Streamflow response to native forest restoration in former Eucalyptus plantations in south central Chile

Global increases in intensive forestry have raised concerns about forest plantation effects on water, but few studies have tested the effects of plantation forest removal and native forest restoration on catchment hydrology. We describe results of a 14-year paired watershed experiment on ecological restoration in south central Chile which documents streamflow response to the early stages of native forest restoration, after clearcutting of plantations of exotic fast-growing Eucalyptus, planting of native trees, and fostering natural regeneration of native temperate rainforest species. Precipitation, streamflow, and vegetation were measured starting in 2006 in four small (3 to 5 ha) catchments with Eucalyptus globulus plantations and native riparian buffers in the Valdivian Coastal Reserve. Mean annual precipitation is 2500 mm, of which 11% occurs in summer. Streamflow increased, and increases persisted, throughout the first 9 years of vigorous native forest regeneration (2011 to 2019). Annual streamflow increased by 40% to >100% in most years and >150% in fall and summer of some years. Streamflow was 50% to 100% lower than before treatment in two dry summers. Base flow increased by 28% to 87% during the restoration period compared to pre-treatment, and remained elevated in later years despite low summer precipitation. Overall, these findings indicate that removal of Eucalyptus plantations immediately increased streamflow, and native forest restoration gradually restored deep soil moisture reservoirs that sustain base flow during dry periods, increasing water ecosystem services. To our knowledge this is the first study to assess catchment streamflow response to native forest restoration in former forest plantations. Therefore, the results of this study are relevant to global efforts to restore native forest ecosystems on land currently intensively managed with fast-growing forest plantations and may inform policy and decision-making in areas experiencing a drying trend associated with climate change.     

Forestal Arauco experimental research catchments; daily rainfall-runoff for 10 catchments with different forest types in Central-Southern Chile

Forestal Arauco (FA), a global manufacturer of forest products, manages more than 1 million ha of forest plantations and oversees the conservation of more than half a million hectares of native forest and vegetation in Brazil, Argentina and Chile. In 2008, FA responded to local concerns about the effect of plantations on water resources and commenced streamflow monitoring in catchments in the coastal range of central-southern Chile between 35° and 39° of latitude south. This data note presents an overview of daily streamflow and rainfall records for 10 small catchments (18–112 ha) from 2008 to 2018. The catchments are covered by three different forest types, namely native forest (2), pine plantations of different ages (6) and eucalypt plantations (2). All of these catchments share similar metamorphic geology. A 90° V notch weir was built at each catchment outlet and data collected at 5 min interval using a pressure transducer that was calibrated monthly. The dataset is part of a research programme aiming to improve our understanding about the role of forest plantations on water balance at a stand and catchment level. It also includes the rainfall data from these catchments estimated using a combination of local rain gauges and data from the longer term records of the Chilean Directorate of Water. This dataset can be used in hydrological modelling and in a wide range of research questions and water management issues regarding forest plantations in a Mediterranean climate.     

Streamflow response to Pinus plantation harvesting: Canobolas State forest,southeastern Australia

Streamflows were measured in two Pinus radiata plantation catchments and one native eucalypt forest catchment in Canobolas State forest from 1999 to 2007. In 2002/2003, clearfall harvesting of 43·2 and 40·3% of two plantation catchments occurred, respectively. Water yields increased by 54 mm (52%), 71 mm (35%) and 50 mm (19%) in the first three years post‐harvest in treated catchment A and by 103 mm (118%), 157 mm (82%) and 119 mm (48%) in treated catchment B relative to the native forest control catchment. In the fourth post‐harvest water year annual rainfall was only 488 mm, which resulted in negligible run‐off in all catchments, regardless of forest cover. In both plantation catchments, monthly streamflows increased significantly (p = 0·01, p < 0·001) due to a significant increase in baseflows (p < 0·001) after harvesting. Monthly stormflows were not significantly affected by harvesting. Flow duration curve analyses indicated a variable response between the two plantation catchments. Treated catchment A was converted from an ephemeral stream flowing 42% of the time pre‐harvest to a temporary stream flowing 82% of the time post‐harvest. These changes occurred throughout all seasons of the year but were most pronounced during summer and autumn when baseflows were maintained post‐harvest but were not observed under native forest or mature pine plantations. By contrast, flow duration increased in treated catchment B from 12% of the time pre‐harvest to 38% of the time post‐harvest with the greatest changes measured during the winter and spring months when streamflow would normally occur under native forest conditions. These observations have important implications for the development of models of plantation water use to be utilized in water resource planning in Australia. Copyright © 2009 John Wiley & Sons, Ltd.     

A comparison of streamflow,salt and water balances in adjacent farmland and forest catchments in south‐western Victoria,Australia

A study of the hydrologic effects of catchment change from pasture to plantation was carried out in Gatum, south‐western Victoria, Australia. This study describes the hydrologic characteristics of two adjacent catchments: one with 97% grassland and the other one with 62% Eucalyptus globulus plantations. Streamflow from both catchments was intermittent during the 20‐month study period. Monthly streamflow was always greater in the pasture‐dominated catchment compared with the plantation catchment because of lower evapotranspiration in the pasture‐based catchment. This difference in streamflow was also observed even during summer 2010/2011 when precipitation was 74% above average (1954–2012) summer rainfall. Streamflow peaks in the plantation‐based catchment were smaller than in the pasture‐dominated system. Flow duration curves show differences between the pasture and plantation‐dominated catchments and affect both high‐flow and low‐flow periods. Groundwater levels fell (up to 4.4 m) in the plantation catchment during the study period but rose (up to 3.2 m) in the pasture catchment. Higher evapotranspiration in the plantation catchment resulted in falling groundwater levels and greater disconnection of the groundwater system from the stream, resulting in lower baseflow contribution to streamflow. Salt export from each catchment increases with increasing flow and is higher at the pasture catchment, mainly because of the higher flow. Reduced salt loading to streams due to tree planting is generally considered environmentally beneficial in saline areas of south‐eastern Australia, but this benefit is offset by reduced total streamflow. Copyright © 2014 John Wiley & Sons, Ltd.     

Comparison of streamflow recession between plantations and native forests in small catchments in Central-Southern Chile

In central Chile, many communities rely on water obtained from small catchments in the coastal mountains. Water security for these communities is most vulnerable during the summer dry season and, from 2010 to 2017, rainfall during the dry season was between 20% and 40% below the long-term average. The rate of decrease in stream flow after a rainfall event is a good measure of the risk of flow decreasing below a critical threshold. This risk of low flow can be quantified using a recession coefficient (α) that is the slope of an exponential decay function relating flow to time since rainfall. A mathematical model was used to estimate the recession coefficient (α) for 142 rainstorm events (64 in summer; 78 in winter) in eight monitored catchments between 2008 and 2017. These catchments all have a similar geology and extend from 35 to 39 degrees of latitude south in the coastal range of south-central Chile. A hierarchical cluster analysis was used to test for differences between the mean value of α for different regions and forest types in winter and summer. The value of α did not differ (p < 0.05) between catchments in winter. Some differences were observed during summer and these were attributed to morphological differences between catchments and, in the northernmost catchments, the effect of land cover (native forest and plantation). Moreover, α for catchments with native forest was similar to those with pine plantations, although there was no difference (p < 0.05) between these and Eucalyptus plantations. The recession constant is a well-established method for understanding the effect of climate and disturbance on low flows and baseflows and can enhance local and regional analyses of hydrological processes. Understanding the recession of flow after rainfall in small headwater catchments, especially during summer, is vital for water resources management in areas where the establishment of plantations has occurred in a drying climate.     

Hydrology and related changes after harvesting native forest catchments and establishing pinus radiata plantations. Part 2. The native forest water balance and changes in streamflow after harvesting

Six small, steep, south-west facing catchments (1.63–4.62 ha) have been monitored in Westland, New Zealand since 1974. Two catchments were retained in native mixed evergreen forest and the rest were subjected to various harvesting and land preparation techniques before being planted with Pinus radiata between 1977 and 1980. The 11-year water balance for the native forest catchments was: rain = streamflow + interception loss + transpiration + seepage (2370mm = 1290mm + 620mm + 360mm + 100mm). In the year after treatment streamflow generally increased by 200–250 mm, except for one treatment (clearfelling, herbicide application, no riparian reserve) where the increase was 550 mm. The catchments were planted with Pinus radiata, but rapid colonization by bracken (Pteridium esculentum) and Himalayan honeysuckle (Leycesteria formosa) led to a rapid decline in streamflow, which returned to pre-treatment levels after an average of about five years. Streamflow yields then continued to decline for another two to three years before stabilizing at a level about 250mm yr^?1 lower than pre-treatment levels. At this time the catchments had a dense bracken/honeysuckle understorey beneath 5 m tall pine trees.     

Jonkershoek: Africa's oldest catchment experiment - 80 years and counting

The Jonkershoek Forestry Research Station was established in the Mediterranean climate region of South Africa in 1935 to implement a multiple catchment experiment to determine the effects of afforestation on water yield. The experiment consists of six neighbouring catchments previously supporting indigenous fynbos shrublands, five of which were sequentially afforested with Pinus radiata plantations every 8 years from 1940 to 1980 and one kept as the control. They conclusively demonstrated a significant impact of afforestation on streamflow. The treatment catchments have seen subsequent plantation rotations since 1980 and rainfall and streamflow observations have been continued to date. Here we describe the site, experimental design, rainfall and streamflow records, instrumentation, and how to access the data. We also provide details of recently installed instrumentation, including full weather stations, fog gauges, and an eddy covariance flux tower. The Jonkershoek catchment experiment was the core of a globally significant interdisciplinary research programme (1935–1992) that shaped most environmental policies and practices relating to biodiversity, forestry, fire and water in South Africa and beyond. The South African Environmental Observation Network (SAEON) inherited the experiment in 2010 and is maintaining it as a long-term eco-hydrological research platform and global change observatory.     

The effects of topography and forest management on water storage in catchments in south‐central Chile

Our work analyses the intra‐annual variability of the volume of water stored in 15 forested headwater catchments from south‐central Chile, aiming at understanding how forest management, hydrology, and climate influence the dynamic components of catchment storage. Thus, we address the following questions: (a) How does the annual water storage vary in catchments located in diverse hydroclimatic conditions and subject to variable forest management? (b) Which natural (i.e., hydrologic regime and physiographic setting) and anthropogenic factors explain the variance in water storage? Results show that the annual catchment storage increases at the beginning of each hydrological year in direct response to increases in rainfall. The maximum water storage ranges from 666 to 1,272 mm in these catchments. The catchments with Pinus or Eucalyptus spp. cover store less water than the catchments with mixed forest species cover. Forest cover (biomass volume, plantation density, and percentage of plantation and age) has the primary control on dynamic storage in all catchments. These results indicate that forest management may alter the catchment water storage.     

Effect of catchment properties on runoff coefficient in a karst area of southwest China

Frequent human activities and climate change in the karst region of southwest China since the 1950s have led to the investigation of response of runoff to climate and catchment properties. Runoff coefficient (Rc) as an expression variable of the catchment response to rainfall is important to describe runoff dynamics and to estimate available streamflow for utilization. In this study, the equations of Rc associated with its attributors of climate condition and catchment property were derived using the Budyko framework. The equations were used to estimate relationship between the Rc and the attributors in the karst catchments in Guizhou province of southwest China. Analysis in the selected 23 karst catchments demonstrates that the spatial distribution of Rc is dominated by the catchment properties, such as the catchment properties of geology, slope and land use and land cover, rather than climate condition of drought index. Correlation analysis indicates that the catchment with a large slope usually has a high value of Rc, and a large proportion of carbonate rock in a catchment reduces Rc in the study area. Temporal increasing trend of Rc during 1961–2000 was found for most catchments in the study area. This increasing trend was primarily resulted from changes of catchment properties, e.g. deforestation in large areas of Guizhou province during the 1950s–1980s. Copyright © 2013 John Wiley & Sons, Ltd.     

Runoff and peak flow responses to timber harvest and forest age in southern Chile

Runoff and peak flows in three experimental catchments with different forest conditions were analysed in a rainy temperate climate in southern Chile. The hydrological effects of clearcutting a Pinus radiata plantation covering 79·4% of the La Reina catchment were studied by analysing runoff and peak flows in the pre‐ and post‐harvesting periods. Mean annual runoff increased 110% after timber harvesting. Clearcutting generated a 32% mean increase in peak flows. Peak flow and runoff were examined in two adjacent catchments with different forest conditions. The older plantation in Los Ulmos 1 increasingly consumed more water than the younger plantation established at Los Ulmos 2, whereas differences in peak flows between these two catchments were not significant. Runoff and peak flows comparisons not only reflected changes in forest cover, but also the effect of rainfall characteristics during the study periods and the basins' morphologies. Comparisons between pre‐ and post‐harvesting peak discharges must be undertaken with caution, because a previous analysis at La Reina using a partial set of data overestimated changes in peak flows after timber harvesting. Copyright © 2005 John Wiley & Sons, Ltd.     

Effects of land-use changes on structural characteristics of tropical high-altitude Andean headwater streams

Streams are usually susceptible to land-use change, mainly in the tropics due to high dynamic climatic conditions. Native forests have been converted for agricultural purposes with significantly impacts in streams. Nowadays, forests plantations are taking place of some degraded land and its influence in headwater streams are not well understood in tropical high-altitude streams. Thus, this study aims to assess effects of land-use changes from pasture to Eucalyptus plantations in Colombian Andean catchments on stream water conditions and structural characteristics of stream channels. The study was conducted in three catchments, one catchment covered by pasture, one catchment that was converted from pasture to Eucalyptus plantations in 1995 and one pristine catchment with native forest cover. Physical, chemical and biological conditions of stream water were assessed by measurements of water temperature, concentration of dissolved oxygen and chlorophyll-a content of epiphytic communities. The structural characteristics of stream channels were evaluated using a visual-based habitat assessment protocol from the United States Environmental Protection Agency. Principal Component Analysis (PCA) showed native forest and Eucalyptus plantations catchments associated with stream conservation characteristics and pasture catchment with overall degraded conditions. However, the Permutational multivariate analysis of variance (PERMANOVA) showed significant differences between all streams indicating that, despite the overall positive conservation aspects of native and Eucalyptus catchments, their still different from each other. Pasture catchment showed the highest values for temperature and chlorophyll-a, and the lowest values for dissolved oxygen and final score for structural characteristics. Therefore, our results demonstrated that the land-use change from pasture to Eucalyptus plantation improved the stream water conditions and the structural characteristics of the studied headwater streams. Additionally, we propose the use of the rapid bioassessment protocol coupled some stream water characteristics as a rapid and useful tool for detecting effects of land-use changes on high-altitude Andean streams.     

Estimating impacts of wildfire and climate variability on streamflow in Victoria,Australia

Wildfires are common in Australia and can cause vegetation loss and affect hydrological processes such as interception, evapotranspiration, soil water storage and streamflow. This study investigates wildfire impacts on catchment mean annual streamflow for 14 Australian catchments that have been severely impacted by the 2009 Victoria wildfire, the second-worst wildfire disaster in Australia. A statistical approach based on sensitivity coefficients was used for quantifying the climate variability impacts on streamflow and the time trend analysis method was used to estimate the annual streamflow changes due to wildfire respectively. Our results show that wildfire has caused a noticeable increase in mean annual streamflow in the catchments with a burnt area above 70% for an immediate post-wildfire period (2009–2015) and the wildfire impact on streamflow is evidently larger than the climate change impact in the majority of burnt catchments. Furthermore, the wildfire impact on mean annual streamflow strongly increases with the burnt percentage area, indicated by R² = 0.73 between the two. The results also illustrate that catchments with high burnt percentage areas can have more potential to gain increased streamflow due to wildfires compared with that due to climate variability and can have significant streamflow change after wildfires above the 70% threshold of burnt area. These results provide evidence for evaluating large-scale wildfire impact on streamflow at small to medium-sized catchments, and guidance for process-based hydrological models for simulating wildfire impacts on hydrological processes for the immediate period after the wildfire.     

Estimation of rainfall elasticity of streamflow in Australia

Abstract

Estimates of rainfall elasticity of streamflow in 219 catchments across Australia are presented. The rainfall elasticity of streamflow is defined here as the proportional change in mean annual streamflow divided by the proportional change in mean annual rainfall. The elasticity is therefore a simple estimate of the sensitivity of long-term streamflow to changes in long-term rainfall, and is particularly useful as an initial estimate of climate change impact in land and water resources projects. The rainfall elasticity of streamflow is estimated here using a hydrological modelling approach and a nonparametric estimator. The results indicate that the rainfall elasticity of streamflow (? _P ) in Australia is about 2.0–3.5 (observed in about 70% of the catchments), that is, a 1% change in mean annual rainfall results in a 2.0–3.5% change in mean annual streamflow. The rainfall elasticity of streamflow is strongly correlated to runoff coefficient and mean annual rainfall and streamflow, where streamflow is more sensitive to rainfall in drier catchments, and those with low runoff coefficients. There is a clear relation-ship between the ? _P values estimated using the hydrological modelling approach and those estimated using the nonparametric estimator for the 219 catchments, although the values estimated by the hydrological modelling approach are, on average, slightly higher. The modelling approach is useful where a detailed study is required and where there are sufficient data to reliably develop and calibrate a hydrological model. The nonparametric estimator is useful where consistent estimates of the sensitivity of long-term streamflow to climate are required, because it is simple to use and estimates the elasticity directly from the historical data. The nonparametric method, being model independent, can also be easily applied in comparative studies to data sets from many catchments across large regions.     

Quantifying the effects of Eucalyptus plantations and management on water resources at plot and catchment scales

Our aim was to quantify the effects of forest plantation and management (clear cut or 30% partial harvest) in relation to pasture, on catchment discharge in southeast Rio Grande do Sul state, Brazil. A paired‐catchment approach was implemented in two regions (Eldorado do Sul and São Gabriel municipalities) where discharge was measured for 4 years at three catchments in each region, two of which were predominantly eucalypt plantation (mainly Eucalyptus saligna, rotation of approximately 7–9 years) with native forest and grass in streamside zones. The third catchment was covered with grazed pasture. Weather, soils, canopy interception, groundwater level, tree growth, and leaf area index were also measured. The 3‐PG process‐based forest productivity model was adapted to predict spatial daily plantation and pasture water balance including precipitation interception, soil evaporation, transpiration, soil moisture, drainage, discharge, and monthly plantation growth. The TOPMODEL framework was used to simulate water pools and fluxes in the catchments. Discharge was higher under pasture than pre‐harvesting plantation and increased for 1–2 years after complete plantation harvest; this change was less pronounced in the catchments under partial harvest. The ratio of discharge to precipitation before harvesting varied from 7% to 13% in the eucalypt catchments and 28% to 29% under pasture. The ratio increases to 23–24% after total harvest, and to 17% after partial harvesting. The ratio under pasture also increases during this period (to 32–44%) owing to increased precipitation. The baseflow, in relation to total discharge, varied from 28% to 62% under Eucalyptus and from 38% to 43% in the pasture catchments. Hence, eucalypt plantations in these regions can be expected to influence discharge regimes when compared with pasture land use, and modelling suggests that partial harvesting would moderate the magnitude of discharge variation compared with a full catchment plantation harvesting. The model efficiency coefficient (Nash–Sutcliffe model efficiency coefficient) varied from 0.665 to 0.799 for the total period of the study. Simulation of alternative harvesting scenarios suggested that at least 20% of the catchment planted area must be harvested to increase discharge. This model could be a useful practical tool in various plantation forestry contexts around the world. Copyright © 2016 John Wiley & Sons, Ltd.     

Bedrock geology controls on catchment storage,mixing, and release: A comparative analysis of 16 nested catchments

The bedrock controls on catchment mixing, storage, and release have been actively studied in recent years. However, it has been difficult to find neighbouring catchments with sufficiently different and clean expressions of geology to do comparative analysis. Here, we present new data for 16 nested catchments (0.45 to 410 km²) in the Alzette River basin (Luxembourg) that span a range of clean and mixed expressions of schists, phyllites, sandstones, and quartzites to quantify the relationships between bedrock permeability and metrics of water storage and release. We examined 9 years' worth of precipitation and discharge data, and 6 years of fortnightly stable isotope data in streamflow, to explore how bedrock permeability controls (a) streamflow regime metrics, (b) catchment storage, and (c) isotope response and catchment mean transit time (MTT). We used annual and winter precipitation–run‐off ratios, as well as average summer and winter precipitation–run‐off ratios to characterise the streamflow regime in our 16 study catchments. Catchment storage was then used as a metric for catchment comparison. Water mixing potential of 11 catchments was quantified via the standard deviation in streamflow δD (σδD) and the amplitude ratio (A_S/A_P) of annual cycles of δ¹⁸O in streamflow and precipitation. Catchment MTT values were estimated via both stable isotope signature damping and hydraulic turnover calculations. In our 16 nested catchments, the variance in ratios of summer versus winter average run‐off was best explained by bedrock permeability. Whereas active storage (defined here as a measure of the observed maximum interannual variability in catchment storage) ranged from 107 to 373 mm, total catchment storage (defined as the maximum catchment storage connected to the stream network) extended up to ~1700 mm (±200 mm). Catchment bedrock permeability was strongly correlated with mixing proxies of σδD in streamflow and δ¹⁸O A_S/A_P ratios. Catchment MTT values ranged from 0.5 to 2 years, based on stable isotope signature damping, and from 0.5 to 10 years, based on hydraulic turnover.     

Long-term impacts of forest treatments on water yield: a summary for northeastern USA

Long-term changes in annual water yield are summarized and compared for 11 catchment studies in the northeastern USA. Substantial increases in water yield of up to 350 mm year⁻¹ were obtained in the first year by clearing forest vegetation and controlling regrowth with herbicides. Commercial clearcutting with natural regrowth resulted in initial increases in water yield of 110–250 mm year⁻¹. This range in response was due to differences in precipitation and configuration of cuttings. Unless regrowth was controlled with herbicides, yield increases declined quickly after cutting, seldom persisting for more than 10 years. However, yield increases were readily extended over 20 years or more with intermediate cuttings and/or repeated control of regrowth with herbicides. Nearly all increases in water yield occur during the growing season as augmentation of baseflow. Changes in species composition after forest cutting on several study catchments eventually resulted in decreased water yields compared with those from uncut, control catchments. Results are discussed in terms of implications for surface water supplies, global climate change, nutrient cycling, hydrological modeling, and long-term research.     

Some factors affecting water yield from mountain ash (Eucalyptus regnans) dominated forests in south-east Australia

An experiment in mountain ash forests in Melbourne's water supply catchments in south-east Australia investigated the impact on long-term water yield of reducing forest density. Fifty-four per cent of basal area was removed from a 17 ha catchment (Black Spur 1) by patch cutting, and the patches were regenerated with mountain ash. A 50% reduction was implemented in Black Spur 3, an 8 ha catchment, through uniform thinning. Uniform thinning was shown to be more effective in enhancing streamflow than patch cutting. A streamflow increase of 25–30% (130–150 mm year⁻¹) was observed after treatment in both catchments. Eleven years later, a treatment effect of 15% was still evident in the selectively thinned catchment (Black Spur 3), but the effect had completely decayed in the patch cut catchment (Black Spur 1).

Research by Melbourne Water has established that streamflow is significantly influenced by forest age. It is hypothesised that this relationship, and the observed decay after patch cutting in Black Spur 1, is largely the result of variation in transpiration. To study the relationship between forest age and transpiration in detail, sap velocity was measured over two summers in four mountain ash plots using the heat-pulse method. The trees on these plots were 50, 90, 150 and 230 years old. On days when measurements were made, the mean sap velocity was not significantly different in the 50-, 90- 230-year-old stands, but was significantly smaller by 14% in the 150-year-old stand. Overstorey sapwood area gradually decreased with plot age, and was 57% lower in the 230-year-old plot than in the 50-year-old plot. When combined with the sap velocity measurements, these data indicated that over the six warmest months of the year, transpiration in the 50-year-old plot was 190 mm more than in the 230-year-old plot. These results support a hypothesis that differences in streamflow between 50-year-old and 230-year-old mountain ash forest can largely be accounted for by differences in transpiration. Further heat-pulse studies in young regrowth and in thinned and unthinned 1939 regrowth will be needed if the streamflow changes in Black Spur 1 and Black Spur 3 are to be fully explained.     

Water yield issues in the jarrah forest of south-western Australia

The jarrah forest of south-western Australia produces little streamflow from moderate rainfall. Water yield from water supply catchments for Perth, Western Australia, are low, averaging 71 mm (7% of annual rainfall). The low water yields are attributed to the large soil water storage available for continuous use by the forest vegetation. A number of water yield studies in south-western Australia have examined the impact on water yield of land use practices including clearing for agricultural development, forest harvesting and regeneration, forest thinning and bauxite mining. A permanent reduction in forest cover by clearing for agriculture led to permanent increases of water yield of approximately 28% of annual rainfall in a high rainfall catchment. Thinning of a high rainfall catchment led to an increase in water yield of 20% of annual rainfall. However, it is not clear for how long the increased water yield will persist. Forest harvesting and regeneration have led to water yield increases of 16% of annual rainfall. The subsequent recovery of vegetation cover has led to water yields returning to pre-disturbance levels after an estimated 12–15 years. Bauxite mining of a high rainfall catchment led to a water yield increase of 8% of annual rainfall, followed by a return to pre-disturbance water yield after 12 years. The magnitude of specific streamflow generation mechanisms in small catchments subject to forest disturbance vary considerably, typically in a number of distinct stages. The presence of a permanent groundwater discharge area was shown to be instrumental in determining the magnitude of the streamflow response after forest disturbance. The long-term prognosis for water yield from areas subject to forest thinning, harvesting and regeneration, and bauxite mining are uncertain, owing to the complex interrelationship between vegetation cover, tree height and age, and catchment evapotranspiration. Management of the forest for water yield needs to acknowledge this complexity and evaluate forest management strategies both at the large catchment scale and at long time-scales. The extensive network of small catchment experiments, regional studies, process studies and catchment modelling at both the small and large scale, which are carried out in the jarrah forest, are all considered as integral components of the research to develop these management strategies to optimise water yield from the jarrah forest, without forfeiting other forest values.     

Long-term annual groundwater storage trends in Australian catchments

The period of direct groundwater storage measurements is often too short to allow reliable inferences of groundwater storage trends at catchment scales. However, as groundwater storage sustains low flows in catchments during dry periods, groundwater storage can also be estimated indirectly from daily streamflow based on hydraulic groundwater theory; this idea was applied herein to 17 selected Australian catchments to examine their long-term (half a century or longer) groundwater storage trends. On average, over past 45 years, groundwater storage exhibited negative trends in all the selected catchments, except in the Katherine River catchment located in the Northern Territory. These negative trends persisted over longer periods, close to 100 years in some catchments and the strongest decreasing trend of 0.241 mm per year was observed in the Barron River catchment in New South Wales. However, groundwater storage exhibited different trends over the different shorter periods. Thus, while during the period of 1997–2007, 15 out of the 17 catchments showed negative trends in groundwater storage, during the period of 1980–2000, 12 out of the 17 catchments exhibited positive trends in groundwater storage; this underscores the fact that record lengths of one or even two decades are inadequate to derive meaningful trends. Strong consistencies in the trends exist across most catchments, indicating that groundwater storage is affected by large-scale climate factors.     

Amplification of hydrological model uncertainties in projected climate simulations of the Upper Indus Basin: Does it matter where the water is coming from?

There is a growing appreciation of the uncertainties in the estimation of snow-melt and glacier-melt as a result of climate change in high elevation catchments. Through a detailed examination of three hydrological models in two catchments, and interpretation of results from previous studies, we observed that many variations in estimated streamflow could be explained by the selection of a best parameter set from the possible good model parameters. The importance of understanding changing glacial dynamics is critically important for our study areas in the Upper Indus Basin where Pakistan's policymakers are planning infrastructure to meet the future energy and water needs of hundreds of millions of people downstream. Yet, the effect of climate on glacial runoff and climate on snowmelt runoff is poorly understood. With the HBV model, for example, we estimated glacial melt as between 56% and 89% for the Hunza catchment. When rainfall was a scaled parameter, the models estimated glacial melt as between 20% and 100% of streamflow. These parameter sets produced wildly different projections of future climate for RCP8.5 scenarios in 2046–2075 compared to 1976–2005. Assuming no glacial shrinkage, for one climate projection, we found that the choice among good parameter sets resulted in projected values of future streamflow across a range from +54% to +125%. Parameter selection was the most significant source of uncertainty in the glaciated catchment and amplified climate model uncertainty, whereas climate model choice was more important in the rainfall dominated catchment. Although the study focuses on Pakistan, the overall conclusions are instructive for other similar regions in the world. We suggest that modellers of glaciated catchments should present results from at least the book-ends: models with low sensitivity to ice-melt and models with high sensitivity to ice-melt. This would reduce confusion among decision makers when they are faced with similar contrasting results.