Catalina Segura

Potential impacts of climate change on soil erosion vulnerability across the conterminous United States

Rainfall runoff erosivity (R) is one key climate factor that controls water erosion. Quantifying the effects of climate change–induced erosivity change is important for identifying critical regions prone to soil erosion under a changing environment. In this study we first evaluate the changes of R from 1970 to 2090 across the United States under nine climate conditions predicted by three general circulation models for three emissions scenarios (A2, A1B, and B1) from the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Then, we identify watersheds that are most vulnerable to future climate change in terms of soil erosion potential. We develop a novel approach to evaluate future trends of R magnitude and variance by incorporating both the rate of change with time as well as the level of agreement between climatic projections. Our results show that mean decadal R values would increase with time according to all nine climatic projections considered between 1970 and 2090. However, these trends vary widely spatially. In general, catchments in the northeastern and northwestern United States are characterized by strong increasing trends in R, while the trends in the midwestern and southwestern United States are either weak or inconsistent among the nine climatic projections considered. The northeastern and northwestern United States will likely experience a significant increase in annual variability of R (i.e., increase in extreme events). Conversely the variability of R is unlikely to change in large areas of the Midwest. At the watershed scale (8-digit Hydrologic Unit Code), the mean vulnerability to erosion scores vary between −0.12 and 0.35 with a mean of 0.04. The five hydrologic regions with the highest mean vulnerability to erosion are 5, 6, 2, 1, and 17, with values varying between 0.06 and 0.09. These regions occupy large areas of Ohio, Maryland, Indiana, Vermont, and Illinois, with mean erosion vulnerability score statewide above 0.08. Future watershed management aiming at reducing soil erosion should focus on areas with the highest soil erosion vulnerability identified by this study.

Coupling fluvial-hydraulic models to predict gravel transport in spatially variable flows

This study investigated spatial-temporal variations of shear stress and bed load transport at three gravel bed river reaches of the Williams Fork River, Colorado. A two-dimensional flow model was used to compute spatial distributions of shear stress (τ) for four discharge levels between one third of bankfull (Qbf) and Qbf. Results indicate that mean τ values are highly variable among sites. However, the properties of the mean-normalized distributions of τ are similar across sites for all flows. The distributions of τ are then used with a transport function to compute bed load transport rates of individual grain size fractions. Probability distributions of the instantaneous unit-width transport rates, qb, indicate that most of the bed load is transported through small portions of the bed with high τ. The mean-normalized probability distributions of qb are different among sites for all flows except at Qbf, when the distributions overlap. We also find that the grain size distribution (GSD) of the bed load adjusts with discharge to resemble the grain size distribution of the subsurface at Qbf. We extend these results to 13 locations in the basin, using the mean-normalized distributions of shear stress and measured subsurface grain sizes to compute bed load transport rates at Qbf. We found a remarkably similar shape of the qb distribution among sites highlighting the basin-wide balance between flow forces and GSD at Qbf and the potential to predict sediment flux at the watershed scale.

Interactions of Forests, Climate, Water Resources, and Humans in a Changing Environment: Research Needs

The aim of the special issueInteractions of Forests, Climate, Water Resources, and Humans in a Changing Environmentis to present case studies on the influences of natural and human disturbances on forest water resources under a changing climate. Studies in this collection of six papers cover a wide range of geographic regions from Australia to Nigeria with spatial research scale spanning from a tree leaf, to a segment of forest road, and large basins with mixed land uses. These studies clearly show the strong interactions among forests, global climate change, water quantity and quality, and human activities at multiple scales. Understanding the underlying processes of response of natural ecosystems and society to global climate change is essential fordeveloping actionable science-based climate change mitigation and adaptation strategies and methodologies. Future research should focus on feedbacks among forests, climate, water, and disturbances, and interactions of ecohydrologic systems ,economics and policies using an integrated approach. Editorial

Relative Influence of Landscape Variables and Discharge on Suspended Sediment Yields in Temperate Mountain Catchments

Suspended sediment is an important regulator of stream habitat quality but notoriously difficult to predict and regulate. This difficulty arises because of high natural variability in suspended sediment yield in space and time. Here we quantified associations between suspended sediment yields and discharge, watershed setting (i.e., physiography and lithology), and disturbance history for 10 temperate mountain watersheds (8.5–6,242 ha) in the U.S. Pacific Northwest (H.J. Andrews Long-Term Ecological Research, LTER) over an ~60-year period. Annual suspended sediment yields varied almost 4 orders of magnitude across space and time. A linear mixed effects model indicated that much of the variation in yields could be explained by the random effect of site (conditional R = 0.74) with additional variation explained by the fixed effects (marginal R = 0.67) of cumulative annual discharge (p < 0.001) and the variability (standard deviation) of watershed slope (p< 0.001). Two annual sediment yield data points were model outliers, that each occurred within a decade after forest management activities and a large-magnitude storm event at sites with high variability of catchment slope. Other sites had low sediment yields for a range of conditions, including management or flood disturbance. Taken together, our study shows that watersheds with high slope variability have higher suspended sediment yields and may be more vulnerable to increases in sediment yields following disturbances.

Water sustainability and watershed storage

The paired watershed approach is the most popular tool for quantifying the effects of forest watershed management on water sustainability. But this approach does not often address the critical factor of water stored in the landscape. Future work needs to quantify storage in paired watershed studies to inform sustainable water management.

A multicatchment analysis of headwater and downstream temperature effects from contemporary forest harvesting

Department of Forest Engineering, Resources, and Management, Oregon State University, Corvallis, OR, USA Water and Natural Resources Division, Otak Inc., Portland, OR, USA Department of Earth and Atmospheric Sciences, University of Northern Colorado, Greeley, CO, USA Weyerhaeuser Company, Springfield, OR, USA Correspondence Kevin D. Bladon, Department of Forest Engineering, Resources, and Management, Oregon State University, Corvallis, OR, USA. Email: bladonk@oregonstate.edu

Enhancing Public Trust in Federal Forest Management

The connections between social and biophysical sciences are being forged in new ways as researchers and practitioners of natural resources seek to understand how lands can be managed for the benefit of human societies and the broader biotic community. Increasingly, we recognize that social and physical systems are tightly integrated, with human actions and decisions both shaping and shaped by the ecological systems in which they are embedded (e.g., Carpenter et al. 2009). In this context, a variety of social actors, including scientists, managers, policy makers, and the public, are collectively playing a larger role in decisions about environmental governance (e.g., collaboratives, chap. 9), drawing upon an accumulating body of knowledge describing the dynamics of complex socioecological systems. Learning-based approaches using adaptive-management experiments (chap. 8) represent one particular type of formal tool that can be appropriated to this process of adaptive environmental governance.