Evaluation of Hexagon Imagery for Regional Mass Balance Study in the Bhutan Himalayas

There is much uncertainty regarding the present and future state of Himalayan glaciers, which supply meltwater for river systems vital to more than 1.4 billion people living throughout Asia. Previous assessments of regional glacier mass balance in the Himalayas using various remote sensing and field-based methods give inconsistent results. In this study, declassified Hexagon stereo imagery is processed to generate a digital elevation model (DEM) in the Bhutan Himalayas. Results indicate that the Hexagon imagery database represents a largely untapped resource for understanding decadal scale patterns of mass balance in the region. Future research will utilize the imagery and DEMs to quantify changes in volume and extent of glaciers in the Bhutan Himalayas by comparing the historical imagery to more recent data and calculating changes in ice volume over an approximately 40 year period

Characterizing the Statistical Properties and Global Distribution of Dansgaard-Oeschger Events

Ice core records from Greenland have shown times of rapid warming during the most recent glacial period, called Dansgaard-Oeschger (D-O) events. D-O events are important to our understanding of both past climate systems and modern climate volatility. In this paper, we present new approaches for sta- tistically evaluating the existence of cyclicity in D-O events and the possible lagged correlation between the Greenland and Antarctica temperature records. Speci cally, we consider permutation testing and bootstrapping methodologies for assessing the cyclicity of D-O events and the correlation between the Green- land and Antarctica records. We nd that there is not enough evidence to conclude that D-O events are cyclical; however, the Antarctica record leads the Greenland record by 545 years with a statistically signi cant correlation of 0.455

Rurality or distance to care and the risk of homelessness among Afghanistan and Iraq veterans

INTRODUCTION: To date, no studies have examined the relationship of rurality and distance to nearest VA facility to risk of homelessness. METHODS: We examined differences in the rate of homelessness within a year of a Veteran's first encounter with the VA following last military separation based on rurality and distance to the nearest VA facility using multivariable log-binomial regressions. RESULTS: In our cohort of 708,120 Veterans, 73% were determined to have a forwarding address in urban areas, 59.2% and 86.7% lived within 40 miles of the nearest VA medical center (VAMC), respectively. Veterans living in a rural area and those living between 20+ miles away from the nearest VAMC were at a lower risk for homelessness. CONCLUSIONS: Our unique dataset allowed us to explore the relationship between geography and homelessness. These results are important to policy makers in understanding the risk factors for homelessness among Veterans and planning interventions

Self-Reported Delays in Care Do not Predict Increased Mortality in a Cohort of Community-Dwelling Elders

Background: Self-reporting of delayed care is a common measure of access to healthcare. The relationship of such reports to worsened health outcomes is often assumed, but few studies have tested this longitudinal connection. Objective: To determine whether self-reports of delayed care predict increased mortality among community-dwelling elderly. Design: 3-year longitudinal retrospective cohort study. Setting: A five county area of North Carolina. Participants: 4,162 randomly sampled individuals age 65 and older. Measurements: The outcome was the proportional hazard ratio (HR) for death stratified by the factor of interest, baseline self-reports of delayed or foregone care. Control variables included predisposing, enabling, and need factors influencing care seeking and/or mortality. Results: Of 3,964 eligible participants reporting, 61% never, 27% once in awhile, and 12% quite often delayed care. 13% of participants died during the study period. Older age, male gender, lower income, less education, lack of supplemental insurance, less social support, more depression, more severe chronic disease, smoking, and worse self-rated health predict increased mortality (pvalues<.0l). Of these, age, lower income, less education, lack of supplemental insurance, less social support, worse self-rated health, and more depression were significantly associated with more self-reported delays in care. In both an unadjusted and fully adjusted survival model, 3-year mortality rates did not differ among cohorts reporting varying degrees of delayed care. Conclusion: Among community dwelling elders, self-reports of delayed care did not predict increased 3-year mortality rates. These results raise questions about self-reporting of delayed or foregone care as a measure of access to the healthcare system.Master of Public Healt

Shrinkage of Nepal's second largest lake (Phewa Tal) due to watershed degradation and increased sediment influx

Phewa Lake is an environmental and socio-economic asset to Nepal and the city of Pokhara. However, the lake area has decreased in recent decades due to sediment influx. The rate of this decline and the areal evolution of Phewa Lake due to artificial damming and sedimentation is disputed in the literature due to the lack of a historical time series. In this paper, we present an analysis of the lake's evolution from 1926 to 2018 and model the 50-year trajectory of shrinkage. The area of Phewa Lake expanded from 2.44 ± 1.02 km2 in 1926 to a maximum of 4.61 ± 0.07 km2 in 1961. However, the lake area change was poorly constrained prior to a 1957-1958 map. The contemporary lake area was 4.02 ± 0.07 km2 in April 2018, and expands seasonally by ~0.18 km2 due to the summer monsoon. We found no evidence to support a lake area of 10 km2 in 1956-1957, despite frequent reporting of this value in the literature. Based on the rate of areal decline and sediment influx, we estimate the lake will lose 80% of its storage capacity in the next 110-347 years, which will affect recreational use, agricultural irrigation, fishing, and a one-megawatt hydroelectric power facility. Mitigation of lake shrinkage will require addressing landslide activity and sediment transport in the watershed, as well as urban expansion along the shores

A New DEM Extraction Method for Hexagon Spy Imagery and Application to Bhutan Glaciers

Declassified Hexagon stereo spy images have near-global coverage extending back to the 1970’s, yet remain a largely untapped resource for land change studies. Unavailable satellite exterior orientation data for these images make digital elevation model (DEM) extraction difficult in terms of time and accuracy. A new automated workflow for DEM extraction is presented that eliminates the need for manual ground control point selection. The method is applied to reconstruct a DEM from 1974 imagery over a large glacierized region in the Bhutan Himalayas. Glacier changes over several decades are visualized using a DEM differencing method. These results demonstrate the value of Hexagon imagery when applied to land change studies

Characteristics of historical precipitation in high mountain asia based on a 15-year high resolution dynamical downscaling

The mountains of High Mountain Asia serve as an important source of water for roughly one billion people living downstream. This research uses 15 years of dynamically downscaled precipitation produced by the Weather Research and Forecasting (WRF) model to delineate contrasts in precipitation characteristics and events between regions dominated by the Indian Summer Monsoon (ISM) versus westerly disturbances during the cool season (December to March). Cluster analysis reveals a more complex spatial pattern than indicated by some previous studies and illustrates the increasing importance of westerly disturbances at higher elevations. Although prior research suggests that a small number of westerly disturbances dominate precipitation in the western Himalaya and Karakoram, the WRF-downscaled precipitation is less dominated by infrequent large events. Integrated vapor transport (IVT) and precipitation are tightly coupled in both regions during the cool season, with precipitation maximizing for IVT from the south-southwest over the Karakoram and southeast-southwest over the western Himalaya. During the ISM, Karakoram precipitation is not strongly related to IVT direction, whereas over the western Himalaya, primary and secondary precipitation maxima occur for flow from the west-southwest and northwest, respectively. These differences in the drivers and timing of precipitation have implications for hydrology, glacier mass balance, snow accumulation, and their sensitivity to climate variability and change