Terms Of Land Cover Research Articles

Fire frequency analysis in Portugal (1975 - 2005), using Landsat-based burnt area maps

Fire frequency in 21 forest planning regions of Portugal during the period 1975–2005 was estimated from historical burnt area maps generated with semi-automatic classification of Landsat Thematic Mapper (TM) satellite imagery. Fire return interval distributions were modelled with the Weibull function and the estimated parameters were used to calculate regional mean, median and modal fire return intervals, as well as regional hazard functions. Arrangement of the available data into three different time series allowed for assessment of the effects of minimum mapping unit, time series length and use of censored data on the Weibull function parameter estimates. Varying the minimum mapping unit between 5 and 35 ha had a negligible effect on parameter estimates, whereas changing the time series length from 22 to 31 years substantially affected the estimates. However, the strongest effect was caused by censored data. Its exclusion led to substantial overestimation of fire frequency and of burning probability dependence on fuel age. We estimated a country-wide mean fire interval of 36 years and an annual burnt area of 1.2%. Regional variations in fire frequency descriptors were interpreted in terms of land cover and land use practices that affect the contemporary fire regime in Portugal.

Size-dependent pattern of wildfire ignitions in Portugal: when do ignitions turn into big fires?

Not all wildfire ignitions result in burned areas of a similar size. The aim of this study was to explore whether there was a size-dependent pattern (in terms of resulting burned area) of fire ignitions in Portugal. For that purpose we characterised 71,618 fire ignitions occurring in the country in the period 2001–2003, in terms of population density in the local parish, land cover type and distance to roads. We then assigned each ignition into subsets of five classes according to the resulting burned area: >5 ha, >50 ha, >100 ha, >250 ha, >500 ha. The probability of an ignition resulting in different burned area classes was modelled using binary logistic regression, and the relative importance, strength and signal (positive or negative) of the three explanatory variables compared across the models obtained for the different classes. Finally, we explored the implications of land cover and population density changes during the period 1990–2000 in Portugal for the likelihood of ignitions resulting in wildfires >500 ha. Population density was the more important variable explaining the resulting burned area, with the probability of an ignition resulting in a large burned area being inversely related to population density. In terms of land cover, ignitions resulting in large burned areas were more likely to occur in shrubland and forest areas. Finally, ignitions farther away from roads were more likely to result in large burns. The current land cover trends (decrease of agricultural land and increase in shrublands) and population trends (decline in population densities except near the coast) are increasing the probability that ignitions will result in large fires in vast regions of the country.

A multi-scale approach to urban thermal analysis

An environmental consequence of urbanization is the urban heat island effect, a situation where urban areas are warmer than surrounding rural areas. The urban heat island phenomenon results from the replacement of natural landscapes with impervious surfaces such as concrete and asphalt and is linked to adverse economic and environmental impacts. In order to better understand the urban microclimate, a greater assessment of the overall urban thermal pattern, including an analysis of the thermal properties of individual land covers, is needed. This study examines the surface thermal pattern by means of thermal land cover response for the Salt Lake City, Utah, study area at two scales: 1) the community level, and 2) the regional or valleywide level. Airborne ATLAS (Advanced Thermal and Land Applications Sensor) data, a high spatial resolution (10-meter) dataset appropriate for an environment containing a concentration of diverse land covers, are used for both land cover and thermal analysis at the community level. The ATLAS data consist of 15 channels covering the visible, near-IR, mid-IR and thermal-IR wavelengths. At the regional level Landsat TM data are used for land cover analysis while the ATLAS channel 13 data are used for the thermal analysis. Results show that a ground-level heat island is evident at both the community and the valleywide level where there is an abundance of impervious surfaces. ATLAS data perform well in community level studies in terms of land cover and thermal exchanges, but other, more coarse-resolution data sets are more appropriate for large-area thermal studies. Thermal response per land cover is consistent at both levels, which suggests potential for comparison with more coarse spatial resolution studies.

衛星リモートセンシングを用いたアジアの被雲率分布特性の解析

An operational scheme for masking cloud-contaminated pixels in Advanced Very High Resolution Radiometer (AVHRR) daytime data was developed, evaluated and presented. Dynamic thresholding was used with channel 1, 2 and 3 to automatically create a cloud mask for a single image. Then the 10-day cloud coverage imagery was generated over the whole Asian region along with cloud-free composite imagery. Finally the monthly based compiling was conducted based on the derived cloud coverage imagery in terms of land cover and country. As a result, it was found that 20-day is required to acquire the cloud free data over the whole asia using NOAA AVHRR. The 10-day cloud coverage and cloud free composite imagery derived in this research is available via the website http: //webpanda.iis.u-tokyo.ac.jp/CloudCover/.

Landscape changes and ecological studies in agricultural regions, Québec, Canada

Most landscape definitions in the western world are based on soil, climatic, or physiographic features and do not integrate humans as an integral part of the landscape. We present an approach where landscape types have been delineated in southern Quebec, Canada based on current land use where anthropogenic and agricultural activities are concentrated as a practical application of the holistic approach in landscape definition. Landsat-TM satellite images were classified and the 27 habitat classes were regrouped into 5 general land cover classes (cash crop, dairy farming, forest, anthropogenic, wetlands) and overlaid onto soil landscape polygons to characterize natural boundary units. Cluster analyses were used to aggregate these polygons into seven agricultural types of land scape forming a gradient from urban and high-intensity cash crop farming activities to landscapes dominated by a mosaic of agriculture and forested areas. Multivariate analyses of raw data and of socio-economic and farming practices variables were used to describe the defined types of landscape and these were projected over three established land classification systems of southern Quebec (Canadian ecoregions, North American Bird Conservation Initiative regions and Corn Heat Unit regions) to compare their similarity in terms of land cover and for planning of future ecological studies. Because agricultural landscapes are highly dynamic, they are bound to undergo changes in the near future. Our landscape delineation may serve as an experimental setup where land scape dynamics and wildlife populations and community structures could be monitored. Because the information we used to delineate and characterize agricultural landscape types is readily available in other countries, our approach could easily be adapted to similar data sources under and a wide variety of landscape types.

Variation in Freshwater Critical Loads Across Two Upland Catchments in the UK: Implications for Catchment Scale Management

In the UK the “critical loads” approach has been used to derive maps based on the 10km x 10km national grid. However, this grid based approach is inappropriate for catchment scale management and these maps cannot be used for “stock at risk” assessments of the number of water bodies or lengths of streams in a given area that may be vulnerable to acidification. Critical loads are determined across two large river catchments in England (The Duddon) and Wales (The Glaslyn). High resolution, digital datasets are used to characterise the attributes of each subcatchment in terms of land cover, soil, geology, topography and topology. Empirical models used to examine the relationship between these attributes and critical loads indicate that the former can be used to account for significant variation in the latter. However, these relationships can vary from catchment to catchment. Thus, although this approach provides the potential for identifying sensitive surface waters on a catchment wide basis, it is likely that models will need to be parameterised on a catchment specific basis.

The use of sighting data to analyse Iberian lynx habitat and distribution

Summary 1. Over a large part of its very restricted and fragmented range, Iberian lynx Lynx pardinus occur in remote mountainous country at low density, where the only information about the species comprises records of incidental sightings obtained by inquiry. In this study we developed an approach for quantifying lynx–habitat relationships and distribution patterns from sighting data, using records from western Algarve (Portugal) in 1990–95. 2. Habitat was described in terms of land cover, topography, human disturbance and rabbit abundance, in 25‐km2 cells surrounding lynx sightings and at random locations within the study area. 3. Lynx sightings were consistently associated with predictable habitat features. Sighting probabilities estimated from a logistic regression model increased with the abundance of rabbits and the proportion of land covered by tall Mediterranean maquis, and declined with road density and the amount of developed land. This model identified correctly 85·7% of lynx sightings; at the same time only 20·7% of the random locations were misclassified. 4. Indices of human presence were never associated positively with lynx sightings, suggesting that observation patterns were not influenced by the spatial distribution of potential observers. 5. Kriging was used to interpolate spatially between sighting probabilities derived from the logistic model in order to produce a map of sighting potential for the Iberian lynx in western Algarve. Jack‐knife resampling assessed the accuracy of this map. Three well‐defined areas of high sighting potential were identified, probably representing the lynx core areas in this region. 6. Our analysis of lynx sighting records suggests that these data may provide a first approximation to lynx habitat and distribution when further information is lacking. The application of this approach to other rare and reclusive species is discussed.

Spectral mixture analysis for mapping land degradation in semi-arid areas

Spectral mixture analysis (SMA) is an image-processing technique used for the analysis of airborne hyperspectral remote-sensing data which consist of a large number of spectral bands, typically over 100. In this paper the possibilities are examined of using SMA for the analysis of Landsat Thematic Mapper satellite data with only six bands in the visible to shortwave-infrared wavelength. We use data from a semi-arid area in the Sanmatenga province of Burkina Faso, an area known to experience land-degradation problems. In SMA, we assume that pixels in an image consist of one or more homogeneous (uniform in character) or pure surfaces, the so called end-members. The end-members were derived from the image data on the basis of specific image characteristics. Field data was collected to describe the characteristics of these end-members in terms of land cover, soil and degradation phenomena. The end-members derived from the image analysis, although statistically pure in terms of image spectral characteristics, prove to be mixtures at a field scale. This lack of purity is explained by the nature of semi-arid areas which is more heterogeneous than that of most other areas. The SMA yielded cover percentages for the end-members from which an unsupervised classification was made. Comparison of the classification with the results of SMA shows that the latter provides information on the amount and spatial distribution of land characteristics such as land degradation.

Interactions between land cover and convective cloud cover over Midwestern North America detected from GOES satellite data

Abstract The region of Midwestern North America from 80-95° W and 35-55° N is examined in terms of land cover and convective cloud cover during the summers of 1985 and 1989, using a combination of published land use maps and GOES visible and infrared satellite imagery, for the presence of favoured convective cloud cover over large areas (~ 100 km scale) of homogeneous forest. Days with synoptic flow are eliminated through analysis of 500-mb winds and surface frontal activity. The resulting ‘weak flow’ days’ imagery is organized into 1° × 1° latitude/longitude cells, within which total cumulus cloud cover is manually determined. Three-hourly analysis of convective cloud cover from visible and infrared imagery shows forests in Ontario and the Appalachians to have greater convective cloud cover and the Great Lakes to have less convective cloud cover, on days without frontal activity. This pattern persists throughout the day, for both 1985 and 1989, despite differences in soil moisture (as determined from Cro...

Test of Landsat-Based Urban Hydrologic Modeling

Many of the models designed to support the hydrologic studies associated with urban water resources planning require input parameters that are defined in terms of land cover. Estimating the land cover is a difficult and expensive task and any innovation that can reduce these problems should be of significant value to the water resources planning community. The purpose of the reported investigation was to compare conventional and Landsat-based methods for determining the land cover inputs of hydrologic planning and design models. Comparisons were based on a case study of the Fourmile Run Watershed in Virginia. Results of the study indicated that for planning model studies the Landsat-based approach is highly cost-effective. However, in the design model investigations the errors encountered when the Landsat date are used were unacceptable.