Regional Hydrological Regime Research Articles

Detecting the impact of the “Grain for Green” program on land use/land cover and hydrological regimes in a watershed of the Chinese Loess Plateau over the next 30 years

To increase vegetation coverage and improve ecosystem services, the government has promulgated and implemented the “Grain for Green” policy since 1999. How and where vegetation cover increases and how land use/land cover (LULC) changes determine regional water resources and hydrological regimes. On the Chinese Loess Plateau (LP), an arid and semiarid area with fragmented topography and the transitional vegetation nature, accurately predicting LULC and vegetation change is particularly important. We employed a simple habitat analogy approach, and the Soil and Water Assessment Tool (SWAT) to predict potential vegetation restoration and LULC change and investigated their impact on the hydrological regime in a watershed of Liujiahe. Results showed that the maximum recoverable vegetation cover of the Liujiahe watershed is 71.1%, of which 9.2% still has potential for vegetation cover and 36.4% of the area vegetation continued to improve in the future. Future suitable afforestation areas are limited to 46.06 km2, which will result in cropland will decrease by 47.4%, and grassland and forestland will increase by 15.8% and 0.7%, respectively. However, SWAT results showed that vegetation restoration between the 1980 s and 2020 s has already reduced the annual mean runoff and soil water content (SW) by 44.2% and 43.9%, respectively, while evapotranspiration (ET) has increased by 12.6%; LULC changes in the next 30 years will further reduce runoff and SW by 15.6% and 11.1% respectively, and increase ET by 1.2%. Overall, large-scale vegetation restoration has greatly affected hydrological regimes on the LP. The area still has potential for vegetation enhancement; however, considering the limited rainfall and water-carrying capacity, the vegetation restoration of this watershed should be based on natural restoration or low water consumption grasses and shrubs to avoid a water resource crisis. These results provide a perspective for modelling LULC changes in areas with fragmented terrain and highly influenced by human activities, and provide an important basis for sustainably managing natural resources on the LP under long-term ecological restoration.

Resilience of temperate peatland vegetation communities to wildfire depends upon burn severity and pre-fire species composition.

Peatland ecosystems are of global conservation and environmental importance storing globally significant amounts of ancient carbon, regulating regional temperatures and hydrological regimes, and supporting unique biodiversity. Livestock grazing, land-use change, drainage, nutrient and acid deposition, and wildfire threaten the composition and function of many peatlands including those in the uplands of the United Kingdom. Presently, little is known about either the short- or long-term effects of wildfires within these systems in the UK. Our study aimed to evaluate how plant communities respond to wildfires across a range of vegetation communities, soil types, and burn severities. We evaluated wildfire burn severity using the ground-based Composite Burn Index adapted for treeless peatlands. Using paired burned-unburned plots, we quantified differences in the abundance of plant families and functional groups, vegetation diversity, and community composition. Multivariate differences in composition between burned and unburned areas were used as an index of community resilience to fire. Plots in heathland communities with shallow organic soils burned at the highest severities and had the greatest reductions in plant diversity and richness. There were significant declines in plot-scale species richness and diversity with increasing burn severity. Graminoids were resilient to fire whilst Ericaceae tended to increase with higher severity. Bryophyte composition was substantially altered-pleurocarpous species declined and acrocarpous species increased with greater burn severity. Community resilience was related to ground layer burn severity with higher burn severity driving greater changes in communities. Wildfire effects on temperate peatlands are a function of fire weather and site environmental and ecological characteristics. Management policy should ensure that the risk of severe wildfires is mitigated to protect ecosystem function and biodiversity. This will require system-specific fire management prescriptions across the gradient of peatland soil and vegetation types.

The assessment of the hydrological regime of the Torysa River by the flashlines index

Climate change has a significant impact on the local and regional hydrological regime. In this study, the hydrological regime and variability of flows in the Torysa river basin were investigated for the period 1973-2020. The flows were evaluated by the RBI index. The results showed that the Torysa river has a large flow variability.

CRONOLOGIA DE VERTENTES QUARTZÍTICAS EM MINAS GERAIS, BRASIL

Quartzitic mountain reliefs developed in a tropical savanna climate tend to have shallow sedimentary deposits. This is due to low level weathering processes of quartzite rocks and formation of colluvium ramps on the slopes. This study aims to determine the characteristics of colluvial materials, particularly grain size, and to analyze sediment chronology above the saprolite, seeking to identify accumulation rates and make correlations with the dynamics of the recent geomorphological evolution of the Canastra range in Minas Gerais, Brazil. Samples collected in different morphological positions were submitted to granulometric analysis and dated by Optically Stimulated Luminescence Single Aliquote Regeneration (OSL/SAR) and radiocarbon dating. Grain size analysis showed a predominance of sandy and gravel materials and demonstrated that the colluvial ramps in the study area contain materials derived from the decomposition of quartzite rocks, accumulated in shallow and sandy profiles. LOE/SAR dating indicated ages between the end of the Pleistocene, not exceeding 30,500 +/- 4,950 BP, to 500 years BP, whereas the 14C dating showed ages between 4460 +/- 30 BP and 1140 +/- 30 BP. These data indicate that the deposits from the study area are relatively recent, which demonstrate that variations in the weathering process and deposit formation have undergone recent changes, probably due to climatic fluctuations and changes in the regional hydrological regime. Keywords: Canastra Range, Paleogeomorphological Reconstruction, Weathering of Quartzites, OSL, Tropical Range

Streamflow droughts in Sweden: Spatiotemporal patterns emerging from six decades of observations

Study RegionSwedenStudy focus:Although Sweden has historically been a country abundant with water, observed changes in temperature and precipitation patterns during the past century have perturbed regional hydrologic regimes, including the severity, frequency and duration of streamflow droughts. This study utilizes the standardized streamflow index (SSI) and the threshold-level method to provide an unprecedented overview of spatiotemporal patterns of streamflow droughts in 50 Swedish catchments over the past six decades. The study catchments were categorized into five clusters, of which each was analyzed for changes in various drought characteristics over the period 1961–2020. New hydrological insights for the regionMultiple severe streamflow drought events were detected over the past 60 years. Remarkably, droughts in 1976 and 1996 were identified as the most extreme and wide-spread events, also compared to the latest 2018 drought. Southern catchments were generally more often and more severely affected than northern catchments. Our results suggest a wetting tendency over the past six decades across the entire country. This occurs in conjunction with less severe, shorter and less frequent droughts, especially during colder winter months. Only in the southernmost regions, a slight drying trend in spring and summer was found. Thus, we argue that a better understanding and regional management of streamflow droughts is essential to secure the needs of the environment, society and economy now and in the future.

Incorporating Industrial and Climatic Covariates into Analyses of Fish Health Indicators Measured in a Stream in Canada’s Oil Sands Region

Industrial and other human activities in Canada’s oil sands region (OSR) influence the environment. However, these impacts can be challenging to separate from natural stresses in flowing waters by comparing upstream reference sites to downstream exposure locations. For example, health indicators of lake chub (Couesius plumbeus) compared between locations in the Ells River (Upper and Lower) in 2013 to 2015 and 2018 demonstrated statistical differences. To further examine the potential sources of variation in fish, we also analyzed data at sites over time. When fish captured in 2018 were compared to pooled reference years (2013–2015), results indicated multiple differences in fish, but most of the differences disappeared when environmental covariates were included in the Elastic Net (EN) regularized regression models. However, when industrial covariates were included separately in the EN, the large differences in 2018 also disappeared, also suggesting the potential influence of these covariables on the health of fish. Further ENs incorporating both environmental and industrial covariates along with other variables which may describe industrial and natural influences, such as spring or summer precipitation and summer wind speeds and distance-based penalty factors, also support some of the suspected and potential mechanisms of impact. Further exploratory analyses simulating changes from zero and the mean (industrial) activity levels using the regression equations respectively suggest effects exceeding established critical effect sizes (CES) for fish measurements may already be present or effects may occur with small future changes in some industrial activities. Additional simulations also suggest that changing regional hydrological and thermal regimes in the future may also cause changes in fish measurements exceeding the CESs. The results of this study suggest the wide applicability of the approach for monitoring the health of fish in the OSR and beyond. The results also suggest follow-up work required to further evaluate the veracity of the suggested relationships identified in this analysis.

Ocean Productivity in the Gulf of Cadiz Over the Last 50 kyr

AbstractReconstructions of ocean primary productivity (PP) help to explain past and present biogeochemical cycles and climate changes in the oceans. We document PP variations over the last 50 kyr in a currently oligotrophic subtropical region, the Gulf of Cadiz. Data combine refined results from previous investigations on dinocyst assemblages, alkenones, and stable isotopes (18O, 13C) in planktonic (Globigerina bulloides) and endobenthic (Uvigerina mediterranea) foraminifera from cores MD04‐2805 CQ and MD99‐2339, with new isotopic measurements on epibenthic (Cibicides pachyderma‐Cibicidoides wuellerstorfi) foraminifera and dinocyst‐based estimates of PP using the new n = 1,968 modern database. We constrain PP variations and export production by integrating qualitative information from bioindicators with dinocyst‐based quantitative reconstructions such as PP and seasonal sea surface temperature and information about remineralization from the benthic Δδ13C (difference between epibenthic and endobenthic foraminiferal δ13C signatures). This study also includes new information on alkenone‐based SST and total organic carbon which provides insights into the relationship between past regional hydrological activity and PP regime change. We show that PP, carbon export, and remineralization were generally high in the NE subtropical Atlantic Ocean during the last glacial period and that the Last Glacial Maximum (LGM) had lower Δδ13C than the Heinrich Stadials with sustained high PP, likely allowing enhanced carbon sequestration. We link these PP periods to the dynamics of upwelling, active almost year‐round during sadials, but restricted to spring‐summer during interstadials and LGM, like today. During interstadials, nutrient advection through freshwater inputs during autumn‐winter needs also to be considered to fully understand PP regimes.

Assessing Long‐Term Changes in Regional Groundwater Recharge Using a Water Balance Model for New Mexico

AbstractIn New Mexico in the arid southwestern United States, groundwater recharge is crucial to sustain groundwater (GW), which is vitally important to life, agriculture, industry, and ecosystems. To better understand the changes in recharge statewide, we explored the changes in groundwater recharge (RE), precipitation (P), surface water inflow (SWin), outflow (SWout), diversions (SWdiv), returns (SWret), and surface water and GW evapotranspiration (SWE and GWET) in five New Mexico counties: Taos, Torrance, Doña Ana, Eddy, and Lea during 1975–2015. The results show that the change‐point of RE was in the 1990s, leading to contrasting tendencies in RE before and after the change‐point with a decreasing rate during the latter one. There was a significant positive relationship between RE and P for Taos. The highest contribution rate (CR) to RE was SWout for Taos, whereas GWET ranked as the top CR for the other counties. Furthermore, the annual CR of GWET to RE increased significantly in all counties except Lea. The above results reveal that P and surface water flows played the dominant role in impacting RE in northern New Mexico where surface water is the primary local water resources, whereas GWET had the highest and increasingly continuous influence in central and southern New Mexico where the surface water is much less than that in northern New Mexico. This study shows that water budgets are important to identify differences in regional hydrological regimes that affect planning to maintain RE to groundwater.

Parametrization of a lake water dynamics model MLake in the ISBA-CTRIP land surface system (SURFEX v8.1)

Abstract. Lakes are of fundamental importance in the Earth system as they support essential environmental and economic services, such as freshwater supply. Streamflow variability and temporal evolution are impacted by the presence of lakes in the river network; therefore, any change in the lake state can induce a modification of the regional hydrological regime. Despite the importance of the impact of lakes on hydrological fluxes and the water balance, a representation of the mass budget is generally not included in climate models and global-scale hydrological modeling platforms. The goal of this study is to introduce a new lake mass module, MLake (Mass-Lake model), into the river-routing model CTRIP to resolve the specific mass balance of open-water bodies. Based on the inherent CTRIP parameters, the development of the non-calibrated MLake model was introduced to examine the influence of such hydrological buffer areas on global-scale river-routing performance. In the current study, an offline evaluation was performed for four river networks using a set of state-of-the-art quality atmospheric forcings and a combination of in situ and satellite measurements for river discharge and lake level observations. The results reveal a general improvement in CTRIP-simulated discharge and its variability, while also generating realistic lake level variations. MLake produces more realistic streamflows both in terms of daily and seasonal correlation. Excluding the specific case of Lake Victoria having low performances, the mean skill score of Kling–Gupta efficiency (KGE) is 0.41 while the normalized information contribution (NIC) shows a mean improvement of 0.56 (ranging from 0.15 to 0.94). Streamflow results are spatially scale-dependent, with better scores associated with larger lakes and increased sensitivity to the width of the lake outlet. Regarding lake level variations, results indicate a good agreement between observations and simulations with a mean correlation of 0.56 (ranging from 0.07 to 0.92) which is linked to the capability of the model to retrieve seasonal variations. Discrepancies in the results are mainly explained by the anthropization of the selected lakes, which introduces high-frequency variations in both streamflows and lake levels that degraded the scores. Anthropization effects are prevalent in most of the lakes studied, but they are predominant for Lake Victoria and are the main cause for relatively low statistical scores for the Nile River However, results on the Angara and the Neva rivers also depend on the inherent gap of ISBA-CTRIP process representation, which relies on further development such as the partitioned energy budget between the snow and the canopy over a boreal zone. The study is a first step towards a global coupled land system that will help to qualitatively assess the evolution of future global water resources, leading to improvements in flood risk and drought forecasting.

Runoff dynamics of the upper Selenge basin, a major water source for Lake Baikal, under a warming climate

The Selenge basin contributes approximately 50% of the total inflow into Lake Baikal and is thus of high significance for the regional hydrological regime. Our study was conducted in the upper reaches of the basin, where the Selenge river and its tributaries flow through the Mongolian forest-steppe. Monthly and maximum runoff, precipitation, and air temperature data from 12 gauging stations collected between 1978 and 2015 were analyzed to characterize the hydrological regime response to climate change. Concomitant with rising temperatures and increased potential evaporation, river runoff in the Mongolian part of the Selenge basin has decreased from the first interval (1978–1995) of our study period compared with the consecutive interval from 1996 to 2015. The decrease in runoff throughout the study area was most likely caused by an increase in potential evapotranspiration (and not reduced precipitation or land use changes) for both summer rainfall- and snowmelt-dominated rivers. Annual maximum runoff has also strongly decreased suggesting that reduced flooding is a contemporary threat for Mongolia’s riverine ecosystems, probably causing the replacement of wetland and mesic habitats.

Assessment of potential impacts of climate change on water resources in Ngerengere catchment, Tanzania

Global climate change has substantial impacts on local and regional hydrological regime. However, the general understanding of how hydrological regime is affected by climate change at catchment scale is limited. In this study, the potential impacts of climate change on water resources in Ngerengere River catchment in Tanzania were assessed. The HBV model was used to undertake water resources assessment for the Ngerengere catchment and subsequently impacts of climate change on the same. Future climate for 2050s (2040–2069) and 2080s (2070–2099) were downscaled using a statistical weather generator (LARS-WG) from outputs of the Global Circulation Model (HadCM3) under SRES A2 scenario.The HBV model was calibrated and validated using observed streamflow data at Mgude gauge station for the baseline period (1971–2000). The Nash-Sutcliffe efficiency (NSE) of 0.7 and 0.6 was attained during calibration and validation respectively. Downscaling results revealed that LARS-WG performed well in generating future rainfall and temperature data series. The results indicated an increase in minimum and maximum temperature of around 0.2–2.6 °C in the 2050s and around 2.7–4.4 °C in the 2080s. Future rainfall is predicted to decrease by 12–37% in April, May, June and July, while rainfall in the remaining months are predicted to increase by 3–58%. The impact assessment on streamflow of the Ngererengere catchment revealed a decline in the mean annual streamflow by 2.1% in 2050s, whereas an increase of up to 58% in mean annual streamflow is predicted in the 2080s.

Assessing climate change impacts on water resources in the Benue River Basin, Northern Cameroon

The Benue River Basin (BRB) is a major tributary of the Niger River Basin (NRB) and the second-largest river in Cameroon. It serves many water resource functions including irrigation, hydroelectricity production and navigation. Previous research has indicated that recent climate change (CC) has had significant impacts on local and regional hydrological regimes of this watershed. In this study, CC scenarios were integrated with a hydrological model to evaluate the influence of CC on water resources in the BRB. Historical and projected scenarios of dynamically downscaled temperature and precipitation from the REMO regional climate model (RCM) forced by the boundary conditions data of the Europe-wide Consortium Earth System Model (EC-ESM) and the Max Planck Institute-Earth System Model (MPI-ESM) general circulation models (GCMs) were used. The historical runs of the REMO simulations were first evaluated after which downscaled temperature and precipitation data were used as input for the HBV-Light hydrological model to simulate water balance components. The mean climate and hydrological variables for the historical (1981–2005) and the two future periods (2041–2065 and 2071–2095) were compared to assess the potential impact of CC on water resources in the middle and late twenty-first century under three greenhouse gases (GHGs) concentration scenarios, the Representative Concentration Pathways (RCPs) 2.6, 4.5 and 8.5. Our results show that (a) the HBV-Light hydrological model could effectively simulate the streamflow change in the BRB; (b) annual precipitation will decrease between 1 and 10% while both annual temperature and potential evapotranspiration (PET) will increase between 8–18 and 6–30%, respectively, under both scenarios, models and future periods; c) the combination of reduced precipitation and increase of PET results in a significant decrease in streamflow in the BRB (up to 51%) and this will move the basin to a much drier environmental state. Therefore, CC adaptation strategies and future development planning in this region must consider these important decreases of discharge.

Climate change impacts on Three Gorges Reservoir impoundment and hydropower generation

Climate change is expected to alter regional hydrological regimes, affecting the operation and performance of reservoirs and hydropower facilities. This study examines the impacts of climate change on the performance of the Three Gorges Reservoir (TGR) by means of a detailed daily reservoir regulation and hydropower model, linked to a physically-based hydrological model, and driven by an ensemble of five General Circulation Models (GCMs) under three Representative Concentration Pathways (RCP2.6, RCP4.5 and RCP8.5). As precipitation in the basin is expected to increase, the projected mean annual inflow and hydropower generation of the TGR will increase by 3.3–5.6% and 0.9–2.3% in 2040–2065, 7.9%-15.2% and 5.2–8.1% in 2080–2099 respectively. These increases are only statistically significant for 2080–2099 and are seasonally concentrated in the spring before the flood season and the early autumn during the end of the flood season. However, the inter-annual variation of power generation will increase specially in the dry season. The reservoir performance is highly sensitive to the changes in the seasonal distribution and extremes of streamflow. Increases in streamflow that occur in the flood season cause significant increases in the amount of spilled water and advance the time when the reservoir reaches the normal storage level. Additionally, increases in both the inter-annual variation of inflow and the intensity of inflow shortages during extreme drought years in the impounding stage drive decreases in the fully filled rate and average water storage level in the dry season. The utilization rate of water resources under projected extreme streamflow is expected to decrease, reshaping the response of power generation to climate change into a non-linear pattern where increases in streamflow do not proportionally translate to increases in power generation. These findings highlight the complexity of hydropower management and production under future climate change scenarios, motivating the need for introducing detailed regulating models for impact assessment studies and adaptive adjustment of the reservoir management to combat climate change.

Dependencia de la variabilidad hidrológica de los fenómenos macroclimaticos. Caso de estudio

Introducción: este artículo es producto de la investigación de la incidencia del fenómeno de oscilación cuasi-bienal sobre el comportamiento hídrico en el norte de abastecimiento de Bogotá realizado en la Universidad Militar Nueva Granada en el año 2017.
 Problema: en la última década, en Colombia, se han presentado años de muy alta y de muy baja humedad relativa, los cuales se asocian con los fenómenos macroclimatológicos que tienen repercusión sobre el régimen hidrológico regional y local, y generan variabilidad de la oferta hídrica.
 Metodología: en este estudio se presenta un análisis estadístico proclive a determinar la influencia de la oscilación cuasi-bienal sobre los caudales medios mensuales de los embalses de Sisga, Tominé y Neusa del sistema de abastecimiento norte de Bogotá, a partir de correlaciones lineales entre las dos variables.
 Resultado: se evidenció una incidencia del fenómeno de oscilación cuasi-bienal sobre los afluentes a los embalses entre un 2,7% y 4,0% que tarda en reflejarse en un periodo de nueve meses.
 Conclusión: el fenómeno de oscilación cuasi-bienal no aporta de manera significativa la escorrentía superficial de las cuencas estudiadas.
 Limitaciones: aunque en el estudio no se ha podido demostrar la incidencia del fenómeno natural, en otras zonas del país este efecto es demostrado. A manera de hipótesis, se puede suponer que la aplicación de otros métodos estadísticos diferentes al aplicado, posibilitará un análisis más profundo de los resultados.
 Originalidad: en el marco nacional son pocos los estudios realizados acerca del fenómeno de oscilación cuasi- bienal y su influencia sobre la variabilidad hídrica interanual.

Complexity Analysis of Precipitation and Runoff Series Based on Approximate Entropy and Extreme-Point Symmetric Mode Decomposition

Many regional hydrological regime changes are complex under the influences of climate change and human activities, which make it difficult to understand the regional or basin al hydrological status. To investigate the complexity of precipitation and the runoff time series from 1960 to 2012 in the Jing River Basin on different time scales, approximate entropy, a Bayesian approach and extreme-point symmetric mode decomposition were employed. The results show that the complexity of annual precipitation and runoff has decreased since the 1990sand that the change occurred in 1995. The Intrinsic Mode Function (IMF)-6 component decomposed by extreme-point symmetric mode decomposition of monthly precipitation and runoff was consistent with precipitation and runoff. The IMF-6 component of monthly precipitation closely followed the 10-year cycle of change, and it has an obvious correlation with sunspots. The correlation coefficient is 0.6, representing a positive correlation before 1995 and a negative correlation after 1995. However, the IMF-6 component of monthly runoff does not have a significant correlation with sunspots, and the correlation coefficient is only 0.41, which indicates that climate change is not the dominant factor of runoff change. Approximate entropy is an effective analytical method for complexity, and furthermore, it can be decomposed by extreme-point symmetric mode decomposition to obtain the physical process of the sequences at different time scales, which helps us to understand the background of climate change and human activity in the process of precipitation and runoff.

Modeling Climate Change Impact on the Hydrology of Keleta Watershed in the Awash River Basin, Ethiopia

Regional and local hydrological regimes are significantly vulnerable to global climate change which threaten water resources and food security of nations. This study investigates the likely impact of climate change on hydrological processes of the Keleta watershed in the Awash River Basin, Ethiopia. Delta statistical downscaling methods were used to downscale 20 global circulation models (GCMs) and 2 representative concentration pathways (RCPs) (RCP 4.5 and RCP 8.5) over the study periods of 2050s and 2080s. The Soil and Water Assessment Tool (SWAT) model was used to simulate hydrological processes. The model was calibrated and validated using monthly observed streamflow data for the baseline year (1985). It performed well with a Nash-Sutcliffe efficiency (NSE) ≥ 0.74, ratio of the root mean square error to the standard deviation of measured data (RSR) ≤ 0.51, and percent bias (PBIAS) ≤ 15.3. The results show that RCP 4.5 predicts an average precipitation increase of 15.2 and 17.2% for mid- and end-of-century data, respectively. Similarly, RCP 8.5 predicts an average precipitation increase of 19.9 and 34.4% for mid- and end-of-century data, respectively. Mid-century minimum and maximum temperature increases range from 1.8 to 1.6 °C (RCP 4.5) to 2.6 to 2.1 °C (RCP 8.5), respectively, while end-of-century increases vary from 2.4 to 2.0 °C (RCP 4.5) and 4.6 to 3.7 °C (RCP 8.5), respectively. This leads to an average increase in runoff by 70%. The increased rainfall, warmer temperature, and significant increment in the hydrologic components, and particularly the excess runoff and associated extreme peak flow over the coming decades, are likely to put a tremendous pressure on the hydrological system of the watershed. This calls for sustainable and effective adaptive measures for future water resource management.

Influence of the Amazon Hydrological Regime on Eutrophication Indicators of a Hydroelectric Power Plant Reservoir.

Dam constructions in the Amazon have increased exponentially in the last decades, causing several environmental impacts and serious anthropogenic impacts in certain hydroelectric power plant reservoirs in the region have been identified. The assessment of the trophic status of these reservoirs is of interest to indicate man-made changes in the environment, but must take into account the hydrological cycle of the area. This can be relevant for environmental management actions, aiding in the identification of the ecological status of water bodies. In this context, physico-chemical parameters and eutrophication indicators were determined in a hydroelectric power plant reservoir in the Brazilian Amazon to assess trophic variations during the regional hydrological regime phases on the reservoir, namely dry, filling, full and emptying stages. The local hydrological regimes were shown to significantly influence TSS and turbidity, as well as NH4, NO3, PO4, with higher values consistently observed during the filling stage of the reservoir. In addition, differences among the sampling stations regarding land use, population and anthropogenic activities were reflected in the PO43- values during the different hydrological phases.

Heterogeneous glacial lake changes and links of lake expansions to the rapid thinning of adjacent glacier termini in the Himalayas

Glacier mass loss in the Himalayas has far-reaching implications for the alteration of regional hydrologic regimes, an increased risk of glacial lake outburst, downstream water resource abundance, and contributions to sea level rise. However, the mass losses of Himalayan glaciers are not well understood towing to the scarcity of observations and the heterogeneous responses of Himalayan glaciers to climate change and local factors (e.g., glacier surge, interacting with proglacial lakes). In particular, there is a lack of understanding on the unique interactions between moraine-dammed glacial lakes and their effects on debris cover on valley glacier termini. In this study, we examined the temporal evolution of 151 large glacial lakes across the Himalayas and then classified these glacial lakes into three categories: proglacial lakes in contact with full or partial debris-covered glaciers (debris-contact lakes), ice cliff-contact lakes, and non-glacier-contact lakes. The results show that debris-contact lakes experienced a dramatic areal increase of 36.5% over the years 2000 to 2014, while the latter two categories of lakes remained generally stable. The majority of lake expansions occurred at the glacier front without marked lake level rises. This suggests that the rapid expansion of these debris-contact lakes can be largely attributed to the thinning of debris-covered ice as caused by the melting of glacial fronts and the subsequent glacial retreat. We reconstructed the height variations of glacier fronts in contact with 57 different proglacial lakes during the years 2000 to 2014. These reconstructed surface elevation changes of debris-covered, lake-contact glacier fronts reveal significant thinning trends with considerable lowering rates that range from 1.0 to 9.7m/y. Our study reveals that a substantial average ice thinning of 3.9m/y occurred at the glacier fronts that are in contact with glacial lakes.

Changes in hydrological regime caused by human intervention in karst: the case of the Rumin Springs

ABSTRACTAny human intervention or action in karst terrains can unexpectedly, suddenly, strongly and, generally, dangerously change a local and/or a regional hydrological regime. A characteristic example of the Dinaric karst is given in this paper. The operation of two reservoirs in Livanjsko Polje at an altitude of about 702 m above sea level (m a.s.l.) and hydro-electric development of the Cetina River system started in 1973. This year marked a drastic and instantaneous change in the regional hydrological regime. A significant drop in the minimum, mean and maximum annual discharges of two neighbouring karst springs, Rumin Mali and Rumin Veliki, was caused by this anthropogenic construction. The exits of the two analysed karst springs, Rumin Mali and Veliki, are located at altitudes of about 326.8 m a.s.l. and 307.6 m a.s.l. respectively. The areal distance between them is 640 m. Their hydrological regimes have been altered in different ways. The drop in discharges is stronger for the Rumin Veliki than for the Rumin Mali. The analysis shows that the system development influenced the redistribution of the regional karst aquifer and, in this manner, contributed to the reduction of both karst springs’ recharge areas.Editor D. Koutsoyiannis Associate editor E. Rozos

Impacts of Climatic Change on Hydrological Regime in the Three-River Headwaters Region, China, 1960-2009

To identify the changing characteristics of runoff and climate change trends and their relationship in the Three-River Headwaters Region (TRHR), this study uses the runoff and meteorological data of three hydrological gauging stations and 12 meteorological stations across the TRHR for the period from January 1960 to December 2009 as the research subjects. The runoff coefficient (RC), ratio of monthly maximum/minimum runoff, and flow duration curves (FDCs) were calculated to identify spatio-temporal variations in runoff and reflect the change in hydrological regime. Results showed an insignificant decrease in annual runoff both in the Yellow River Headwater Region (YERHR) and the Lantsang River Headwater Region (LARHR), whereas it increased in the Yangtze River Headwater Region (YARHR). The RC of the three sub-regions showed a decreasing trend, the LARHR maintained a high mean value of 0.55, followed by a lower value in the YERHR (0.32), and that in the YARHR was the lowest at only 0.23. The variations in monthly maximum/minimum runoff were synchronized; their ratios were relatively steady in the study period. The flow duration analysis showed a remarkable decline in high runoff (at a frequency of 5–15%) in the three sub-regions after 1990. The runoff characteristics showed an overall decrease in the YERHR, the moderate runoff (at the frequency of 15–30% and 40–70%) of the YARHR showed an obviously increase, and the runoff of the LARHR was relatively steady. The relationship between precipitation, temperature and runoff illustrated that precipitation was the dominant factor in runoff generation, whereas the impacts of temperature on regional hydrological regime should not be neglected. Results of this study are of practical significance for water resources management and evaluation of the impacts of climatic change on the hydrological regime in a long-term consideration.