UMD Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/3
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Item GLOBAL BARE GROUND GAIN BETWEEN 2000 AND 2012 AND THE RELATIONSHIP WITH SOCIOECONOMIC DEVELOPMENT(2020) Ying, Qing; Hansen, Matthew C; Geography; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Bare ground gain -- the complete removal of vegetation due to land use changes, represents an extreme land cover transition that completely alters the structure and functioning of ecosystems. The fast expansion of bare ground cover is directly associated with increasing population and urbanization, resulting in accelerated greenhouse gas emissions, intensified urban heat island phenomenon, and extensive habitat fragments and loss. While the economic return of settlement and infrastructure construction has improved human livelihoods, the negative impacts on the environment have disproportionally affected vulnerable population, creating inequality and tension in society. The area, distribution, drivers, and change rates of global bare ground gain were not systematically quantified; neither was the relationship between such dynamics and socioeconomic development. This dissertation seeks methods for operational characterization of bare ground expansion, advances our understanding of the magnitudes, dynamics, and drivers of global bare ground gain between 2000 and 2012, and uncovers the implications of such change for macro-economic development monitoring, all through Landsat satellite observations. The approach that employs wall-to-wall maps of bare ground gain classified from Landsat imagery for probability sample selection is proved particularly effective for unbiased area estimation of global, continental, and national bare ground gain, as a small land cover and land use change theme. Anthropogenic land uses accounted for 95% of the global bare ground gain, largely consisting of commercial/residential built-up, infrastructure development, and resource extraction. China and the United States topped the total area increase in bare ground. Annual change rates of anthropogenic bare ground gain are found as a leading indicator of macro-economic change in the study period dominated by the 2007-2008 global financial crisis, through econometric analysis between annual gains in the bare ground of different land use outcomes and economic fluctuations in business cycles measured by detrended economic variables. Instead of intensive manual interpretation of land-use attributes of probability sample, an approach of integrating a pixel- and an object- based deep learning algorithms is proposed and tested feasible for automatic attribution of airports, a transportation land use with economic importance.Item THE TIBETAN PLATEAU SURFACE ENERGY BUDGET AND ITS TELECONNECTION WITH THE EAST ASIAN SUMMER MONSOON: EVIDENCE FROM GROUND OBSERVATIONS, REMOTE SENSING, AND REANALYSIS DATASETS(2015) Shi, Qinqing; Liang, Shunlin; Geography; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Estimations from meteorological stations indicate that the surface sensible heat flux over the Tibetan Plateau has been decreasing continuously since the 1980s. Modeling studies suggest that such change is physically linked to the weakening of the East Asian summer monsoon through Rossby wave trains. However, the relationship between the surface energy budget over the entire Tibetan Plateau and the East Asian summer monsoon rainfall has rarely been examined. The objective of this study is to quantify the relationship between the surface energy budget over the Tibetan Plateau and the East Asian summer monsoon, using ground observations, remote sensing, and reanalysis datasets with three specific questions: What are the spatiotemporal characteristics of the surface radiation and energy budgets over the Tibetan Plateau in recent decades? How does the interannual variation of the surface radiation and energy budgets correlate to, respond to, and impact the observed regional surface and atmospheric anomalies? And can the changes of the surface energy budget component over the Tibetan Plateau explain the weakening of the East Asian summer monsoon and associated precipitation changes in China? To address those questions, I 1) develop a fused monthly surface radiation and energy budgets dataset over the Tibetan Plateau using ground and satellite observations and reanalysis datasets; 2) analyze the spatial distribution of the fused surface radiation and energy budgets, and assess its correlations with the observed surface and atmospheric conditions over the Tibetan Plateau; and 3) test the hypothesis of whether the Asian summer monsoon rainfall is under the impact of the spring sensible heat flux over the Tibetan Plateau through correlation analysis, regression analysis, Granger causality test, and composite analysis. The root mean square errors from cross validation are 18.9 Wm-2, 10.3 Wm-2, 14.3 Wm-2 for the fused monthly surface net radiation, latent heat flux, and sensible heat flux. The fused downward shortwave irradiance, sensible heat flux, and latent heat flux anomalies are consistent with those estimated from meteorological stations. The associations among the fused surface radiation and energy budgets and the related surface anomalies such as mean temperature, temperature range, snow cover, and Normalized Difference Vegetation Index in addition to the atmospheric anomalies such as cloud cover and water vapor show seasonal dependence over the Tibetan Plateau. The decreased late spring sensible heat flux, which is sustained throughout the summer, has been associated with suppressed summer rainfall in the north of China and the north of Indian and enhanced rainfall in the west of India. The mechanism of those associations is found through a lower-level Rossby wave train as a result of anomalous sensible heating over the Tibetan Plateau. The decreased late spring sensible heat flux has also been associated with dry weather in the Yangtze River basin through a descending motion to the east of the Tibetan Plateau. This dissertation is the first synthesized analysis of the surface radiation and energy budgets at a spatial scale covering the entire Tibetan Plateau over a temporal period of two decades. The results of this study could contribute to a better understanding of the land-atmosphere interactions over the Tibetan Plateau, and the role of the Tibetan Plateau sensible heating in regulating the strength of the Asian summer monsoon. This study demonstrates a linkage between the spring sensible heat over the Tibetan Plateau and the Asian summer monsoon rainfall that affect about one fourth of the world's population, which has implications that will benefit local agriculture practices, disaster management, and climate change mitigation.Item SPATIAL PATTERNS AND POTENTIAL MECHANISMS OF LAND DEGRADATION IN THE SAHEL(2013) Rishmawi, Khaldoun; Prince, Stephen; Geography; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)There is a great deal of debate on the extent, causes and even the reality of land degradation in the Sahel. On one hand, extrapolations from field-scale studies suggest widespread and serious reductions in biological productivity threatening the livelihoods of many communities. On the other hand, coarse resolution remote sensing studies consistently reveal a net increase in vegetation production exceeding that expected from the recovery of rainfall following the extreme droughts of the 1970s and 1980s, thus challenging the notion of widespread, subcontinental-scale degradation. Yet, the spatial variations in the rates of vegetation recovery are not fully explained by rainfall trends which suggest additional causative factors. In this dissertation, it is hypothesized that in addition to rainfall other climatic variables and anthropogenic uses of the land have had measurable impacts on vegetation production. It was found that over most of the Sahel, the interannual variability in growing season sum NDVI (used as a proxy of vegetation productivity) was strongly related to rainfall, humidity and temperature while the relationship with rainfall alone was generally weaker. The climate- sum NDVI relationships were used to predict potential NDVI; that is the NDVI expected in response to climate variability alone excluding any human-induced changes in productivity. The differences between predicted and observed NDVI were regressed against time to detect any long term (positive or negative) trends in vegetation productivity. It was found that over most of the Sahel the trends either exceeded or did not significantly depart from what is expected from the trends in climate. However, substantial and spatially contiguous areas (~8% of the total area of the Sahel) were characterized by significant negative trends. To test whether the negative trends were in fact human-induced, they were compared with the available data on population density, land use pressures and land biophysical properties that determine the susceptibility of land to degradation. It was found that the spatial variations in the trends of the residuals were not only well explained by the multiplicity of land use pressures but also by the geography of soil properties and percentage tree cover.Item The impact of agricultural irrigation on land surface characteristics and near surface climate in China(2012) Zhu, Xiufang; Liang, Shunlin; Geography; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)It is well known that land cover and land use change can significantly influence the climate system by modulating surface-atmosphere exchanges. Land management, such as irrigation, also has a profound influence on the climate system. Irrigation can alter the water and energy flux from ground surface to the atmosphere and further influence near surface climate. Considering its dramatic expansion during the last century, the widespread use of irrigation has had an ongoing impact on our climate system. However, until now, this relationship between increased irrigation and its effect on climate system has not been well examined. The main objective of this dissertation is to quantify the irrigation impacts on land surface characteristics and near surface climate over China by using both observational (remote sensing and meteorological observation) and modeling studies with four specific questions: Where are the irrigated areas in China? What might have happened in the past? What will happen as a result of irrigation expansion in the future? And what is the relationship between the land cover land use change (LCLUC) impact and the irrigation impact on near surface climate in China? To answer these questions, I 1) developed three irrigation potential indices and produced a high resolution irrigation map of China; 2)analyzed and compared meteorological and remote sensing observations in irrigated and non-irrigated agriculture areas of China; 3) simulated both irrigation and LCLUC impact on land surface energy balance components (i.e., land surface temperature, latent flux, and sensible flux) and near surface climate (i.e., air temperature, water vapor, relative humidity) of China in the past (1978-2004) and also in two future time periods (2050 and 2100) by using the Community Land Model and compared the impact of irrigation with that of LUCC. Meteorological observations in Jilin Province show that the temperature differences between highly and lightly irrigated areas are statistically significant. The differences are highly correlated with the effective irrigation area (EIA) and sown area of crop (CSA). Results from satellite observations show that highly irrigated areas corresponded to lower albedo and daytime land surface temperature (LST), and higher normalized difference vegetation index (NDVI) and evapotranspiration (ET). The difference between highly and lightly irrigated areas is bigger in drier areas and in drier years. The modeling studies show that the irrigation impact on temperature is much less in the future than in the 20th century and that irrigation impacts more on the maximum air temperature than on the minimum air temperature. Both contemporary and future irrigation simulations show, nationally, irrigation decreases daily maximum temperature (Tmax) but increase daily minimum temperature (Tmin). Daily mean temperature (Tmean) decreases in contemporary irrigation simulations but increases in most of the cases in future irrigation simulations. In the 20th century, nationally, the spray irrigation leads to a decrease in Tmax of 0.079K and an increase in Tmin of 0.022K. Nationally, the spray irrigation leads to a decrease in Tmax between 0.022K and 0.045K and an increase in Tmin between 0.019K and 0.057K under future scenarios. This study demonstrates that the irrigation patterns (flood irrigation and spray irrigation) have statistically significant impacts on local climate. Moreover, this study suggests that, in the national respective, the impacts of changes in land management on climate are not comparable to the impacts of changes in land cover land use. This dissertation on irrigation and its impact is the first study which focuses solely on China using observational and modeling methods. The results from this dissertation contribute to a better understanding of the irrigation impact on near-surface climate which can improve our knowledge of how human activities influence climate, guide future policies aimed at mitigating or adapting to climate change, and help design a precise model to project the impact of irrigation on the climate system and irrigation requirements in the future. It can also be useful in assessing future food and water security issues.