Continuous separation of land use and climate effects on the past and future water balance

Understanding the combined and separate effects of climate and land use change on the water cycle is necessary to mitigate negative impacts. However, existing methodologies typically divide data into discrete (before and after) periods, implicitly representing climate and land use as step changes when in reality these changes are often gradual. Here, we introduce a new regression-based methodological framework designed to separate climate and land use effects on any hydrological flux of interest continuously through time, and estimate uncertainty in the contribution of these two drivers. We present two applications in the Yahara River watershed (Wisconsin, USA) demonstrating how our approach can be used to understand synergistic or antagonistic relationships between land use and climate in either the past or the future: (1) historical streamflow, baseflow, and quickflow in an urbanizing subwatershed; and (2) simulated future evapotranspiration, drainage, and direct runoff from a suite of contrasting climate and land use scenarios for the entire watershed. In the historical analysis, we show that ~60% of recent streamflow changes can be attributed to climate, with approximately equal contributions from quickflow and baseflow. However, our continuous method reveals that baseflow is significantly increasing through time, primarily due to land use change and potentially influenced by long-term increases in groundwater storage. In the simulation of future changes, we show that all components of the future water balance will respond more strongly to changes in climate than land use, with the largest potential land use effects on drainage. These results indicate that diverse land use change trajectories may counteract each other while the effects of climate are more homogeneous at watershed scales. Therefore, management opportunities to counteract climate change effects will likely be more effective at smaller spatial scales, where land use trajectories are unidirectional

Validating DayCent-CR for cropland soil carbon offset reporting at a national scale

Regenerative soil management practices have been shown to increase soil organic carbon in cropland previously under conventional management, and farmers that adopt regenerative practices could be eligible to participate in carbon offset programs. Due to the high cost of soil sampling at large scales, project developers of agricultural carbon offset programs may employ a hybrid measurement and modeling approach to SOC quantification. While biogeochemical models allow for carbon crediting to occur on larger scales than soil sampling alone would allow, any model used must be unbiased and shown to adequately predict SOC changes, with known uncertainty, across the crops, practice changes, and geographies of interest. The “credit-ready” version of the DayCent ecosystem model, DayCent-CR, was evaluated for performance across 14 combinations of crops and practice categories. Model calibration and validation was performed with a Bayesian Markov chain Monte Carlo approach using k-fold cross validation and 668 SOC stock change measurements from 41 agricultural research sites. Overall model performance met the guidelines established by Climate Action Reserve’s Soil Enrichment Protocol: ≥90% of model prediction intervals covered the measured value, and mean bias in all categories was less than pooled measurement uncertainty. Importantly, posterior distributions of DayCent-CR parameters and variance components enable the calculation of variance, which can then be used to calculate an uncertainty deduction that is applied to overall project credits to ensure conservatism. The calibrated model parameters are therefore valid for use in crediting programs within the domain of the validation dataset

Plausible futures of a social-ecological system: Yahara watershed, Wisconsin, USA

Agricultural watersheds are affected by changes in climate, land use, agricultural practices, and human demand for energy, food, and water resources. In this context, we analyzed the agricultural, urbanizing Yahara watershed (size: 1345 km², population: 372,000) to assess its responses to multiple changing drivers. We measured recent trends in land use/cover and water quality of the watershed, spatial patterns of 10 ecosystem services, and spatial patterns and nestedness of governance. We developed scenarios for the future of the Yahara watershed by integrating trends and events from the global scenarios literature, perspectives of stakeholders, and models of biophysical drivers and ecosystem services. Four qualitative scenarios were created to explore plausible trajectories to the year 2070 in the watershed's social-ecological system under different regimes: no action on environmental trends, accelerated technological development, strong intervention by government, and shifting values toward sustainability. Quantitative time-series for 2010-2070 were developed for weather and land use/cover during each scenario as inputs to model changes in ecosystem services. Ultimately, our goal is to understand how changes in the social-ecological system of the Yahara watershed, including management of land and water resources, can build or impair resilience to shifting drivers, including climate