Patterns in the Landscape – Analyses of Cause and Effect

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For two decades, USGS scientists with the Land Cover Trends team have used satellite data to study landscape change across the United States. Increasingly, research is focused on understanding why change occurs. Insights into the underlying causes of shifts in land use and land cover (LULC) will allow managers and stakeholders to make more informed decisions about how to respond to future environmental and climatic conditions.

USGS investigations into the causes of land change are called ‘driving forces’ studies.  Driving forces are different processes--economic, demographic, technological, institutional, cultural, environmental, and climatic--that transform or maintain LULC.

The Land Cover Trends team is now undertaking research that quantifies the complex spatial and temporal relationships between land change and its driving forces in order to develop more accurate land-cover assessments and forecasts.

The goal of the PLACE project is to develop and implement a systematic approach for identifying the rates, patterns, and causes of land change at regional to national scales. Advances in high performance computing and cloud computing have ushered in a new era of landscape analysis, in which scientists can easily process and analyze massive amounts of data.  The ability to track landscape changes at frequent (monthly and annual) time-steps over broad geographical extents improves the reliability and accuracy of detected patterns of change and makes it easier to determine and quantify the contributions of underlying forcing agents. The PLACE team will leverage this detail to isolate abiotic influences, explore land change sensitivity to extreme weather events and sustained climate changes, and investigate effects across a wide range of explanatory parameters.

In late 2016 PLACE team members began development of regional-scale methods, largely focused on the western United States. Early published efforts covered logging characteristics in the Pacific Northwest, causes of vegetation change in Sierra Nevada meadows, and mapping surface water change monthly throughout California. The regional focus has provided the opportunity both to test method efficacy prior to a national-scale rollout and to tailor outreach products to regional resource managers, researchers, and local governments for assessment and utilization.

Relevance

The benefits of identifying the rates and causes of LULC change are far-reaching.  More informed understanding of drivers allows insights into the environmental impacts of past change and more precise estimates of future responses to specific processes and climate scenarios. The use of scenario-based LULC projections enables an assessment of the interactions among climate, land-use, policy, and socioeconomic driving forces. This information can facilitate land-use planning and restoration efforts. 

Surface water maps derived from Landsat 30-m imagery

Diagram illustrating surface water fluctuations using select March snapshots of Friant Dam outside of Fresno, CA (black background represents March maximum water extent across 31 years. Christopher Soulard, USGS. Public domain.

Resource managers. non-governmental organizations, and private stakeholders are increasingly interested in knowing how altered environmental conditions will affect priorities such as preserving plant and animal species of concern, mitigating the negative impacts of development projects, and planning for protection of communities in flood-and-drought-prone areas. Understanding the factors that lead to landscape change provides an opportunity to identify, isolate, and manage risk by highlighting areas of particular vulnerability or resistance to change under different future scenarios.

Example of flood at a USGS stream gage

Gagehouse at 06225500 Wind River near Crowheart, WY just before it washed away.  Jul 01 2011; 13,900 ft3/s.  Credit: Jerrod Wheeler, USGS. Public domain.

Accomplishments

In the first two years of the PLACE project, the team has focused on developing methods and data that will lead to improved LULC detection at a national scale, while approaches to quantify the causes of change have been tested at regional scales. The monitoring products that PLACE has published characterize land-use practices across the entire United States with improved accuracy, and currently serve as some of the best available empirical data for land-use modeling applications. These results are a bridge between past generations of intermittent, limited-scope LULC maps and the annual, nation-wide ones of the future. To that end, PLACE is actively working on cloud-based methods to generate a series of LULC products, including annualized maps of development and monthly maps of surface water.

As the PLACE team heads into a second year studying the patterns and causes of surface water change, we have created a scalable, transferable method to validate and interpolate monthly map time series wherever stream gage information is available. These methods have also been useful for mapping surface water changes elsewhere around the globe where gage data are sparse. Continuous, long-term estimates of surface water change can form the backbone of subsequent analyses into the rates, patterns, and causes of change. Quantifying the linkages between mapped changes and monthly weather records over a span of 30 years will help determine how precipitation events contribute to the timing, location, and extent of flooding and drought.

comparison illustrating streamflow along the San Fransiquito Creek

Photo comparison illustrating streamflow along the San Fransiquito Creek (Palo Alto, CA) associated with different atmospheric river precipitation events in February 2017 (left) and February 2019 (right). Credit: Christopher Soulard, USGS. Public domain.

 Linking surface water change to climate is just one example of how important the PLACE project is in advancing research into LULC change drivers beyond qualitative or anecdotal observations of individual forcing agents.