Samuel C. Zipper

Scenarios reveal pathways to sustain future ecosystem services in an agricultural landscape

Sustaining food production, water quality, soil retention, flood, and climate regulation in agricultural landscapes is a pressing global challenge given accelerating environmental changes. Scenarios are stories about plausible futures, and scenarios can be integrated with biophysical simulation models to explore quantitatively how the future might unfold. However, few studies have incorporated a wide range of drivers (e.g., climate, land-use, management, population, human diet) in spatially explicit, process-based models to investigate spatial-temporal dynamics and relationships of a portfolio of ecosystem services. Here, we simulated nine ecosystem services (three provisioning and six regulating services) at 220xa0×xa0220 m from 2010 to 2070 under four contrasting scenarios in the 1,345-km2 Yahara Watershed (Wisconsin, USA) using Agro-IBIS, a dynamic model of terrestrial ecosystem processes, biogeochemistry, water, and energy balance. We asked (1) How does ecosystem service supply vary among alternative future scenarios? (2) Where on the landscape is the provision of ecosystem services most susceptible to future social-ecological changes? (3) Among alternative future scenarios, are relationships (i.e., trade-offs, synergies) among food production, water, and biogeochemical services consistent over time? Our results showed that food production varied substantially with future land-use choices and management, and its trade-offs with water quality and soil retention persisted under most scenarios. However, pathways to mitigate or even reverse such trade-offs through technological advances and sustainable agricultural practices were apparent. Consistent relationships among regulating services were identified across scenarios (e.g., trade-offs of freshwater supply vs. flood and climate regulation, and synergies among water quality, soil retention, and climate regulation), suggesting opportunities and challenges to sustaining these services. In particular, proactive land-use changes and management may buffer water quality against undesirable future climate changes, but changing climate may overwhelm management efforts to sustain freshwater supply and flood regulation. Spatially, changes in ecosystem services were heterogeneous across the landscape, underscoring the power of local actions and fine-scale management. Our research highlights the value of embracing spatial and temporal perspectives in managing ecosystem services and their complex interactions, and provides a system-level understanding for achieving sustainability of the food-water-climate nexus in agricultural landscapes.

Socio-environmental drought response in a mixed urban-agricultural setting: synthesizing biophysical and governance responses in the Platte River Watershed, Nebraska, USA

Ensuring global food and water security requires a detailed understanding of how coupled socio-environmental systems respond to drought. Using the Platte River Watershed in Nebraska (USA) as an exemplar mixed urban-agricultural watershed, we quantify biophysical response to drought in urban (Lincoln NE) and agricultural systems alongside a qualitative analysis of governance response and adaptive capacity of both sectors. Synthesis of results highlights parallels and discontinuities between urban and agricultural preparations for and response to drought. Whereas drought prompted an increase in well installations and expansion of water-intensive crops, e.g., corn, in the agricultural sector, outdoor water use restrictions rapidly curtailed water withdrawals in the urban sector, where water conservation has gradually decoupled total withdrawals from population growth. Water governance institutions at the municipal, district, and statewide levels showed evidence of learning and adaptive management, facilitated by a shared regional identity around agriculture. We conclude that, rather than exacerbating intersectoral conflict, cities may introduce a high-value and flexible water use that can be rapidly curtailed during drought. The ability to rapidly reduce urban water use and thereby avoid limiting agricultural irrigation during drought enables cities to provide adaptive capacity in mixed urban-agricultural watersheds, particularly where crops are highly reliant on irrigation.

Groundwater Pumping Impacts on Real Stream Networks: Testing the Performance of Simple Management Tools

Quantifying reductions in streamflow due to groundwater pumping (‘streamflow depletion’) is essential for conjunctive management of groundwater and surface water resources. Analytical models are widely used to estimate streamflow depletion but include potentially problematic assumptions such as simplified stream-aquifer geometry and rely on largely untested depletion apportionment equations to distribute depletion from a well among different stream reaches. Here, we use archetypal numerical models to evaluate the sensitivity of five depletion apportionment equations to stream networks with varying drainage densities, topographic relief, and groundwater recharge rates; and statistically evaluate the sources of error for each equation. We introduce a new depletion apportionment equation called web squared which considers stream network geometry, and find that it performs the best under most conditions tested. For all depletion apportionment equations, performance decreases with increases in drainage density, relief, or recharge rates, and all equations struggle to estimate depletion in short stream reaches. Poorly performing apportionment equations tend to underestimate streamflow depletion relative to numerical model results, leading to a negative bias and underpredicted variability, while error in the best performing apportionment equations tends to be due to imperfect correlation. From a management perspective, apportionment equations with error due to bias and variability are preferable as they correctly identify which reaches will be affected and can be statistically corrected. Overall, these results indicate that the web squared method introduced here, which explicitly considers stream geometry, performs the best over a range of real-world conditions, and will be most accurate in flatter and drier environments.

Sociohydrological Impacts of Water Conservation Under Anthropogenic Drought in Austin, TX (USA)

Municipal water providers increasingly respond to drought by implementing outdoor water use restrictions to reduce urban water withdrawals and maintain water availability. However, restricting urban outdoor water use to support watershed-scale drought resilience may generate unanticipated cross-scale interactions, for example, by altering drought response and recovery in urban vegetation or urban streamflow. Despite this, urban water conservation is rarely conceptualized or modeled as endogenous to the water cycle. Here, we investigate cross-scale interactions among urban water conservation and water availability, water use, and sociohydrological response in Austin, TX (USA) during a recent anthropogenic (human-influenced) drought. Multi-scalar statistical analyses demonstrated that outdoor water conservation for reservoir management at the municipal scale produced responses that can cascade both ‘upwards from the city to the watershed (e.g., decoupling streamflow patterns upstream and downstream of Austin at the watershed scale) and ‘downwards to exert heterogeneous effects within the city (e.g., redistributing water along a socioeconomic gradient at sub-municipal scales, with effects on terrestrial and aquatic ecosystems). We suggest that adapting to anthropogenic drought through irrigation curtailment requires sustained engagement between hydrology and social sciences to integrate socioeconomic status and political feedbacks within and among irrigator groups into the water cycle. Findings from this cross-disciplinary study highlight the importance of a multi-scalar and spatially-explicit perspectives in urban sociohydrology research to uncover how water conservation as adaptation to anthropogenic drought links hydrological processes with issues of socioeconomic inequality and spatiotemporal scale in the Anthropocene.

Does hillslope trenching enhance groundwater recharge and baseflow in the Peruvian Andes

Department of Earth and Planetary Sciences, McGill University, 3450 University Street, Montreal, QC H3A 0E8, Canada Department of Civil Engineering, University of Victoria, PO Box 1700 STN CSC, Victoria, BC V8W 2Y2, Canada Byrd Polar and Climate Research Centre, The Ohio State University, 108 Scott Hall, 1090 Carmack Rd, Columbus, OH 43210, USA 4 Instituto Geofísico del Perú, Calle Badajoz #169, Mayorazgo IV Etapa, Ate Vitarte, Lima, Peru Départment de génie de la construction, École de technologie supérieure, 1100 rue Notre‐Dame Ouest, Montreal, QC H3C 1K3, Canada Correspondence Lauren D. Somers, Department of Earth and Planetary Sciences, McGill University, 3450 University Street, Montreal, QC, Canada, H3A 0E8. Email: Lauren.Somers@mail.mcgill.ca