Decrease In Streamflow Research Articles

Impacts of Solar Radiation Management on Hydro-Climatic Extremes in Southeast Asia

Solar radiation management (SRM), or solar geoengineering, reduces the earth’s temperature by reflecting more sunlight back to space. However, the impacts of SRM remain unclear, making it difficult to project the benefits as well as consequences should this approach be adopted to combat climate change. To provide novel insight into the SRM impact on hydro-climatic extremes in Southeast Asia, this study conducts a simulation experiment for the Kelantan River Basin (KRB) in Malaysia by incorporating three bias-corrected Stratospheric Aerosol Geoengineering Large Ensemble (GLENS) members into the Soil and Water Assessment Tool Plus (SWAT+) model. The study found that SRM practices could generate substantial cooling effects on regional temperatures, leading to a reduction in projected annual precipitation and monthly precipitation during the flooding season (from November to mid-January) under SRM relative to the Representative Concentration Pathway 8.5 (RCP8.5) scenario. In addition, SRM could reduce the number of days with heavy precipitation as well as the intensity of maximum daily precipitation as compared to RCP8.5, during the 2045–2064 and 2065–2084 periods, leading to a reduction in high flows. Nevertheless, under SRM impacts, the driest months from February to May would experience comparable decreases in monthly precipitation and streamflow.

Dynamics of DOC concentration and flux in different propagation stages of hydrological drought: Patterns and drivers

Droughts influence dissolved organic carbon (DOC) export. DOC concentration and flux dynamics during different propagation stages of hydrological drought (HD) are complex and poorly understood. Long-term (from 1978 to 2018) weekly (biweekly) DOC concentration and daily streamflow at four headwater streams of Harp Lake catchment, Ontario, Canada were used to examine the effects of HD on the dynamics. Identified HD were divided into four propagation stages: pre-drought (P1), intensification (P2), recovery (P3) and post-drought (P4). The potential mechanisms underlying the patterns in DOC were also investigated. First, HD reduced DOC concentration by an average of 19.24% relative to non-HD periods. DOC concentrations and fluxes of streams were different during different propagation stages. Second, DOC flux patterns among streams were consistent with “fast decline-slow rise-fast rise” trends over the P2, P3, and P4, relative to each previous stage. However, DOC concentration pattern differed among four streams, showing a “fast decline-slow decline-fast rise” trend across four stages in two streams, but a “fast decline-slow rise-fast rise” pattern at other two. Initially, DOC flux during HD was primarily dominated by streamflow, but DOC concentration eventually became an important co-factor. Third, the rapid decrease (or increases) in streamflow during P2 (P4) relative to P1 (P3) led to a fast decline (or rise) in DOC concentration. Differences in DOC concentration responses among streams were probably due to differences in local hydrologic features (e.g., wetlands) and unnatural activities. pH and SO4 can also influence DOC concentration dynamics during HD, but just under the specific hydrothermal combinations. This study provides an updated perspective to understand the dynamic patterns of DOC concentration and flux and their drivers during droughts, and it could be used to improve the modeling and management capability of water quality.

The impacts of climate changes on watershed streamflow and total dissolved nitrogen in Danjiang Watershed, China

Abstract The impacts of future climate change on the watershed streamflow and total dissolved nitrogen (TDN) fluxes upstream of the Danjiang River were estimated. The newest shared socioeconomic pathways (SSP) in CMIP6 were used as a climate change scenario. The ensembles of downscaled GCM outputs from WorldClim were used as future climate change information. A combined modeling approach is proposed, including the Long Ashton Research Station Weather Generator (LARS-WG) model as a weather generator and the generalized watershed loading function (GWLF) model for watershed hydrochemical process model and scenario analysis. The results show that there is generally less annual streamflow but more annual TDN flux under future climate change scenarios. The monthly streamflow and TDN flux increased from May to July and decreased from August to October. Changes in streamflow and TDN fluxes were the greatest in the worst uncontrolled scenario of SSP 5-85, with a 12.1% decrease in annual streamflow in the 2070s and a 4.82% increase in annual TDN flux in the 2090s. This indicates that active climate policies can mitigate the impact of climate change on watersheds. Furthermore, the source apportionments of TDN from agricultural sources will increase to nearly 50% by the 2090s, and targeted management strategies should be implemented.

Migration in drought: Receding streams contract the seaward migration window of endangered salmon

AbstractProlonged migration windows buffer migratory animal populations against uncertainty in resource availability. Understanding how intensifying droughts from climate change influence the migration window is critical for biodiversity conservation in a warming world. We explored how drought affects the seaward migration of endangered coho salmon (Oncorhynchus kisutch) near the southern extent of their range in California, USA. We tracked stream departures of juvenile coho, measuring streamflow and temperature in seven streams over 13 years, spanning a historic drought with extreme dry and warm conditions. Linear mixed effects models indicate that, over the range of observations, a decrease in seasonal streamflow (from 4.5 to 0.5 mm/day seasonal runoff) contracted the migration window by 31% (from 11 to 7 weeks). An increase from 10.2 to 12.8°C in mean seasonal water temperature hastened the migration window by three weeks. Pacific salmon have evolved to synchronize ocean arrival with productive ocean upwelling. However, earlier and shorter migration windows during drought could lead to mismatches, decreasing fitness and population stability. Our study demonstrates that drought‐induced low flows and warming threaten coho salmon in California and suggests that environmental flow protections will be needed to support the seaward migration of Pacific salmon in a changing climate.

Tracking snowmelt during hydrological surface processes using a distributed hydrological model in a mesoscale basin on the Tibetan Plateau

Mountain snowpack is an important water resource in high altitude and latitude regions where terrain is typically complex. However, only limited information has been published on snowmelt pathways in such regions and their de facto contributions to streamflow and soil moisture. To fill this knowledge gap, this study integrated a snowmelt pathway tracking algorithm to the high-resolution physically based Distributed Hydrology Soil Vegetation Model (DHSVM) to track snowmelt movement and to quantify snowmelt contributions during surface hydrologic processes. A simple reservoir operation scheme was also integrated into the model. The modified model was applied to a dammed mesoscale watershed in the northeastern region of the Tibetan Plateau, China, to explore relevant snow and reservoir effects. Results show that both the annual snow contribution to soil moisture (SC-SM) and the snow contribution to streamflow (SC-S) significantly decreased between 1965 and 2019. On a monthly scale, SC-SM amplitudes were highest in the upper soil layer, while peaks in deeper layers lagged behind those in upper layers. Moreover, mean monthly SC-S from all stations revealed bimodal distributions that corresponded to the snowfall season. Finally, reservoir regulation measures only exerted minimal impacts (≤2.0 %) on SC-S. If current climate change rates continue on the same trajectory, mountain snowpack reductions will be the primary cause for decreases in monthly and annual streamflow at the outlet of this basin. To mitigate climate change impacts, better water resource management is needed in this watershed.

Hydrological response to future climate change in a mountainous watershed in the Northeast of Tibetan Plateau

Study regionUpper reach of the Heihe River basin (UHRB) Study focusWe quantified the potential changes in future climate and streamflow, as well as their corresponding contribution to the annual variations. And the dominant factors of streamflow change were explored in further. Robust multivariate bias correction was applied to correct the outputs of the general circulation method (GCMs) before applying the climate projection. The Soil and Water Assessment Tool model was applied to explore streamflow characteristics under the climate projection of bias-corrected GCMs under four representative emission scenarios (SSP1–2.6, SSP2–4.5, SSP3–7.0, and SSP5–8.5). New hydrological insights for the regionBy the end of the 21st century, climate will follow a warming and wetting trend within the basin; the annual streamflow is projected to increase by > 18 % in the 2030 s, and > 36 % in the 2050 s and 2090 s. Overall, the minimum temperature had a positive impact on streamflow in the cold seasons, especially in spring, contributing the most to the annual streamflow increment. When the temperature increase is greater than 5.42 °C, the peak streamflow will shift forward from May to April. Moreover, evapotranspiration will increase with temperature, leading to a decrease in summer streamflow. The results enable us to better understand the climate and streamflow changes at different time scales and provide guidance for the development of climate change response strategies and water resource management planning.

Hydrologic impacts of cascading reservoirs in the middle and lower Hanjiang River basin under climate variability and land use change

Study regionMiddle and lower Hanjiang River (MLHR) basin, China. Study focusChanges in streamflow are often due to intertwined factors like climatic variability, land use change, and hydraulic constructions, whose relative impact is however poorly understood. In this study, we disentangled these effects by comparing real data and modelled scenarios of catchment behaviour. Modelled scenarios employ the soil and water assessment tool (SWAT), whereas the scenario comparison uses the Indicators of Hydrologic Alteration (IHA). New hydrological insights for the regionOur analyses show that (1) watershed inlet was the major factor altered the streamflow regime at the watershed outlet, which pointed us to consider only the relative catchment contribution in further analyses. (2) Climate variability was the main driver of the net changes in natural hydrological regime, which downplayed the effect of land use change on streamflow variability. (3) The streamflow regulation associated to the progressive increase in reservoirs and their operation significantly altered the flow pattern, causing a general decrease in average streamflow, an attenuation of extreme events indicators, and an alteration of the pulse pattern with more frequent but shorter pulses. (4) The average water withdrawals at MLHR were estimated, which were 8.03 × 109 m3/year. Overall, this research provides a path to assess the hydrologic impact of cascading reservoirs at the basin level under climate variability and land use change elsewhere.

Impacts of climate change on streamflow and reservoir inflows in the Upper Manyame sub-catchment of Zimbabwe

This study focused on the Upper Manyame sub-catchment which covers an area of approximately 3 786 km2 and forms part of the Manyame catchment, one of the seven catchments of Zimbabwe. Manyame catchment has its source in Marondera town and drains into the Zambezi River downstream of the Kariba Dam and upstream of the Cahora Bassa Dam, in the northern part of the country. This study assessed potential climate change impacts on the streamflow and reservoir inflows in the Upper Manyame sub-catchment. Hydrologic simulations for future climate (2030s and 2060s) were carried out using statistically downscaled bias-corrected variables from the HadCM3 (HadCM3A2a and HadCM3B2a scenarios) and CanESM2 (RCP2.6 and RCP8.5) global circulation models. The HEC–HMS hydrological model was set up for two gauged micro-catchments and eight ungauged tributary micro-catchments. Model calibration for gauged micro-catchments of Upper Manyame over the period from 2000–2010 revealed satisfactory model performance of 4.3% (RVE) and 0.1 (bias) for Mukuvisi micro-catchment and 9.5% (RVE) and 0.15 (bias) for Marimba micro-catchment. Model simulations resulted in a projected decrease in streamflow by 7.4–26.4% for HadCM3. For CanESM2, simulations resulted in a projected decrease in streamflow by 2.5–34.7%. Reservoir inflows into Lake Chivero and Lake Manyame, the main water supply sources for Harare, will decrease by 10.5–18% for HadCM3 and by 8–33.6% for CanESM2.

Meteorological and hydrological drought hazard, frequency and propagation analysis: A case study in southeast Australia

Study regionSoutheast Australia. Study focusWe investigated meteorological and hydrological drought characteristics using Standardized Precipitation Index (SPI), Standardized Streamflow Index (SSFI) and Effective Drought Index (EDI). Drought Hazard Index (DHI) was derived based on the probability of drought occurrence and Thiessen polygons using SPI/EDI, whereas Drought Frequency Index (DFI) was derived based on number of drought events, and data length using SPI, EDI, and SSFI. The modified Mann-Kendall test was applied to detect trends in streamflow data and hydrological droughts. Furthermore, correlation between meteorological and hydrological drought indices for different timesteps was assessed through Pearson’s and Spearman’s rank correlation analysis. Finally, the drought propagation time (DPT) from meteorological to hydrological drought was estimated by ‘theory of run.’ New hydrological insights for the regionOur major findings include: (i) The spatial coverage of DHI and DFI, based on SPI/EDI, illustrate that mainly south and coastal regions of the study area are the most ‘drought-prone’ (ii) A considerable proportion of streamflow stations shows a significant trend of decrease in annual streamflow, with the most dominant year of abrupt change is 1996; (iii) Hydrological droughts are increasing in the study area; (iv) Performance of EDI with SSFI is found to be better than SPI at 3-month timestep; and (v) DPT can be found using ‘theory of run’ however, defined DPT cannot be directly applied to other regions.

Identifying nutrient sources and sinks to the South Platte River and Cherry Creek, Denver, CO, during low‐flow conditions in 2019–2020

AbstractElevated concentrations and loads of nutrients in the South Platte River and Cherry Creek in Denver, Colorado, may have adverse effects on those streams and downstream water bodies, including increased production of algae, eutrophication, and decreased recreational opportunities. This article describes streamflow and concentrations and loads of nutrients for the South Platte River and Cherry Creek in Denver based on data collected during two longitudinal Lagrangian sampling campaigns in low‐flow conditions in fall of 2019 and 2020. The results are used to assess sources and sinks of nutrients in the study area and help to establish baseline conditions against which future changes in nutrient concentrations and loads can be assessed. Discharges from Chatfield and Cherry Creek Reservoirs, storm drains, and most tributaries to the South Platte River, and Cherry Creek were generally small sources of streamflow and nutrient loads in both years. The Marcy Gulch, South Platte Water Renewal, and Robert W. Hite wastewater treatment plants were larger sources of streamflow and nutrient loads. The Burlington Ditch was a sink for streamflow and nutrient loads, diverting more than 95% of the South Platte River during the two sampling campaigns. Most other sinks were associated with decreases in streamflow between sampling sites. Golf courses were a potential source of nutrients for Cherry Creek but not for the South Platte River.

Potential Hydrological Impacts of Planting Switchgrass on Marginal Rangelands in South Central Great Plains

Woody plant encroachment is an ongoing global issue. In the Southern Great Plains of the United States, the rapid encroachment and coalescence of woody plants are transforming herbaceous-dominated rangelands into woodlands with a detrimental impact on water quality and quantity. In this study, we conducted modeling simulations to assess how converting juniper (Juniperus virginiana) woodland and low to moderately productive grassland into switchgrass (Panicum virgatum) biomass production system would affect streamflow and sediment yields in the Lower Cimarron River, Oklahoma. First, the grassland areas in the basin were divided into productivity classes suitable for rangeland activities based on the soil productivity index. Next, the Soil and Water Assessment Tool was used to develop the basin hydrologic model, calibrated and validated for streamflow in five gaging stations with a percent bias of <10%, Nash–Sutcliffe Efficiency index of >0.76, and R2 of >0.77. Then, the model was used to simulate evapotranspiration (ET), streamflow, groundwater recharge, and sediment loads under different land use conversion scenarios. Results showed that converting existing juniper woodlands, ~4% of the basin, to switchgrass had limited impacts on the water budget and sediment yield. A hypothetical scenario of converting low to moderately productive rangeland to switchgrass increased annual ET by 2.6%, with a decrease in streamflow by 10.8% and a reduction in sediment yield by 39.2% compared to the baseline model. Results indicated that switchgrass could be considered a potential land use alternative to address the juniper encroached grassland with minimal loss in streamflow but a substantial reduction in sediment yield in the southcentral region of the Great Plains.

Enhanced streamflow simulations using nudging based optimization coupled with data-driven and hydrological models

Study regionVarahi River originating from the Western Ghats of India. Study focusWe developed a hybrid model that integrates process-based hydrological model (PHM) and data-driven (DD) techniques to generate streamflow simulations precisely. The hybrid modeling framework is practical as it respects hydrological processes through the PHM while considering the advantage of the DD model's ability to simulate the complex relationship between residuals and input variables. Further, we have proposed an optimization-based nudging scheme for post-processing the hybrid model simulated streamflow to overcome the limitations in PHM and DD. New hydrological insights for the regionWe formulated two approaches for simulating streamflow ensembles using DD and PHM models. In approach− 1, DD models are initially used to ensemble meteorological variables and then use the ensembles in a PHM to simulate streamflows. In approach− 2, PHM is forced with different sets of meteorological variables to simulate multiple streamflow sets and then use DD models to ensemble the PHM-derived streamflows. Random forest exhibited better performance for ensembling precipitation, temperature, and streamflow datasets compared to the other five DD algorithms in the study. Streamflows generated using approach− 2 showed reliable estimates when compared against observed streamflow values. However, post-processing the hybrid streamflows using an optimization-based nudging scheme outperformed the streamflows generated in approach− 1 and approach− 2 with better model fit statistics (R2 and NSE of 0.69 and 0.66). The output from the nudging scheme was further utilized for streamflow predictions under the combined impact of land use/cover (LULC) and climate change (CC) under the Representative Concentration Pathway 4.5 scenario. It depicted a decrease in monthly and seasonal stream flows with − 22.65 %, − 31.77 %, − 11.81 % for winter, summer, and monsoon seasons, respectively. These results suggest that water availability will decline, and water scarcity will increase in the study region. These variations in streamflow might negatively impact agriculture and natural ecosystems and even lead to water restrictions in the region.

Evaluation of Surface Water Resource Availability under the Impact of Climate Change in the Dhidhessa Sub-Basin, Ethiopia

Climate change, with its reaching implications, has become a popular topic in recent years. Among the many aspects of climate change, one of the most pressing concerns has been identified as the impact on the terrestrial water cycle, which has a direct impact on human settlement and ecosystems. The paper begins by reviewing previous studies, and then identifies their flaws and future research directions. The effects of climate change on surface water resources in the Dhidhessa Sub-basin, Abbay Basin, Ethiopia, were studied as practices. For future potential climate change, the results of global climate models (GCMs) and high-resolution regional climate models (RCMs) from multiple climate models were combined with data from Representative Concentration Pathways (RCPs) prepared by the Intergovernmental Panel on Climate Change from the CCAFS Data Distribution Center web page. To evaluate the impacts on water resources, various distributed hydrologic models based on local underlying surfaces were developed. The future potential climate change of the Dhidhessa Sub-basin Province was evaluated by integrating RCP outputs, whereas the climate change of the Dhidhessa River was directly derived from the results of different RCP. Dhidhessa stream flow will decrease in the future compared to the baseline era. The predictions of future discharge (stream flow) were based on climate scenarios data from 1991 to 2020 and for the future with two time windows, 2044 (2030–2059) and 2084 (2070–2099), on a monthly time-step after bias correction to both precipitation and temperature in the future climate described in the under each RCP. According to model results, the quantity of surface water resources in the Dhidhessa river region will decrease over the next 100 years, the percent decrease in mean annual stream flow by 10%, in 2044, and 6.3% in 2084, respectively, making the impact of temperature increase on runoff greater than that of precipitation. The distribution of runoff would be more even across years but more uneven across years in the long-term window, implying a higher possibility of drought and flooding. In general, this study discovered that any effect on this river that results in a decrease in flow will have a direct impact on the area’s ongoing water resource development and socioeconomic development.

Juvenile fish stranding induced by upstream gate operation: A risk assessment through eco-hydraulic modeling

Rapidly changing flows in regulated rivers can significantly impair freshwater biotas. At present, this issue is mostly addressed by hydropeaking research. In contrast, only limited information is available concerning the environmental effects of sharp streamflow variations determined by manmade manipulation other than hydroelectricity generation.In this paper, we assessed the stranding risk of juvenile marble trout (Salmo marmoratus), an endemic species of particular interest in the study area, during rapid streamflow decrease controlled by upstream gate operation. Our investigation focused on the falling limb of a regulated flood hydrograph in a residual-flow reach of the Ticino River, located few kilometers below its outlet from Lake Maggiore (Northern Italy).The stranding risk assessment was carried out by coupling two-dimensional unsteady flow simulation and standard habitat suitability modeling. Specifically, we adopted univariate habitat suitability curves, and a threshold for the critical rate of decrease of the water surface elevation (downramping rate), commonly used in hydropeaking assessments. Our results evidenced potential stranding occurrence of the target fish species, and possible mitigation by reducing the rate of streamflow decrease before restoring the minimum flow after flood spilling. However, more reliable estimates, including partitioning the stranding risk into classes, are challenged in our opinion by difficulties arising from extensive field validation and related selection of model parameters.In a global context characterized by the urgent need of mitigating the hydro-morphological alteration of regulated rivers, we are confident that the presented approach could support an improved streamflow management in river reaches below reservoirs and regulated lakes, therefore arousing attention and research advancement by the scientific community.

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.

Climate Change Impacts on Hydrological Processes in a South-Eastern European Catchment

The output extracted from CNRM, MPR, and ICHEC Global Circulation Models for RCP 4.5 and RCP 8.5 Representative Concentration Pathways has been used in conjunction with the SWAT model for evaluating the impacts of future climate changes on hydrological processes in a Romanian catchment (Neajlov, 3720 km2 area) in the short (2021–2050) and long term (2071–2100). During the growing season, precipitation will decrease by up to 7.5% and temperature will increase by up to 4.2 °C by 2100. For the long term (2071–2100), the decrease in soil water content (i.e., 14% under RCP 4.5 and 21.5% under RCP 8.5) and streamflow (i.e., 4.2% under RCP 4.5 and 9.7% under RCP 8.5) during the growing season will accentuate the water stress in an already water-deficient area. The snow amount will be reduced under RCP 8.5 by more than 40% for the long term, consequently impacting the streamflow temporal dynamics. In addition, our results suggest that hydrological processes in the lower portions of the catchment are more sensitive to climate change. This study is the first Romanian catchment-scale study of this nature, and its findings support the development of tailored climate adaptation strategies at local and regional scales in Romania or elsewhere.

Trends and Climate Elasticity of Streamflow in South-Eastern Brazil Basins

Trends in streamflow, rainfall and potential evapotranspiration (PET) time series, from 1970 to 2017, were assessed for five important hydrological basins in Southeastern Brazil. The concept of elasticity was also used to assess the streamflow sensitivity to changes in climate variables, for annual data and 5-, 10- and 20-year moving averages. Significant negative trends in streamflow and rainfall and significant increasing trend in PET were detected. For annual analysis, elasticity revealed that 1% decrease in rainfall resulted in 1.21–2.19% decrease in streamflow, while 1% increase in PET induced different reductions percentages in streamflow, ranging from 2.45% to 9.67%. When both PET and rainfall were computed to calculate the elasticity, results were positive for some basins. Elasticity analysis considering 20-year moving averages revealed that impacts on the streamflow were cumulative: 1% decrease in rainfall resulted in 1.83–4.75% decrease in streamflow, while 1% increase in PET induced 3.47–28.3% decrease in streamflow. This different temporal response may be associated with the hydrological memory of the basins. Streamflow appears to be more sensitive in less rainy basins. This study provides useful information to support strategic government decisions, especially when the security of water resources and drought mitigation are considered in face of climate change.

Impacts of Climate Change and Non-Point-Source Pollution on Water Quality and Algal Blooms in the Shoalhaven River Estuary, NSW, Australia

This study quantifies some of the potential impacts of climate change and nutrient pollution to identify the most important factors on water quality changes and algal blooms in the study region. Three variables, air temperature and streamflow, representing climate change, and nutrient runoff, were varied in eight hypothetical scenarios to determine their impact on water quality and algal blooms by the calibrated and validated water quality model QUAL2K. Water quality was assessed by the concentrations of dissolved oxygen, total nitrogen, and phosphorus. Algal blooms were identified by phytoplankton concentration. An increase in air temperature of up to 2 °C resulted in an average increase of 3% in water temperature and 4.79% in phytoplankton concentration, and an average decrease of 0.48% in dissolved-oxygen concentration. Projected decreases in streamflow not only made the above phenomenon more significant but also significantly increased the concentration of total nitrogen, total phosphorus, and phytoplankton with the same pollution inputs. Under climate change, the biggest cause of concern for estuarine water quality is reduced streamflow due to decreases in rainfall. Water quality improvement is possible by regulating the concentration of non-point-source pollution discharge. By reducing nutrient runoff, the total nitrogen and phosphorus concentrations were also reduced, resulting in a significant increase in the dissolved oxygen concentration. This study highlights the most significant factors for managing water quality in estuaries subject to climate change.

Impacts of the landscape changes in the low streamflows of Pantanal headwaters—Brazil

AbstractThe Upper Paraguay Basin Plateau (UPRB) concentrates the headwaters and the largest volume of rain that supply the Pantanal biome and is essential for maintaining its water regime. Given the region's changes in land use and cover, this research sought to identify their influence on headwater flows. The use of conceptual models and time series analysis showed that the replacement of natural vegetation with pasture and the more recent activity of irrigated agriculture have produced changes in the hydrological response of the headwaters. There was a decreasing tendency of low flows during dry periods, which was correlated with anthropic changes in the use and cover of the land in the region. The research results point out changes in land use and cover as the cause of a significant decrease in streamflows during drier periods. Such behaviour at the headwaters of the Pantanal can have consequences for this biome, reducing the resilience of the system against droughts and damaging the biodiversity of the biome.

Intermittency as an indicator of drought in streamflow and groundwater

AbstractUnder normal precipitation conditions, increasing water demand causes groundwater level to deplete and streamflow to decrease. This results in more frequent intermittency. The so‐called intermittency cycle hypothesis is examined in this study. It is a vicious circle in hydrology making both surface and groundwater resources less efficient in supplying ever‐increasing water demand. To test the hypothesis, a data‐based analysis is applied to Gediz, Kucuk Menderes, and Ergene river basins in western Turkey. Results at basin‐ and station‐scale show no change in precipitation while streamflow fluctuates with a tendency to decrease and groundwater steeply declines. Groundwater is used excessively to meet the drastically increased water demand. With the overuse of groundwater, water table descends, streamflow decreases and intermittency increases. Intermittency ratio of a river is found related to the decrease in streamflow and the drop in groundwater level. It can trigger drought in streamflow and groundwater. It is concluded that intermittency can be taken as a quantitative indicator of drought in streamflow and groundwater.