Snow cover variability and snowmelt in a high‐altitude ungauged catchment

Snow variability is an integrated indicator of climate change, and it has important impacts on runoff regimes and water availability in high‐altitude catchments. Remote sensing techniques can make it possible to quantitatively detect the snow cover changes and associated hydrological effects in those poorly gauged regions. In this study, the spatial–temporal variations of snow cover and snow melting time in the Tuotuo River basin, which is the headwater of the Yangtze River, were evaluated based on satellite information from the Moderate Resolution Imaging Spectroradiometer snow cover product, and the snow melting equivalent and its contribution to the total runoff and baseflow were estimated by using degree–day model. The results showed that the snow cover percentage and the tendency of snow cover variability increased with rising altitude. From 2000 to 2012, warmer and wetter climate change resulted in an increase of the snow cover area. Since the 1960s, the start time for snow melt has become earlier by 0.9–3 days/10a and the end time of snow melt has become later by 0.6–2.3 days/10a. Under the control of snow cover and snow melting time, the equivalent of snow melting runoff in the Tuotuo River basin has been fluctuating. The average contributions of snowmelt to baseflow and total runoff were 19.6% and 6.8%, respectively. Findings from this study will serve as a reference for future research in areas where observational data are deficient and for planning of future water management strategies for the source region of the Yangtze River. Copyright © 2015 John Wiley & Sons, Ltd.     

Identifying run‐off contributions during melt‐induced run‐off events in a glacierized alpine catchment

We analysed contributions to run‐off using hourly stream water samples from seven individual melt‐induced run‐off events (plus one rainfall event) during 2011, 2012 and 2013 in two nested glacierized catchments in the Eastern Italian Alps. Electrical conductivity and stable isotopes of water were used for mixing analysis and two‐component and three‐component hydrograph separation. High‐elevation snowmelt, glacier melt and autumn groundwater were identified as major end‐members. Discharge and tracers in the stream followed the diurnal variations of air temperature but markedly reacted to rainfall inputs. Hysteresis patterns between discharge and electrical conductivity during the melt‐induced run‐off events revealed contrasting loop directions at the two monitored stream sections. Snowmelt contribution to run‐off was highest in June and July (up to 33%), whereas the maximum contribution of glacier melt was reached in August (up to 65%). The maximum groundwater and rainfall contributions were 62% and 11%, respectively. Run‐off events were generally characterized by decreasing snowmelt and increasing glacier melt fractions from the beginning to the end of the summer 2012, while run‐off events in 2013 showed less variable snowmelt and lower glacier melt contributions than in 2012. The results provided essential insights into the complex dynamics of melt‐induced run‐off events and may be of further use in the context of water resource management in alpine catchments. Copyright © 2015 John Wiley & Sons, Ltd.     

Projected glacier meltwater and river run‐off changes in the Upper Reach of the Shule River Basin,north‐eastern edge of the Tibetan Plateau

Glacier meltwater change in the north‐eastern edge of the Tibetan Plateau is greatly important for the projection of the impact of future climate change on local water resource management. Although the glaciated area is only approximately 4% of the Upper Reach of the Shule River Basin (URSRB), the average glacier meltwater contribution to river run‐off was approximately 23.6% during the periods 1971/1972 to 2012/2013. A new glacier melting module coupled with the macroscale hydrologic Variable Infiltration Capacity model (VIC‐CAS) was adopted to simulate and project changes in the glacier meltwater and river run‐off of the URSRB forced by downscaled output of the BCC‐CSM1.1(m), CANESM2, GFDL‐CM3, and IPSL‐CM5A‐MR models. Comparisons between the observed and simulated river run‐offs and glacier area changes during the periods 2000/2001, 2004/2006, 2008/2009, and 2012/2013 suggest that the simulation is reasonable. Due to increases in precipitation, the annual total run‐off is projected to increase by approximately 2.58–2.73 × 10⁸ m³ in the 2050s and 0.28–1.87 × 10⁸ m³ in the 2100s compared with run‐off in the 2010s based on the RCP2.6 (low greenhouse gas emission) and RCP4.5 (moderate greenhouse gas emission) scenarios, respectively. The contribution of glacier meltwater to river run‐off will more likely decrease to approximately 10% and less than 5% during the 2050s and 2100s, respectively.     

Use of a parsimonious rainfall–run‐off model for predicting hydrological response in ungauged basins

A new parameter parsimonious rainfall–run‐off model, the Distance Distribution Dynamics (DDD) model, is used to simulate hydrological time series at ungauged sites in the Lygne basin in Norway. The model parameters were estimated as functions of catchment characteristics determined by geographical information system. The multiple regression equations relating catchment characteristics and model parameters were trained from 84 calibrated catchments located all over Norway, and all model parameters showed significant correlations with catchment characteristics. The significant correlation coefficients (with p‐value < 0.05) ranged from 0.22 to 0.55. The suitability of DDD for predictions in ungauged basins was tested for 17 catchments not used to estimate the multiple regression equations. For ten of the 17 catchments, deviations in Nash–Sutcliffe efficiency (NSE) criteria between the calibrated and regionalised model were less than 0.1, and for two calibrated catchments within the Lygne basin, the deviations were less than 0.08. The median NSE for the regionalized DDD for the 17 catchments for two time series was 0.66 and 0.72. Deviations in NSE between calibrated and regionalised models are well explained by the deviations between calibrated and regressed parameters describing spatial snow distribution and snowmelt respectively. The quality of the simulated run‐off series for the ungauged sites in the Lygne basin was assessed by comparing flow indices describing high, medium and low flow estimated from observed run‐off at the 17 catchments and for the simulated run‐off series. The indices estimated for the simulated series were generally well within the ranges defined by the 17 observed series. Copyright © 2014 John Wiley & Sons, Ltd.     

Modelling soil solute release and transport in run‐off on a loessial slope with and without surface stones

Stone covers on loessial slopes can increase the time of infiltration by slowing the velocity of the overland flow, which reduces the transport of solutes, but few mechanistic models have been tested under water‐scouring conditions. We carried out field experiments to test a previously proposed, physically based model of water and solute transport. The area of soil infiltration was calculated from the uncovered surface area, and Richards' equation and the kinematic wave equation were used to describe water infiltration and flow along slopes with stone covers. The transport of chemicals into the run‐off from the surface soil, presumably by diffusion, and their movement in the soil profile could be described by the convection–diffusion equations of the model. The simulated and measured data correlated well. The stones on the soil surface reduced the area available for infiltration but increased the Manning coefficient, eventually leading to increased water infiltration and decreased solute loss with run‐off. Our results indicated that the traditional model of water movement and solute migration could be used to simulate water transport and solute migration for stone‐covered soil on loessial slopes.     

Response of a mid‐latitude cirque glacier to climate over the last two decades: Mangaehuehu Glacier,Mt Ruapehu

The recent loss of mountain glaciers in response to climate warming has been reported across a range of latitudes globally, but the processes involved are not always straightforward. In southern Pacific mid‐latitudes, twentieth‐century glacier fluctuations are thought to reflect the strength of westerly atmospheric circulation, which brings increased precipitation, leading to mass gains. We present a study of the response of Mangaehuehu Glacier, a cirque glacier on Mt Ruapehu, to climate over the last two decades. Glacier surface area fluctuated in size over this period, corresponding closely with mean end‐of‐summer snowlines in the Southern Alps. The key control on glacier extent appears to be ablation season temperature, itself controlled by regional atmospheric circulation, including El Niño‐Southern Oscillation, Interdecadal Pacific Oscillation (IPO), and to a lesser extent, Southern Annular Mode (SAM). Copyright © 2011 John Wiley & Sons, Ltd.     

Assessing the effects of precipitation and temperature changes on hydrological processes in a glacier‐dominated catchment

The processes by which climate change affects streamflow in alpine river basins are not entirely understood. This study evaluated the impacts of temperature and precipitation changes on runoff and streamflow using glacier‐enhanced Soil and Water Assessment Tool model. The study used observed and detrended historical meteorological data for recent decades (1961–2005) to analyse individual and combined effects of temperature and precipitation changes on snow and glacier melts and discharges in the Sary‐Djaz‐Kumaric River Basin (SRB), Tianshan Mountains. The results showed a 1.3% increase in annual snowmelt in the basin, mainly because of an increase in precipitation. Snowmelt in the basin varied seasonally, increasing from April through May because of increasing precipitation and decreasing from July through September because of rising temperature. Glacier melt increased by 5.4%, 5.0% of which was due to rising temperature and only 0.4% due to increasing precipitation. Annual streamflow increased by 4.4%, of which temperature and precipitation increases accounted for 2.5% and 1.9%, respectively. The impacts of temperature and precipitation changes on streamflow were especially significant after 1980 and even more so in September. Glacier melt, due to temperature rise, was the dominant driver of increasing streamflow in the glacier‐dominated SRB, Tianshan Mountains. Copyright © 2015 John Wiley & Sons, Ltd.     

Implications of decadal to century scale glacio‐hydrological change for water resources of the Hood River basin,OR, USA

In glacier‐fed rivers, melting of glacier ice sustains streamflow during the driest times of the year, especially during drought years. Anthropogenic and ecologic systems that rely on this glacial buffering of low flows are vulnerable to glacier recession as temperatures rise. We demonstrate the evolution of glacier melt contribution in watershed hydrology over the course of a 184‐year period from 1916 to 2099 through the application of a coupled hydrological and glacier dynamics model to the Hood River basin in Northwest Oregon, USA. We performed continuous simulations of glaciological processes (mass accumulation and ablation, lateral flow of ice and heat conduction through supra‐glacial debris), which are directly linked with seasonal snow dynamics as well as other key hydrologic processes (e.g. evapotranspiration and subsurface flow). Our simulations show that historically, the contribution of glacier melt to basin water supply was up to 79% at upland water management locations. We also show that supraglacial debris cover on the Hood River glaciers modulates the rate of glacier recession and progression of dry season flow at upland stream locations with debris‐covered glaciers. Our model results indicate that dry season (July to September) discharge sourced from glacier melt started to decline early in the 21st century following glacier recession that started early in the 20th century. Changes in climate over the course of the current century will lead to 14–63% (18–78%) reductions in dry season discharge across the basin for IPCC emission pathway RCP4.5 (RCP8.5). The largest losses will be at upland drainage locations of water diversions that were dominated historically by glacier melt and seasonal snowmelt. The contribution of glacier melt varies greatly not only in space but also in time. It displays a strong decadal scale fluctuations that are super‐imposed on the effects of a long‐term climatic warming trend. This decadal variability results in reversals in trends in glacier melt, which underscore the importance of long‐time series of glacio‐hydrologic analyses for evaluating the hydrological response to glacier recession. Copyright © 2016 John Wiley & Sons, Ltd.     

Water repellency as run‐off and soil detachment controlling factor in a dry‐Mediterranean hillslope (South of Spain)

This study examines the effect of water repellency on controlling temporal variability of runoff generation mechanisms and soil detachment on metamorphic derived soils under dry‐Mediterranean climate. The research is carried out in an unburnt Mediterranean hillslope in souther Spain characterized by a patchy vegetation pattern and shallow soils. The Water Drop Penetration Time test (WDPT) is applied to measure water repellency at the end of summer (Sep‐2008), mid autumn (Nov‐2008) and mid winter (Feb‐2009). Rainfall simulations were used to obtain runoff generation and soil detachment in the same periods of time. The main shrub specie is Cistus monspeliensis which leaves a load of litter during the summer due to the lack of water. This great amount of organic material is accumulated under the shrubs triggering an extreme water repellence (WDPT > 6,000 s) that limits infiltration processes. This process is enforced due to the low soil water content at the end of dry season. Certain water repellency (WDPT > 1,500 s) is also observed on bare soil as consequence of their sandier texture and the accumulation of annual plants which die at the end of the wet season. Soil moisture increases during the autumn and water repellency disappears in both shrub and bare soil at the middle of the wet season (WDPT < 5 s). The main consequence is that the temporal trend of water repellency controls the mechanism and frequency of runoff generation and, hence, soil detachment. At the end of the summer, Hortonian mechanisms predominates when water repellency is extreme, even in soils under Cistus monspeliensis where runoff generation can reach higher peaks of overland flow and sediment concentration. Conversely, only the saturation of soil could generate runoff during the wet season being this quite less frequent in bare soil and absent in shrub. Copyright © 2010 John Wiley & Sons, Ltd.     

Runoff evolution in the Swiss Alps: projections for selected high‐alpine catchments based on ENSEMBLES scenarios

The Alps are often referred to as the ‘water tower of Europe’. In Switzerland, many branches of the economy, especially the hydropower industry, are closely linked to and dependent on the availability of water. Assessing the impact of climate change on streamflow runoff is, thus, of great interest. Major efforts have already been made in this respect, but the analyses often focus on individual catchments and are difficult to intercompare. In this article, we analysed nine high‐alpine catchments spread over the Swiss Alps, selected for their relevance to a wide range of morphological characteristics. Runoff projections were carried out until the end of the current century by applying the Glacier Evolution Runoff Model (GERM) and climate scenarios generated in the framework of the ENSEMBLES project. We focused on assessing the uncertainty induced by the unknown climate evolution and provided general, statistically based statements, which should be useful as a ‘rule of thumb’ for analyses addressing questions related to water management. Catchments with a high degree of glacierization will undergo the largest changes. General statements about absolute variations in discharge are unreliable, but an overall pattern, with an initial phase of increased annual discharge, followed by a phase with decreasing discharge, is recognizable for all catchments with a significant degree of glacierization. In these catchments, a transition from glacial and glacio‐nival regime types to nival will occur. The timing of maximal annual runoff is projected to occur before 2050 in all basins. The time of year with maximal daily discharges is expected to occur earlier at a rate of 4·4 ± 1·7 days per decade. Compared to its present level, the contribution of snow‐ and icemelt to annual discharge is projected to drop by 15 to 25% until the year 2100. Copyright © 2011 John Wiley & Sons, Ltd.     

A modified monthly degree‐day model for evaluating glacier runoff changes in China. Part I: model development

The retreat of mountain glaciers and ice caps has dominated the rise in global sea level and is likely to remain an import component of eustatic sea‐level rise in the 21st century. Mountain glaciers are critical in supplying freshwater to populations inhabiting the valleys downstream who heavily rely on glacier runoff, such as arid and semi‐arid regions of western China. Owing to recent climate warming and the consequent rapid retreat of many glaciers, it is essential to evaluate the long‐term change in glacier melt water production, especially when considering the glacier area change. This paper describes the structure, principles and parameters of a modified monthly degree‐day model considering glacier area variation. Water balances in different elevation bands are calculated with full consideration of the monthly precipitation gradient and air temperature lapse rate. The degree‐day factors for ice and snow are tuned by comparing simulated variables to observation data for the same period, such as mass balance, equilibrium line altitude and glacier runoff depth. The glacier area–volume scaling factor is calibrated with the observed glacier area change monitored by remote sensing data of seven sub‐basins of the Tarim interior basin. Based on meteorological data, the glacier area, mass balance and runoff are estimated. The model can be used to evaluate the long‐term changes of melt water in all glacierized basins of western China, especially for those with limited observation data. Copyright © 2011 John Wiley & Sons, Ltd.     

Rainfall,run‐off,and sediment transport dynamics in a humid mountain badland area: Long‐term results from a small catchment

In this study, we investigated rainfall, run‐off, and sediment transport dynamics (414 run‐off events and 231 events with sediment information) of a humid mountain badland area—the Araguás catchment (Central Pyrenees, Spain)—from October 2005 to September 2016. Use of this long‐term database allows characterization of the hydrological response, which consist of low‐magnitude/high‐frequency events and high‐magnitude/low‐frequency events, and identification of seasonal dynamics and rainfall‐run‐off thresholds. Our results indicate that the Araguás catchment, similarly to other humid badlands, had high hydrological responsiveness (mean annual run‐off coefficient: 0.52), a non‐linear relationship of rainfall with run‐off (common in Mediterranean environments), and seasonal hydrological and sedimentological dynamics. We created and validated a multivariate regression model to characterize the hydrological variables (stormflow and peak discharge) and sedimentological variables (mean and maximum suspended sediment concentrations and total suspended sediment load). In summer and at the beginning of autumn, the response was mainly related to rainfall intensity, suggesting a predomination of Hortonian flows. In contrast, in spring and winter, the responses were mainly related to the antecedent conditions (previous rainfall and baseflow), suggesting the occurrence of saturated excess flow processes, and the contribution of neighbouring vegetated areas. The multivariate analysis also showed that total sediment load is better predicted by a multivariate regression model that integrates pre‐event, rainfall, and run‐off variables. In general, our models provided more accurate predictions of small‐magnitude/high‐frequency events than high‐magnitude/low‐frequency events. This study highlights the high inter‐ and intra‐annual variability response in humid badland areas and that long‐term records are needed to reduce the uncertainty of hydrological and sedimentological responses in Mediterranean badland areas.     

Erosion of a high‐altitude,low‐relief area on the Korean Peninsula: implications for its development processes and evolution

The processes involved in the development of high‐altitude, low‐relief areas (HLAs) are still poorly understood. Although cosmogenic nuclides have provided insights into the evolution of HLAs interpreted as paleo‐surfaces, most studies focus on estimating how slowly they erode and thereby their relative stability. To understand actual development processes of HLAs, we applied several techniques of cosmogenic nuclides in the Daegwanryeong Plateau, a well‐known HLA in the Korean Peninsula. Our denudation data from strath terraces, riverine sediments, soils, and tors provide the following conclusions: (1) bedrock incision rate in the plateau (~127 m Myr^?1) is controlled by the incision rate of the western part of the Korean Peninsula, and is similar to the catchment‐wide denudation rate of the plateau (~93 m Myr^?1); (2) the soil production function we observed shows weak depth dependency that may result from highly weathered bedrock coupled with frequent frost action driven by alpine climate; (3) a discrepancy between the soil production and catchment‐wide denudation rates implies morphological disequilibrium in the plateau; (4) the tors once regarded as fossil landforms of the Tertiary do not reflect Tertiary processes; and (5) when compared with those of global paleo‐surfaces (<20 m Myr^?1), our rapid denudation rates suggest that the plateau cannot have maintained its probable initial paleo landscape, and thus is not a paleo‐surface. Our data contribute to understanding the surface processes of actively eroding upland landscapes as well as call into question conventional interpretations of supposed paleo‐surfaces around the world. Copyright © 2015 John Wiley & Sons, Ltd.     

Glacier retreat and landform production on an overdeepened glacier foreland: the debris‐charged glacial landsystem at Kvíárjökull,Iceland

Glacier recession and landform development in a debris‐charged glacial landsystem characterized by an overdeepening is quantified using digital photogrammetry, digital elevation model (DEM) construction and mapping of the Icelandic glacier Kvíárjökull for the period 1945–2003. Melting of ice‐cores is recorded by surface lowering rates of 0·8 m yr^–1 (1945–1964), 0·3 m yr^–1 (1964–1980), 0·015 m yr^–1 (1980–1998) and 0·044 m yr^–1 (1998–2003). The distribution/preservation of pushed and stacked ice‐cored moraine complexes are determined by the location of the long‐term glacial drainage network in combination with retreat from the overdeepening, into which glacifluvial sediment is being directed and where debris‐rich ice masses are being reworked and replaced by esker networks produced in englacial meltwater pathways that bypassed the overdeepening and connected to outwash fans prograding over the snout. Recent accelerated retreat of Kvíárjökull, potentially due to increased mass balance sensitivity, has made the snout highly unstable, especially now that the overdeepening is being uncovered and the snout flooded by an expanding pro‐glacial, and partially supraglacial, lake. This case study indicates that thick sequences of debris‐charged basal ice/controlled moraine have a very low preservation potential but ice‐cored moraine complexes can develop into hummocky moraine belts in de‐glaciated terrains because they are related to the process of incremental stagnation, which at Kvíárjökull has involved periodic switches from transport‐dominant to ablation‐dominant conditions. Glacier recession is therefore recorded temporally and spatially by two suites of landforms relating to two phases of landform production which are likely typical for glaciers occupying overdeepenings: an early phase of active, temperate recession recorded by push moraines and lateral moraines and unconfined pro‐glacial meltwater drainage; and a later phase of incremental stagnation and pitted outwash head development initiated by the increasing topographic constraints of the latero‐frontal moraine arc and the increasing importance of the overdeepening as a depo‐centre. Copyright © 2012 John Wiley & Sons, Ltd.     

A modified monthly degree‐day model for evaluating glacier runoff changes in China. Part II: application

The glacier mass balance, area change, and glacier runoff in the Yarkant River Basin (YRB) and the Beida River Basin (BRB) were estimated from 1961 to 2006 by employing a modified monthly degree‐day model. Comparisons between the simulated and observed mass balance, equilibrium line altitude, and glacier runoff suggest that the model can be used to analyze the long‐term changes of glacier mass balance and runoff in the YRB and the BRB. The glacier mass balances of the YRB and the BYB both have a significantly decreasing trend with ?4.39 mm a^‐1 and ?8.15 mm a^‐1 from 1961 to 2006 because of a significant increase in ablation caused by increasing summer air temperatures, especially since 1996. The total runoff in glacier areas has a significant increasing trend with 0.23 × 10⁸ m³ a^‐1 and 0.02 × 10⁸ m³ a^‐1 in the YRB and the BRB, respectively. By comparing the mean mass balance during the period 1961 to 1986 with that of the 1987 to 2006, the BRB glacier mass balance's sensitivity to temperature is at 0.33 m a^‐1 °C, nearly twice as much as that of the YRB at 0.16 m a^‐1 °C. The difference between the glacier temperature sensitivity in the YRB and the BRB is primarily because the glacier elevation band area weighted altitude of the YRB is about 700 m higher than that of BRB. The glacier elevation band area weighted summer air temperature in the YRB is around 2 °C lower than that of the BRB. Therefore, the annual positive degree‐day of the YRB and the BRB increases by about 21.0 °C and 77.3 °C respectively when the summer air temperature increases by 1 °C, resulting into more glacier ablation and runoff in the BRB than in the YRB. Copyright © 2011 John Wiley & Sons, Ltd.     

Interannual variability in glacier contribution to runoff from a high‐elevation Andean catchment: understanding the role of debris cover in glacier hydrology

We present a field‐data rich modelling analysis to reconstruct the climatic forcing, glacier response, and runoff generation from a high‐elevation catchment in central Chile over the period 2000–2015 to provide insights into the differing contributions of debris‐covered and debris‐free glaciers under current and future changing climatic conditions. Model simulations with the physically based glacio‐hydrological model TOPKAPI‐ETH reveal a period of neutral or slightly positive mass balance between 2000 and 2010, followed by a transition to increasingly large annual mass losses, associated with a recent mega drought. Mass losses commence earlier, and are more severe, for a heavily debris‐covered glacier, most likely due to its strong dependence on snow avalanche accumulation, which has declined in recent years. Catchment runoff shows a marked decreasing trend over the study period, but with high interannual variability directly linked to winter snow accumulation, and high contribution from ice melt in dry periods and drought conditions. The study demonstrates the importance of incorporating local‐scale processes such as snow avalanche accumulation and spatially variable debris thickness, in understanding the responses of different glacier types to climate change. We highlight the increased dependency of runoff from high Andean catchments on the diminishing resource of glacier ice during dry years.     

Structure,morphology and water flux of a subglacial drainage system,Midtdalsbreen, Norway

Digital elevation models of the surface and bed of Midtdalsbreen, Norway are used to calculate subglacial hydraulic potential and infer drainage system structure for a series of subglacial water pressure assumptions ranging from atmospheric to ice overburden. A distributed degree‐day model is used to calculate the spatial distribution of melt on the glacier surface throughout a typical summer, which is accumulated along the various drainage system structures to calculate water fluxes beneath the glacier and exiting the portals for the different water pressure assumptions. In addition, 78 dye‐tracing tests were performed from 33 injection sites and numerous measurements of water discharge were made on the main proglacial streams over several summer melt seasons. Comparison of the calculated drainage system structures and water fluxes with dye tracing results and measured proglacial stream discharges suggests that the temporally and spatially averaged steady‐state water pressures beneath the glacier are ~70% of ice overburden. Analysis of the dye return curves, together with the calculated subglacial water fluxes shows that the main drainage network on the eastern half of the glacier consists of a hydraulically efficient system of broad, low channels (average width/height ratio ≈ 75). The smaller drainage network on the west consists of a hydraulically inefficient distributed system, dominated by channels that are exceptionally broad and very low (average width/height ratio ≈ 350). The even smaller central drainage network also consists of a hydraulically inefficient distributed system, dominated by channels that are very broad and exceptionally low (average width/height ratio ≈ 450). The channels beneath the western and central glacier must be so broad and low that they can essentially be thought of as a linked cavity system. Copyright © 2011 John Wiley & Sons, Ltd.     

Predicting dry‐season flows with a monthly rainfall–runoff model: Performance for gauged and ungauged catchments

Hydrologic models are useful to understand the effects of climate and land‐use changes on dry‐season flows. In practice, there is often a trade‐off between simplicity and accuracy, especially when resources for catchment management are scarce. Here, we evaluated the performance of a monthly rainfall–runoff model (dynamic water balance model, DWBM) for dry‐season flow prediction under climate and land‐use change. Using different methods with decreasing amounts of catchment information to set the four model parameters, we predicted dry‐season flow for 89 Australian catchments and verified model performance with an independent dataset of 641 catchments in the United States. For the Australian catchments, model performance without catchment information (other than climate forcing) was fair; it increased significantly as the information to infer the four model parameters increased. Regressions to infer model parameters from catchment characteristics did not hold for catchments in the United States, meaning that a new calibration effort was needed to increase model performance there. Recognizing the interest in relative change for practical applications, we also examined how DWBM could be used to simulate a change in dry‐season flow following land‐use change. We compared results with and without calibration data and showed that predictions of changes in dry‐season flow were robust with respect to uncertainty in model parameters. Our analyses confirm that climate is a strong driver of dry‐season flow and that parsimonious models such as DWBM have useful management applications: predicting seasonal flow under various climate forcings when calibration data are available and providing estimates of the relative effect of land use on seasonal flow for ungauged catchments.     

Impacts of forest structure on precipitation interception and run‐off generation in a semiarid region in northern China

Water resource scarcity and uneven distribution are 2 major environmental issues in China today. Forest structure is a dominant factor that influences hydrological processes, but the specific interactions remain uncertain due to the predominant use of individual or 1‐dimensional forest structure metrics in previous studies. In this study, forest structures in 8 run‐off plots on Mount Miaofeng in north China were parameterized by metrics of different dimensionalities. The relation between canopy interception and forest structure, shrub/litter interception, and forest structure as well as run‐off and forest structure were analysed by regression method and validated by leave‐one‐out cross test. The results showed that canopy interception rates ranged from less than 0.10 all the way to 0.80, affected by forest structure and precipitation, with interception rate decreasing logarithmically as precipitation increased. Forests with a larger canopy area (CA), leaf area index (LAI), and higher average height (H) had a narrow range of canopy interception rates, and forest with larger value of diameters at breath height (DBH), H, LAI, vertical heterogeneity coefficient (T), and structure complexity index (SCI) had higher interception rates. Forests with higher value of DBH, H, and horizontal heterogeneity coefficient (R) had higher shrub/litter interception rates on the forest floor. The run‐off coefficient was only significantly associated with LAI, T, and SCI. The validation test indicated that regression analysis of canopy interception rates and shrub interception are reliable and SCI is a key factor to influence the run‐off coefficient. However, the regression results of litter interception have a relatively large error. According to the results, to reduce the risks of the landslides and floods, forest managers should complicate the canopy and preserve trees with thicker stems and larger canopies. By contrast, to obtain more water resource from run‐off in arid regions, forest managers should harvest trees with large canopies and construct complex vertical structures by intermediate cutting.     

Quantifying the impacts of climate change on water resources in northern Tuscany,Italy, using high‐resolution regional projections

This paper investigates the potential impacts of climate change on water resources in northern Tuscany, Italy. A continuous hydrological model for each of the seven river basins within the study area was calibrated using historical data. The models were then driven by downscaled and bias‐corrected climate projections of an ensemble of 13 regional climate models (RCMs), under two different scenarios of representative concentration pathway (RCP4.5 and RCP8.5). The impacts were examined at medium term (2031–2040) and long term (2051–2060) in comparison with a reference period (2003–2012); the changes in rainfall, streamflow, and groundwater recharge were investigated. A high degree of uncertainty characterized the results with a significant intermodel variability, the period being equal. For the sake of brevity, only the results for the Serchio River basin were presented in detail. According to the RCM ensemble mean and the RCP4.5, a moderate decrease in rainfall, with reference to 2003–2012, is expected at medium term (?0.6%) and long term (?2.8%). Due to the warming of the study area, the reduction in the streamflow volume is two times the precipitation decrease (?1.1% and ?6.8% at medium and long term, respectively). The groundwater recharge is mainly affected by the changes in climate with expected percolation volume variations of ?3.3% at 2031–2040 and ?8.1% at 2051–2060. The impacts on the Serchio River basin water resources are less significant under the RCP8.5 scenario. The presence of artificial structures, such as dam‐reservoir systems, can contribute to mitigate the effects of climate change on water resources through the implementation of appropriate regulation strategies.