Atmospheric Processes Associated with Snow Cover Ablation Events and their Effect on the Flood Hydroclimatology of the Chesapeake Bay. Gina Henderson and Daniel J. Leathers Center for Climatic Research University of Delaware. Chesapeake Bay watershed. The Susquehanna. The Potomac. The James. - PowerPoint PPT Presentation
Atmospheric Processes Associated Atmospheric Processes Associated with Snow Cover Ablation Events and with Snow Cover Ablation Events and their Effect on the Flood their Effect on the Flood Hydroclimatology of the Chesapeake Hydroclimatology of the Chesapeake Bay Bay Gina Henderson Gina Henderson and Daniel J. Leathers and Daniel J. Leathers Center for Climatic Research Center for Climatic Research University of Delaware University of Delaware
Transcript
Atmospheric Processes Associated with Snow Atmospheric Processes Associated with Snow Cover Ablation Events and their Effect on the Cover Ablation Events and their Effect on the
Flood Hydroclimatology of the Chesapeake BayFlood Hydroclimatology of the Chesapeake Bay
Gina HendersonGina Henderson and Daniel J. Leathersand Daniel J. LeathersCenter for Climatic ResearchCenter for Climatic Research
University of DelawareUniversity of Delaware
Chesapeake Bay watershedChesapeake Bay watershedThe SusquehannaThe Susquehanna
The PotomacThe Potomac
The JamesThe James
www.usgs.govwww.usgs.gov
Research QuestionsResearch Questions
1.1. How important is the ablation of snow cover to the flood How important is the ablation of snow cover to the flood hydroclimatology of the Chesapeake Bay watershed?hydroclimatology of the Chesapeake Bay watershed?
2.2. Are their distinctive types of snow ablation events that Are their distinctive types of snow ablation events that contribute to flooding in this area?contribute to flooding in this area?
3.3. What are the general atmospheric processes What are the general atmospheric processes associated with these ablation events and how does this associated with these ablation events and how does this impact the hydrology of the region?impact the hydrology of the region?
www.usgs.govwww.usgs.gov
The Susquehanna, The Susquehanna, Potomac and James rivers Potomac and James rivers account for the majority of account for the majority of
Chesapeake dischargeChesapeake discharge
The three gaging stations The three gaging stations used were:used were:
1.1. Harrisburg, PAHarrisburg, PA
2.2. Point of Rocks, MDPoint of Rocks, MD
3.3. Bucanan, VABucanan, VA
Data SourcesData Sources
Snow Depth DataSnow Depth Data
11o o X 1X 1o o gridded daily snow depth gridded daily snow depth data set developed by Mote et al. data set developed by Mote et al.
Utilizes U.S. COOP and Canadian Utilizes U.S. COOP and Canadian daily surface observations daily surface observations
Extensive quality control routinesExtensive quality control routines
Gridded snow cover data used to Gridded snow cover data used to identify basin or sub-basin wide identify basin or sub-basin wide ablation episodes.ablation episodes.
Chesapeake watershed: 23 grid boxes used to calculate Chesapeake watershed: 23 grid boxes used to calculate
Area of the watershed Area of the watershed ~ 165,759 km~ 165,759 km22 (64,000 (64,000 mimi22) )
MethodologyMethodology
1.1. Identify major flooding events during the fifty year period Identify major flooding events during the fifty year period for the Chesapeake Bay watershed using stream flow for the Chesapeake Bay watershed using stream flow and snow depth criteria.and snow depth criteria.
2.2. Classify events based on type of snow cover ablation Classify events based on type of snow cover ablation taking place.taking place.
3.3. Identify principle atmospheric features associated with Identify principle atmospheric features associated with each classification type.each classification type.
4.4. Use SNTHERM to model atmosphere snow cover Use SNTHERM to model atmosphere snow cover interactions.interactions.
Selection of flooding eventsSelection of flooding events
Top flooding events were Top flooding events were identified from the period identified from the period 1950-20001950-2000
Selection criteria:Selection criteria:– > 4247 m> 4247 m33 s s-1 -1 (150,000 cf/s)(150,000 cf/s)– > 3.0 cm change in snow > 3.0 cm change in snow
depth from the previous depth from the previous dayday
– Only winter months Only winter months considered considered
Ablation episodes selected from the top 5% of daily discharge values.
ResultsResults
Selection of eventsSelection of events
Three types of ablation events:Three types of ablation events:1.1. AblationAblation2.2. Rain on snowRain on snow3.3. Ablation to rainAblation to rain
We will look at one of each type of eventWe will look at one of each type of event
1950 to 20001950 to 2000 23 events23 events 8 events8 events
Annual cycle of river discharge:Annual cycle of river discharge:Chesapeake watershedChesapeake watershed
Discharge based on the total of the Susquehanna, the Potomac and Discharge based on the total of the Susquehanna, the Potomac and the James Riversthe James Rivers
On average, spring months show highest discharge valuesOn average, spring months show highest discharge values Some maximum discharges occur in summer/autumn Some maximum discharges occur in summer/autumn tropical tropical
precipitationprecipitation
Annual cycle of snow depth:Annual cycle of snow depth:Chesapeake watershedChesapeake watershed
On average, largest snow depth months are January and FebruaryOn average, largest snow depth months are January and February Large decrease in snow depth in MarchLarge decrease in snow depth in March Maximum daily snow depth shows largest decrease in snow depth Maximum daily snow depth shows largest decrease in snow depth
from March to April from March to April late season ablation events late season ablation events
1.1. Ablation event: 16Ablation event: 16thth March 1978 March 1978
1.1. Ablation event: 16Ablation event: 16thth March 1978 March 1978
Steady ablation for 5 days Steady ablation for 5 days before flooding eventbefore flooding event
Decrease in snow depth from Decrease in snow depth from approx 28 cm to 5 cmapprox 28 cm to 5 cm
No significant precipitation No significant precipitation eventsevents
Discharge peaks at approx Discharge peaks at approx 8000 m8000 m33/s/s
1.1. Identify major flooding events during the fifty year period Identify major flooding events during the fifty year period for the Chesapeake Bay watershed using stream flow for the Chesapeake Bay watershed using stream flow and snow depth criteria.and snow depth criteria.
2.2. Classify events based on type of snow cover ablation Classify events based on type of snow cover ablation taking place.taking place.
3.3. Identify principle atmospheric features associated with Identify principle atmospheric features associated with each classification type.each classification type.
4.4. Use SNTHERM to model atmosphere snow cover Use SNTHERM to model atmosphere snow cover interactions.interactions.
Calculation of energy fluxes during ablation events with Calculation of energy fluxes during ablation events with SNTHERM snow pack model…. developed by Jordan (1991)SNTHERM snow pack model…. developed by Jordan (1991)
1.1. It is possible to isolate the snow ablation signal for the It is possible to isolate the snow ablation signal for the Chesapeake Bay watershed.Chesapeake Bay watershed.
2.2. A common theme is strong low pressure in the lower A common theme is strong low pressure in the lower Great Lakes Region bringing warm and moist air across Great Lakes Region bringing warm and moist air across the Chesapeake watershed.the Chesapeake watershed.
3.3. Large values of sensible and latent heat flux are Large values of sensible and latent heat flux are typically the largest components of the energy budget typically the largest components of the energy budget during the most during the most intense ablation events.intense ablation events.
Questions or comments?Questions or comments?
Contact info:Contact info:
Gina HendersonGina HendersonDepartment of GeographyDepartment of Geography
