Definitions and Mapping of East African Wetlands: A Review <s> The Contribution of Global Maps <s> Review: Wetlands In Danger: A World Conservation Atlas Edited by Patrick Dugan Reviewed by Daniel L. Tufford University of South Carolina Dugan, Patrick , editor. Wetlands In Danger: A World Conservation Atlas. New York: Oxford University Press, 1993. 192 pp. US $35.00 cloth ISBN:0-19-520942-7. For sheer excellence of presentation, Wetlands In Danger exceeds the value of its sale price. The work is well-organized and illustrated with high-quality photography. Anyone interested in wetland issues will find useful information here. In addition to physical geography, the authors discuss wetland biology and ecology, anthropogenic pressures on wetlands, and the political, economic, and cultural geography of wetlands. The first four chapters are an introduction to the atlas itself. The first chapter defines wetlands and gives an overview of each type. The authors use the wetland definition agreed to at the 1971 Ramsar convention sponsored by the International Union for Conservation of Nature and Natural Resources (IUCN). Many readers will be unfamiliar with the inclusion of lakes as wetlands, but the Ramsar definition includes water up to 6 meters deep. The second chapter introduces wetland ecology, a science still viewed as fundamentally biological. This chapter effectively shows that landscape- scale hydrologic and geochemical processes are essential elements of the role of wetlands in both local and regional ecology. However, the biological ecology of wetlands remains the most obvious and most easily explained to a diverse audience. Thus, the third chapter discusses the unique life in wetlands and the unique role wetlands play in the life cycle of animals not confined to a wetland habitat. The fourth chapter discusses the historical causes and extent of wetland loss worldwide, including the once prevailing notion that wetland use for agriculture was a positive expression of human control over nature. Here, the theme of the book is clarified. Wetland loss is occurring in devastating proportions, and we are only beginning to understand the <s> BIB001 </s> Definitions and Mapping of East African Wetlands: A Review <s> The Contribution of Global Maps <s> Abstract Drawing upon a variety of existing maps, data and information, a new Global Lakes and Wetlands Database (GLWD) has been created. The combination of best available sources for lakes and wetlands on a global scale (1:1 to 1:3 million resolution), and the application of Geographic Information System (GIS) functionality enabled the generation of a database which focuses in three coordinated levels on (1) large lakes and reservoirs, (2) smaller water bodies, and (3) wetlands. Level 1 comprises the shoreline polygons of the 3067 largest lakes (surface area ≥50 km2) and 654 largest reservoirs (storage capacity ≥0.5 km3) worldwide, and offers extensive attribute data. Level 2 contains the shoreline polygons of approx. 250,000 smaller lakes, reservoirs and rivers (surface area ≥0.1 km2), excluding all water bodies of level 1. Finally, level 3 represents lakes, reservoirs, rivers, and different wetland types in the form of a global raster map at 30-second resolution, including all water bodies of levels 1 and 2. In a validation against documented data, GLWD proved to represent a comprehensive database of global lakes ≥1 km2 and to provide a good representation of the maximum global wetland extent. GLWD-1 and GLWD-2 establish two global polygon maps to which existing lake registers, compilations or remote sensing data can be linked in order to allow for further analyses in a GIS environment. GLWD-3 may serve as an estimate of wetland extents for global hydrology and climatology models, or to identify large-scale wetland distributions and important wetland complexes. <s> BIB002 </s> Definitions and Mapping of East African Wetlands: A Review <s> The Contribution of Global Maps <s> Information regarding the spatial extent and timing of flooding in the world's major wetlands is important to a wide range of research questions including global methane models, water management, and biodiversity assessments. The Florida Everglades is one of the largest wetlands in the US, and is subject to substantial development and pressures that require intensive hydrological modeling and monitoring. The Moderate Resolution Imaging Spectrometer (MODIS) is a global sensor with high frequency repeat coverage and significant potential for mapping wetland extent and dynamics at moderate spatial resolutions. In this study, empirical models to predict surface inundation in the Everglades were estimated using MODIS data calibrated to water stage data from the South Florida Water Management District for the calendar year 2004. The results show that hydropatterns in the Florida Everglades are strongly correlated to a Tasseled Cap wetness index derived from MODIS Nadir Bidirectional Reflectance Function Adjusted Reflectance data. Several indices were tested, including the Normalized Difference Wetness Index and the diurnal land surface temperature difference, but the Tasseled Cap wetness index showed the strongest correlation to water stage data across a range of surface vegetation types. Other variables included in the analysis were elevation and percent tree cover present within a pixel. Using logistic regression and ensemble regression trees, maps of water depth and flooding likelihood were produced for each 16-day MODIS data period in 2004. The results suggest that MODIS is useful for dynamic monitoring of flooding, particularly in wetlands with sparse tree cover. <s> BIB003 </s> Definitions and Mapping of East African Wetlands: A Review <s> The Contribution of Global Maps <s> Recent advances in remote sensing provide opportunities to map plant species and vegetation within wetlands at management relevant scales and resolutions. Hyperspectral imagers, currently available on airborne platforms, provide increased spectral resolution over existing spacebased sensors that can document detailed information on the distribution of vegetation community types, and sometimes species. Development of spectral libraries of wetland species is a key component needed to facilitate advanced analytical techniques to monitor wetlands. Canopy and leaf spectra at five sites in California, Texas, and Mississippi were sampled to create a common spectral library for mapping wetlands from remotely sensed data. An extensive library of spectra (n ¼ 1336) for coastal wetland communities, across a range of bioclimatic, edaphic, and disturbance conditions were measured. The wetland spectral libraries were used to classify and delineate vegetation at a separate location, the Pacheco Creek wetland in the Sacramento Delta, California, using a PROBE-1 airborne hyperspectral data set (5 m pixel resolution, 128 bands). This study discusses sampling and collection methodologies for building libraries, and illustrates the potential of advanced sensors to map wetland composition. The importance of developing comprehensive wetland spectral libraries, across diverse ecosystems is highlighted. In tandem with improved analytical tools these libraries provide a physical basis for interpretation that is less subject to conditions of specific data sets. To facilitate a global approach to the application of hyperspectral imagers to mapping wetlands, we suggest that criteria for and compilation of wetland spectral libraries should proceed today in anticipation of the wider availability and eventual space-based deployment of advanced hyperspectral high spatial resolution sensors. 2008 Elsevier Ltd. All rights reserved. <s> BIB004 </s> Definitions and Mapping of East African Wetlands: A Review <s> The Contribution of Global Maps <s> Emerging global role of small lakes and ponds: little things mean a lot Until recently, small continental waters have been completely ignored in virtually all global processes and cycles. This has resulted from the neglect of these systems and processes by ecologists and the assumption that ecosystems with a small areal extent cannot play a major role in global processes. Recent inventories based on modern geographical and mathematical approaches have shown that continental waters occupy nearly twice as much area as was previously believed. Further, these inventories have shown that small lakes and ponds dominate the areal extent of continental waters, correcting a century- long misconception that large lakes are most important. The global importance of any ecosystem type in a process or cycle is the product of the areal extent and the intensity of the process in those ecosystems. Several analyses have shown the disproportionately great intensity of many processes in small aquatic ecosystems, indicating that they play an unexpectedly major role in global cycles. Assessments of the global carbon cycle underscore the need for aquatic scientists to view their work on a global scale in order to respond to the Earth's most pressing environmental problems. <s> BIB005 </s> Definitions and Mapping of East African Wetlands: A Review <s> The Contribution of Global Maps <s> Large-scale estimates of the area of terrestrial surface waters have greatly improved over time, in particular through the development of multi-satellite methodologies, but the generally coarse spatial resolution (tens of kms) of global observations is still inadequate for many ecological applications. The goal of this study is to introduce a new, globally applicable downscaling method and to demonstrate its applicability to derive fine resolution results from coarse global inundation estimates. The downscaling procedure predicts the location of surface water cover with an inundation probability map that was generated by bagged derision trees using globally available topographic and hydrographic information from the SRTM-derived HydroSHEDS database and trained on the wetland extent of the GLC2000 global land cover map. We applied the downscaling technique to the Global Inundation Extent from Multi-Satellites (GIEMS) dataset to produce a new high-resolution inundation map at a pixel size of 15 arc-seconds, termed GIEMS-D15. GIEMS-D15 represents three states of land surface inundation extents: mean annual minimum (total area, 6.5 x 10(6) km(2)), mean annual maximum (12.1 x 10(6) km(2)), and long-term maximum (173 x 10(6) km(2)); the latter depicts the largest surface water area of any global map to date. While the accuracy of GIEMS-D15 reflects distribution errors introduced by the downscaling process as well as errors from the original satellite estimates, overall accuracy is good yet spatially variable. A comparison against regional wetland cover maps generated by independent observations shows that the results adequately represent large floodplains and wetlands. GIEMS-D15 offers a higher resolution delineation of inundated areas than previously available for the assessment of global freshwater resources and the study of large floodplain and wetland ecosystems. The technique of applying inundation probabilities also allows for coupling with coarse-scale hydro-climatological model simulations. (C) 2014 Elsevier Inc All rights reserved. <s> BIB006
Downing BIB005 contends that small, aquatic ecosystems are systematically ignored in global surveys, principally due to issues of scale rather than any lack of knowledge or awareness. The "small and fragmented nature of wetlands" BIB003 along with their diverse surface features are sources of underestimation in global wetland maps. As summarized in Table 4 , substantial deviations in global wetland area estimates are repeatedly documented [24] . One of the most significant global wetlands data layers was produced in 2004 by Lehner and Döll BIB002 . It is part of a Global Lakes and Waterbodies Database that is publicly distributed by the World Wildlife Fund (WWF). This dataset is based on seven digital maps of the world, principally the 1993 ESRI Digital Chart of the World and the 1993 World Conservation Monitoring Center (WCMC) Wetlands Map. These data are represented in a 30-arc-second spatial resolution grid and combine spatial resources on different scales. Considering the difficulties in worldwide classification and validation of water bodies and wetlands by remotely-sensed data, the authors of this map do not rely solely on these data, but rather they collect information from "…existing lake and wetland registers, maps and databases" BIB002 . Most of the datasets used in this project are now more than twenty years old. Due to extensive losses in wetlands globally BIB001  and the disparity among wetland area estimates, an update would be of significant value to wetland researchers and global climate modellers  . The controversy and difficulties of scale in global wetland area estimation are obvious when reviewing comments regarding the Lehner and Döll dataset. Zomer et al. BIB004 observe that, while the task of developing a global wetland inventory is difficult and this dataset is based on the best available data, it is insufficient for regional or local wetland management. However, the dataset is also called the "…most detailed…inventory…in the past 20 years and maybe the most accurate" [24] . * Spatially-explicit dataset, global wetland map available, not necessarily in digital mode. Table 4 shows existing global wetland datasets and the variety in area estimation of global wetland maps and catalogues. Wetland area estimates differ by more than 100%, ranging between 5.6 × 10 8 ha BIB001 and 1.2 × 10 9 ha  . At this date, no global dataset of wetlands exists that is compiled solely through the use of satellite remote sensing data. However, researchers supported by NASA currently are compiling a global inundated areas dataset using spaceborne microwave data  . The remotely-sensed global inundation products resulting from this work have the potential to provide estimates of global wetland areas. Selected inundation data layers, including coverage of the state of Alaska, are now complete and available. A complementary time series of coarse resolution (~25 km) global inundation is also available online via NASA's Jet Propulsion Laboratory homepage  . From this effort, interactive inundation time series data are available globally, again via web access at the Alaska Satellite Facility  . Comparing this map to the GlobE Wetlands project test sites leads to the conclusion that the Alaska Satellite Facility dataset does not reliably depict wetlands. In another wetland mapping effort, Fluet-Chouinard et al. BIB006 have utilized a downscaling approach to integrate global land use/land cover estimates with the Lehner and Döll Global Lakes and Wetlands Database. The high-resolution global inundation map generated in this study is currently available to users BIB006 . We consider inundation to be an important proxy for wetland formation, and the datasets described here can be expected to significantly support future wetland mapping efforts.