The tropics are undergoing profound, rapid landscape change. Humid tropical regions occupy about a quarter of Earth’s land surface, yet they contribute a substantially higher fraction of the water, solutes, and sediment discharged to the world’s oceans. Nearly half of Earth’s population lives in the tropics where development stresses can potentially harm soil resources, water quality, water supply, and increase landslide and flood hazards.

El Yunque Peak as seen across the Mameyes River valley. El Yunque National Forest, Puerto Rico.

“As our influence on Earth’s lands and waters grows more substantial, we need to understand and quantify these effects to preserve our well-being,” said Matt Larsen, USGS Associate Director for Climate and Land Use Change. “Earth sciences are central to meeting this need because they guide the monitoring, assessment, and modeling of natural processes that help us to understand our interaction with the environment.”

Puerto Rico is representative of rapid, ongoing change in the tropics. Many agricultural lands are undergoing reforestation, while coastal areas are becoming heavily urbanized. The area is also changing because of the introduction of nonnative species, water supply projects, and the construction of roads and other kinds of infrastructure. Slower, larger scale factors are also at work in environmental change, such as the deposition of airborne pollutants and natural and human-induced climate change.

In eastern Puerto Rico, four humid-tropical watersheds exhibit varying types of underlying geology while their waters flow through or near the mature forest of the Luquillo Experimental Forest (also known as the El Yunque National Forest). Lying within a relatively small geographic footprint, the four watersheds provide a natural laboratory that allows scientists to quantify and characterize landscape change in this region.

In recognition of this opportunity, scientists from the USGS have conducted research in eastern Puerto Rico for several decades, in collaboration with scientists from the U.S. Forest Service. The scientists’ aim is to study hydrologic, geologic, geomorphic (Earth-shaping), and anthropogenic (human-driven) processes in the area with the goal of generalizing their investigation to the broader tropical world.

These findings have recently been published by the USGS. Because eastern Puerto Rico resembles many tropical regions in terms of geology and patterns of development, implications from this study are transferable to other tropical regions facing deforestation, rapid land-use change, and climate change.

Location, location — and precipitation

Focusing on four small watersheds in eastern Puerto Rico allowed the scientists to integrate studies of hydrologic and chemical processes. Two watersheds are located on coarse-grained granitic rocks; two are located on fine-grained volcanic rocks. For each bedrock type, one watershed is covered with mature rainforest. The other two watersheds, like most of the rest of Puerto Rico, were subjected to intensive agriculture in the 19th and early 20^thcentury, but they have been undergoing reforestation as a result of a shift from an agricultural economy to an industrial one and the related human migration to urban areas.

The long term study focused on four watersheds that have varied geology and land cover characteristics.

Owing to the island’s steep topography, low water-storage capacity, and dependence on trade-wind precipitation, Puerto Rico’s people, ecosystems, and water supply are vulnerable to extreme weather such as hurricanes, floods, and droughts. At the same time, rainfall varies greatly over small distances in eastern Puerto Rico, based on differences in elevation, topographic position and aspect, and proximity to the ocean.

Puerto Rico lies directly in the path of the easterly trade winds, which deliver steady rainfall to the mountains and steer weather systems called tropical waves toward the island. Hurricanes and tropical storms derived from these systems typically deliver the majority of yearly rainfall, but northern cold fronts can also deliver heavy rainfall for several days at a time, usually from December through February.

These rain events vary greatly in frequency and intensity, contributing to substantial differences in annual precipitation. A unique aspect of this study is that USGS scientists sampled and chemically analyzed river water during major storms using automated equipment. Such intense storms had never before been studied in this manner.

The largest storms can have profound geomorphic consequences, such as landslides, debris flows, and deep gullying on deforested lands. Past deforestation and agricultural activities in the developed watersheds led to greatly accelerated erosion and soil loss. Rates of erosion in two forested watersheds were considerably higher than expected, presenting a new area for future study.

Regional weather patterns and the sources of air masses influence the type and timing of atmospheric contributions to the land. Eastern Puerto Rico receives marine salts and Saharan Desert dust in rainfall, while nitrogen loads in precipitation have roughly doubled since measurements began in 1985.

A matrix of factors in landscape change

The 15-year Water, Energy, and Biogeochemical Budget dataset, including data on stream discharge, field parameters, suspended sediment, and nutrients, is available from the USGS National Water Information System (NWIS). The dataset provides a baseline for characterizing future environmental change in eastern Puerto Rico and will improve our understanding of the interdependencies of land, water, and biological resources and their responses to changes in climate and land use.

Publication Citation

A sampling of historic hurricanes that have hit Puerto Rico. Large storms can have profound geomorphic (land changing) consequences.

Murphy, S.F., and Stallard, R.F., eds., 2012, Water quality and landscape processes of four watersheds in eastern Puerto Rico: U.S. Geological Survey Professional Paper 1789, 292 p.

Links and resources

USGS Caribbean Water Science Center

USGS Water Data for Puerto Rico

Geology of Puerto Rico

Hi, my name is Kaitlyn Bednar but everyone calls me Kati. I am currently a Student Trainee Hydrologist with the California Water Science Center (CAWSC) in Sacramento. I am also a full-time geology and geography student at California State University of Sacramento, and a part-time student at American River College within their G.I.S. certificate program. It may seem like a lot, but I enjoy keeping busy and learning new things.

How did you start working for the USGS?

I first heard about the Student Temporary Employment Program (STEP) with the USGS during my sophomore year of high school from my chemistry teacher. She knew how interested and excited I was about science and highly recommended that I look into the position and apply. Before I knew it, I was being offered the position and started my student employment with the USGS while finishing up high school.

Once I graduated, I immediately knew I wanted to continue to pursue a career with the USGS and declared my major as geology. Over the next few years, because of my student employment and involvement in geology, I was also exposed to the fields of geography and G.I.S., and converted into the Student Career Experience Program (SCEP). That played a huge role with my decision to also pursue an additional degree and certificate to contribute to the skills I use every day at work when trying to locate field sites and querying their corresponding data.

What is a day in your life like?

Right now I work in Data Management where I mainly establish new sites and also work with historical data and other unique data sets that require special attention. For example, I have looked at descriptions of sites that were recorded as far back as the 1900s and used G.I.S. data to locate them. That process helps us to pinpoint and monitor exact sites overtime. I also help people enter their censored data into the National Water Information System (NWIS), making sure their metadata is not only correct, but that it also fully describes their dataset and matches exactly in both places.

During spring, summer, and winter breaks from school, I try and get out in the field as much as possible with any group that needs an extra set of hands. So far, I have had the opportunity to work with projects studying groundwater, surface water, soils, gases, and some biological samples that have allowed me to gain a wide range of experience by completing tasks above my level. In the near future, I hope to transition into a position that has more responsibility, as a technician or hydrologist, and to be in charge of my own field runs.

What is your most memorable experience with the USGS so far?

I have had so many memorable experiences working with the USGS that this is a hard decision to make. If I had to choose just one, I would have to say I will never forget the summer of 2010 when I had the opportunity to collect groundwater samples for water level measurements and water quality analysis. The field crew and I were collecting samples along the west coast all the way up from Sacramento to Crescent City and back. Never have I seen as much of California as I did that summer collecting samples. There is nothing more exciting than being pushed out of the “usual” and into an unfamiliar place that is filled with natural beauty, talking to people I would never have met, and doing the job I continue to love that always has had some unexpected twist waiting for me to solve.

What do you see as the most valuable part of your work?

The most valuable part of my work has been having the opportunity to gain experience in all areas by collecting, processing, and analyzing samples to establish them in our database. In my opinion, everyone should have at least one opportunity to see how each step is performed so that they too can have a general understanding of how what they do affects the bigger picture.

What are your future plans?

While finishing up with my degrees, I plan to continue working with the USGS and get out in the field as much as possible traveling throughout California and wherever else the USGS takes me. With the USGS I hope to fully gain an understanding of the hydrological issues that we are going to face in the near future, particularly those dealing with climate change and water availability.

Why is the USGS a good place for students to work?

I would have to say that the USGS is a great place to work because they taught me many life values that any teenager could benefit from. I am most thankful to have such amazing coworkers who have not only taught me essential work related skills but have also shared valuable life experiences that have inspired me to be the person I am today. They have been supportive of not only my career related goals, but also have been understanding of my personal goals and have put my education first. Many of my coworkers are now even close friends with whom I can see myself remaining in contact many years down the road.

If you would like to know more about me or what I do, please don’t hesitate to contact me at kbednar@usgs.gov and introduce yourself. I love meeting new people and sharing stories.

Ice Waves. Along the southeastern coast of Greenland, an intricate network of fjords funnels glacial ice to the Atlantic Ocean. Landsat 7 Image.

During a span of 40 years, since 1972, the Landsat series of Earth observation satellites has become a vital reference worldwide for understanding scientific issues related to changes on the Earth’s surface.

To celebrate the 40th Anniversary of Landsat, the U.S. Geological Survey (USGS) and the National Aeronautics and Space Administration (NASA) would like your help in selecting the top five “Earth as Art” images from the more than 120 images in the collection.

The poll is now open and will close on July 6.

Learn more and get details on how to cast your vote.

The top five “Earth as Art” images will be announced on July 23 in Washington, D.C. at a special event commemorating the launch of the first Landsat satellite.

Information as Art

Built by NASA and operated by the USGS, Landsat satellites supply Earth scientists, land-resource managers, and policy makers with objective data about changes across the global landscape. Some changes, like major floods or volcanic eruptions, come quickly; others, like urban sprawl or regrowth from forest fires, appear gradually. Landsat impartially records these and many other changes to the land that are induced by people or nature.

Beyond the scientific information they confer, some Landsat images are simply striking to look at — presenting spectacular views of mountains, valleys, and islands; forests, grasslands, and agricultural patterns. By selecting certain features and coloring them from a digital palate, the USGS has created a series of “Earth as Art” perspectives that demonstrate an artistic resonance in land imagery and provide a special avenue of insight about the geography of each scene.

NASA is preparing to launch the next Landsat satellite in 2013, which will be turned over to USGS for operations and data distribution.

The Lena River, some 2,800 miles (4,500km) long, is one of the largest rivers in the world. The Lena Delta Reserve is the most extensive protected wilderness area in Russia. It is an important refuge and breeding grounds for many species of Siberian wildlife. Landsat 7 Image.

More Information

Earth as Art Image Gallery

Earth as Art at the Library of Congress (exhibit extended through August 31, 2012)

USGS Landsat

NASA Landsat

Contest URL:  http://eros.usgs.gov/eaa_voting/

This stretch of Iceland's northern coast resembles a tiger's head complete with stripes of orange, black, and white. The tiger's mouth is the great Eyjafjorour, a deep fjord that juts into the mainland between steep mountains. The name means "island fjord," derived from the tiny, tear-shaped Hrisey Island near its mouth. The ice-free port city of Akureyri lies near the fjord's narrow tip, and is Iceland's second largest population center after the capital, Reykjavik. Landsat 7 Image.

Young boys working in a newly cropped field in Africa.

USGS geographer Michael Marshall has been studying the effects of evaporative processes on land – water emitted into the atmosphere from the soil and from plants – in East Africa and in the Sahel belt that crosses north-central Africa. Using output from a land surface model, Marshall found substantial drying over much of the Sahel and East Africa during the growing seasons.

“The Sahel is getting drier, and the land process that buffers the decline in rainfall is breaking down under increased warming,” said Marshall, a postdoctoral scholar with the USGS Western Geographic Science Center based in Flagstaff, Ariz. Marshall studies evapotranspiration – the combined effects of water entering the atmosphere via evaporation from the soil or from a plant surface, as well as transpiration, in which plants open their stomata (pores) to take in carbon from the atmosphere for food.

Most research into the effect of evaporation on global climate change deals with the oceans, since they form more than 75 percent of the earth’s surface. But evaporative processes on land are also important, because these processes can more easily be influenced by human activity and because, in some places, they can have a local effect on climate. Evapotranspiration triggers convection – the movement of columns of air – and rainfall. In the Sahel, evapotranspiration and localized convection are especially important because of the distance from the ocean or other large water bodies.

Using remote sensing satellite data and surface reanalysis data, downscaled from global general-circulation models, Marshall and his team analyzed evaporation in Africa over a 31-year period. In contrast to many Intergovernmental Panel on Climate Change (IPCC) simulations, which predict increased moisture over the Sahel, they identified substantial drying over much of the Sahel during the growing season, particularly in the last 10 to 12 years. To explain the discrepancy, Marshall suggested that the negative impacts of warming temperatures may be overcoming any possible rainfall recovery across the Sahel. He hypothesized that lands converted from natural vegetation to agriculture might have contributed to the change.

A herder moves cattle through a barren landscape in eastern Africa.

“The climate models for Africa tend to be uncertain in general, due to a lack of station data in Africa and the complexity of climate in the tropics. There is still much to be learned,” Marshall said.

Marshall suggested that the new agricultural crops, which have smaller root systems and are in the ground for a shorter time than the native perennials, may be so stressed by their harsh conditions that they are releasing less water into the atmosphere and thus affecting the climate. Very few African farmers have access to irrigation. Thus, any disruption of the process that creates convection and rainfall would greatly affect them in the long term.

Marshall aims in further research to use higher-resolution data to compare satellite and ground information from Africa with data from the central United States and from India, where the movement of air produced by evapotranspiration can also induce rainfall.  He hopes his work will give land managers tools to better understand these regions.

Marshall’s research supports the Famine Early Warning Systems Network (FEWS NET), which helps target more than $1.5 billion of food-related assistance to more than 40 countries each year. The USGS is actively involved in FEWS NET, which is sponsored by the U.S. Agency for International Development (USAID) Office of Food for Peace. FEWS NET examines the populations of the developing world with the most food insecurity, identifying critical situations in which food aid will be needed. Often the populations most in need are those whose livelihoods are tied to subsistence rain-fed agriculture and pastoralism.

Marshall’s findings, published in a recent issue of Climate Dynamics, are available online.

More Information:

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