Elsevier

Global Environmental Change

Volume 58, September 2019, 101938
Global Environmental Change

Insights from watershed simulations around the world: Watershed service-based restoration does not significantly enhance streamflow

https://doi.org/10.1016/j.gloenvcha.2019.101938Get rights and content

Highlights

  • Restoring <10% of a watershed, as in many programs, has minimal streamflow impact.

  • Streamflow changes are not related in a simple way to watershed characteristics.

  • Most watershed service programs should avoid promising large changes in streamflow.

Abstract

Increased water yield and baseflow and decreased peak flow are common goals of watershed service programs. However, is the forest management often used in such programs likely to provide these beneficial watershed services? Many watershed service investments such as water funds typically change less than 10% of watershed land cover. We simulate the effects of 10% forest-cover change on water yield, low flow, and high flow in hydrologic models of 29 watersheds around the world. The forest-cover changes considered are: forest restoration from degraded natural lands or agriculture, forest conversion to agriculture, and forest conversion to urban cover. We do not consider grassland restoration by removal of alien tree species from riparian zones, which does increase water yield and low flow. Forest restoration from locally-predominant agricultural land resulted in median loss in annual water yield of 1.4%. Forest restoration reduced low flow and high flow by ∼3%. After forest restoration, low flow increased in ∼25% of cases while high flow and water yield declined in nearly all cases. Development of forest to agriculture or urban cover resulted in a 1–2% median increase in water yield, a 0.25–1% increase in low flow, and a 5–7% increase in high flow. We show that hydrologic responses to forest cover changes are not linearly related to climate, physiography, initial land cover, nor a multitude of watershed characteristics in most cases. These results suggest that enhanced streamflow watershed services anticipated from forest restoration or conservation of 10% or less of a watershed are generally modest.

Introduction

Watershed services are a key driver of ecosystem service investments, and globally $24 billion was spent to protect, restore, and sustainably manage watersheds in 2016 (Bennett and Ruef, 2016; Brauman, 2015; Bremer et al., 2016). Water funds and similar programs have grown rapidly. In Latin America, there are now more than 40 water funds--payments for watershed service programs in which downstream stakeholders invest in upstream watershed management and hope to receive an improved water supply and other watershed services in return (Bremer et al., 2016). Watershed service programs in the U.S., China, Africa, and elsewhere (Bennett and Ruef, 2016; Melanson, 2014; The Nature Conservancy, 2019; Vogl et al., 2016) often include increased dry-season flow and water yield as primary objectives (Bennett and Carroll, 2014; Bremer et al., 2016; Zheng et al., 2016; Kang, personal communication). Afforestation and reforestation are key activities for 20% of programs, while sustainable forest management and landscape protection, including forest, comprise an additional 30% of program activities (Bennett and Carroll, 2014). Many programs target less than 10% of the watershed for restoration because of limited funds (e.g., Kroeger et al., 2017; Podolak et al., 2017; Vogl et al., 2016).

We note two large counterexamples. South Africa’s Working for Water program has removed alien tree species from more than 25,000 km2 in select watersheds to enhance water quantity by maintaining natural grasslands. These programs have been well-studied and have beneficial effects (Le Maitre et al., 2002; Preston et al., 2018; van Wilgen and Wannenburgh, 2016). China’s Sloping Land Conversion Program and Natural Forest Conservation Program conserve forest and reforest agricultural land to maintain water quality and reduce flooding, and have also been extensively studied (Liu et al., 2008; Ouyang et al., 2016).

However, few studies have focused on the effects of smaller watershed service programs on streamflow (e.g., Kareiva et al., 2011; Podolak et al., 2017) rather than water quality (Kroeger et al., 2017; McDonald and Shemie, 2014; Melanson, 2014; Podolak et al., 2017; Vogl et al., 2016). Success for such programs may require realizing promised streamflow changes even when other objectives include carbon, biodiversity, and poverty alleviation (Bremer et al., 2016, 2014a, 2014b; Brouwer et al., 2011; Goldman-Benner et al., 2012; Suyanto et al., 2007). Without those streamflow enhancements, such programs may incur significant reputational risk. Here we investigate whether there are significant impacts of such forest change on the desired outcomes of increased water yield and dry-season flow under realistic forest restoration or conservation to inform watershed service investments.

Many studies have used a paired-catchment approach to investigate the annual hydrologic response to afforestation, increasing native tree cover or introducing plantation monocultures of alien trees, or deforestation, removing alien trees or destroying natural forest. Such studies found that an increase in forest cover reduces annual water yield and a decrease in forest cover increases annual water yield (Bosch and Hewlett, 1982; Brown et al., 2005; Filoso et al., 2017; Sahin and Hall, 1996; Stednick, 1996; Whitehead and Robinson, 1993). However, the effects varied strongly across sites--water yield changes varied by more than 500 mm within the same vegetation type or for similar precipitation (Brown et al., 2005). The differences also vary over time, with deforestation sites trending back to the pre-treatment baseline as trees regrow (e.g., Baker, 1986), but the direction of change varying interanually (e.g., Brown, 1971; Clary et al., 1974). Forest changes in the riparian area have larger effects than those in the uplands in many cases (Everson et al., 2007; Scott, 1999; Scott et al., 2004). Studies suggest that we cannot statistically discriminate changes in water yield after forest change of less than 20% of the watershed area (Bosch and Hewlett, 1982; Stednick, 1996), but it may be feasible to predict the change in water yield for smaller land-cover change (Brown et al., 2005).

A few paired catchment studies investigate the highly variable changes in low flow after land-cover change. Brown et al. (2005) and Scott and Lesch (1997) found that afforestation decreased low flow by 10–90%. Ogden et al. (2013) and Price et al. (2011) found that forested watersheds had higher low flows than similar watersheds with land cover such as pasture and secondary forest. Biederman et al. (2015) found minimal changes in low flow after tree die-off. Agricultural and urban development have similarly complex effects on streamflow, with both water yield and low flow increasing or decreasing depending on conditions (Bhaskar et al., 2016; Grogan et al., 2017; Koelliker, 1998; McGrane, 2016; Mukherjee et al., 2018).

Instead of studying change in individual watersheds, catchment classification investigates the relationship between forest cover and hydrologic behavior by considering a larger number of watersheds relatively unaffected by humans. Globally, on average, tropical and temperate forested catchments have lower water yield than non-forested catchments in the same climate (Peel et al., 2010; Zhang et al., 2001). However, both Peel et al. (2010) and Zhang et al. (2001) show significant overlap in ET values for forests and non-forests in most conditions.

Hydrologic simulation is the primary alternative to experimental studies for assessing the effects of land-cover change on flow. These models allow controlled land-cover changes while holding other factors constant, but require significant simplifications, including to groundwater, riparian areas, and soil structure. Continuing work in hydrology seeks to address these shortcomings while remaining tractable (Bailey et al., 2016; Easton et al., 2008; Strauch and Volk, 2013; White et al., 2011). Despite these simplifications, hydrologic simulation with many models and across many sites has shown great promise and strong results for building understanding about the mechanisms and specific hydrologic responses to land-cover change (Khoi and Suetsugi, 2014a; Liang et al., 1994; Logsdon and Chaubey, 2013; Schoups et al., 2006; Somura et al., 2012; Strauch et al., 2013; Volk et al., 2010; Wada et al., 2011; Warburton et al., 2012; Zhang et al., 2015). However, no previous work has built a global understanding of the hydrologic response to forest change across the broad variety of climates, land covers, and geology from which people obtain important watershed services from a consistent modeling framework. This is key to answering the question addressed in this paper: Are there significant impacts of forest restoration and conservation as practiced by many watershed service programs on water quantity watershed services?

In this work we explore the streamflow effects of forest restoration and conservation based on hydrologic simulation of 29 site models from around the globe and different climate zones. For each site model, we analyze the effect of 10% land-cover change, an amount which 1) allows controlled comparison across sites, and 2) is in the upper range of land-cover change for which watershed service investments are typically made (Kroeger et al., 2017; Ma et al., 2016; Podolak et al., 2017; Vogl et al., 2016). We explore three land-cover change scenarios: “forest restoration”, in which degraded natural lands and agriculture are replaced by natural forest forest; “agricultural development”, in which forest is converted to agriculture; and “urban development” in which forest is converted to urban cover. The latter two scenarios may represent the inverse of forest conservation scenarios in many cases. We investigate whether hydrologic response to forest restoration and conservation is related to climate, physiography, initial or changed land cover, and other watershed characteristics.

Section snippets

Methods

We use a novel dataset of 29 watershed site models across global gradients in climate and land cover (Fig. 1), perform daily timestep hydrologic simulations before and after land-cover changes for each site, and explore the response to the scenarios across these gradients. Details on the watersheds are available in Appendix A.1 and the sites are described in Appendix A.2. The site models were collected from the published literature by contacting site-model authors and requesting their model

Results and discussion

We present the results in two steps. First, we describe the general pattern of land-cover change impacts on water yield, low flow and high flow in the watershed site models and then particular cases where land-cover changes had a greater effect on hydrologic response. Second, we review the results of the statistical tests and show that there are few linear dependencies of the hydrologic response on watershed characteristics, and some apparent non-linear relationships.

Other considerations

This work investigates the effects of forest restoration and conservation around the world. Though we specifically collected site models stratified by climate zone, and they include 6 continents, this collection of sites still under-samples South America, Australia, and Africa. We also note that in some places removing alien tree species to restore riparian grasslands likely would have effects opposite those discussed here (Le Maitre et al., 2002; Preston et al., 2018; van Wilgen and

Conclusions

We find that 10% forest-cover changes cause relatively little change in key water quantity watershed services based on simulated hydrologic responses of 29 watersheds distributed globally across climatic zones. Water yield changes due to forest changes, including both afforestation and deforestation representing the inverse of forest conservation, are typically limited, with a median magnitude of <1.5% given a 10% land-cover change representing forest restoration, or agricultural or urban

Acknowledgements

This work was supported in part by the National Science Foundation under grant ICER/EAR-1829999 to Stanford University as part of the Belmont Forum – Sustainable Urbanisation Global Initiative (SUGI)/Food-Water-Energy Nexus theme. Any opinions, findings, conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation. The authors also thank Stanford University's Department of Earth System Science for

References (130)

  • D.C. Fukunaga et al.

    Application of the SWAT hydrologic model to a tropical watershed at Brazil

    CATENA

    (2015)
  • M. Glavan et al.

    Water quality targets and maintenance of valued landscape character – experience in the Axe catchment, UK

    J. Enviro. Manag.

    (2012)
  • P.W. Keys et al.

    Approaching moisture recycling governance

    Glob. Environ. Chang. Part A

    (2017)
  • D.C. Le Maitre et al.

    Invasive alien trees and water resources in South Africa: case studies of the costs and benefits of management

    For. Ecol. Manage.

    (2002)
  • R.A. Logsdon et al.

    A quantitative approach to evaluating ecosystem services

    Ecol. Modell.

    (2013)
  • S. Ma et al.

    Valuation of ecosystem services to inform management of multiple-use landscapes

    Ecosyst. Serv.

    (2016)
  • J.E. Nash et al.

    River flow forecasting through conceptual models part I — a discussion of principles

    J. Hydrol. (Amst)

    (1970)
  • R. Niraula et al.

    Determining the importance of model calibration for forecasting absolute/relative changes in streamflow from LULC and climate changes

    J. Hydrol. (Amst)

    (2015)
  • K. Podolak et al.

    Informing watershed planning and policy in the Truckee River basin through stakeholder engagement, scenario development, and impact evaluation

    Environ. Sci. Policy

    (2017)
  • V. Sahin et al.

    The effects of afforestation and deforestation on water yields

    J. Hydrol. (Amst)

    (1996)
  • J.G. Arnold et al.

    Large area hydrologic modeling and assessment part I: model development

    J. Am. Water Resour. Assoc.

    (1998)
  • J.G. Arnold et al.

    New developments in the SWAT ecohydrology model

    21st Century Watershed Technology: Improving Water Quality and Environment Conference Proceedings

    (2010)
  • R.T. Bailey et al.

    Assessing regional-scale spatio-temporal patterns of groundwater–surface water interactions using a coupled SWAT-MODFLOW model

    Hydrol. Process.

    (2016)
  • M.B. Baker

    Effects of ponderosa pine treatments on water yield in Arizona

    Water Resour. Res.

    (1986)
  • A. Basilevsky

    Statistical Factor Analysis and Related Methods: Theory and Applications, Wiley Series in Probability and Mathematical Statistics

    (1994)
  • G. Bennett et al.

    Gaining Depth: State of Watershed Investment 2014

    (2014)
  • G. Bennett et al.

    Alliances for Green Infrastructure: State of Watershed Investment 2016, Ecosystem Marketplace

    (2016)
  • A.S. Bhaskar et al.

    Urban base flow with low impact development: urban base flow with low impact development

    Hydrol. Process.

    (2016)
  • J.A. Biederman et al.

    Recent tree die-off has little effect on streamflow in contrast to expected increases from historical studies

    Water Resour. Res.

    (2015)
  • K. Bieger et al.

    Using residual analysis, auto- and cross-correlations to identify key processes for the calibration of the SWAT model in a data scarce region

    Adv. Geosci.

    (2012)
  • K. Bieger et al.

    The impact of land use change in the Xiangxi Catchment (China) on water balance and sediment transport

    Reg. Environ. Change

    (2013)
  • K. Bieger et al.

    Simulation of streamflow and sediment with the soil and water assessment tool in a data scarce catchment in the three gorges region, China

    J. Enviro. Quality

    (2014)
  • K. Bieger et al.

    Detailed spatial analysis of SWAT-simulated surface runoff and sediment yield in a mountainous watershed in China

    Hydrol. Sci. J. Des Sci. Hydrol.

    (2015)
  • K.A. Brauman

    Hydrologic ecosystem services: linking ecohydrologic processes to human well-being in water research and watershed management

    WIREs Water

    (2015)
  • R. Brouwer et al.

    Meta-analysis of institutional-economic factors explaining the environmental performance of payments for watershed services

    Environ. Conserv.

    (2011)
  • H.E. Brown

    Evaluating watershed management alternatives

    J. Irr. Drainage Division

    (1971)
  • L.A. Bruijnzeel et al.

    Hydrometeorology of tropical montane cloud forests: emerging patterns

    Hydrol. Process.

    (2011)
  • W.P. Clary et al.

    Effects of Pinyon-Juniper Removal on Natural Resource Products and Uses in Arizona (Research Paper No. RM-128)

    (1974)
  • D. Ellison et al.

    On the forest cover-water yield debate: from demand- to supply-side thinking

    Glob. Chang. Biol.

    (2012)
  • L.E. Erban et al.

    Groundwater extraction, land subsidence, and sea-level rise in the Mekong Delta, Vietnam

    Environ. Res. Lett.

    (2014)
  • C.S. Everson et al.

    Effective Management of the Riparian Zone Vegetation to Significantly Reduce the Cost of Catchment Management and Enable Greater Productivity of Land Resources

    (2007)
  • D.L. Ficklin et al.

    Development and application of a hydroclimatological stream temperature model within the Soil and Water Assessment Tool

    Water Resour. Res.

    (2012)
  • D.L. Ficklin et al.

    Projections of 21st century sierra Nevada local hydrologic flow components using an ensemble of general circulation models

    J. Am. Water Resour. Assoc.

    (2012)
  • D.L. Ficklin et al.

    Effects of climate change on stream temperature, dissolved oxygen, and sediment concentration in the Sierra Nevada in California

    Water Resour. Res.

    (2013)
  • D.L. Ficklin et al.

    Effects of projected climate change on the hydrology in the Mono Lake Basin, California

    Climatic Change

    (2013)
  • S. Filoso et al.

    Impacts of forest restoration on water yield: a systematic review

    PLoS One

    (2017)
  • J. Friedman et al.

    Regularization paths for generalized linear models via coordinate descent

    J. Stat. Softw.

    (2010)
  • P.W. Gassman et al.

    The soil and water assessment tool: historical development, applications, and future research directions invited review series

    Am. Soc. Agri. Bio. Eng.

    (2007)
  • M. Glavan et al.

    Evaluation of river water quality simulations at a daily time step - experience with SWAT in the axe catchment, UK

    CLEAN - Soil, Air, Water

    (2011)
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