Decline In Streamflow Research Articles

Mid-Holocene climate of the Tibetan Plateau and hydroclimate in three major river basins based on high-resolution regional climate simulations

Abstract. The Tibetan Plateau (TP) contains the headwaters of major Asian rivers that sustain billions of people and plays an important role in both regional and global climate through thermal and mechanical forcings. Understanding the characteristics and changes to the hydrological regimes on the TP during the mid-Holocene (MH) will help in understanding the expected future changes. Here, an analysis of the hydroclimates over the headwater regions of three major rivers originating in the TP, namely the Yellow, Yangtze, and Brahmaputra rivers, is presented, using dynamically downscaled climate simulations constructed using the Weather Research and Forecasting Model (WRF) coupled to the hydrological model WRF-Hydro. Green Sahara (GS) boundary conditions have also been incorporated into the global model so as to capture the remote feedbacks between the Saharan vegetation and the river hydrographs over the TP. Model–data comparisons show that the dynamically downscaled simulations significantly improve the regional climate simulations over the TP in both the modern day and the MH, highlighting the crucial role of downscaling in both present-day and past climates. TP precipitation is also strongly affected by the greening of the Sahara, with a particularly large increase over the southern TP, as well as a delay in the monsoon withdrawal. The simulation results were first validated over the upper basins of the three rivers before the hydrological responses to the MH forcing for the three basins were quantified. Both the upper Yellow and Yangtze rivers exhibit a decline in streamflow during the MH, especially in summer, which is a combined effect of less snowmelt and stronger evapotranspiration. The GS forcing caused a rise in temperature during the MH, as well as larger rainfall but less snowfall and greater evaporative water losses. The Brahmaputra River runoff is simulated to increase in the MH due to greater net precipitation.

Resilience to hydrological droughts in the northern Murray-Darling Basin, Australia

We respond to the problem of declining streamflows in the northern Murray–Darling Basin, Australia, a region that suffers from hydrological droughts and a drying trend. We partitioned the effect of meteorological trends from anthropogenic drivers on annual streamflow, quantified the effect of annual streamflow decline on waterbird abundance, estimated the effects of streamflow change on a measure of ecosystem resilience, and calculated the net benefits of in-stream water reallocation. The anthropogenic drivers of hydrological droughts were assessed by comparing the Lower Darling (hereafter the Barka) River, which has large recorded water extractions, with the adjacent Paroo River, which has very little recorded water extractions. Findings include: (1) only about one-third of the recent reduced streamflow of the Barka River is due to a meteorological drying trend; (2) statistically significant declines in waterbird species richness and abundance have occurred on both rivers between 1983–2000 and 2001–2020; (3) declines in waterbird abundance have been much larger along the Barka River than the Paroo River; and (4) ecosystem resilience, as measured by waterbird abundance, wasgreater on the Paroo River. Our four-step framework is applicable in any catchment with adequate time-series data and supports adaptive responses to hydrological droughts. This article is part of the Royal Society Science+ meeting issue ‘Drought risk in the Anthropocene’.

Different Hydroclimate Modelling Approaches Can Lead to a Large Range of Streamflow Projections under Climate Change: Implications for Water Resources Management

The paper compares future streamflow projections for 133 catchments in the Murray–Darling Basin simulated by a hydrological model with future rainfall inputs generated from different methods informed by climate change signals from different global climate models and dynamically downscaled datasets. The results show a large range in future projections of hydrological metrics, mainly because of the uncertainty in rainfall projections within and across the different climate projection datasets. Dynamical downscaling provides simulations at higher spatial resolutions, but projections from different datasets can be very different. The large number of approaches help provide a robust understanding of future hydroclimate conditions, but they can also be confusing. For water resources management, it may be prudent to communicate just a couple of future scenarios for impact assessments with stakeholders and policymakers, particularly when practically all of the projections indicate a drier future in the Basin. The median projection for 2046–2075 relative to 1981–2010 for a high global warming scenario is a 20% decline in streamflow across the Basin. More detailed assessments of the impact and adaptation options could then use all of the available datasets to represent the full modelled range of plausible futures.

Improving Future Estimation of Cheliff-Mactaa-Tafna Streamflow via an Ensemble of Bias Correction Approaches

The role of climate change in future streamflow is still very uncertain, especially over semi-arid regions. However, part of this uncertainty can be offset by correcting systematic climate models’ bias. This paper tries to assess how the choice of a bias correction method may impact future streamflow of the Cheliff-Mactaa-Tafna (CMT) rivers. First, three correction methods (quantile mapping (QM), quantile delta mapping (QDM), and scaled distribution mapping (SDM)) were applied to an ensemble of future precipitation and temperature coming from CORDEX-Africa, which uses two Representative Concentration Pathways: RCP4.5 and RCP8.5. Then, the Zygos model was used to convert the corrected time series into streamflow. Interestingly, the findings showed an agreement between the three methods that revealed a decline in future streamflow up to [−42 to −62%] in autumn, [+31% to −11%] in winter, [−23% to −39%] in spring, and [−23% to −41%] in summer. The rate of decrease was largest when using QM-corrected model outputs, followed by the raw model, the SDM-corrected model, and finally, the QDM-corrected model outputs. As expected, the RCP presents the largest decline especially by the end of the 21st Century.

A multivariate-driven approach for disentangling the reduction in near-natural Iberian water resources post-1980

Abstract. Although the literature still debates how several anthropogenic and natural factors have contributed to the recent streamflow decline in the Iberian Peninsula, a continuing decrease in winter precipitation (WP) has been noticed in this area since the 1980s and has been associated with large-scale atmospheric drivers. This contribution assesses the potential propagation of this WP deficit into water resource variability. For this purpose, the novel “NEar-Natural Water Inflows to REservoirs of Spain” (NENWIRES) dataset was created. The results highlight that higher decreases in winter water inflows (WWIs) are always related to WP reductions. However, while the decline in WP was strongly provoked by the enhancement of the North Atlantic Oscillation index (NAOi) during the study period, WWI reductions could not be essentially linked to the NAOi behaviour in several NENWIRES catchments. Instead, the intensification of drought conditions and forest extension promoted WWI decreases over the target area and aided in understanding why WWI reductions were generally higher than WP decreases. In summary, most humid catchments registered a WWI decline that was mainly promoted by NAOi enhancement, whereas the extension of forest and evapotranspiration increases seem to explain WWI losses in semi-arid environments. This contribution sheds light on the recent debate regarding the magnitude and drivers of water resource decline over southern European regions.

The Recent Decline of Apalachicola–Chattahoochee–Flint (ACF) River Basin Streamflow

The Apalachicola–Chattahoochee–Flint (ACF) basin is arguably the most litigated interstate river system in the eastern United States. Given the complicated demands for water use within this basin, it has been difficult to ascertain if the recent multi-decadal decline in streamflow is a product of human disturbance, changing climate, natural variability, or some combination of the above factors. To overcome these challenges, we examined unimpaired streamflow and precipitation within and adjacent to the ACF basin, upstream of the Apalachicola River at Chattahoochee, and the Florida streamflow station (ARCF), which has historically been identified to be representative of hydrologic variability in the ACF basin. Several of the upstream, unimpaired, streamflow stations selected were identified in rural watersheds where land-cover changes and human disturbance were minimal during the study period. When applying a series of statistical evaluations, ARCF streamflow variability generally reflects the natural variability of the ACF basin. Additionally, unimpaired streamflow variability from the neighboring Choctawhatchee River compared favorably with ARCF variability. The recent multi-decadal decline was consistent in all records, with the 2000s being the most severe in the historic record.

Estimation of climatic and anthropogenic contributions to streamflow change in southern Romania

ABSTRACT This research investigated the contributions of climate- and human-induced change to streamflow alteration between 1966 and 2010 in four catchments in southern Romania (Vedea, Argeș, Ialomița and Buzău). We examined trends and break points in streamflow, precipitation and potential evapotranspiration and we estimated climate elasticity with Fu’s equation within the Budyko framework to further separate the contributions of climate and human changes to streamflow alterations. Results showed break points in streamflow in all catchments between 1981 and 1985, followed by decreases in average annual streamflow that varied between −28.1% and −53.4%. Most of the streamflow decline was found to be due to climate contribution: 63.1% in Argeș (the most anthropized catchment), 71.2% in Buzău, 79.2% in Ialomița and 80.2% in Vedea basin. Due to the environmental changes impacting water resources in Romania, estimating the contribution of the main drivers of streamflow change is highly important for their sustainable management.

Attribution of runoff variation to climate and human-driven changes in the transition zone between the Qinling Mountains and the Loess Plateau under vegetation greening

AbstractThe need for water safety management has increased in the transition zone between the Qinling Mountains and the Loess Plateau, China due to streamflow decline over the past 30 years. Vegetation greening, largely due to the result of the ‘Grain for Green’ program implemented in the Loess Plateau, is affecting regional streamflow together with climate change and direct human impacts. There is thus an urgent need to evaluate the relative importance of causes of streamflow variation in this region. A Hydrological Model of L′École de Technologie Supérieure (HMETS)-based segment identification analysis framework was presented to quantify the impacts of climate and human-driven changes on runoff under regional vegetation greening. Results showed that climate change and human interference were alternately dominant in the hydrological cycle from 1976 to 2015. Climate change played a major role in affecting runoff variation before 2000, and then human interference dominated. It is worth noting that temperature increases resulted in runoff reduction and induced more changes in streamflow when precipitation was high. Vegetation greening contributed highly to streamflow attenuation, and its impact on runoff variation was more significant after 2007. Generally, understanding the effects of temperature increases and vegetation greening on streamflow is important for the development of appropriate adaptation strategies for the planning and management of regional water resources.

Analysis of the Evolution of Climatic and Hydrological Variables in the Tagus River Basin, Spain

During the second half of the 20th century, several Spanish rivers experienced a decrease in the availability of water resources which coincided with an increase in human water demands. This situation is expected to be exacerbated by climate change. This study analyses the evolution of annual streamflow in 16 sub-basins of the Tagus River basin (Spain) during the 1950–2010 period and its relationship with selected variables. Our main objective is to characterize changes in in-stream flows and to identify what factors could have contributed to them. First, we used non-parametric tests to detect trends in the hydro-climatic series. Then, we analyzed changes in the runoff coefficient and applied regression-based techniques to detect anthropic drivers that could have influenced the observed trends. The analysis revealed a general decreasing trend in streamflow and an increasing trend in air temperature, while trends in precipitation are less clear. Residuals from regression models indicate that the evolution of several non-climatic factors is likely to have influenced the decline in streamflow. Our results suggest that the combination of the expansion of forested areas (a 60% increase from 1950 to 2010) and irrigated land (a 400% increase since 1950) could have played an important role in the reduction of streamflow in the Tagus basin.

Climatic and anthropogenic drivers of a drying Himalayan river

Abstract. Streamflow regimes are rapidly changing in many regions of the world. Attribution of these changes to specific hydrological processes and their underlying climatic and anthropogenic drivers is essential to formulate an effective water policy. Traditional approaches to hydrologic attribution rely on the ability to infer hydrological processes through the development of catchment-scale hydrological models. However, such approaches are challenging to implement in practice due to limitations in using models to accurately associate changes in observed outcomes with corresponding drivers. Here we present an alternative approach that leverages the method of multiple hypotheses to attribute changes in streamflow in the Upper Jhelum watershed, an important tributary headwater region of the Indus basin, where a dramatic decline in streamflow since 2000 has yet to be adequately attributed to its corresponding drivers. We generate and empirically evaluate a series of alternative and complementary hypotheses concerning distinct components of the water balance. This process allows a holistic understanding of watershed-scale processes to be developed, even though the catchment-scale water balance remains open. Using remote sensing and secondary data, we explore changes in climate, surface water, and groundwater. The evidence reveals that climate, rather than land use, had a considerably stronger influence on reductions in streamflow, both through reduced precipitation and increased evapotranspiration. Baseflow analyses suggest different mechanisms affecting streamflow decline in upstream and downstream regions, respectively. These findings offer promising avenues for future research in the Upper Jhelum watershed, and an alternative approach to hydrological attribution in data-scarce regions.

Streamflow decline threatens water security in the upper Yangtze river

The annual streamflow in the upper Yangtze River (UYR) declined by 36.6 billion m3 from 1961 to 2015. However, the contributions to this streamflow decline from different tributaries and the underlying causes remain unclear. Here we quantify the streamflow decline in the UYR and the impacts of climate change and human activities using a distributed hydrological model and statistical methods. Results show that the streamflow decline increased from the upstream to downstream regions. Combining hydrological simulation and statistical analysis, the contributions of climate change, human water consumption, reservoir impoundment and human-induced vegetation change on streamflow decline are estimated to be 62.5%, 19.7%, 18.4% and 1.8%, respectively. Specifically, human water consumption growth is consistent with the spatial pattern of population growth and industrial development, and the reservoir impoundments are mainly located in the middle and lower parts of the mainstream. In the Jialingjiang, the tributary with the largest drainage area in the UYR, human activities account for 63.6% of the streamflow decline, with the largest decline induced by human water consumption growth. Under climate change and population growth, the population under water stress (water resources available less than 1000 m3/capita/yr) increases in the Mintuojiang and Jialingjiang, where the major cities are centralized and the population density is high. This study provides a new perspective for understanding the status of water resources in the UYR and offers insights into the sustainable utilization of water resources in the future.

Climate change impact on water quality in the integrated Mahabad Dam watershed-reservoir system

Climate change, besides global warming, is expected to intensify the hydrological cycle, which can impact watershed nutrient yields and affect water quality in the receiving water bodies. The Mahabad Dam Reservoir in northwest Iran is a eutrophic reservoir due to excessive watershed nutrient input, which could be exacerbated due to climate change. In this regard, a holistic approach was employed by linking a climate model (CanESM2), watershed-scale model (SWAT), and reservoir water quality model (CE-QUAL-W2). The triple model investigates the cumulative climate change effects on hydrological parameters, watershed yields, and the reservoir’s water quality. The SDSM model downscaled the output of the climate model under moderate (RCP4.5) and extreme (RCP8.5) scenarios for the periods of 2021–2040 and 2041–2060. The impact of future climate conditions was investigated on the watershed runoff and total phosphorus (TP) load, and consequently, water quality status in the dam’s reservoir. The results of comparing future conditions (2021–2060) with observed present values under moderate to extreme climate scenarios showed a 4–7% temperature increase and a 6–11% precipitation decrease. Moreover, the SWAT model showed a 9–16% decline in streamflow and a 12–18% decline in the watershed TP load for the same comparative period. Finally, CE-QUAL-W2 model results showed a 3–8% increase in the reservoir water temperature and a 10–16% increase in TP concentration. It indicates that climate change would intensify the thermal stratification and eutrophication level in the reservoir, especially during the year’s warm months. This finding specifies an alarming condition that demands serious preventive and corrective measures.

Modeling streamflow sensitivity to climate warming and surface water inputs in a montane catchment

Study regionGordon Gulch, an upper-montane forest watershed in the Colorado Front Range. Study focusAs the climate warms, the fraction of precipitation falling as snow is expected to decrease and the timing of snowmelt is expected to shift earlier in spring. In snow-dominated regions, these changes in snow accumulation and melt prompt us to examine downstream changes in streamflow. The objective of this study is to understand how changes in precipitation phase and snowmelt timing alter the timing of surface water inputs (i.e. rainfall and snowmelt) and the partitioning of these inputs between evapotranspiration and streamflow. We used the Distributed Hydrology Soil Vegetation Model and Weather Research and Forecasting Model-based projections of future climatic conditions to simulate streamflow. New hydrological insights for the regionModeled annual streamflow decreased by 22% for the period 2071–2100. Surface water inputs increased during winter when atmospheric water demand was relatively low. Subsequently, the winter-period partitioning of water (as rain or snowmelt) to streamflow (as opposed to evapotranspiration) increased, by 15%, while partitioning to evapotranspiration decreased, effectively buffering what would have otherwise been a larger net streamflow decline associated with warming. Seasonal streamflow buffering is unique to snow-influenced systems, as the magnitude and timing of water released from snowpacks is sensitive to warming. This effect may diminish as warming drives snow-influenced systems toward rain-dominance, with implications for hydrological and ecological processes and water-resource management.

Streamflow trends during recent decades at some near-natural catchments in Iran

ABSTRACT In this study, we assessed the impacts of climate variations on streamflow in 28 near-natural catchments in Iran. To this end, we analysed the trend of annual streamflow, precipitation, and temperatures using the Mann-Kendall test and Sen’s slope between water years 1982 and 2011. We evaluated the frequency of precipitation in different classes, i.e. below 5, 5–10, 10–15, and above 15 mm/day. Our results indicate a decline in streamflow at 25 catchments, at a rate of −5.66 to −0.19 mm/year. The annual precipitation amount did not decrease significantly, while the frequency of light precipitation events (<5 mm/day) increased. About 60% of the upward trend was significant. Mean temperature increased at all studied catchments, at an average rate of 0.055°C/year. In short, our results indicate that increases in temperature and the frequency of light precipitation events are two leading factors in streamflow reduction across studied catchments.

Hydro-climatic Variability and Trend Analysis of Modjo River Watershed, Awash River Basin of Ethiopia

Climate change and variability is expected to trigger changes in temperature and precipitation series. This study aimed at assessing variability and trend of hydro-climatic variables at Modjo River watershed. Long-term climate data of 5 representative stations with in the watershed (1981-2010) and streamflow data of Modjo gauging station (1983 -2010) were used. Rainfall variability was analyzed using Coefficient of variation (CV), Precipitation concentration index (PCI) and Standardized anomaly index (SAI). Climate trends were evaluated using Sen’s slope estimator and Mann–Kendall trend test methods. The study revealed Most of the stations showed low variation in annual rainfall (CV% &lt;20) while the main (Kiremt) and short (Belg) season rainfall exhibited CV ranging from low to high. Both annual and seasonal rainfall showed a non-significant trend at all stations for the past 30 years. However, majority of stations showed an increasing trend in annual daily average temperature ranging from 0.2 to 0.6ºC per decade. Following increases in temperature and the subsequent rise in evapotranspiration, streamflow has shown a high significant declining trend. The temporal decline in streamflow at Modjo watershed could likely affect downstream Koka dam water reserve. Thus, any watershed management strategy that can optimize water conservation for sustainable crop production and option that can improve flow to the reserve is vital. Keywords: Climate change, Climate variability, Hydro-climate, trend, Modjo river watershed DOI: 10.7176/JEES/11-9-04 Publication date: September 30 th 2021

Recent decline in streamflow and sediment discharge in the Godavari basin, India (1965–2015)

Godavari River representing the largest catchment in Peninsular India records a significant decline in streamflow and sediment discharge since 1965 with a sharp fall after ~1990. The present study documented changes in water and sediment discharge based on analysis of a large time-series database of daily streamflow from 57 gauging stations and sediment discharge from 25 stations during the period from 1965 to 2015 in the Godavari basin. Linear regression, Mann-Kendall non-parametric test, Sen’s slope, and Pettitt tests were conducted to examine the trends and abrupt changes in the time series. Many stations recorded a decline in sediment discharge (up to 90%) after 1990. At the terminal gauging station (Polavaram), the average annual sediment discharge for the period between 1970 and 1990 was 142 × 106 t, while it decreased to 59 × 106 t from 1991 to 2013. The outcomes of this study revealed a critical drop in sediment discharge after 1990 because of very high sediment entrapment by extensive dam constructions. This resulted in a substantial decrease in sediment supply contrasting to the increasing sea level, further implicating significant coastal erosion in the near future.

Hydroclimatic Variability in the Bilate Watershed, Ethiopia

It is important to understand variations in hydro-meteorological variables to provide crucial information for water resource management and agricultural operation. This study aims to provide comprehensive investigations of hydroclimatic variability in the Bilate watershed for the period 1986 to 2015. Coefficient of variation (CV) and the standardized anomaly index (SAI) were used to assess the variability of rainfall, temperature, and streamflow. Changing point detection, the Mann–Kendell test, and the Sen’s slope estimator were employed to detect shifting points and trends, respectively. Rainfall and streamflow exhibited higher variability in the Bega (dry) and Belg (minor rainy) seasons than in the Kiremt (main rainy) season. Temperature showed an upward shift of 0.91 °C in the early 1990s. Reduction in rainfall (−11%) and streamflow (−42%) were found after changing points around late 1990s and 2000s, respectively. The changing points detected were likely related to the ENSO episodes. The trend test indicated a significant rise in temperature with a faster increase in the minimum temperature (0.06 °C/year) than the maximum temperature (0.02 °C/year). Both annual mean rainfall and streamflow showed significant decreasing trends of 8.32 mm/year and 3.64 mm/year, respectively. With significant increase in temperature and reduction in rainfall, the watershed has been experiencing a decline in streamflow and a shortage of available water. Adaptation measures should be developed by taking the increasing temperature and the declining and erratic nature of rainfall into consideration for water management and agricultural activities.

Spatially variable hydrologic impact and biomass production tradeoffs associated with Eucalyptus (E. grandis) cultivation for biofuel production in Entre Rios, Argentina

AbstractClimate change and energy security promote using renewable sources of energy such as biofuels. High woody biomass production achieved from short‐rotation intensive plantations is a strategy that is increasing in many parts of the world. However, broad expansion of bioenergy feedstock production may have significant environmental consequences. This study investigates the watershed‐scale hydrological impacts of Eucalyptus (E. grandis) plantations for energy production in a humid subtropical watershed in Entre Rios province, Argentina. A Soil and Water Assessment Tool (SWAT) model was calibrated and validated for streamflow, leaf area index (LAI), and biomass production cycles. The model was used to simulate various Eucalyptus plantation scenarios that followed physically based rules for land use conversion (in various extents and locations in the watershed) to study hydrological effects, biomass production, and the green water footprint of energy production. SWAT simulations indicated that the most limiting factor for plant growth was shallow soils causing seasonal water stress. This resulted in a wide range of biomass productivity throughout the watershed. An optimization algorithm was developed to find the best location for Eucalyptus development regarding highest productivity with least water impact. E. grandis plantations had higher evapotranspiration rates compared to existing terrestrial land cover classes; therefore, intensive land use conversion to E. grandis caused a decline in streamflow, with January through March being the most affected months. October was the least‐affected month hydrologically, since high rainfall rates overcame the canopy interception and higher ET rates of E. grandis in this month. Results indicate that, on average, producing 1 kg of biomass in this region uses 0.8 m3 of water, and the green water footprint of producing 1 m3 fuel is approximately 2150 m3 water, or 57 m3 water per GJ of energy, which is lower than reported values for wood‐based ethanol, sugar cane ethanol, and soybean biodiesel.

Study and analysis of the streamflow decline in North Algeria

This research analyses the variability of hydrometeorology data in the Sebaou watershed, (Northern Algeria) and examines the impacts of Climate Change (CC) and Human Activities (HA) on the streamflow decrease, using the climate elasticity model and hydrologic modelling. The results of tests, used to identify the trends and breakpoints in the data series, show significant downward trends and breakpoints, through the 1980s in streamflow. At the Sebaou outlet, the decrease of runoff, after 1985 is assessed; 34.8%, 35.8%, 28.5%, 41.6% and 40.1% in year, autumn, winter, spring and summer, respectively. The results obtained, by climate elasticity model, reveal that a 10% change in rainfall ensues in around 16–25% variation in streamflow. Besides the factors (CC and HA) have an effect of 58% and 42% respectively, on the reduction of streamflow in the Sebaou. The land use maps analysis approve those of the elasticity method and the GR2M model.

Climate change impact on water availability in the olifants catchment (South Africa) with potential adaptation strategies

Increasing population and economic growth has intensified water supply pressure on the Olifants River Basin causing it to become water-stressed. Climate change is expected to aggravate existing water supply challenges in the basin if urgent interventions are not implemented. This study evaluates the impacts of climate change on water availability and demand in the Olifants River Basin of South Africa, and assesses to what extent a combination of management strategies can mitigate current and longer term impacts using the Water Evaluation and Planning (WEAP) model. The results demonstrated by the two projected climate change scenarios (RCP4.5 and RCP8.5) showed a rise in temperature of approximately 1 °C–4 °C, and a decrease in precipitation of 5%–30%, as compared to the baseline climate of 1976–2005. Results also showed that pressure on water supply due to increased economic activities and a decline in streamflow will increase unmet water demand by 58% and 80% for the mid and end century periods respectively. Results further revealed that the combination of management measures proposed by decision makers is expected to decrease future unmet water demand from 1006MCM to 398MCM, 1205MCM to 872MCM and 1251MCM to 940MCM for reference, RCP4.5 and RCP 8.5 scenario respectively. The study therefore concludes that the combination of management strategies provides a much better and more efficient solution to water scarcity issues in the basin, compared to a reliance on a single strategy.