NHI uses science to better understand climate change impacts on ecosystem services  provided by wetlands and watersheds, thereby offering valuable information to water system managers and policy makers about how to effectively (and most affordably) address climate change. The Intergovernmental Panel on Climate Change (IPCC) has produced compelling analysis suggesting that elevated GHG concentrations will cause global climate alterations that could impact the components of the hydrologic cycle, including precipitation, evapotranspiration, soil moisture, and runoff. The hydrologic alternations associated with changing climates will challenge governments in many regions to develop water management strategies that protect the full range of goods and services that they currently derive from their national water resources.
For example, according to the A2 scenario developed by the IPCC, the future for California will be much warmer and drier, making water an even more contentious issue. Simulations suggest that the average annual delivery of water to irrigated agriculture may be reduced as much as 30%. Urban growth in the region has the potential to claim as much as 20% of available water supplies under this climate future, much higher than the 8% now dedicated to this sector. Environmentally important flow patterns in the systems that now occur roughly once every 2 years will potentially be absent 3 years of out 4 in the future. Water temperatures in the river may render impossible the goal of restoring certain anadromous fish runs in the system. These results have already been used to inform water management policy makers in California about what they may have to do to cope with the impacts of climate change.
In the past, research on the potential impacts of climate change on the hydrologic cycle has been narrowly focused on isolated components of the cycle, for example watershed response, agricultural yield, and land cover change. In our view, there is an urgent need is for integrated and holistic analysis that can illuminate the full suite of potential conflicts and tradeoffs that climate change may foist upon water managers in the coming decades. Utilization of this type of analysis can assist national policy makers in evaluating GHG reduction mechanisms that may render future climates less disruptive to the provision of important aquatic ecosystem services. Further, it is our hope that such a holistic watershed analysis will also motivate major GHG producers to commit themselves to the search for an aggressive action plan for reducing GHG emissions on a global level.
Since 2001, NHI has been engaged in two projects in the climate change arena:
- From 2001-2003, the Natural Heritage Institute and the National Center for Atmospheric Research worked in collaboration to develop tools that contribute to crafting a policy relevant narrative for climate change. Capitalizing on recent advances in water resource modeling capability that allows natural hydrologic processes to be dynamically coupled with the hydraulic infrastructure of heavily engineered watersheds, NHI began to explore the water resource tradeoff landscape associated with climate change. These efforts produced the Water Evaluation And Planning (WEAP) system that integrates climate scenarios, regional hydrology, along with water management infrastructure and institutions in balancing competing water demands under various formulations of demand priorities and supply preferences. WEAP has been applied to the Sacramento River system in Northern California in order to understand the tradeoffs that might occur between the provision of water to irrigated agriculture, water supplies for growing metropolitan areas, and flow regimes required to assure the viability of important fish species in the watershed. [NHI plans to recreate the analysis performed in the Sacramento River system in a high profile river basin in China and another in India.]
- The Sustainability of Tidal Marsh and Freshwater Ecosystem Goods and Services in South San Francisco Bay in Response to Climate Change and Sea Level Rise: Tidal marshes and the services they provide are products of the shifting interface between oceans, estuaries, and upstream watersheds. NHI has a project-in-progress that will set out to develop an analytical framework to investigate this interface under current and potential future conditions. A central tenet is that changes in ecosystem services provided by tidal marshes cannot be based solely on sea level rise. Importantly, the freshwater and sediment issuing from their associated watersheds must be considered, and in fact, could aid in mitigating service reductions due to climate change, while still providing watershed services. The watersheds of many inter-tidal zones are heavily managed and opportunities likely exist for climate change adaptations. The South San Francisco Bay of California will be our laboratory, which is timely in the light of expensive tidal marsh restoration efforts currently underway. 
The project will link a set of models to produce estimates of water and sediment flux to the intertidal zone, and then simulate and predict the distribution of wetlands and marsh vegetation classes under sea level rise and changes in salinity. Habitat Suitability models will use parameters from the watershed model and the Sea Level Affecting Marshes Model (SLAMM) to evaluate the likely impacts of any actual or potential changes in habitat quality on carrying capacity. Multiple scenarios to drive the models will be derived from sea-level rise scenarios and climate scenario ensembles via statistical downscaling.
Results from this study will 1) test whether water and sediment management strategies are available to sustain restored tidal marshes and the services that they provide, and if so, will 2) develop watershed management strategies to ameliorate the negative impacts of global warming and sea-level rise on the ecosystem services of the tidal marsh. We will also gain a more quantitative understanding of how watersheds contribute to the maintenance and sustainability of the intertidal zone (salt marshes and mud flats).
 Ecosystem services are defined as the processes by which the environment produces resources that benefit and are used by humans, such as clean water, timber, and habitat for fisheries. Freshwater aquatic ecosystem services include flood and drought alleviation, waste assimilation and purification capacity, and recreational opportunities. Goods include water for irrigation, domestic and industrial uses, hydropower generation, harvestable aquatic species and others.
 I.E. The South San Francisco Salt Pond Restoration Project.