A key challenge for resource and land managers is predicting the consequences of climate warming on streamflow and water resources. Over the last century in the western US, significant reductions in snowpack and earlier snowmelt have led to an increase in the fraction of annual streamflow during winter, and a decline in the summer. This study explores the relative roles of snowpack accumulation and melt, and landscape characteristics or 'drainage efficiency', in influencing streamflow. An analysis of streamflow during 1950-2010 for 81 watersheds across the western US indicates that summer streamflows in watersheds that drain slowly from deep groundwater and receive precipitation as snow are most sensitive to climate warming. During the spring, however, watersheds that drain rapidly and receive precipitation as snow are most sensitive to climate warming. Our results indicate that not all trends in the western US are associated with changes in snowpack dynamics; we observe declining streamflow in late fall and winter in rain-dominated watersheds as well. These empirical findings have implications for how streamflow sensitivity to warming is interpreted across broad regions.
Water stress represents a common mechanism for many of the primary disturbances affecting forests, and forest management needs to explicitly address the very large physiological demands that vegetation has for water. This study demonstrates how state-of-science ecohydrologic models can be used to explore how different management strategies might improve forest health.
Widespread threats to forests due to drought stress prompt re-thinking of priorities for water management on forest lands. In contrast to the widely held view that forest management should emphasize providing water for downstream uses, we argue that maintaining forest health in the face of environmental change may require focusing on the forests themselves and strategies to reduce their vulnerability to increasing water stress in the context of a changing climate. Management strategies would need to be tailored to specific landscapes but could include: a) thinning; 2) encouraging drought-tolerant species; 3) irrigation; and 4) strategies that make more water available to plants for transpiration. Hydrologic modeling reveals that specific management actions could reduce tree mortality due to drought stress. Adopting water conservation for vegetation as a priority for managing water on forest lands would represent a fundamental change in perspective and potentially involve tradeoffs with other downstream uses of water.
Environmental Protection Agency, Oregon State University
The Environmental Protection Agency’s (EPA) Climate Economics Branch (CEB) analyzes cost-effective strategies to reduce greenhouse gas (GHG) emissions, both in the U.S. and internationally. EPA relies on the Forest and Agricultural Sector Optimization Model with Greenhouse Gas (FASOM-GHG) model for analysis of GHG mitigation from the U.S. forest, agriculture and bioenergy sectors. This project will involve model development, results interpretation, testing, analyses, and documentation associated with the forestry and bioenergy sectors and related land use in the FASOM-GHG. The overarching objectives of the project are to make the forest sector portion more flexible, able to simulate a broader range of alternative bioenergy and CO2 sequestration policies, and to simplify the basic model code to reduce compilation and run time.
The Environmental Protection Agency’s (EPA) Climate Economics Branch (CEB) analyzes cost-effective strategies to reduce greenhouse gas (GHG) emissions, both in the U.S. and internationally. EPA relies on the Forest and Agricultural Sector Optimization Model with Greenhouse Gas (FASOM-GHG) model for analysis of GHG mitigation from the U.S. forest, agriculture and bioenergy sectors. The model is developed and maintained by the FASOM-GHG team, with expert members at Texas A&M University, Oregon State University, the Nicholas Institute at Duke University, Research Triangle Institute, Electric Power Research Institute, Environmental Protection Agency, USDA and the U.S. Forest Service.
Restoring riparian forests on streams where historic land uses have created open meadows could reduce maximum stream temperatures by as much as 7o C relative to current conditions, even under a future climate when air temperatures are 4o C warmer than today.
Summer maximum stream temperatures are near thresholds of thermal tolerance for salmon and trout in many streams throughout the interior Columbia River Basin. Salmon and trout populations in many of these streams are severely depressed, resulting in efforts to restore stream and riparian habitat. Climate change raises serious questions about the long-term outcomes of restoration because projected warming could make many of these streams and rivers uninhabitable for salmon and trout within a few decades.
We used the mechanistic stream temperature model, HeatSource, to examine future changes in stream temperature on the upper Middle Fork John Day River. Our model scenarios examined: 1) a +4 oC increase in air temperature; 2) ±30% changes in stream discharge from both changes in irrigation withdrawals and climate-change related loss of winter snowpacks; and 3) four riparian vegetation scenarios: 3a) current conditions where effective stream shade averages 19%; 3b) a post-wild fire scenario with maximum vegetation height of 1 m and 10% canopy density resulting in 7% effective stream shade; 3c) an intermediate condition representing a young-open forest or tall-shrub dominated vegetation with trees or shrubs 10-m tall and with 30% canopy density resulting in 34% effective shade; and 3d) a restored riparian forest with trees 30-m high and canopy density of 50% resulting in 79% effective stream shade.
Our model results showed the composition and structure of riparian vegetation were the single biggest factor determining future stream temperatures. In contrast, changing air temperature or stream discharge had relatively small influence on future stream temperatures. The post-wildfire and the current-vegetation scenarios were warmer than today, but in both cases, effective shade was low, so the stream was sensitive to air temperature increases due to climate change. The intermediate restoration, simulating a young-open forest or a tall-shrub dominated riparian zone, was slightly cooler than today. The biggest change resulted from restoring the riparian forest which decreased summer maximum temperatures by ~ 7 oC.
The CUFR Tree Carbon Calculator (CTCC) provides quantitative data on carbon dioxide sequestration and building heating/cooling energy effects provided by individual trees. CTCC outputs can be used to estimate GHG (greenhouse gas) benefits for existing trees or to forecast future benefits. The CTCC is programmed in an Excel spreadsheet and provides carbon-related information for trees located in one of sixteen United States climate zones.
This Carbon Calculator provides quantitative data on carbon dioxide sequestration and building heating/cooling energy effects provided by individual trees.
The National Climate Change Viewer allows users to visualize projected changes in climate (maximum and minimum air temperature and precipitation) and the water balance (snow water equivalent, runoff, soil water storage and evaporative deficit) for any state, county and USGS Hydrologic Units (HUC) in the continental United States. USGS HUCs are hierarchical units associated with watersheds and analogous to states and counties that span multistate areas. HUC levels 2, 4 and 8 are used in the viewer.
This viewer allows users to visualize past and projected changes in climate and the water balance for any state, county and USGS Hydrologic Unit.