Deforestation of water‐repellent soils in Galicia (NW Spain): effects on surface runoff and erosion under simulated rainfall

At three adjacent sites in steeply sloping woodland in Galicia (NW Spain), surface runoff and associated erosion under simulated rainfall (64 mm h^?1) were measured on five occasions between June 1998 and July 1999. Two of the three sites had recently been deforested and topsoil added, and one of these two had been sown with grass, which was germinating at the onset of the study. Deforestation greatly increased runoff and erosion rates, and the recovery of plant cover reduced erosion. All three soils were very hydrophobic due to high levels of poorly humified organic matter, which led to higher runoff rates than expected, especially during dry periods. However, great structural stability prevented there being a significant correlation between runoff rate and soil erosion. Copyright © 2003 John Wiley & Sons, Ltd.     

Quantifying the impact of no-till on sediment yield in southern Brazil at the hillslope and catchment scales

No-till (NT) is a soil management system designed to protect soil resources from water erosion and provide numerous benefits compared to conventional tillage through the increase of organic matter inputs into the soil. However, NT in isolation is not sufficient to control erosion processes caused by an excessive production of surface runoff. This study evaluated soil losses on agricultural hillslopes under no-till characterized by contrasted water, soil, and crop management conditions. To this end, water and soil losses were monitored between 2014 and 2018 at two scales, including four macroplots (0.6 ha; 27 events) and two paired zero-order catchments (2.4 ha; 63 events). The resulting dataset covered a wide range of rainfall conditions that occurred in contrasted soil, crop, and runoff management conditions. Hyetographs, hydrographs, and sedigraphs were constructed, and these data were used to evaluate the impact of management on sediment yields, including that of terraces, scarification, and phytomass on sediment yield. The installation of terraces reduced sediment yield by 58.7%, mainly through surface runoff control. Crop management including an increased phytomass input efficiently controlled soil losses (63%), although it did not reduce runoff volume and peak flow. In contrast, scarification had no impact on runoff and soil losses. The current research demonstrated the need to combine the installation of terraces and leaving a high amount of phytomass on the soil to control surface runoff and erosion and reduce sediment yield. The current research therefore reinforces the relevance of the monitoring strategy conducted at the scale of macroplots and zero-order catchments to evaluate the impact of contrasted water, soil, and crop management methods and select the most effective conservation agriculture practices.     

Role of epikarst in near‐surface hydrological processes in a soil mantled subtropical dolomite karst slope: implications of field rainfall simulation experiments

Epikarst exerts a strong control on run‐off generation in karst regions, but it is still unclear in karst regions. Our study aimed to demonstrate the effect of epikarst on near‐surface hydrological processes in a subtropical cockpit karst region of southwest China, using plot‐scale rainfall simulation experiments with different rainfall intensities (low and high) and antecedent moisture conditions (dry and wet). A trench excavated to the epikarst lower boundary allowed identification of flow pathways in the entire soil–epikarst architecture system, thus facilitating the water balance calculations using a conceptual model with the assumption of a two‐stage hydrological evolution. More than 70% of the total rainfall water moved vertically through the shallow soil layer and then was redistributed by the epikarst as subsurface flow occurring on the soil–epikarst interface, depression filling on epikarst surface, water held by epikarst and deep percolation. Epikarst water regulation capacity, defined as the sum of depression filling on epikarst surface, water held by epikarst, epikarst seepage flow and deep percolation, was 58 mm (wet antecedent condition) and 223 mm (dry antecedent condition). Total run‐off from the soil–epikarst system was dominated by saturated subsurface flow showing a threshold process controlled by epikarst storage capacity (storing as much as 181 mm of rainfall water under dry antecedent condition). Our study proved that despite the epikarst being relatively poorly developed and covered by a soil mantle, it still exerted a strong influence on near‐surface hydrological processes and thus should be adequately considered in future modelling of water recharge and depletion dynamics in this integrated soil–epikarst system. Copyright © 2015 John Wiley & Sons, Ltd.     

Comparison of the effects of litter covering and incorporation on infiltration and soil erosion under simulated rainfall

Plant litter can either cover on soil surface or be incorporated into top-soil layer in natural ecosystems. Their effects on infiltration and soil erosion are likely quite different. This study was performed to compare the effects of litter covering on soil surface and being incorporated into top-soil layer on infiltration and soil erosion under simulated rainfall. Four litter types (needle-leaf, broad-leaf, brush, and herb) were collected from fields and applied to cover on soil surface or to be incorporated into top-soil layer (5 cm) at the same rate (0.2 kg/m²). The simulated rainfalls (40 and 80 mm/hr) were run at two slope angles (10° and 20°). The results showed that the mean infiltration rate of litter covering treatment was 1.4 times as great as that of litter incorporated. Litter covering enhanced infiltration via protecting surface from soil sealing. Whereas, litter incorporation affected infiltration by its water repellency. Soil erosion of litter incorporated treatment was 5.4 times as large as that of litter covered treatment, which was attributed to the changes in surface litter coverage and soil erosion resistance. Litter type affected soil erosion through the variations in litter coverage and litter morphology. For litter covering treatment, litter coverage can explain the major variance of soil loss on the slopes. Whereas, for litter incorporated treatment, both the influences of litter coverage and litter length on soil erosion resistance were considered necessary to well explain the variance of soil loss. The results also showed that the benefits of litter to control soil erosion declined with rainfall intensity and slope gradient for both covering and incorporated treatments. The results of this study are helpful to understand the mechanisms of litter influencing hydrological and erosion processes on hillslopes.     

Spatial and temporal variations of overland flow during rainfall events and in relation to catchment conditions

Improved knowledge on overland flow (OF) generation and its dynamics (i.e. spatial and temporal variations) is essential to understand catchment hydrology, a prerequisite for better water resources and soil management. In this study, our main objective was to quantify the dynamics of OF during rainfall events and to assess its main factors of control. The research study was undertaken in an agricultural 23‐ha catchment of a communal pasture in KwaZulu‐Natal (South Africa) experiencing Mediterranean climate and with variations of soil, topography and vegetation conditions. The dynamics of OF was evaluated during three rainfall seasons (2007 to 2010) by using 1 × 1‐m² microplots (n = 15) located at five landscape positions. At each location, a microplot was equipped with an automatic tipping bucket linked to a logger to estimate the delay between the start of the rain and the start of OF [i.e. the time to runoff initiation (TRI)]. Multivariate analysis was applied to the total OF and TRI data and the information on selected environmental factors (rainfall characteristics; soil type; soil clay content, Clay; proportion of the soil surface covered by vegetation, Cov; proportion of the soil surface covered by crusting, Crust; mean slope gradient, S; soil bulk density, ρ_b; soil water tension at different depths, SWT). The average OF rate over the 3‐year study period varied 2.3‐fold across the catchment (from 15% footslope to 35% backslope), whereas the average TRI varied by a 10.6‐fold factor (between 0.6 min at bottomland and 6.4 min at footslope). TRI temporal variations correlated the most with event duration (r = 0.8) and cumulative amount of rainfall since the onset of the rainy season (r = ?0.47), whereas TRI spatial variations were controlled the most by Crust (?0.97 < r < ?0.77). Ultimately, TRI spatial variations were modelled and mapped in an attempt to model OF dynamics over the entire microcatchment. Copyright © 2012 John Wiley & Sons, Ltd.     

Characteristics of surface runoff and throughflow in a purple soil of Southwestern China under various rainfall events

In order to harvest runoff to palliate water disaster as well as effectively manage irrigation and fertilizer application in the studied region, it is necessary to better understand the runoff processes. A newly designed runoff collection system for a plot scale was used to partition runoff under contrasting rainfall events into surface flow and subsurface flow to obtain characteristics of surface runoff and throughflow in a purple soil (Regosols in FAO taxonomy, Entisol in USDA taxonomy) of Sichuan, China. Under small rainfall (shower and drizzle), only surface runoff was observed. It is noted that, under shower, particularly with antecedent dry soil conditions, the highest peak surface runoff significantly lagged behind that of rainfall, because air‐locked soil pores of the top layer appeared temporally. Under rainstorm and downpour, surface runoff and throughflow both commenced and showed hysteresis. The hydrograph of surface runoff better resembled that of rainfall than throughflow did. The durations of throughflow discharge of post‐rainfall‐end were near the same (within 24 h) under various rainfalls and rather dependent upon the soil properties than the rainfall characteristics. Throughflow is about 60–90% of total runoff, and especially significant in a ploughed layer under downpour. The chloride concentration of throughflow was over twice that of surface runoff and rainfall, implying that throughflow contains more nutrients than surface runoff. Presumably, surface runoff was primarily governed by an infiltration‐excess or saturated excess‐infiltration mechanism under unsaturated or saturated soil conditions. Therefore, the management of water and fertilizer, and the harvesting of water flow in the ploughed soil layer, should be emphasized in this region. Copyright © 2005 John Wiley & Sons, Ltd.     

The effects of slope shape and polyacrylamide application on runoff,erosion and nutrient loss from hillslopes under simulated rainfall

Natural hillslopes are mostly composed of complex slope shapes, which significantly affect soil erosion. However, existing studies have mainly focused on uniform slopes to simplify complex hillslopes, and the mechanisms responsible for the influence of slope shape on soil and nutrient losses are still not well understood, especially in the application of soil improvers to reduce soil loss. To investigate the effects of slope shape and polyacrylamide (PAM) application on runoff, soil erosion and nutrient loss, this study conducted artificial field rainfall experiments involving two PAM application rates and nine slope shapes. The results indicate that the average amount of soil loss from convex slopes was 1.5 and 1.3 times greater than that from concave and uniform slopes, respectively, and the average amount of ammonia nitrogen loss and phosphate loss increased by 24.0%–58.6%. Soil and nutrient losses increased as the convexity of the convex slopes increased. For runoff, there was little difference between concave and convex slopes, but the runoff amount for both slopes was greater than that for uniform slopes. After PAM application, the soil loss decreased by more than 90%, and the nutrient loss decreased by 28.2%–68.1%. The application of PAM was most effective in reducing soil erosion and nutrient loss from convex slopes, and it is recommended to appropriately increase the PAM application rate for convex slopes. A strong linear relationship between ammonia nitrogen and phosphate concentrations and sediment concentrations was found in the runoff on slopes with no PAM application. However, this linear relationship weakened for slopes with PAM application. The findings of this study may be valuable for optimizing nonpoint source pollution management in basins.     

Water balance,nutrient and carbon export from a heath forest catchment in central Amazonia,Brazil

Carbon storage values in the Amazon basin have been studied through different approaches in the last decades in order to clarify whether the rainforest ecosystem is likely to act as a sink or source for carbon in the near future. This water balance, dissolved organic carbon (DOC) and nutrient export study were carried out in a micro‐scale heath forest (Campina) catchment in central Amazonia, Brazil. For a 1‐year study period (18 March 2007 until 19 March 2008), rainfall amounted to 3054 mm; of which, 1532 mm was evaporated by the forest (4.1 mm day^?1). Rainfall interception loss amounted to 15.6% of gross rainfall. Surface runoff amounted to 485 mm, whereas another 1071 mm was discharged as regional groundwater outflow. Accumulated DOC exports in surface runoff amounted to 15.3 g m^?2 year^?1, whereas the total carbon exported was 55.9 g m^?2. This is much higher than that observed for a nearby tall rainforest catchment in central Amazonia (DOC export < 20 g m^?2). As Campina heath forest areas cover a significant proportion of the Amazon Basin, these differences in ecosystem hydrological carbon exports should be taken into account in future studies assessing the carbon budget for the Amazon Basin. Macro‐nutrient exports were low, but those of calcium and potassium were higher than those observed for tall rainforest in the Amazon, which may be caused by a lower retention capacity of the heath forest ecosystem. Copyright © 2015 John Wiley & Sons, Ltd.     

The role of rainfall temporal and spatial averaging in seasonal simulations of the terrestrial water balance

The partitioning of rainfall into surface runoff and infiltration influences many other aspects of the hydrologic cycle including evapotranspiration, deep drainage and soil moisture. This partitioning is an instantaneous non-linear process that is strongly dependent on rainfall rate, soil moisture and soil hydraulic properties. Though all rainfall datasets involve some degree of spatial or temporal averaging, it is not understood how this averaging affects simulated partitioning and the land surface water balance across a wide range of soil and climate types. We used a one-dimensional physics-based model of the near-surface unsaturated zone to compare the effects of different rainfall discretization (5-min point-scale; hourly point-scale; hourly 0.125° gridded) on the simulated partitioning of rainfall for many locations across the United States. Coarser temporal resolution rainfall data underpredicted seasonal surface runoff for all soil types except those with very high infiltration capacities (i.e., sand, loamy sand). Soils with intermediate infiltration capacities (i.e., loam, sandy loam) were the most affected, with less than half of the expected surface runoff produced in most soil types when the gridded rainfall dataset was used as input. The impact of averaging on the water balance was less extreme but non-negligible, with the hourly point-scale predictions exhibiting median evapotranspiration, drainage and soil moisture values within 10% of those predicted using the higher resolution 5-min rainfall. Water balance impacts were greater using the gridded hourly dataset, with average underpredictions of ET up to 27% in fine-grained soils. The results suggest that “hyperresolution” modelling at continental to global scales may produce inaccurate predictions if there is not parallel effort to produce higher resolution precipitation inputs or sub-grid precipitation parameterizations.     

Changes in rainfall and relative humidity in river basins in northwest and central India

Seasonal and annual trends of changes in rainfall, rainy days, heaviest rain and relative humidity have been studied over the last century for nine different river basins in northwest and central India. The majority of river basins have shown increasing trends both in annual rainfall and relative humidity. The magnitude of increased rainfall for considered river basins varied from 2–19% of mean per 100 years. The maximum increase in rainfall is observed in the Indus (lower) followed by the Tapi river basin. Seasonal analysis shows maximum increase in rainfall in the post‐monsoon season followed by the pre‐monsoon season. There were least variations in the monsoon rainfall during the last century and winter rainfall has shown a decreasing trend. Most of the river basins have experienced decreasing trends in annual rainy days with a maximum decrease in the Mahanadi basin. The heaviest rain of the year has increased from 9–27 mm per 100 years over different river basins with a maximum of 27 mm for the Brahamani and Subaranrekha river basins. A combination of increase in heaviest rainfall and reduction in the number of rainy days suggest the possibility of increasing severity of floods. Such information is useful in the planning, development and management of water resources in the study area. Further, the majority of river basins have also experienced an increasing trend in relative humidity both on seasonal and annual scales. An increase in annual mean relative humidity for six river basins has been found in the range of 1–18% of mean per 100 years, while a decrease for three river basins from ? 1 to ? 13% of mean per 100 years was observed, providing a net increase in the study area by 2·4% of mean per 100 years. It is understood that an increase in areal extent of vegetation cover as well as rainfall over the last century has increased the moisture in the atmosphere through enhanced evapotranspiration, which in turn has increased the relative humidity. Copyright © 2007 John Wiley & Sons, Ltd.     

Using stable isotopes to identify major flow pathways in a permafrost influenced alpine meadow hillslope during summer rainfall period

Global warming has leaded to permafrost degradation, with potential impacts on the runoff generation processes of permafrost influenced alpine meadow hillslope. Stable isotopes have the potential to trace the complex runoff generation processes. In this study, precipitation, hillslope surface and subsurface runoff, stream water, and mobile soil water (MSW) at different hillslope positions and depths were collected during the summer rainfall period to analyse the major flow pathway based on stable isotopic signatures. The results indicated that (a) compared with precipitation, the δ²H values of MSW showed little temporal variation but strong heterogeneity with enriched isotopic ratios at lower hillslope positions and in deeper soil layers. (b) The δ²H values of middle-slope surface runoff and shallow subsurface flow were similar to those of precipitation and MSW of the same soil layer, respectively. (c) Middle-slope shallow subsurface flow was the major flow pathway of the permafrost influenced alpine meadow hillslope, which turned into surface runoff at the riparian zone before contributing to the streamflow. (d) The slight variation of δ²H values in stream water was shown to be related to mixing processes of new water (precipitation, 2%) and old water (middle-slope shallow subsurface flow, 98%) in the highly transmissive shallow thawed soil layers. It was inferred that supra-permafrost water levels would be lowered to a less conductive, deeper soil layer under further warming and thawing permafrost, which would result in a declined streamflow and delayed runoff peak. This study explained the “rapid mobilization of old water” paradox in permafrost influenced alpine meadow hillslope and improved our understanding of permafrost hillslope hydrology in alpine regions.     

Influences of grass and moss on runoff and sediment yield on sloped loess surfaces under simulated rainfall

It is important to evaluate the impacts of grasses on soil erosion process so as to use them effectively to control soil and water losses on the Loess Plateau. Laboratory-simulated rainfall experiments were conducted to investigate the runoff and sediment processes on sloped loess surfaces with and without the aboveground parts of grasses and moss (GAM: grass and moss; NGAM: no grass and moss) under slope gradients of 5°, 10°, 15°, 20°, 25° and 30°. The results show that runoff from GAM and NGAM plots increased up to a slope gradient of 10° and decreased thereafter, whereas the runoff coefficients increased with gradient. The average runoff rates and runoff coefficients of NGAM plots were less than those of GAM plots except for the 5° slope. This behaviour may be due to the reduction in water infiltration under moss. The difference between GAM and NGAM plots in average runoff rates varied from 1·4 to 8%. At the same gradients, NGAM plots yielded significantly (α = 0·05) more sediment than GAM plots. Average sediment deliveries for different slopes varied from 0·119 to 3·794 g m⁻² min⁻¹ from GAM plots, and from 0·765 to 16·128 g m⁻² min⁻¹ from NGAM plots. Sediment yields from GAM plots were reduced by 45 to 85%, compared with those from the NGAM plots. Plots at 30° yielded significantly higher sediments than at the other gradients. Total sediments S increased with slope gradients G in a linear form, i.e. S = 9·25G − 39·6 with R² = 0·77*, for the GAM plots, and in an exponential model, i.e. S = 40·4 exp(0·1042G) with R² = 0·93**, for the NGAM plots. In all cases, sediment deliveries decreased with time, and reached a relative steady state at a rainfall duration of 14 min. Compared with NGAM plots, the final percentage reductions in sediment delivery from GAM plots were higher than those at the initial time of rainfall at all slopes. Copyright © 2006 John Wiley & Sons, Ltd.     

Quantifying the impact of no-till on runoff in southern Brazil at hillslope and catchment scales

No-till (NT) is a conservation system that improves the hydrological regime of agricultural slopes by providing greater surface protection and benefits to the physical and hydrological properties of soils. However, the isolated use of NT is not enough to control runoff and its associated degradation processes. Therefore, this study aimed to evaluate the runoff of agricultural slopes under NT under different runoff control conditions by monitoring 63 rainfall events in two 2.4-ha zero-order catchments and 27 rainfall events in four 0.6-ha macroplots. The catchments are paired and similar in terms of the type of soil and relief, but different regarding the presence of terraces. The macroplots have different soil and crop management systems. By using monitoring techniques, the hyetographs and hydrographs revealed the influence of the different types of management on the catchments and macroplots and allowed rainfall characteristics, runoff volume, runoff coefficients, water infiltration, peak runoff, response times, and curve number to be analysed. The terraces positively affected the NT and controlled runoff and related variables, in addition to infiltration significantly increasing and runoff reducing in the terraced catchment. All the hydrological information assessed pointed to the positive effects provided by the presence of the terraces. The results in the macroplots showed that high amounts of phytomass and/or chiselling do not control runoff and its correlated variables in medium and high magnitude events. The study concludes by underlining the need for additional measures to control runoff (terraces), even in areas under NT and with high phytomass production. Additionally, the study emphasizes the importance of monitoring at the catchment scale to better understand the hydrological behaviour of agricultural areas and provide the necessary parameters to effectively control runoff.     

Investigating hydrological regimes and processes in a set of catchments with temporary waters in Mediterranean Europe

Abstract

Seven catchments of diverse size in Mediterranean Europe were investigated in order to understand the main aspects of their hydrological functioning. The methods included the analysis of daily and monthly precipitation, monthly potential evapotranspiration rates, flow duration curves, rainfall—runoff relationships and catchment internal data for the smaller and more instrumented catchments. The results showed that the catchments were less “dry” than initially considered. Only one of them was really semi-arid throughout the year. All the remaining catchments showed wet seasons when precipitation exceeded potential evapotrans-piration, allowing aquifer recharge, “wet” runoff generation mechanisms and relevant baseflow contribution. Nevertheless, local infiltration excess (Hortonian) overland flow was inferred during summer storms in some catchments and urban overland flow in some others. The roles of karstic groundwater, human disturbance and low winter temperatures were identified as having an important impact on the hydrological regime in some of the catchments.     

Hillslope‐scale probabilistic characterization of soil moisture dynamics and average water balance

Probabilistic water balance modelling provides a useful framework for investigating the interactions between soil, vegetation, and the atmosphere. It has been used to estimate temporal soil moisture dynamics and ecohydrological responses at a point. This study combines a nonlinear rainfall–runoff theory with probabilistic water balance model to represent varied source area runoff as a function of rainfall depth and a runoff coefficient at hillslope scale. Analytical solutions of the soil‐moisture probability density function and average water balance model are then developed. Based on a sensitivity analysis of soil moisture dynamics, we show that when varied source area runoff is incorporated, mean soil moisture is always lower and total runoff higher, compared with the original probabilistic water balance model. The increased runoff from the inclusion of varied source area runoff is mainly because of a reduction in leakage when the index of dryness is less than one and evapotranspiration when the index of dryness is greater than one. Inclusion of varied source area runoff in the model means that the actual evapotranspiration is limited by less available water (i.e. water limit), which is stricter than Budyko’s and Milly’s water limit. Application of the model to a catchment located in Western Australia showed that the method can predict annual value of actual evapotranspiration and streamflow accurately. Copyright © 2012 John Wiley & Sons, Ltd.     

Impact of redox and transport processes in a riparian wetland on stream water quality in the Fichtelgebirge region,southern Germany

Biologically mediated redox processes in the riparian zone, like denitrification, can have substantially beneficial impacts on stream water quality. The extent of these effects, however, depends greatly on the hydrological boundary conditions. The impact of hydrological processes on a wetland's nitrogen sink capacity was investigated in a forested riparian fen which is drained by a first‐order perennial stream. Here, we analysed the frequency distributions and time‐series of pH and nitrogen, silica, organic carbon and oxygen concentrations in throughfall, soil solution, groundwater and stream water, and the groundwater levels and stream discharges from a 3‐year period. During baseflow conditions, the stream was fed by discharging shallow, anoxic groundwater and by deep, oxic groundwater. Whereas the latter delivered considerable amounts of nitrogen (～0·37 mg l^?1) to the stream, the former was almost entirely depleted of nitrogen. During stormflow, near‐surface runoff in the upper 30 cm soil layer bypassed the denitrifying zone and added significant amounts to the nitrogen load of the stream. Nitrate‐nitrogen was close to 100% of deep groundwater and stream‐water nitrogen concentration. Stream‐water baseflow concentrations of nitrate, dissolved carbon and silica were about 1·6 mg l^?1, 4 mg l^?1 and 7·5 mg l^?1 respectively, and >3 mg l^?1, >10 mg l^?1 and <4 mg l^?1 respectively during discharge peaks. In addition to that macroscale bypassing effect, there was evidence for a corresponding microscale effect: Shallow groundwater sampled by soil suction cups indicated complete denitrification and lacked any seasonal signal of solute concentration, which was in contrast to piezometer samples from the same depth. Moreover, mean solute concentration in the piezometer samples resembled more that of suction‐cup samples from shallower depth than that of the same depth. We conclude that the soil solution cups sampled to a large extent the immobile soil‐water fraction. In contrast, the mobile fraction that was sampled by the piezometers exhibited substantially shorter residence time, thus being less exposed to denitrification, but predominating discharge of that layer to the stream. Consequently, assessing the nitrogen budget based on suction‐cup data tended to overestimate the nitrogen consumption in the riparian wetland. These effects are likely to become more important with the increased frequency and intensity of rainstorms that are expected due to climate change. Copyright © 2006 John Wiley & Sons, Ltd.     

Using high resolution tracer data to constrain water storage,flux and age estimates in a spatially distributed rainfall‐runoff model

Models simulating stream flow and conservative tracers can provide a representation of flow paths, storage distributions and mixing processes that is advantageous for many predictive purposes. Compared with models that only simulate stream flow, tracer data can be used to investigate the internal consistency of model behaviour and to gain insight into model performance. Here, we examine the strengths and weaknesses of a data‐driven, spatially distributed tracer‐aided rainfall‐runoff model. The model structure allowed us to assess the influence of landscape characteristics on the routing and mixing of water and tracers. The model was applied to a site in the Scottish Highlands with a unique tracer data set; ~4 years of daily isotope ratios in stream water and precipitation were available, as well as 2 years of weekly soil and ground water isotopes. The model structure was based on an empirically based, lumped tracer‐aided model previously developed for the catchment. The best model runs were selected from Monte Carlo simulations based on dual calibration criteria using objective functions for both stream isotopes and discharge at the outlet. Model performance for these criteria was reasonable (Nash–Sutcliffe efficiencies for discharge and isotope ratios were ~0.4–0.6). The model could generally reproduce the variable isotope signals in the soils of the steeper hill slopes where storage was low, and damped isotope responses in valley bottom cells with high storage. The model also allowed us to estimate the age distributions of internal stores, water fluxes and stream flow. Average stream water age was ~1.6 years, integrating older groundwater in the valley bottom and dynamic younger soil waters. By tracking water ages and simulating isotopes, the model captured the changes in connectivity driven by distributed storage dynamics. This has substantially improved the representation of spatio‐temporal process dynamics and gives a more robust framework for projecting environmental change impacts. Copyright © 2016 The Authors Hydrological Processes Published by John Wiley & Sons Ltd.     

Hydrological behaviour and modelling of a volcanic tropical cultivated catchment

The hydrological behaviour of the cultivated Féfé catchment (17·8 ha) on the tropical volcanic island of Guadeloupe was studied to identify flow paths, to quantify water fluxes, and finally, to build a lumped model to simulate discharge and piezometer levels. The approach combined two steps, an experimental step and a modelling step, which covered two time scales, the annual and the storm event scale. The hydrological measurements were conducted over 2 years. The Féfé catchment is characterized by heavy rainfall (4229 mm year^?1) on permeable Andosols; the results showed that underground flow paths involved two overlapping aquifers, and that the annual water balance in 2003 was shared among outflows of the deep aquifer (42%), evapotranspiration (31%), and streamflow (27%). On the event scale, the surface runoff coefficient ranges between 6·2% and 24·4% depending on antecedent dry or wet moisture conditions. Hortonian overland flow predominated over subsurface and saturation overland flow processes. Recharge of the shallow aquifer is mainly governed by a constant infiltration capacity of the Andosols with depth in the vadose zone. Outflows of this shallow aquifer were the baseflow of the main stream and the recharge of the deep aquifer. Volcanic deposits at Féfé promoted the underground flow path, and cultivated areas seemed to explain the high stormflow values relative to other tropical small catchments under rain forest. A conceptual lumped model integrating runoff, infiltration, evapotranspiration, and fluctuations of the two overlapping aquifers was developed. The model has six parameters and was calibrated and validated on the hydrograph at the outlet and on the two piezometers of the shallow and the deep aquifers. The results show fair to good agreement between measured and simulated variables, and consequently, the model was consistent with the main hydrological processes observed from experimental results in wet conditions. Copyright © 2008 John Wiley & Sons, Ltd.