Satellite-based precipitation estimation using watershed segmentation and growing hierarchical self-organizing map

This paper outlines the development of a multi-satellite precipitation estimation methodology that draws on techniques from machine learning and morphology to produce high-resolution, short-duration rainfall estimates in an automated fashion. First, cloud systems are identified from geostationary infrared imagery using morphology based watershed segmentation algorithm. Second, a novel pattern recognition technique, growing hierarchical self-organizing map (GHSOM), is used to classify clouds into a number of clusters with hierarchical architecture. Finally, each cloud cluster is associated with co-registered passive microwave rainfall observations through a cumulative histogram matching approach. The network was initially trained using remotely sensed geostationary infrared satellite imagery and hourly ground-radar data in lieu of a dense constellation of polar-orbiting spacecraft such as the proposed global precipitation measurement (GPM) mission. Ground-radar and gauge rainfall measurements were used to evaluate this technique for both warm (June 2004) and cold seasons (December 2004-February 2005) at various temporal (daily and monthly) and spatial (0.04 and 0.25) scales. Significant improvements of estimation accuracy are found classifying the clouds into hierarchical sub-layers rather than a single layer. Furthermore, 2-year (2003-2004) satellite rainfall estimates generated by the current algorithm were compared with gauge-corrected Stage IV radar rainfall at various time scales over continental United States. This study demonstrates the usefulness of the watershed segmentation and the GHSOM in satellite-based rainfall estimations

Spatial and temporal changes in the rainfall patterns of Botswana, 1998-2013

A Research Report submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in partial fulfilment of the requirements for the degree of Master of Science. Johannesburg, October 2016.Rainfall is a complex phenomenon, which has previously been explored by assessing rainfall patterns in time and space, typically using ground-based weather stations. Rainfall patterns in southern Africa tend to have a direct impact on vegetation growth and surface water availability, and an indirect impact on animal movement. This study investigated rainfall in Botswana by analysing changes in spatial and temporal patterns from 1998 to 2013, using satellite imagery. Tropical Rainfall Measuring Mission (TRMM) 3B43 dataset (1998-2013) was used to document monthly rainfall magnitude and variability over the 15-year period. Additionally, a GIS spatial analysis approach, the Anselin Local Moran’s I tool, was used to determine changes (i.e. persistence) of rainfall conditions on a year by year basis during the study period. WorldClim precipitation data (1950-2000) were utilised as a longer term average reference dataset against which TRMM data could be compared. This study found that the rainy season consisted of relatively high rainfall magnitudes and variability, while the post rainy season consisted of relatively lower rainfall magnitudes and variability across Botswana. Higher magnitudes persisted into April, indicating the occurrence of late summer rainfall during this observation period. From a regional perspective, the Okavango Delta remained a region of relatively higher rainfall magnitude and variability compared to surrounding regions, regardless of the season. The rainy season was associated with a high frequency of rainfall events above the long term WorldClim average, and the post rainy season with a high frequency of rainfall below the long term WorldClim average. The spatial analysis indicated an annual persistence of high rainfall clusters in northern Botswana, and a persistence of low rainfall clusters in southern Botswana throughout the 15-year analysis. In addition, a progressive drying trend towards the end of the time series was observed. These findings suggest that Botswana has experienced both wetter conditions and drier conditions within the 15-year analysis period, than have been historically documented. The progressive drying trend towards the end of the time series may be indicative of a changing climate in Botswana. However, due to the length of this analysis period it cannot be proven conclusively that the detected wetter and drier conditions, than historically documented, are a signal of climate change. This rainfall analysis provides a comprehensive understanding of recent spatial and temporal rainfall patterns and changes in Botswana. More specifically, this rainfall study fits into a bigger research project focused on herbivore conservation in Botswana. Together, these studies will collectively enable protected areas authorities to better manage herbivore migration, improving conservation in Botswana over time. Ultimately, this study stands to make a positive contribution towards the development of existing conservation practices in Botswana.LG201

A model assessment of alternative land-use strategies

Changing climatic conditions and unsustainable land use are major threats to savannas worldwide. Historically, many African savannas were used intensively for livestock grazing, which contributed to widespread patterns of bush encroachment across savanna systems. To reverse bush encroachment, it has been proposed to change the cattle-dominated land use to one dominated by comparatively specialized browsers and usually native herbivores. However, the consequences for ecosystem properties and processes remain largely unclear. We used the ecohydrological, spatially explicit model EcoHyD to assess the impacts of two contrasting, herbivore land-use strategies on a Namibian savanna: grazer- versus browser-dominated herbivore communities. We varied the densities of grazers and browsers and determined the resulting composition and diversity of the plant community, total vegetation cover, soil moisture, and water use by plants. Our results showed that plant types that are less palatable to herbivores were best adapted to grazing or browsing animals in all simulated densities. Also, plant types that had a competitive advantage under limited water availability were among the dominant ones irrespective of land-use scenario. Overall, the results were in line with our expectations: under high grazer densities, we found heavy bush encroachment and the loss of the perennial grass matrix. Importantly, regardless of the density of browsers, grass cover and plant functional diversity were significantly higher in browsing scenarios. Browsing herbivores increased grass cover, and the higher total cover in turn improved water uptake by plants overall. We concluded that, in contrast to grazing-dominated land-use strategies, land-use strategies dominated by browsing herbivores, even at high herbivore densities, sustain diverse vegetation communities with high cover of perennial grasses, resulting in lower erosion risk and bolstering ecosystem services

A Study of African Savanna Vegetation Structure, Patterning, and Change

African savannas cover roughly half of the continent, are home to a great diversity of wildlife, and provide ecosystem services to large populations. Savannas showcase a great diversity in vegetation structure, resulting from variation in climatic, edaphic, topographic, and biological factors. Fires play a large role as savannas are the most frequently burned ecosystems on Earth. To study how savanna vegetation structure shifts with environmental factors, it is necessary to gather site data covering the full gradient of climatic and edaphic conditions. Several earlier studies have used coarse resolution satellite remote sensing data to study variation in woody cover. These woody cover estimates have limited accuracy in drylands where the woody component is relatively small, and the data cannot reveal more detailed information on the vegetation structure. We therefore know little about how other structural components, tree densities, crown sizes, and the spatial pattern of woody plants, vary across environmental gradients. This thesis aimed to examine how woody vegetation structure and change in woody cover vary with environmental conditions. The analyses depended on access to very high spatial resolution (\u3c1 \u3em) satellite imagery from sites spread across African savannas. The high resolution data combined with a crown delineation method enabled me to estimate variation in tree densities, mean crown size and the level of aggregation among woody plants. With overlapping older and newer imagery at most of the sites, I was also able to estimate change in woody cover over a 10-year period. I found that higher woody plant aggregation is associated with drier climates, high rainfall variability, and fine-textured soils. These same factors were also indicative of the areas where highly organized periodic vegetation patterns were found. The study also found that observed increases in woody cover across the rainfall gradient is more a result of increasing crown sizes than variation in tree density. The analysis of woody cover change found a mean increase of 0.25 % per year, indicating an ongoing trend of woody encroachment. I could not attribute this trend to any of the investigated environmental factors and it may result from higher atmospheric CO₂ concentrations, which has been proposed in other studies. The most influential predictor of woody cover change in the analysis was the difference between potential woody cover and initial woody cover, which highlights the role of competition for water and density dependent regulation when studying encroachment rates. The second most important predictor was fire frequency. To better understand and explain the dominant ecosystem processes controlling savanna vegetation structure, I constructed a spatially explicit model that simulates the growth of herbaceous and woody vegetation in a landscape. The model reproduced several of the trends in woody vegetation structure earlier found in the remote sensing analysis. These include how tree densities and crowns sizes respond differently to increases in precipitation along the full rainfall range, and the factors controlling the spatial pattern of trees in a landscape

Herbivore Communities and Plant Diversity as Key Drivers of Savanna Ecosystem Resilience in a Changing Climate - A Model Assessment

Savannas play a crucial role in providing essential ecosystem services, including carbon sequestration, biodiversity conservation, and water regulation. However, these ecosystems face threats from changing climatic conditions and unsustainable rangeland practices. Intensive livestock grazing has led to widespread degradation of savanna systems, characterised by shrub encroachment and loss of ecosystem functions. Shifting rangeland use from cattle grazing to native herbivores is proposed to reverse these negative trends, but the consequences for ecosystem properties and processes are not yet clear. Climate change and extreme events such as droughts exacerbate the challenges faced by savannas, potentially affecting the provision of essential ecosystem services on which local people’s livelihoods depend. Ensuring savanna resilience to environmental stressors, especially increased aridity, is essential for sustaining these vital services. This resilience largely depends on the interaction between herbivores, vegetation composition, and climate. Unfortunately, our understanding of this interaction is limited, and current research has not addressed how savannas will respond to uncertain future climate conditions under different rangeland management practices. In this thesis, I used the ecohydrological simulation model EcoHyD to investigate the effects of different rangeland practices on vegetation and water resources of a semi-arid savanna under current and future climate. This research makes two important contributions, first by examining the impacts of different future climate projections at a regional scale, which has not been the case in previous studies, and second by modelling rangeland types beyond grazing. In Chapter II of the study, I examined the impacts of grazing and browsing herbivores on plant diversity and ecosystem functioning. The results showed that intensive grazing negatively affects grass cover and water availability, whereas browsing herbivores increased vegetation cover, plant functional diversity, and water use. However, these outcomes may depend on herbivore community composition and climate contexts, especially when extreme events Summary like prolonged droughts occur. In Chapter III, I addressed these context-dependencies by investigating how different rangeland management options (i.e., grazer-dominated, mixed- feeders or browser-dominated herbivore communities) impact savanna ecosystems during droughts of varying durations. I found that diverse herbivore communities with a higher proportion of browsers combined with high plant functional diversity improve plant community resistance to drought and recovery after drought events, thus leading to enhanced ecosystem functioning and resilience. However, to fully understand ecosystem responses to climate change, temperature increases, precipitation changes and droughts need to be considered together. In Chapter IV, I therefore analysed the potential use of wild herbivore communities in regional climate adaptation plans to ensure the long-term resilience of savanna rangelands to the impacts of all aspects of uncertain climate change. My results have shown that while climate change alone does not necessarily lead to ecosystem degradation, in combination with poor management practices such as intensive grazing it can quickly lead to critical thresholds being exceeded. On the other hand, I have found that reducing the density of grazers and including mixed herbivores and browsers can promote ecosystem stability and resilience. Crossing tipping points can thus be delayed, or even avoided. In conclusion, my research suggests that utilising diverse herbivores and functionally diverse plant communities in rangeland management strategies can improve ecosystem resilience, minimise the risk of irreversible degradation, and better manage uncertainties associated with climate change

Report from the Passive Microwave Data Set Management Workshop

Passive microwave data sets are some of the most important data sets in the Earth Observing System Data and Information System (EOSDIS), providing data as far back as the early 1970s. The widespread use of passive microwave (PM) radiometer data has led to their collection and distribution over the years at several different Earth science data centers. The user community is often confused by this proliferation and the uneven spread of information about the data sets. In response to this situation, a Passive Microwave Data Set Management Workshop was held 17 ]19 May 2011 at the Global Hydrology Resource Center, sponsored by the NASA Earth Science Data and Information System (ESDIS) Project. The workshop attendees reviewed all primary (Level 1 ]3) PM data sets from NASA and non ]NASA sensors held by NASA Distributed Active Archive Centers (DAACs), as well as high ]value data sets from other NASA ]funded organizations. This report provides the key findings and recommendations from the workshop as well as detailed tabluations of the datasets considered

Investigating the benefits an early green-up strategy can provide for two semi-arid savanna trees

A thesis submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg in fulfilment of the requirements for the degree of Doctor of Philosophy, 2017Plant phenology, the study of the timing of biological events such as leaf flush, has been identified as a key tool in monitoring and understanding the impacts that changing climates may have on the world. Unfortunately there is a noticeable lack of phenological research in Africa’s savannas in comparison to other global ecosystems, such as temperate forests. Savannas are known for their complexity in structure and composition and the phenology of their flora is no exception to this. Owing to the highly seasonal climates in this system, plants have had to evolve a range of phenological strategies to cope with the limited window of suitable growth conditions during the periodic wet season in the austral summer. One of these phenological strategies is that of early-greening; where deciduous trees will produce new flush prior to the onset of seasonal rainfall when the environmental conditions are at their driest. There is likely no other ecosystem in the world where the early-greening phenomenon occurs, however, it has been recorded in savannas from Africa, Australia, Asia and South America. The global prevalence of this strategy suggests that early-greening trees must gain some benefit from utilising this seemingly risky leaf flushing strategy. The main aim of this study was to investigate two of the hypothesised benefits of an earlygreening strategy for semi-arid savanna trees. The first hypothesis suggested that earlygreeners are extending their growing season beyond that of grasses and late-greeners – whose leaf flush is limited by the availability of water through the onset of seasonal rainfall. The second hypothesis is that early-greeners produce new leaves ahead of the emergence of invertebrate herbivores with the onset of the first rains, therefore decreasing the risk of damage to the vulnerable tissues and allowing the defence mechanisms within/upon the leaf to develop. This study took place in the Nylsvley Nature Reserve (NNR) over three consecutive austral growing seasons (August 2012 to April 2015) and was conducted on the two dominant deciduous broad-leaved trees: Burkea africana and Terminalia sericea. Burkea africana is known to flush prior to the onset of seasonal rainfall and was considered the earlygreening species in this study. Terminalia sericea has been recorded as flushing leaves prior to the onset of rainfall, but is more often a facultative-greener – rapidly producing new leaves with the onset of seasonal rainfall. This study experienced high seasonal variability between years with early-greening only occurring during the final (2014-2015) season. Nevertheless, I was able to assess the weekly green-up phenology of both species during the first three months of green-up and found that the green-up of the trees was largely disconnected from the main system driver – water – while grass green-up was closely linked to the onset of rainfall. This complements the theory of temporal niche separation; however, when assessing the functionality of the new leaves produced, carbon gain only occurred after the first two weeks post bud-break. In a system such as the NNR where rainfall onset variability is high, trees will only gain the advantage of an extended growing season if the onset of rainfall is more than two weeks after the start of flush. Using historical rainfall records (1980-2014), I estimated that 46% of years could have potentially experienced early-greening with rainfall commencing after the 15th October – the earliest date of green-up prior to rainfall onset in the NNR during this study. One of the benefits tested relating to early-greening in this study was that early-greeners avoid invertebrate herbivore damage on vulnerable new leaves. This study provided evidence for the use of a phenological defence strategy to cope with invertebrate herbivory pressure. Leaves which emerged before the rains had lower rates of herbivore damage than those which emerged after. Moreover, it was demonstrated that the constant turnover of leaves with high photosynthetic rates (T. sericea) is a reasonable mechanism for dealing with high leaf herbivory, and can result in equivalent end of season leaf area (and carbon gain) to species which invest in defence and have slower turnover rates (B. africana). Using the ground-based phenological measures in conjunction with remotely sensed NDVI imagery, the frequency of early-greening across seven comparable broad-leaved woodland sites in southern Africa from 2002 to 2014 was quantified. Of the environmental variables considered, the predictability of early-season rain (rather than total rainfall amount) was best correlated with early-greening. In savannas where rainfall onset and annual amounts were highly variable (such as the NNR), early-greening was less frequent (20% of the years) while in savannas closer to the equator where rainfall amounts were consistently >900 mm per annum and the onset dates began within a two week window each season, early-greening occurred in 80-90% of all years. The decrease in the proportion of early-greening events in the NNR from the 1980s to the past decade could be driven by the changing rainfall regimes over South Africa – with a predicted decrease in the number of precipitation events, but an increase in the storm intensity and rainfall amounts in each of these events. Fewer precipitation events may increase the risks associated with the early-greening strategy and this may be driving the NNR trees to use this strategy less frequently. This study has highlighted the need for a long-term phenological monitoring network within southern Africa’s savannas and has illustrated how early-greening species can benefit over other flora when environmental conditions are suitable for them to commence early leaf flush. This thesis has shown that early-greening broad-leaved savannas trees in South African savannas are more likely to avoid invertebrate herbivory than extend their growing seasons.XL201

NASA earth science and applications division: The program and plans for FY 1988-1989-1990

Described here are the Division's research goals, priorities and emphases for the next several years and an outline of longer term plans. Included are highlights of recent accomplishments, current activities in FY 1988, research emphases in FY 1989, and longer term future plans. Data and information systems, the Geodynamics Program, the Land Processes Program, the Oceanic Processes Program, the Atmospheric Dynamics and Radiation Program, the Atmospheric Chemistry Program, and space flight programs are among the topic covered

Satellite Remote Sensing of Woody and Herbaceous Leaf Area for Improved Understanding of Forage Resources and Fire in Africa

In sub-Saharan Africa (SSA) tree-grass systems commonly referred to as savannas dominating drylands, play a critical role in social, cultural, economic and environmental systems. These coupled natural-human systems support millions of people through pastoralism, are important global biodiversity hotspots and play a critical role in global biogeochemical cycles. Despite the importance of SSA savannas, they have been marginalized for years as most governments neglect dryland resources in favor of agricultural research and development assistance. Hence, lack of spatially and temporally accurate information on the status and trends in savanna resources has led to poor planning and management. This scenario calls for research to derive information that can be used to guide development, management and conservation of savannas for enhanced human wellbeing, livestock productivity and wildlife management. The above considerations motivated a more detailed study of the composition, temporal and spatial variability of savannas, comprising of three components. Remote sensing data was combined with field and literature data to: partition Moderate Resolution Imaging Spectroradiometer (MODIS) total leaf area index (LAIA) time series into its woody (LAIW) and herbaceous (LAIH) constituents for SSA; and application of the partitioned LAI to determine how changes in herbaceous and woody LAI, affect fire regimes and livestock herbivory in SSA. The results of this analysis include presentation of algorithm for partitioning of MODIS LAIA from 2003-2015. Biome phenologies, seasonality and distribution of woody and herbaceous LAI are presented and the long-term average 8-day phenologies availed for evaluation and research application. In determining how changes in herbaceous and woody LAI affect fire regimes in SSA, we found that herbaceous fuelload (indexed as LAIH) correlated more closely with fire, than with LAIW, providing more explanatory power than overall biomass in fire activity. We observed an asymptotic relationship between herbaceous fuel-load and fire with trees promoting fires in dry ecosystems but suppressing fires in wetter regions. In the livestock herbivory analysis we found that the more refined forage indices (LAIH and LAIW) explained more of the variability in livestock distribution than the aggregate biomass, with livestock favoring moderate to nutrient rich forage resources dependent on animal body size

Mission to Planet Earth. Strategic enterprise plan, 1995-2000

Mission to Planet Earth (MTPE) provides long-term understanding of the earth system needed to protect and improve our environment, now and for future generations. This MTPE Strategic Enterprise Plan states how NASA intends to meet its responsibility to the Nation for developing a long-term, integrated program of environmental observation in support of informed decision-making. This plan implements the NASA Strategic Plan for the MTPE Enterprise; it is the first version of a rolling 5-year plan that will be updated annually. It is consistent with the interagency program developed by the Committee on Environment and Natural Resources of the National Science and Technology Council and implemented in large part through the U.S. Global Change Research Program. This report consists of the following sections: (1) introduction; (2) scientific foundation; (3) mission (destination and purposes); (4) principle of operation (ethical and quality assurance standards); (5) customer base (to ensure that the right products and services are delivered); (6) internal and external assessments; (7) assumptions; (8) goals, objectives, and strategies; (9) linkages to other strategic enterprises; and (10) summary