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- Ayala, Ana I., et al.
(författare)
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Analysis of summer heat budget of lakes under a changing climate across a geographic gradient
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Warming surface water temperature is the most direct consequence of climate change in lakes and therefore, predicting the heat exchange at the air-water interface is important to understand how atmospheric forcing will affect lake temperature and thermal structure. Here, we forced a one-dimensional hydrodynamic lake model with outputs from four different climate models under three future greenhouse gas emission scenarios from 1976 to 2099. To investigate the changes in summer (June to August or December to February in the northern or southern hemisphere, respectively) net surface heat flux and the individual flux components for 47 lakes with varying in size and geographic location were analysed. The results show that in the most extreme case (RCP 8.5) summer lake surface temperature is projected to increase by 4.72±0.70 °C by the end of the 21st century, due to increasing absorption of solar radiation (17.40±8.81 W m-2) and of long-wave radiation (33.01±5.44 W m-2). The increased lake surface temperature, also lead to higher heat losses to the atmosphere by outgoing long-wave radiation (27.54±4.07 W m-2) and by latent heat flux (25.10±7.37 W m-2), while a lower heat loss by sensible heat flux is projected (-3.20±1.94 W m-2). Altogether, the net heat balance and thus the accumulation of heat in the lakes over summer remains almost unchanged. However, a shift in the contributions of the individuals heat fluxes is projected, with the latent heat flux gaining relative importance.
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- Bastviken, David, Professor, 1971-, et al.
(författare)
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Measuring greenhouse gas fluxes : what methods do we have versus what methods do we need?
- 2022
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Appropriate methods to measure greenhouse gas (GHG) fluxes are critical for our ability to detect fluxes, understand regulation, make adequate priorities for climate change mitigation efforts, and verify that these efforts are effective. Ideally, we need reliable, accessible, and affordable measurements at relevant scales. We surveyed present GHG flux measurement methods, identified from an analysis of >11000 scientific publications and a questionnaire to sector professionals and analysed method pros and cons versus needs for novel methodology. While existing methods are well-suited for addressing certain questions, this presentation presents fundamental limitations relative to GHG flux measurement needs for verifiable and transparent action to mitigate many types of emissions. Cost and non-academic accessibility are key aspects, along with fundamental measurement performance. These method limitations contribute to the difficulties in verifying GHG mitigation efforts for transparency and accountability under the Paris agreement. Resolving this mismatch between method capacity and societal needs is urgently needed for effective climate mitigation. This type of methodological mismatch is common but seems to get high priority in other knowledge domains. The obvious need to prioritize development of accurate diagnosis methods for effective treatments in healthcare is one example. This presentation provides guidance regarding the need to prioritize the development of novel GHG flux measurement methods.
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- Bohman, Anna, 1975-, et al.
(författare)
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Visual Water : En visualiseringsplattform för dagvatten- och skyfallsplanering i ett klimat under förändring
- 2021
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Visual Water (http//visualwater.se) är en interaktiv webbaserad visualiseringsplattform som syftar till att stötta svenska kommuner i arbetet för en hållbar dagvatten- och skyfallshantering. Plattformen är utformad för att svara mot centrala utmaningar som lyfts av svenska dagvattenaktörer som befinner sig i skiftet bort från de rörbundna nätverksidealen för avledning av dagvatten och strävar efter en högre grad av grön-blå och öppna lösningar i stadsmiljön.
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- Karlson, Martin
(författare)
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Remote Sensing of Woodland Structure and Composition in the Sudano-Sahelian zone : Application of WorldView-2 and Landsat 8
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Woodlands constitute the subsistence base of the majority of people in the Sudano-Sahelian zone (SSZ), but low availability of in situ data on vegetation structure and composition hampers research and monitoring. This thesis explores the utility of remote sensing for mapping and analysing vegetation, primarily trees, in the SSZ. A comprehensive literature review was first conducted to describe how the application of remote sensing has developed in the SSZ between 1975 and 2014, and to identify important research gaps. Based on the gaps identified in the literature review, the capabilities of two new satellite systems (WorldView-2 and Landsat 8) for mapping woodland structure and composition were tested in an area in central Burkina Faso.The results shows that WorldView-2 represents a useful data source for mapping individual trees: 85.4% of the reference trees were detected in the WorldView-2 data and tree crown area was estimate with an average error of 45.6%. In addition, WorldView-2 data produced high classification accuracies for five locally important tree species. The highest overall classification accuracy (82.4%) was produced using multi-temporal WorldView-2 data. Landsat 8 data proved more suitable for mapping tree canopy cover as compared to aboveground biomass in the woodland landscape. Tree canopy cover and aboveground biomass was predicted with 41% and 66% root mean square error, respectively, at pixel level.This thesis demonstrates the potential of easily accessible data from two satellite systems for mapping important tree attributes in woodland areas, and discusses how the usefulness of remote sensing for analyzing vegetation can be further enhanced in the SSZ.
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| 9. |
- Ngaruye, Innocent
(författare)
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Small Area Estimation for Multivariate Repeated Measures Data
- 2014
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis considers Small Area Estimation with a main focus on estimation and prediction theory for repeated measures data. The demand for small area statistics is for both cross-sectional and repeated measures data. For instance, small area estimates for repeated measures data may be used by public policy makers for different purposes such as funds allocation, new educational or health programs and in some cases, they might be interested in a given group of population.It has been shown that the multivariate approach for model-based methods in small area estimation may achieve substantial improvement over the usual univariate approach. In this work, we consider repeated surveys including the same subjects at different time points. The population from which a sample has been drawn is partitioned into several subpopulations and within all subpopulations there is the same number of group units. For this setting a multivariate linear regression model is formulated. The aim of the proposed model is to borrow strength across small areas and over time with a particular interest of growth profiles over time. The model accounts for repeated surveys, group individuals and random effects variations.The estimation of model parameters is discussed with a restricted maximum likelihood based approach. The prediction of random effects and the prediction of small area means across time points, per group units and for all time points are derived. The theoretical results have also been supported by a simulation study and finally, suggestions for future research are presented.
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