River channel-floodplain dynamics along the Canadian River in Oklahoma

In 1820, the lower Canadian River meandered through a densely forested floodplain. By 1898, most of the floodplain had been cleared for agriculture and changes in channel geometry and specific stream power followed, particularly channel widening and straightening with a lower potential specific stream power. In 1964, a large upstream hydropower dam was constructed, which changed the flow regime in the lower Canadian River and consequently the channel geometry. Without destructive overbank floods, the channel narrowed rapidly and considerably due to encroachment by floodplain vegetation. The lower Canadian River, which was once a highly dynamic floodplain-river system, has now been transformed into a relatively static river channel. These changes over the past 200 years have not been linear or independent. In this study, we used a variety of data sources to assess these historical changes along the lower Canadian River floodplain and identify feedbacks among floodplain cultivation, dam construction, specific stream power, and channel width, slope, and sinuosity. Finally, we combined the results of our study with others in the region to present a biogeomorphic response model for large Great Plains rivers that characterizes channel width changes in response to climate variability and anthropogenic disturbances.

References

Julian JP, Thomas RE, Said S, Hoagland BW, Tarhule A.  2012.  Historical variability and feedbacks among land cover, stream power, and channel geometry along the lower Canadian River floodplain in Oklahoma.  Earth Surface Processes and Landforms 37: 449-458, doi:10.1002/esp.2272.

Development of an accurate fine-resolution land cover timeline: Little Rock, Arkansas, USA (1857-2006)

The need for accurate and compatible historical land cover datasets is increasing due to the growing interest in the drivers and impacts of landscape changes. In this article, we present a framework that uses readily available data to develop historical land cover timelines over large areas with fine resolution. We applied this framework to a 10,000-km2 area around Little Rock, Arkansas (USA) to document land cover changes at 60 m resolution from 1857 to 2006. First, we improved the earliest available maps of the region (1857) and digitized the first available aerial photographs (1943). We then modified the first national land cover dataset (GIRAS, 1975) to make it compatible with the contemporary national land cover database (1994-2006). These modifications increased the overall mapping accuracy of GIRAS from 66.5% to 77.8%, mainly by improving its resolution so that small, heterogeneous land cover patches were
represented. Finally, we used our newly created fine-resolution land cover timeline to characterize major transitions in central Arkansas, which over a 149 y period was converted from a forest- and wetland-dominated landscape to an urban- and agriculture-dominated landscape. By applying our framework to other regions, researchers can begin to understand the drivers and impacts of land cover changes.

Little Rock, Arkansas (USA) in 1871

 

 

References

Jawarneh RN, Julian JP. 2012. Development of an accurate fine-resolution land cover timeline: Little Rock, Arkansas, USA (1857 – 2006). Applied Geography 35: 104-113.

Interactive effects of climate and land management on water quality in New Zealand rivers

Land cover change is heavily influenced by climate and land management. In places where the land is managed intensively and the climate is highly variable, interactions between these two variables can produce dramatic land cover changes over very short periods, daily in some cases. Given that rivers collect runoff from landscapes, these frequent and intense land cover changes can have considerable impacts on river water quality. A great place to study these landscape dynamics is New Zealand because (1) it has a highly variable climate over both space and time, (2) it has a wide variety and extent of management intensive land uses such as plantation forestry and rotational livestock grazing, (3) it has one of the most comprehensive and consistent water quality datasets in the world, and (4) its political boundaries coincide with watershed/catchment boundaries, which makes it easier to assess some of the political and socio-economic drivers of land use changes. Thus, we are using New Zealand as a case study to investigate how water quality is affected by interactions between climate and land management at fine spatial (30 meter) and temporal (8 day) resolutions. We are currently in the process of creating this 8-day, 30-meter land cover dataset for the entire country of New Zealand using novel and advanced remote sensing techniques.

Strip grazing (upper-left) and plantation forestry (bottom-right) in New Zealand.

 

 

Funding

NSF Geography and Spatial Sciences, Jason Julian (PI) with Kirsten de Beurs (PI) and Chris Weaver (co-I), 2014-2017.

NASA Land Cover Land Use Change Program, Jason Julian (PI) and Kirsten de Beurs (co-PI), 2013-2015.

Fulbright Scholar Program, Jason Julian (PI), 2012.

 

References

Julian JP, Davies-Colley RJ, Gallegos CL, Tran TV.  2013.  Optical water quality of inland waters: A landscape perspective.  Annals of the Association of American Geographers 103: 309-318.

Land Cover Influences on Watershed Runoff Patterns in Eastern Piedmont of USA

Physiography and land cover determine the hydrologic response of watersheds to climatic events. However, vast differences in climate regimes and variation of landscape attributes among watersheds (including size) have prevented the establishment of general relationships between land cover and runoff patterns across broad scales. This project addressed these difficulties by using 87 watersheds within the same physiographic region (eastern Piedmont, USA), thereby minimizing variation in physiography. Power spectral analysis was used to characterize area-normalized runoff patterns for the 87 watersheds, which were then compared to the attributes of the watersheds. The effect of land cover on runoff patterns was confirmed. Urban-dominated watersheds were flashier and had less hydrologic memory compared with
forest-dominated watersheds, whereas watersheds with high wetland coverage had greater hydrologic memory. We also detected a 10–15% urban threshold above which urban coverage became the dominant control on runoff patterns. When spectral
properties of runoff were compared across stream orders, a threshold after the third order was detected at which watershed processes became dominant over precipitation regime in determining runoff patterns. Finally, we present a matrix that characterizes the hydrologic signatures of rivers based on precipitation versus landscape effects and low-frequency versus high-frequency events. The concepts and methods presented can be generally applied to all river systems to characterize multiscale patterns of watershed runoff.

 

 

 

References

Julian JP, Gardner RH.  2014.  Land cover effects on runoff patterns in eastern Piedmont (USA) watersheds.  Hydrological Processes 28: 1525-1538.

The use of Landsat and MODIS data to remotely estimate Russia’s sown area

The intensity of crop management is one of the most important management decisions that affect soil carbon stocks in croplands. In this study, we use satellite data at two spatial resolutions (30m Landsat and 500m MODIS) and field observations to determine arable lands in a portion of the Russian grain belt. Once arable lands are established we map cropping intensity between 2002 and 2009 to get a better understanding of the activity occurring on arable lands. Our arable land estimates compare favourably with the 2006 all Russian agricultural census. We also compare three global datasets that quantify croplands against the census data. Finally, we show that our cropping intensity map compares very well to the available regional statistical data on cropping intensity. Our crop intensity map reveals that  areas in the southern part of our study region are successfully cropped  during fewer years than more central areas of the study region.

The use of Landsat and MODIS data to remotely estimate Russia’s sown area. Journal of Land Use Science. In press.

Cropland (intensity) data created in this project.

Cropland data Russia oblasts.

This project is funded by NASA’s Land Cover Land Use Change Program.

A land surface phenology assessment of the northern polar regions using MODIS reflectance time series

The study of changes in phenology and, in particular, land surface phenology (LSP) provides an important approach to detecting responses to climate change in terrestrial ecosystems. LSP has been studied primarily through analysis of time series of vegetation indices retrieved from passive optical sensors, such as the series of AVHRRs on polar-orbiting satellites and the pair of MODIS sensors on the Terra and Aqua platforms that provide higher spatial, spectral, and radiometric resolution. Most broad-scale vegetation studies use normalized difference vegetation index (NDVI) data. Here, we provide an overview of the LSP of the northern polar and high-latitude regions (§60uN) based on MODIS data at climate modeling grid (0.05u) resolution. We demonstrate the relationship between three onset-of-greening measures and snow cover and accumulated growing degree-days.We show that the Arctic Oscillation index is significantly correlated with the peak timing of the growing seasons since 2000 for a range of ecoregions, and we demonstrate that there were more than three times as many negative NDVI changes since 2000 as positive changes (25.3% versus 7.3%) based on all land area above 60uN. We reveal that these changes are predominantly driven by minimum temperature changes.

References

  • de Beurs, K.M., Henebry, K.M. 2010.A land surface phenology assessment of the northern polar regions using MODIS reflectance time series.Canadian Journal of Remote Sensing, Volume 36, Supplement S1, S87-110.
  • de Beurs, K.M., Henebry, G.M., 2008.Northern Annular Mode effects on the Land Surface Phenologies of Northern Eurasia.Journal of Climate, 21:4257-4279

Land surface phenology of North American mountain environments using moderate resolution imaging spectroradiometer data

Monitoring and understanding plant phenology is becoming an increasingly important way to identify and model global changes in vegetation life cycle events. High elevation biomes cover twenty percent of the Earth’s land surface and provide essential natural resources.  These areas experience limited resource availability for plant growth, development, and reproduction, and are one of the first ecosystems to reflect the harmful impact of climate change. Despite this, the phenology of mountain ecosystems has historically been understudied due to the rough and variable terrain and inaccessibility of the area. In addition, although numerous studies have used synoptically sensed data to study phenological patterns at the continental and global scale, relatively few have focused on characterizing the land surface phenology in mountainous areas. Here we use the MODIS/Terra+Aqua satellite 8-day 500m Nadir BRDF Adjusted Reflectance product to quantify the land surface phenology. We relate independent data for elevation, slope, aspect, solar radiation, and temperature as well as longitude and latitude with the derived phenology estimates. We present that satellite derived SOS can be predicted based on topographic and weather variables with a significant R² between 0.56 and 0.62 for the entire western mountain range. Elevation and latitude exhibit the most significant influences on the timing of SOS throughout our study area. When examined at both the local and regional scale, as well as when accounting for aspect and temperature, SOS follows closely with Hopkins’ Bioclimatic Law with respect to elevation and latitude.

References

** Hudson-Dunn, A., de Beurs, K.M., 2011. Land Surface Phenology of North American Mountain Environments Using Moderate Resolution Imaging Spectroradiometer data. Remote Sensing of Environment, vol 115(5), p1220-1233.

The response of African land surface phenology to large scale climate oscillations

Variations in agricultural production due to rainfall and temperature fluctuations are a primary cause of food insecurity on the continent in Africa.  Analysis of changes in phenology can provide quantitative impact of climate variability on growing seasons in agricultural regions. Using a robust statistical methodology, we describe the relationship between phenology metrics derived from the 26 year AVHRR NDVI record and the North Atlantic Oscillation index (NAO), the Indian Ocean Dipole (IOD), the Pacific Decadal Oscillation (PDO), and the Multivariate ENSO Index (MEI).  We map the most significant positive and negative correlation for the four climate indices in Eastern, Western and Southern Africa between two phenological metrics and the climate indices.  Our objective is to provide evidence of whether climate variability captured in the four indices has had a significant impact on the vegetative productivity of Africa during the past quarter century. We found that the start of season and cumulative NDVI were significantly affected by large scale variations in climate. The particular climate index and the timing showing highest correlation depended heavily on the region examined. In Western Africa the cumulative NDVI correlates with PDO in September-November. In Eastern Africa the start of the June-October season strongly correlates with PDO in March-May, while the PDO in December-February correlates with the start of the February-June season. The cumulative NDVI over this last season relates to the MEI of March-May. For Southern Africa, high correlations exist between SOS and NAO of September-November, and cumulative NDVI and MEI of March-May. The research shows that climate indices can be used to anticipate late start and variable vigor in the growing season of sensitive agricultural regions in Africa.

References

Brown, M.E., de Beurs, K.M., Vrieling, A. 2010. The response of African land surface phenology to large scale climate oscillations. Remote Sensing of Environment, vol 114(10), p2286-2296

Urbanization Effects on Riverbank Erosion and Channel Geometry

This study identified and assessed the controls on hydraulic erosion of cohesive riverbanks along a 600-m reach of an urban stream in the heart of downtown Aiken, South Carolina, USA.  We examined hydraulic bank erosion by separating bank shear stress into four properties: magnitude, duration, event peak, and variability.  Results showed that the event peak (maximum peak) of excess shear stress best predicted cohesive bank erosion at transects with moderate critical shear stresses (1.93 – 4.08 N/m2), while the variability (all peaks) of excess shear stress best predicted erosion at the transect with low critical shear stress (0.95 N/m2).  These results suggest the increased flow peak intensities from urbanized watersheds increase hydraulic erosion of riverbanks, resulting in deeper and wider channels. The results of this study were combined with results from previous bank erosion studies to produce a conceptual model for estimating bank erosion rates based on their silt-clay content.

References

Julian JP, Torres R.  2006.  Hydraulic erosion of cohesive riverbanks. Geomorphology 76: 193-206.

Effects of Riparian Deforestation on Stream Ecosystems

An emerging issue in stream ecology and ecohydrology is the role of light in fluvial ecosystem dynamics. In this project, we investigated how photosynthetically active radiation (PAR) influences the hydrogeomorphology and biogeochemistry of a 2nd-order temperate stream in central Wisconsin with varying riparian communities; from heavily shaded forest sections to unshaded grass sections. First, in-stream PAR was compared to submerged aquatic vegetation distributions along a 1.2-km reach. We then analyzed the effects of vegetation on water depth, sediment size, sediment volume, organic matter accumulation, and nutrient uptake. Compared to forested sites, deforested sites had three times more benthic PAR, which resulted in a quadrupling of vegetation biomass. This greater biomass at deforested sites increased water depth, sediment accumulation, and the uptake of soluble reactive phosphorous (SRP). Finally, we used the above relations to estimate biogeochemical differences between a completely forested reach and a deforested reach. Compared to a forested reach, the deforested reach accumulated almost twice as much bed sediment and retained more than four times as much SRP. Thus, changes in riparian conditions may create a cascade through which shading drives changes in stream habitat, which in turn drives changes in hydrogeomorphology and biogeochemical cycles.

 

References

  • Julian JP, Seegert SZ, Powers SM, Stanley EH, Doyle MW.  In press, available online.  Light as a first-order control on ecosystem structure in a temperate stream.  Ecohydrology, doi: 10.1002/eco.144.
  • Julian JP, Doyle MW, Stanley EH. 2008.  Empirical modeling of light availability in rivers. Journal of Geophysical Research – Biogeosciences 113: G03022, doi:10.1029/2007JG000601.
  • Riggsbee JA, Manners R, Julian JP, Doyle MW, Muehlbauer J, Sholtes J, Small MJ. Accepted. Influence of aquatic organisms on channel forms and processes. In Treatise in Fluvial Geomorphology. Ed. Wohl E. Elsevier.