Assessing the effects of land cover and future climate conditions on the provision of hydrological services in a medium‐sized watershed of Portugal

The separated and combined effects of land‐cover scenarios and future climate on the provision of hydrological services were evaluated in Vez watershed, northern Portugal. Soil and Water Assessment Tool was calibrated against daily discharge, sediments and nitrates, with good agreements between model predictions and field observations. Four hypothetical land‐cover scenarios were applied under current climate conditions (eucalyptus/pine, oak, agriculture/vine and low vegetation). A statistical downscaling of four General Circulation Models, bias‐corrected with ground observations, was carried out for 2021–2040 and 2041–2060, using representative concentration pathway 4.5 scenario. Also, the combined effects of future climate conditions were evaluated under eucalyptus/pine and agriculture/vine scenario. Results for land cover revealed that eucalyptus/pine scenario reduced by 7% the annual water quantity and up to 17% in the summer period. Although climate change has only a modest effect on the reduction of the total annual discharge (?7%), the effect on the water levels during summer was more pronounced, between ?15% and ?38%. This study shows that climate change can affect the provision of hydrological services by reducing dry season flows and by increasing flood risks during the wet months. Regarding the combined effects, future climate may reduce the low flows, which can be aggravated with eucalyptus/pine scenario. In turn, peak flows and soil erosion can be offset. Future climate may increase soil erosion and nitrate concentration, which can be aggravated with agriculture scenario. Results moreover emphasize the need to consider both climate and land‐cover impacts in adaptation and land management options at the watershed scale. Copyright © 2015 John Wiley & Sons, Ltd.     

Identifying separate impacts of climate and land use/cover change on hydrological processes in upper stream of Heihe River,Northwest China

Climate change and land use/cover change (LUCC) are two factors that produce major impacts on hydrological processes. Understanding and quantifying their respective influence is of great importance for water resources management and socioeconomic activities as well as policy and planning for sustainable development. In this study, the Soil and Water Assessment Tool (SWAT) was calibrated and validated in upper stream of the Heihe River in Northwest China. The reliability of the SWAT model was corroborated in terms of the Nash–Sutcliffe efficiency (NSE), the correlation coefficient (R), and the relative bias error (BIAS). The findings proposed a new method employing statistical separation procedures using a physically based modeling system for identifying the individual impacts of climate change and LUCC on hydrology processes, in particular on the aspects of runoff and evapotranspiration (ET). The results confirmed that SWAT was a powerful and accurate model for diagnosis of a key challenge facing the Heihe River Basin. The model assessment metrics, NSE, R, and BIAS, in the data were 0.91%, 0.95%, and 1.14%, respectively, for the calibration period and 0.90%, 0.96%, and ?0.15%, respectively, for the validation period. An assessment of climate change possibility showed that precipitation, runoff, and air temperature exhibited upward trends with a rate of 15.7 mm, 6.1 mm, and 0.38 °C per decade for the 1980 to 2010 period, respectively. Evaluation of LUCC showed that the changes in growth of vegetation, including forestland, grassland, and the shrub area have increased gradually while the barren area has decreased. The integrated effects of LUCC and climate change increased runoff and ET values by 3.2% and 6.6% of the total runoff and ET, respectively. Climate change outweighed the impact of LUCC, thus showing respective increases in runoff and ET of about 107.3% and 81.2% of the total changes. The LUCC influence appeared to be modest by comparison and showed about ?7.3% and 18.8% changes relative to the totals, respectively. The increase in runoff caused by climate change factors is more than the offsetting decreases resulting from LUCC. The outcomes of this study show that the climate factors accounted for the notable effects more significantly than LUCC on hydrological processes in the upper stream of the Heihe River.     

Sensitivity of streamflow from a Himalayan catchment to plausible changes in land cover and climate

Global climate change will likely increase temperature and variation in precipitation in the Himalayas, modifying both supply of and demand for water. This study assesses combined impacts of land‐cover and climate changes on hydrological processes and a rainfall‐to‐streamflow buffer indicator of watershed function using the Soil Water Assessment Tool (SWAT) in Kejie watershed in the eastern Himalayas. The Hadley Centre Coupled Model Version 3 (HadCM3) was used for two Intergovernmental Panel on Climate Change (IPCC) emission scenarios (A2 and B2), for 2010–2099. Four land‐cover change scenarios increase forest, grassland, crops, or urban land use, respectively, reducing degraded land. The SWAT model predicted that downstream water resources will decrease in the short term but increase in the long term. Afforestation and expansion in cropland will probably increase actual evapotranspiration (ET) and reduce annual streamflow but will also, through increased infiltration, reduce the overland flow component of streamflow and increase groundwater release. An expansion in grassland will decrease actual ET, increase annual streamflow and groundwater release, while decreasing overland flow. Urbanization will result in increases in streamflow and overland flow and reductions in groundwater release and actual ET. Land‐cover change dominated over effects on streamflow of climate change in the short and middle terms. The predicted changes in buffer indicator for land‐use plus climate‐change scenarios reach up to 50% of the current (and future) range of inter‐annual variability. Copyright © 2010 John Wiley & Sons, Ltd.     

The responses of hydrological processes and sediment yield to land‐use and climate change in the Be River Catchment,Vietnam

In this study, we investigated the responses of hydrology and sediment yield with impacts of land‐use and climate change scenarios in the Be River Catchment, using the Soil and Water Assessment Tool (SWAT) hydrological model. The calibration and validation results indicated that the SWAT model is a powerful tool for simulating the impact of environmental change on hydrology and sediment yield in this catchment. The hydrologic and sediment yield responses to land‐use and climate changes were simulated based on the calibrated model. The results indicated that a 16.3% decrease in forest land is likely to increase streamflow (0.2 to 0.4%), sediment load (1.8 to 3.0%), and surface runoff (SURQ) (4.8 to 10.7%) and to decrease groundwater discharge (GW_Q) (3.5 to 7.9%). Climate change in the catchment leads to decreases in streamflow (0.7 to 6.9%) and GW_Q (3.0 to 8.4%), increase in evapotranspiration (0.5 to 2.9%), and changes in SURQ (?5.3 to 2.3%) and sediment load (?5.3 to 4.4%). The combined impacts of land‐use and climate changes decrease streamflow (2.0 to 3.9%) and GW_Q (12.3 to 14.0%), increase evapotranspiration (0.7 to 2.8%), SURQ (8.2 to 12.4%), and sediment load (2.0 to 7.9%). In general, the separate impacts of climate and land‐use changes on streamflow, sediment load, and water balance components are offset each other. However, SURQ and some component of subsurface flow are more sensitive to land‐use change than to climate change. Furthermore, the results emphasized water scarcity during the dry season and increased soil erosion during the wet season. Copyright © 2012 John Wiley & Sons, Ltd.     

Modelling hydrological response to different land‐use and climate change scenarios in the Zamu River basin of northwest China

Changes in climate and land use can significantly influence the hydrological cycle and hence affect water resources. Understanding the impacts of climate and land‐use changes on streamflow can facilitate development of sustainable water resources strategies. This study investigates the flow variation of the Zamu River, an inland river in the arid area of northwest China, using the Soil and Water Assessment Tool distributed hydrological model. Three different land‐use and climate‐change scenarios were considered on the basis of measured climate data and land‐use cover, and then these data were input into the hydrological model. Based on the sensitivity analysis, model calibration and verification, the hydrological response to different land‐use and climate‐change scenarios was simulated. The results indicate that the runoff varied with different land‐use type, and the runoff of the mountain reaches of the catchment increased when grassland area increased and forestland decreased. The simulated runoff increased with increased precipitation, but the mean temperature increase decreased the runoff under the same precipitation condition. Application of grey correlation analysis showed that precipitation and temperature play a critical role in the runoff of the Zamu River basin. Sensitivity analysis of runoff to precipitation and temperature by considering the 1990s land use and climate conditions was also undertaken. Copyright © 2007 John Wiley & Sons, Ltd.     

Individual and combined effects of land use/cover and climate change on Wolf Bay watershed streamflow in southern Alabama

Land use/cover (LULC) and climate change are two main factors affecting watershed hydrology. In this paper, individual and combined impacts of LULC and climate change on hydrologic processes were analysed applying the model Soil and Water Assessment Tool in a coastal Alabama watershed in USA. Temporally and spatially downscaled Global Circulation Model outputs predict a slight increase in precipitation in the study area, which is also projected to experience substantial urban growth in the future. Changes in flow frequency and volume in the 2030s (2016–2040) compared to a baseline period (1984–2008) at daily, monthly and annual time scales were explored. A redistribution of daily streamflow is projected when either climate or LULC change was considered. High flows are predicted to increase, while low flows are expected to decrease. Combined change effect results in a more noticeable and uneven distribution of daily streamflow. Monthly average streamflow and surface runoff are projected to increase in spring and winter, but especially in fall. LULC change does not have a significant effect on monthly average streamflow, but the change affects partitioning of streamflow, causing higher surface runoff and lower baseflow. The combined effect leads to a dramatic increase in monthly average streamflow with a stronger increasing trend in surface runoff and decreasing trend in baseflow. Copyright © 2013 John Wiley & Sons, Ltd.     

Evaluating relative sensitivity of SWAT‐simulated nitrogen discharge to projected climate and land cover changes for two watersheds in North Carolina,USA

We investigated how projected changes in land cover and climate affected simulated nitrate (NO₃^?) and organic nitrogen discharge for two watersheds within the Neuse River Basin, North Carolina, USA, for years 2010–2070. We applied the Soil and Water Assessment Tool watershed model to predict nitrogen discharge using (1) atmospheric carbon dioxide (CO₂) concentrations predicted by the Intergovernmental Panel on Climate Change, (2) land cover change predicted by the Integrated Climate and Land Use Change project and (3) precipitation and temperature simulated by two statistically downscaled and bias‐corrected Global Circulation Models. We determined the sensitivity of simulated nitrogen discharge to separate changes in each treatment [(1) CO₂, (2) land cover and (3) precipitation and temperature (PT)] by comparing each treatment to a reference condition. Results showed that nitrogen discharges were most sensitive to changes in PT over the 60‐year simulation. Nitrogen discharges had similar sensitivities to the CO₂ and land cover treatments, which were only one‐tenth the influence of the PT treatment. Under the CO₂ treatment, nitrogen discharges increased with increasing ambient CO₂. NO₃^? discharge decreased with increased urbanization; however, organic nitrogen had a varied response. Under the PT treatment, there was high spatial variability in nitrogen discharges. In a single year, certain sub‐basins showed an 80% increase in nitrogen discharge relative to reference, while others showed a 400% decrease. With nitrogen discharge showing high sensitivity to PT change, we suggest that more emphasis should be placed on investigating impacts of PT on nutrient transport in the Neuse River Basin. Published 2015. This article is a U.S. Government work and is in the public domain in the USA     

Effects of land‐use changes on hydrological processes in the middle basin of the Heihe River,northwest China

The effects of land‐use changes on the runoff process in the midstream plain of this arid inland river basin are a key factor in the rational allocation of water resources to the middle and lower reaches. The question is whether and by how much increasingly heavy land use impacts the hydrological processes in such an arid inland river basin. The catchment of the Heihe River, one of the largest inland rivers in the arid region of northwest China, was chosen to investigate the hydrological responses to land‐use change. Flow duration curves were used to detect trends and variations in runoff between the upper and lower reaches. Relationships among precipitation, upstream runoff, and hydrological variables were identified to distinguish the effects of climatic changes and upstream runoff changes on middle and downstream runoff processes. The quantitative relation between midstream cultivated land use and various parameters of downstream runoff processes were analysed using the four periods of land‐use data since 1956. The Volterra numerical function relation of the hydrological non‐linear system response was utilized to develop a multifactor hydrological response simulation model based on the three factors of precipitation, upstream runoff, and cultivated land area. The results showed that, since 1967, the medium‐ and high‐coverage natural grassland area in the midstream region has decreased by 80·1%, and the downstream runoff has declined by 27·32% due to the continuous expansion of the cultivated land area. The contribution of cultivated land expansion to the impact on the annual total runoff is 14–31%, on the annual, spring and winter base flow it is 44–75%, and on spring and winter discharge it is 23–64%. Once the water conservation plan dominated by land‐use structural adjustments is implemented over the next 5 years, the mean annual discharge in the lower reach could increase by 8·98% and the spring discharge by 26·28%. This will significantly alleviate the imbalance between water supply and demand in both its quantity and temporal distribution in the middle and lower reaches. Copyright © 2006 John Wiley & Sons, Ltd.     

Responses of hydrological processes to climate change in the Yarlung Zangbo River basin

ABSTRACT

Climate change alters hydrological processes and results in more extreme hydrological events, e.g. flooding and drought, which threaten human livelihoods. In this study, the large-scale distributed variable infiltration capacity (VIC) model was used to simulate future hydrological processes in the Yarlung Zangbo River basin (YZRB), China, with a combination of the CMIP5 (Coupled Model Intercomparison Project, fifth phase) and MIROC5 (Model for Interdisciplinary Research on Climate, fifth version) datasets. The results indicate that the performance of the VIC model is suitable for the case study, and the variation in runoff is remarkably consistent with that of precipitation, which exhibits a decreasing trend for the period 2046–2060 and an increasing trend for 2086–2100. The seasonality of runoff is evident, and substantial increases are projected for spring runoff, which might result from the increase in precipitation as well as the increase in the warming-induced melting of snow, glaciers and frozen soil. Moreover, evapotranspiration exhibits an increase between 2006–2020 and 2046–2060 over the entire basin, and soil moisture decreases in upstream areas and increases in midstream and downstream areas. For 2086–2100, both evapotranspiration and soil moisture increase slightly in the upstream and midstream areas and decrease slightly in the downstream area. The findings of this study could provide references for runoff forecasting and ecological protection for similar studies in the future.     

Potential wind erosion rate response to climate and land‐use changes in the watershed of the Ningxia–Inner Mongolia reach of the Yellow River,China, 1986–2013

Climate and land‐use changes could strongly affect wind erosion and in turn cause a series of environmental problems. Thus, the objective of this study was to assess potential wind erosion rate (PWER) response to climate and land‐use changes in the watershed of the Ningxia–Inner Mongolia Reach of the Yellow River (NIMRYR), China. The watershed of NIMRYR suffers from serious wind erosion hazards, and over recent decades, wind erosion intensity and distribution has changed, following climate and land‐use changes. To understand these processes in the NIMRYR watershed, the Integrated Wind Erosion Modelling System (IWEMS) and the Revised Wind Erosion Equation (RWEQ) were used to calculate the PWER under different climate conditions and land‐use scenarios, and to assess the influences of climate and land‐use changes on the PWER. The results show the PWER in the whole watershed had a significant declining trend from 1986 to 2013. The results of the relationship among PWER, climate change, and land‐use changes showed that climate change was the dominant control on the PWER change in this watershed. Compared to the period 1986–1995, the average PWER decreased 23.32% and 64.98% as a result of climate change in the periods 1996–2005 and 2006–2013, respectively. In contrast with climate change, the effects of land‐use changes on the average PWER were much lower, and represented a change in PWER of less than 3.3% across the whole watershed. The study method we used could provide some valuable reference for wind erosion modelling, and the research results should help climate and land‐use researchers to develop strategies to reduce wind erosion. Copyright © 2017 John Wiley & Sons, Ltd.     

SWAT‐simulated hydrological impact of land‐use change in the Zanjanrood basin,Northwest Iran

Understanding the impacts of land‐use changes on hydrology at the watershed scale can facilitate development of sustainable water resource strategies. This paper investigates the hydrological effects of land‐use change in Zanjanrood basin, Iran. The water balance was simulated using the Soil and Water Assessment Tool (AVSWAT2000). Model calibration and uncertainty analysis were performed with sequential uncertainty fitting (SUFI‐2). Simulation results from January 1998 to December 2002 were used for parameter calibration, and then the model was validated for the period of January 2003 to December 2004. The predicted monthly streamflow matched the observed values: during calibration the correlation coefficient was 0·86 and the Nash–Sutcliffe coefficient 0·79, compared with 0·80 and 0·79, respectively, during validation. The model was used to simulate the main components of the hydrological cycle, in order to study the effects of land‐use changes in 1967, 1994 and 2007. The study reveals that during 1967 a 34·5% decrease of grassland with concurrent increases of shrubland (13·9%), rain‐fed agriculture (12·1%), bare ground (5·5%) irrigated agriculture (2·2%), and urban area (0·7%) led to a 33% increase in the amount of surface runoff and a 22% decrease in the groundwater recharge. Furthermore, the area of sub‐basins that was influenced by high runoff (14–28 mm) increased. The results indicate that the hydrological response to overgrazing and the replacing of rangelands (grassland and shrubland) with rain‐fed agriculture and bare ground (badlands) is nonlinear and exhibits a threshold effect. The runoff rises dramatically when more than 60% of the rangeland is removed. For groundwater this threshold lies at an 80% decrease in rangeland. Copyright © 2009 John Wiley & Sons, Ltd.     

Response of runoff to climate change in the Wei River basin,China

Abstract

Climate change will likely have severe effects on water shortages, flood disasters and the deterioration of aquatic systems. In this study, the hydrological response to climate change was assessed in the Wei River basin (WRB), China. The statistical downscaling method (SDSM) was used to downscale regional climate change scenarios on the basis of the outputs of three general circulation models (GCMs) and two emissions scenarios. Driven by these scenarios, the Soil and Water Assessment Tool (SWAT) was set up, calibrated and validated to assess the impact of climate change on hydrological processes of the WRB. The results showed that the average annual runoff in the periods 2046–2065 and 2081–2100 would increase by 12.4% and 45%, respectively, relative to the baseline period 1961–2008. Low flows would be much lower, while high flows would be much higher, which means there would be more extreme events of droughts and floods. The results exhibited consistency in the spatial distribution of runoff change under most scenarios, with decreased runoff in the upstream regions, and increases in the mid- and lower reaches of the WRB.

Editor Z.W. Kundzewicz; Associate editor D. Yang     

Effects of land‐cover changes on the hydrological response of interior Columbia River basin forested catchments

The topographically explicit distributed hydrology–soil–vegetation model (DHSVM) is used to simulate hydrological effects of changes in land cover for four catchments, ranging from 27 to 1033 km², within the Columbia River basin. Surface fluxes (stream flow and evapotranspiration) and state variables (soil moisture and snow water equivalent) corresponding to historical (1900) and current (1990) vegetation are compared. In addition a sensitivity analysis, where the catchments are covered entirely by conifers at different maturity stages, was conducted. In general, lower leaf‐area index (LAI) resulted in higher snow water equivalent, more stream flow and less evapotranspiration. Comparisons with the macroscale variable infiltration capacity (VIC) model, which parameterizes, rather than explicitly represents, topographic effects, show that runoff predicted by DHSVM is more sensitive to land‐cover changes than is runoff predicted by VIC. This is explained by model differences in soil parameters and evapotranspiration calculations, and by the more explicit representation of saturation excess in DHSVM and its higher sensitivity to LAI changes in the calculation of evapotranspiration. Copyright © 2002 John Wiley & Sons, Ltd.     

Effects of mid‐twenty‐first century climate and land cover change on the hydrology of the Puget Sound basin,Washington

The distributed hydrology–soil–vegetation model (DHSVM) was used to study the potential impacts of projected future land cover and climate change on the hydrology of the Puget Sound basin, Washington, in the mid‐twenty‐first century. A 60‐year climate model output, archived for the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4), was statistically downscaled and used as input to DHSVM. From the DHSVM output, we extracted multi‐decadal averages of seasonal streamflow, annual maximum flow, snow water equivalent (SWE), and evapotranspiration centred around 2030 and 2050. Future land cover was represented by a 2027 projection, which was extended to 2050, and DHSVM was run (with current climate) for these future land cover projections. In general, the climate change signal alone on sub‐basin streamflow was evidenced primarily through changes in the timing of winter and spring runoff, and slight increases in the annual runoff. Runoff changes in the uplands were attributable both to climate (increased winter precipitation, less snow) and land cover change (mostly reduced vegetation maturity). The most climatically sensitive parts of the uplands were in areas where the current winter precipitation is in the rain–snow transition zone. Changes in land cover were generally more important than climate change in the lowlands, where a substantial change to more urbanized land use and increased runoff was predicted. Both the annual total and seasonal distribution of freshwater flux to Puget Sound are more sensitive to climate change impacts than to land cover change, primarily because most of the runoff originates in the uplands. Both climate and land cover change slightly increase the annual freshwater flux to Puget Sound. Changes in the seasonal distribution of freshwater flux are mostly related to climate change, and consist of double‐digit increases in winter flows and decreases in summer and fall flows. Copyright © 2010 John Wiley & Sons, Ltd.     

Assessing sensitivity of hydrologic responses to climate change from forested watershed in Mississippi

The climatic processes such as changes in precipitation, temperature and atmospheric CO₂ concentration can intensify the effects on water resources. An assessment of the effects of long‐term climate change on water resources is essential to the development of water quality improvement programs. This study was conducted in the Upper Pearl River Watershed (UPRW) in east‐central Mississippi to assess the effects of long‐term potential future climate change on average mean monthly stream flow from the five spatially distributed U. S. Geological Survey (USGS) gage stations in the UPRW using the Soil and Water Assessment Tool. The model was calibrated (January 1981 to December 1994) and validated (January 1995 to September 2008) using monthly measured stream flow data. The calibrated and validated model determined good to very good performance for stream flow prediction (R² and E from 0·60 to 0·86) between measured and predicted stream flow values. The root mean square error values (from 14 to 37 m³ s^?1) were estimated at similar levels of errors during model calibration and validation. The results showed that long‐term (50 years) average monthly stream flow sensitivity due to climate change effects was found the greatest as a result of percentage change in the precipitation followed by carbon dioxide (CO₂) concentration and temperature. The long‐term model simulation scenarios as compared with the base scenario for all five spatially distributed USGS gage stations in the UPRW estimated an average monthly stream flow decrease (from 54 to 67%) and average monthly stream flow increase (from 67 to 79%) depending on the spatial characteristics of the USGS gage stations. Overall, the results indicate that the UPRW hydrology is very sensitive to potential future climate changes and that these changes could stimulate increased streamflow generation from the watershed. Copyright © 2010 John Wiley & Sons, Ltd.     

Long‐term hydrological response to reforestation in a large watershed in southeastern China

The long‐term hydrological response to reforestation is critical to regional water management, especially in areas where large‐scale reforestation has been practiced. In this study, we investigated the long‐term hydrological response to reforestation in the 579 km² basin in southeastern China through ground‐based monitoring of water yield, sedimentation, vegetation cover and climate in the basin. The vegetation dynamics were also examined by remote sensing data (MSS, Landsat and AVHRR NDVI). We found that forest cover increased 23% or 13 593 ha from 1975 to 2002. Meanwhile, annual water yield decreased 86–88 mm from 1971–1983 (i.e. pre‐reforestation) to 1984–2009 (i.e. post‐reforestation). These decreases were significant statistically according to both regression and double mass analyses. Time series analysis demonstrated that there was a clear decline in annual sediment yield and an increase in annual evapotranspiration (ET) over the period from 1971 to 2009. We concluded that reforestation could significantly reduce annual water yield and sediment yield in the basin because of the forest cover change and forest growth. This conclusion is consistent with findings from widely paired‐watershed studies and literatures published on the impact of reforestation in large watersheds. Our results also have important strategic implications and provide insight into more sustainable forest management practices for the future. Copyright © 2013 John Wiley & Sons, Ltd.     

Hydrological responses to climate shifts for a minimally disturbed mountainous watershed in northwestern China

Much attention has been focused on investigating the effects of precipitation and temperature changes on runoff; however, the influence of wind speed, relative humidity and total solar radiation on hydrological components needs to be studied further. Hydrological responses to climate variations in a minimally disturbed mountainous watershed in the period 1971–2012 are identified and evaluated by statistical analysis and hydrological simulation. The results indicate that the impact of climate component changes on the hydrological process cannot be discounted. The temperature and relative humidity exhibit significant upward trends, while the wind speed exhibits a clear downward trend. The potential and actual evapotranspiration dramatically increased, but the observed pan evaporation substantially decreased. The surface water, soil water, baseflow and water yield are positively correlated with precipitation and relative humidity but negatively correlated with the temperature, wind speed and solar radiation.     

Permafrost‐thaw‐induced land‐cover change in the Canadian subarctic: implications for water resources

Climate warming and human disturbance in north‐western Canada have been accompanied by degradation of permafrost, which introduces considerable uncertainty to the future availability of northern freshwater resources. This study demonstrates the rate and spatial pattern of permafrost loss in a region that typifies the southern boundary of permafrost. Remote‐sensing analysis of a 1·0 km² area indicates that permafrost occupied 0·70 km² in 1947 and decreased with time to 0·43 km² by 2008. Ground‐based measurements demonstrate the importance of horizontal heat flows in thawing discontinuous permafrost, and show that such thaw produces dramatic land‐cover changes that can alter basin runoff production in this region. A major challenge to northern water resources management in the twenty‐first century therefore lies in predicting stream flows dynamically in the context of widely occurring permafrost thaw. The need for appropriate water resource planning, mitigation, and adaptation strategies is explained. Copyright © 2010 John Wiley & Sons, Ltd.     

Modelling the impact of recent land‐cover changes on the stream flows in northeastern Puerto Rico

We investigated the influence of recent and future land‐cover changes on stream flow of a watershed northeastern Puerto Rico using hydrological modeling and simulation analysis. Monthly and average annual stream flows were compared between an agricultural period (1973–1980) and an urbanized/reforested period (1988–1995) using the revised Generalized Watershed Loading Function model. Our validated results show that a smaller proportion of rainfall became stream flows in the urbanized/forested period compared with the agricultural period, apparently because of reforestation. Sensitivity analysis of the model showed that evapotranspiration, precipitation, and curve number were the most significant factors influencing stream flow. Simulations of projected land‐cover scenarios indicate that annual stream flows would increase by 9·6% in a total urbanization scenario, decrease by 3·6% in a total reforestation scenario, and decrease by 1·1% if both reforestation and urbanization continue at their current rates to 2020. An imposed hurricane event that was similar in scale to the largest recent event on the three land‐cover scenarios would increase the daily stream flow by 62·1%, 68·4% and 67·1% respectively. Owing to the environmental setting of eastern Puerto Rico, where sea breezes caused by temperature differences between land surface and the ocean dominate the local climate, we suggest that managing local land‐cover changes can have important consequences for water management. Copyright © 2007 John Wiley & Sons, Ltd.     

Simulated impacts of climate change and land‐clearing on runoff from a small Sahelian catchment

In the Sahel, there are few long‐term data series available to estimate the climatic and anthropogenic impacts on runoff in small catchments. Since 1950, land clearing has enhanced runoff. The question is whether and by how much this anthropogenic effect offsets the current drought. To answer this question, a physically based distributed hydrological model was used to simulate runoff in a small Sahelian catchment in Niger, from the 1950–1998 rain‐series. The simulation was carried out for three soil surface states of the catchment (1950, 1975 and 1992). The catchment is characterized by an increase in cultivated land, with associated fallow, from 6% in 1950 to 56% in 1992, together with an increase in the extent of eroded land (from 7 to 16%), at the expense of the savanna. Effects of climate and land use are first analysed separately: irrespective of the land cover state, the simulated mean annual runoff decreases by about 40% from the wet period (1950–1969) to the dry period (1970–1998); calculated on the 1950–1998 rainfall‐series, the changes that occurred in land cover between 1950 and 1992 multiplies the mean annual runoff by a factor close to three. The analysis of a joint climatic and anthropogenic change shows that the transition from a wet period under a ‘natural’ land cover (1950) to a dry period under a cultivated land cover (1992) results in an increase in runoff of the order of 30 to 70%. At the scale of a small Sahelian catchment, the anthropogenic impact on runoff is probably more important than that of drought. This figure for relative increase in runoff contributions to ponds, preferential sites of seepage to groundwater, is less than that currently estimated for aquifer recharge, which has been causing a significant continuous water table rise over the same period. Copyright © 2004 John Wiley & Sons, Ltd.