflow derived from a tree-ring network.

The Sakarya River Basin (SRB) contains one of the most important agricultural areas for Turkey. Here, we use a network of 18 tree-ring chronologies and present a reconstruction of the mean June-July Kocasu River discharge, one of the main channels in the SRB, during the period 1803-2002 CE, and place the short period of instrumental flows (since 1953 CE) into historical context. Over the past two centuries, we found 33 dry and 28 wet events and observed the longest wet period between the years 1880 and 1920. The driest years were 1845 and 1873, and the wettest years were 1859 and 1960. Our reconstruction showed that the extreme short-term drought events that occurred in recent years were minor compared to the severity and duration of droughts that occurred previous to instrumental data. We found four pre-instrumental severe and sustained low streamflow events during the periods 1819-1834, 1840-1852, 1861-1875, and 1925-1931, during which historical records show reduced agricultural production, death, famine, plague, economic crisis, and widespread human migrations. More concerning, however, are current hydroclimate conditions in the SRB, marked by decadal-scale mean flows that dip below the long-term mean (1803-1953) in the late 1970s and have since failed to recover. With the Mediterranean region currently likely experiencing the worst drought in the past ca 1000years due to human-induced climate change, the future outlook of water resource availability in the SRB could prove catastrophic for human and natural systems.

Possible Impacts of Climate Change on Daily Streamflow and Extremes at Local Scale in Ontario, Canada. Part II: Future Projection

The paper forms the second part of an introduction to possible impacts of climate change on daily streamflow and extremes in the Province of Ontario, Canada. Daily streamflow simulation models developed in the companion paper (Part I) were used to project changes in frequency of future daily streamflow events. To achieve this goal, future climate information (including rainfall) at a local scale is needed. A regression-based downscaling method was employed to downscale eight global climate model (GCM) simulations (scenarios A2 and B1) to selected weather stations for various meteorological variables (except rainfall). Future daily rainfall quantities were projected using daily rainfall simulation models with downscaled future climate information. Following these projections, future daily streamflow volumes can be projected by applying daily streamflow simulation models. The frequency of future daily high-streamflow events in the warm season (May–November) was projected to increase by about 45%-55% late this century from the current condition, on average of eight-GCM A2 projections and four selected river basins. The corresponding increases for future daily low-streamflow events and future daily mean streamflow volume could be about 25%-90% and 10%-20%, respectively. In addition, the return values of annual one-day maximum streamflow volume for various return periods were projected to increase by 20%-40%, 20%-50%, and 30%-80%, respectively for the periods 2001-50, 2026-75, and 2051-2100. Inter-GCM and interscenario uncertainties of future streamflow projections were quantitatively assessed. On average, the projected percentage increases in frequency of future daily high-streamflow events are about 1.4-2.2 times greater than inter-GCM and interscenario uncertainties.

Possible impacts of climate change on extreme weather events at local scale in south–central Canada

Synoptic weather typing and regression-based downscaling approaches have become popular in evaluating the impacts of climate change on a variety of environmental problems, particularly those involving extreme impacts. One of the reasons for the popularity of these approaches is their ability to categorize a complex set of meteorological variables into a coherent index, facilitating the projection of changes in frequency and intensity of future daily extreme weather events and/or their impacts. This paper illustrated the capability of the synoptic weather typing and regression methods to analyze climatic change impacts on a number of extreme weather events and environmental problems for south–central Canada, such as freezing rain, heavy rainfall, high-/low-streamflow events, air pollution, and human health. These statistical approaches are helpful in analyzing extreme events and projecting their impacts into the future through three major steps or analysis procedures: (1) historical simulation modeling to identify extreme weather events or their impacts, (2) statistical downscaling to provide station-scale future hourly/daily climate data, and (3) projecting changes in the frequency and intensity of future extreme weather events and their impacts under a changing climate. To realize these steps, it is first necessary to conceptualize the modeling of the meteorology, hydrology and impacts model variables of significance and to apply a number of linear/nonlinear regression techniques. Because the climate/weather validation process is critical, a formal model result verification process has been built into each of these three steps. With carefully chosen physically consistent and relevant variables, the results of the verification, based on historical observations of the outcome variables simulated by the models, show a very good agreement in all applications and extremes tested to date. Overall, the modeled results from climate change studies indicate that the frequency and intensity of future extreme weather events and their impacts are generally projected to significantly increase late this century over south–central Canada under a changing climate. The implications of these increases need be taken into consideration and integrated into policies and planning for adaptation strategies, including measures to incorporate climate change into engineering infrastructure design standards and disaster risk reduction measures. This paper briefly summarized these climate change research projects, focusing on the modeling methodologies and results, and attempted to use plain language to make the results more accessible and interesting to the broader informed audience. These research projects have been used to support decision-makers in south–central Canada when dealing with future extreme weather events under climate change.

IOD and ENSO impacts on the extreme stream-flows of Citarum river in Indonesia

Extreme stream-flow events of Citarum River are derived from the daily stream-flows at the Nanjung gauge station. Those events are identified based on their persistently extreme flows for 6 or more days during boreal fall when the seasonal mean stream-flow starts peaking-up from the lowest seasonal flows of June–August. Most of the extreme events of high-streamflows were related to La Nina conditions of tropical Pacific. A few of them were also associated with the negative phases of IOD and the newly identified El Nino Modoki. Unlike the cases of extreme high streamflows, extreme low streamflow events are seen to be associated with the positive IODs. Nevertheless, it was also found that the low-stream-flow events related to positive IOD events were also associated with El Nino events except for one independent event of 1977. Because the occurrence season coincides the peak season of IOD, not only the picked extreme events are seen to fall under the IOD seasons but also there exists a statistically significant correlation of 0.51 between the seasonal IOD index and the seasonal streamflows. There also exists a significant lag correlation when IOD of June–August season leads the streamflows of September–November. A significant but lower correlation coefficient (0.39) is also found between the seasonal streamflow and El Nino for September–November season only.

Intensified pluvial conditions during the twentieth century in the inland Heihe River Basin in arid northwestern China over the past millennium

Past streamflow variability is of special significance in the inland river basin, i.e., the Heihe River Basin in arid northwestern China, where water shortage is a serious environmental and social problem. However, the current knowledge of issues related to regional water resources management and long-term planning and management is limited by the lack of long-term hydro-meteorological records. Here we present a 1009-year annual streamflow (August–July) reconstruction for the upstream of the Heihe River in the arid northwestern China based on a well-replicated Qilian juniper ( Sabina przewalskii Kom.) ring-width chronology. This reconstruction accounts for 46.9% of the observed instrumental streamflow variance during the period 1958–2006. Considerable multidecadal to centennial flow variations below and above the long-term average are displayed in the millennium streamflow reconstruction. These periods 1012–1053, 1104–1212, 1259–1352, 1442–1499, 1593–1739 and 1789–1884 are noteworthy for the persistence of low-level river flow, and for the fact that these low streamflow events are not found in the observed instrumental hydrological record during the recent 50 years. The 20th century witnessed intensified pluvial conditions in the upstream of the Heihe River in the arid northwestern China in the context of the last millennium. Comparison with other long-term hydrological reconstructions indicates that the intensification of the hydrological cycle in the twentieth century from different regions could be attributable to regional to large-scale temperature increase during this time. Furthermore, from a practical perspective, the streamflow reconstruction can serve as a robust database for the government to work out more scientific and more reasonable water allocation alternatives for the Heihe River Basin in arid northwestern China.

Impacts of Large-Scale Circulation Variability on Low Streamflows over Canada: A Review

Low streamflows constitute an important component of hydro-climatic extremes. This is particularly true for Canada where reduced flows can affect several economic and environmental activities ranging from less hydro-electric production and increased freshwater transportation costs, to reduced water quality and ecological habitat destruction. This paper reviews past research regarding the impacts of large-scale circulation patterns on streamflow variability (including low flows) over Canada. Results from the various studies reveal that streamflow responses are generally consistent with those observed for large-scale climate. For western Canada, this includes a higher frequency of low-flow events in association with the warmer/drier conditions during El Niño events and positive phases of the Pacific Decadal Oscillation (PDO) and the Pacific North American (PNA) pattern. Relationships in northern/northeastern regions of the country are less robust but in general, reduced streamflows occur during positive phases of the North Atlantic Oscillation (NAO) and Arctic Oscillation (AO). However, it is clearly evident that the spatial and temporal aspects of these relationships are greatly influenced by hydro-climatic complexities associated with individual watersheds, especially in the cordilleran areas of Canada. Future research requires more in-depth analyses into the spatial and temporal aspects of relationships between circulation variability and low-flow occurrences over critical watersheds within Canada including the combination of climatic patterns and associations with regional, synoptic-scale circulation. The incorporation of fully coupled climate and hydrologic models to assess the impacts of projected climate change on future low-flow occurrences is also needed. This research would result in a better understanding and enhanced prediction of low streamflow events that is critical for the current and future efficient management of water resources throughout the country.

Historical evidences of streamflow fluctuations in the Mendoza River, Argentina, and their relationship with ENSO

Documentary sources are used to construct records of high and low flows of the Mendoza River and to relate these to ENSO over the historical period. The historical data are calibrated against measured discharge (ad 1909–1940) and validated by precipitation discharge-series reconstructed from tree-rings (ad 1600–1960). An increase in the number of high-streamflow events since the mid-seventeenth century is accompanied by several intervals with an above-average number of high-streamflow events; some of these intervals are also characterized by an above-average number of low-streamflow events. A considerable number of high-streamflow events do not coincide with ENSO events, which are regarded as a necessary but not sufficient cause of the extreme streamflow variations.