23 June 2011

Forests and Water, part 1: Where there's smoke...

Author's Note: the following is derived from a project proposal to the National Science Foundation (NSF) that I co-authored in 2009 with a colleague at Northern Arizona University (NAU).  More context on the narrative given here is provided in part 0 of this series.



Photograph of the 2011 Wallow Fire in eastern Arizona by John Burfiend,
provided by the National Interagency Fire Center (NIFC),
Southwest Coordination Center (SWCC)
Global climate change and regional drought, coupled with population growth and traditional forest resource management policies, have led to land cover changes and resource challenges across the southwestern U.S. Scientists, researchers, and natural resource managers seek to understand the hydro-ecological impacts of climate variability while the needs of the community, the spread of invasive species, and the threat of catastrophic forest fires persist. Vast quantities of data are collected by state and federal agencies, municipalities, researchers, and watershed management groups using a wide variety of technologies and methods, producing numerous data types of highly variable accuracy and often oriented on specific management tasks. There is a compelling need to integrate the numerous observational datasets, process-oriented models and decision-making tools that are used by resource managers to protect important ecosystem aspects and services including forest health, water quality, and water quantity.

The complexity of managing forest and water resources on both public and private lands, and in the context of widely varied physical and societal pressures, makes it necessary for researchers and decision-makers to develop efficient methods for handling, exchange, and re-use of datasets for multiple purposes. Standardized and often automated data access has become an unstated necessity for research intended to support planning and decision-making on short-term (daily to annual) time scales and for long-term policy development. Integration of datasets and analytical tools can help improve data mining methods for information discovery and access. More specifically, water resources and forest health officials must assimilate a consistent stream of information on historic and current climate, meteorological analyses, the status and trends of the resources under management, and the implications of potential future climate and hydrologic conditions in making decisions that will meet ecological and societal needs. Long-term observational datasets in combination with remote sensing and geospatial products can form the basis for predictive models, but the quality of model output depends inherently on accurate input information.

Runoff from forested areas in the western U.S. contributes a significant portion of the flow in streams and the storage volume in reservoirs [1]. In disturbed areas, such as a burned hillslope, degradation or absence of organic material promotes disproportionate runoff and erosion from the hillslopes and deposition of undesirable sediments in the receiving waters, often leading to flood events in streams and the degradation of water quality throughout the resource system [2]. Healthy forests serve both hydrological and ecological functions, retaining water that is more slowly released from stable hillslope soil to receiving streams, all the time providing biochemical processing through ecological functions that lead to significant water quality improvements. The causal differences between an often dry ephemeral stream that is prone to flash floods and supports little biological diversity, and a perennial stream along which ecological processes contribute to biodiversity and in which flood events occur in a natural pattern that enhances riparian health and diversity, can often be found in a brief survey of the hillslopes contributing to that stream reach. The former scenario may indicate recent disturbance or an external forcing that is not in balance with the established ecosystem (e.g., climate change), and thus a candidate area for "ecological restoration" efforts where a pressing need is determined. In the latter scenario, vegetated catchment areas and riparian buffers function as natural water filters, contributing an "ecosystem service" in which a healthy balance of ecology and hydrology may be observed.

Natural resources and environmental quality are at risk of wildfire across 190 million acres of American forests and rangeland. Wildfires have affected more than three million acres in Arizona since 2002, destroying hundreds of structures and causing significant damage to forests, rangelands, watersheds, wildlife and fish habitats, and invaluable natural and cultural resources. Recent data from the National Interagency Fire Center (NIFC) indicate that Arizona experienced yearly forest losses to wildfires in one decade at nearly seven times the average annual rate over the prior century [3]. The severity of fires has intensified as well, posing an increasing threat to life and property. Spatial analysts have identified 3,350 square miles of wildland–urban interface (WUI) in more than 150 Arizona communities [4, 5] that could be susceptible to wildfire.

Large, severe fires are symptomatic of poor forest health that may be caused or exacerbated by prolonged drought and invasive species. Studies suggest that recent morbidity in piñon and ponderosa pine trees across the Southwest, attributed primarily to bark beetles, is probably more extensive and severe than previous events because of unusually warm conditions during the present drought [6]. In a larger sense, conditions of long-term hydrologic drought in the Southwest may actually be the "new normal" as a regional impact of global climate change [7, 8]. Recent high-profile scientific reports have attempted to focus national and international attention on the triplet of climate change, drought, and water supplies. Most prominent are the 4th Assessment Report of the IPCC [9], Synthesis and Assessment Product 4.3 of the U.S. Climate Change Science Program [10], and a report by the U.S. Global Change Research Program [11]. Some studies have raised concerns about water in the Southwest, including a U.S. National Research Council report [12] and a report released by the Pew Center on Global Climate Change [13]. Studies have addressed specific issues of concern such as climate change and water resources management in the Colorado River Basin, most notably Garrick et al. [14] and a federal multi-agency effort led by the USGS [15]. The consensus among climate models indicates higher temperatures to come in the Southwest, but a lack of clear consensus among models for precipitation over the Southwest suggests that the region could see increased variability in precipitation occurrence and intensity, factors that can affect forest health and fire regime significantly [16].

Recent studies indicate that climate change impacts on ecosystems in the western U.S. have already begun, and that the Southwest is far from prepared for the possibility of long-term drought within the larger context of persistent global warming. When an accumulated precipitation deficit due to extended drought is combined with higher temperatures, these factors lead to greater moisture stress in forest species and greater fire risk in forested areas. Adams et al. [17] and van Mantgem et al. [18] concluded that regional warming has helped to accelerate tree mortality across the West. An increase in large western forest fires is correlated with warming and the earlier arrival of spring [19], conditions that are also correlated with diminished winter snowpack and earlier snowmelt runoff in the region [20, 21, 22, 23]. Rapid climate change can lead to cascading effects, from tree mortality [6] to increased catastrophic disturbance such as forest fires [24] to shifting zones of species-specific habitat suitability that will alter forest patterns across the West [25, 26].

Finally, in addition to long-term climatological effects on forest health through drought and rapid climate change, we observe also that forested lands in Arizona occur in the direct path of annual North American monsoon (NAM) [27] moisture flows from the Pacific Ocean and Gulf of California to the Colorado Plateau. Mountainous areas in the American Southwest, such as the Mogollon Rim that stretches across Arizona, provide orographic meteorological forcing that enhances the development of summer thunderstorms, especially during the NAM season. Cloud-to-ground lightning produced by these thunderstorms often strikes in the very locations where orographically-enhanced rainfall has made the surface more hospitable to forest survival and growth, and is recognized as the proximate cause of most forest fires in the Southwest [28, 29].

The condition of a forested watershed has a direct impact on both the quantity and quality of water supplies that are available for human and ecosystem uses. The size, density, species composition and other aspects of the forest ecosystem affect the partitioning of precipitation to runoff, which eventually appears in streams as surface water and may ultimately recharge groundwater aquifers. Recent trends toward larger and more severe forest fires in the western U.S. indicate a threat to the sustainability of both evergreen and deciduous forests in semi-arid environments, as throughout Arizona, where the ecosystems might have adapted naturally to frequent, low-intensity fires that clear ground fuels on a somewhat regular basis. With fire severity we also consider the speed of forest recovery: more severe fires tend to delay re-vegetation and leave the burned area exposed to increased runoff potential and soil surface erosion during later storm events. There are direct and known connections between land cover, vegetation and water resource characteristics. However, the physical models developed for surface hydrology and water resources management are generally not compatible with the physical models that inform decisions in fire treatment and prevention and in forest and rangeland management. We aim to remedy such disparities in data and model interoperability in order to facilitate decision-making that retains the best interests of the combined community of practice, and to employ the solutions developed here as a template for the treatment of similar disparities in the application of spatial analysis and hydrologic science to the decision-making process in other communities of practice.

ResearchBlogging.orgReferences

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