Passive microwave derived snowmelt timing: significance, spatial and temporal variability, and potential applications

Snow accumulation and melt are dynamic features of the cryosphere indicative of a changing climate. Spring melt and refreeze timing are of particular importance due to the influence on subsequent hydrological and ecological processes, including peak runoff and green-up. To investigate the spatial and temporal variability of melt timing across a sub-arctic region (the Yukon River Basin (YRB), Alaska/Canada) dominated by snow and lacking substantial ground instrumentation, passive microwave remote sensing was utilized to provide daily brightness temperatures (Tb) regardless of clouds and darkness. Algorithms to derive the timing of melt onset and the end of melt-refreeze, a critical transition period where the snowpack melts during the day and refreezes at night, were based on thresholds for Tb and diurnal amplitude variations (day and night difference). Tb data from the Special Sensor Microwave Imager (1988 to 2011) was used for analyzing YRB terrestrial snowmelt timing and for characterizing melt regime patterns for icefields in Alaska and Patagonia. Tb data from the Advanced Microwave Scanning Radiometer for EOS (2003 to 2010) was used for determining the occurrence of early melt events (before melt onset) associated with fog or rain on snow, for investigating the correlation between melt timing and forest fires, and for driving a flux-based snowmelt runoff model. From the SSM/I analysis: the melt-refreeze period lengthened for the majority of the YRB with later end of melt-refreeze and earlier melt onset; and positive Tb anomalies were found in recent years from glacier melt dynamics. From the AMSR-E analysis: early melt events throughout the YRB were most often associated with warm air intrusions and reflect a consistent spatial distribution; years and areas of earlier melt onset and refreeze had more forest fire occurrences suggesting melt timing\u27s effects extend to later seasons; and satellite derived melt timing served as an effective input for model simulation of discharge in remote, ungauged snow-dominated basins. The melt detection methodology and results present a new perspective on the changing cryosphere, provide an understanding of melt\u27s influence on other earth system processes, and develop a baseline from which to assess and evaluate future change. The temporal and spatial variability conveyed through the regional context of this research may be useful to communities in climate change adaptation planning

Risk Analysis in Setting Allowable Harvests: Annual Catch Limits under the Magnuson Stevens Reauthorization Act

Under the reauthorized Magnuson-Stevens Act (MSRA), US fisheries management councils must specify an annual catch limit (ACL) for each managed species and institute accountability measures (AMs) to ensure that actual harvest will not cause the stock to be overfished. While the details of implementation are still being developed, a set of Proposed Guidelines for performing ACL analysis has been developed. The purpose of this paper is to provide a preliminary assessment of these guidelines. The MSRA specifies two principles to be used as a framework for determining how Councils can comply with the ACL and AM measures. Both deal with uncertainty in the overall fisheries management process. The first is the separation between science and policy in setting the upper level on allowable harvests. The second is the requirement to take strong management actions to ensure that, given real world enforcement issues, the actual harvest in any year does not surpass the allowable harvest level. The procedure for applying the principles is quite complex and it goes beyond a strict interpretation of the written language in the law. However, it is consistent with current procedures and with commonly accepted principles in fisheries management policy. The Proposed Guidelines suggest that a distinction be made between scientific and implementation uncertainty. While the distinction may follow from the two principles, a preliminary look at the logical process of developing the required control rules for specifying Acceptable Biological Catch and Annual Catch Targets raises questions about the usefulness of this distinction in actual policy analysis

Early snowmelt events: detection, distribution, and significance in a major sub-arctic watershed

High latitude drainage basins are experiencing higher average temperatures, earlier snowmelt onset in spring, and an increase in rain on snow (ROS) events in winter, trends that climate models project into the future. Snowmelt-dominated basins are most sensitive to winter temperature increases that influence the frequency of ROS events and the timing and duration of snowmelt, resulting in changes to spring runoff. Of specific interest in this study are early melt events that occur in late winter preceding melt onset in the spring. The study focuses on satellite determination and characterization of these early melt events using the Yukon River Basin (Canada/USA) as a test domain. The timing of these events was estimated using data from passive (Advanced Microwave Scanning Radiometer—EOS (AMSR-E)) and active (SeaWinds on Quick Scatterometer (QuikSCAT)) microwave remote sensors, employing detection algorithms for brightness temperature (AMSR-E) and radar backscatter (QuikSCAT). The satellite detected events were validated with ground station meteorological and hydrological data, and the spatial and temporal variability of the events across the entire river basin was characterized. Possible causative factors for the detected events, including ROS, fog, and positive air temperatures, were determined by comparing the timing of the events to parameters from SnowModel and National Centers for Environmental Prediction North American Regional Reanalysis (NARR) outputs, and weather station data. All melt events coincided with above freezing temperatures, while a limited number corresponded to ROS (determined from SnowModel and ground data) and a majority to fog occurrence (determined from NARR). The results underscore the significant influence that warm air intrusions have on melt in some areas and demonstrate the large temporal and spatial variability over years and regions. The study provides a method for melt detection and a baseline from which to assess future change.Lehigh University and NASA Headquarters under the NASA Earth and Space Science Fellowshi