NWS PRESENTATION TO ECIWCI MEETING
November 15, 2019
W. Scott Lincoln Senior Service Hydrologist National Weather Service Chicago, IL
1 OVERVIEW
NWS river forecast services How can the public help with NWS river forecasts? Recent trends in rainfall and river stream flow
2 NWS RIVER FORECAST SERVICES
3 MAKING RIVER FORECASTS
Hydrologists focus on water at the earth’s surface
Computer models are used to help determine runoff, the amount of rain water which heads directly to streams.
Based upon expected river levels and impacts, the NWS issues watches, warnings, or advisories.
Conflicting attributions 4 MAKING RIVER FORECASTS
How quickly will runoff reach the rivers? Where is it going to fall?
How much precipitation… has fallen? + will fall?
5 MAKING RIVER FORECASTS
A forecast based upon a forecast… River forecasts highly dependent on weather forecasts Small shifts in rainfall can move water into a different riverL basin entirely MAKING RIVER FORECASTS
A forecast based upon a forecast… River forecasts use 24 hours of future rainfall in the summer, 48 hours of future rainfall in the winter
Summer 1 day PAST Winter 2 days FUTURE MAKING RIVER FORECASTS
River forecasts are complicated…
How saturated is the soil? Is there snow cover?
Will any precipitation be blocked or evaporated NOAA/NWS by vegetation? 8 MAKING RIVER FORECASTS
Other important notes about river forecasts… Updated twice daily when flooding is expected Represent the best guess, middle expectation of future water levels… in reality there is more of a range of possibilities MAKING RIVER FORECASTS
River Forecast Centers Local Weather Forecast Offices Hydrology Forecasters: Hydrology Program Managers: Provide river forecasts to local Document the impacts from flooding weather forecast offices Work with local communities to determine Develop and calibrate hydrology water levels of concern models Coordinate flood watches, warnings, and advisories based upon forecasts from river forecast centers NWS FLOODING TERMS: IMPACT CATEGORIES
An established gage height where action Minor Minimal property damage, but possibly Action is taken in preparation for possible some public threat. Stage significant hydrologic activity. Flood This may include inundation of roads. Stage
Forecast The stage where the National Weather Moderate Some inundation of structures and Service begins issuing forecasts. roads. Evacuations of people and/or Issuance By default, this stage is set the same as Flood transfer of property to higher Stage action stage. Stage elevations.
Major Extensive inundation of structures and roads. Significant evacuations of people Flood and/or transfer of property to higher Stage elevations.
11 NWS FLOODING TERMS: IMPACT CATEGORIES
Minor Action Flood Impact Categories and Other Flood Stage Thresholds Stage Forecast Moderate • Are set based upon actual impacts due Issuance Flood to river flooding Stage Stage Major • Are set based upon the entire stretch of Flood river covered by a gauge Stage • Are NOT meant to apply to any specific person or neighborhood 12 NWS FLOODING TERMS: RIVER REACHES
Each gauge represents a section of river
Each river gauge is tied to a section of river called a “reach”
River flood impacts along each section of river are tied to a stage on Gauge the river gauge
13 KANKAKEE & IROQUOIS BASIN HYDROLOGY
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18 RIVER BASINS
Kankakee & Vermilion Basins
• Water reaches the Kankakee River from portions of numerous counties in NW Indiana and E Illinois • *The Iroquois Basin is a small subsection of the Kankakee Kankakee Basin • Water reaches the Vermilion *Iroquois above Chebanse River mostly from Livingston Vermilion Basin County 106th District 19 TERRAIN AND RIVERS
Kankakee & Vermilion Basins
• Elevation ranges from about 900 ft in portions of Indiana to 500 ft at the Illinois River in Will County
Higher Elevation Lower Elevation
20 LAND COVER
1800s Land Cover
• Land cover prior to humans was a mix of prairie and wetland, with some forest • By the 1990s, majority 1992 agriculture • By the 2010s, only small 2011 changes Wetland/Water Forest Prairie Agriculture Developed 21 RIVER GAUGES
Gauges we watch Kankakee River Vermilion River Dunn’s Bridge Pontiac Kouts Leonore Shelby Sugar Creek Momence Milford Wilmington Iroquois River Rensselaer Foresman Iroquois Chebanse 22 RAIN GAUGES
Gauges we watch
A couple river gauges also have automated rain gauges. Also airport weather stations: Greater Kankakee Airport Pontiac Municipal Airport Jasper County Airport (Rensselaer)
23 FLOOD THREATS
26 FLOOD CONCERNS
Heavy Rainfall or Snow Melt Heavy rainfall or rapid snow melt can lead to flooding along the Kankakee River if it occurs in blue/green shaded area, or the Vermilion River if it occurs in the orange shaded area.
Heavy rainfall can occur most times of the year, but snow melt is most typical in the late winter or early spring.
27 FLOOD CONCERNS
Ice Jams Ice jams common during winter along Kankakee River near Wilmington and from near Momence to near Shelby.
28 OTHER FLOOD CONCERNS
No stream gauge in Watseka No stream gauge in Kankakee Difficult to determine flood severity in Difficult to determine flood severity in Watseka due to lack of gauge just Kankakee due to lack of gauge just below Sugar Creek/Iroquois River below Kankakee/Iroquois confluence. confluence.
29 HOW CAN PEOPLE HELP IMPROVE RIVER FORECASTS?
30 IMPROVING RIVER FORECASTS
Some Sources of Uncertainty in River Forecasts Issues with estimating observed precipitation across a river basin Issues with weather forecasts (future Which factor is precipitation) biggest? Which factors Issues with river forecasts (computer models can’t perfectly represent the can we improve? land/rivers)
31 IMPROVING RIVER FORECASTS
Observed Rainfall
Information from rain gauges where we have them Estimates from radar where we don’t have gauges
Areas where rain gauges are sparse
32 IMPROVING RIVER FORECASTS
Observed Rainfall
Volunteer observers fill in some gaps Daily information provided by volunteer observers may include: Precipitation Snowfall Snow depth Snow water equivalent
33 IMPROVING RIVER FORECASTS
CoCoRaHS
Community Collaborative Rain Hail and Snow network Morning observations (around 12 UTC) each day More information: cocorahs.org IMPROVING RIVER FORECASTS
You can also help by…. Reporting Flooding
Become a storm spotter Become a river ice spotter mPING phone app (mping.nssl.noaa.gov) TRENDS IN PRECIPITATION AND RIVER STREAMFLOW
36 RECENT TRENDS IN PRECIPITATION AND STREAMFLOW
~15% Increase RECENT TRENDS IN PRECIPITATION AND STREAMFLOW
How can a small increase in rainfall be a big deal?
~15% Increase
38 RECENT TRENDS IN PRECIPITATION AND STREAMFLOW
Water Balance for a River Basin
• Amount of water leaving the basin is equal to water entering the basin
Precipitation (Rain/Snow)
Evapotranspiration (Plants) Runoff (River Flow)
39 RECENT TRENDS IN PRECIPITATION AND STREAMFLOW
Kankakee River Basin Vermilion River Basin 1950s 2010s 1950s 2010s The answer is… …the amount of water 36.3 41.1 35.2 40.0 Precipitation P that leaves a basin Evapotranspiration 24.5 24.5 ET 27.0 27.0 through evaporation and Runoff 11.8 16.6 R 8.2 13.0 transpiration is much larger than water that turns into river flow! ~40% ~60% Increase Increase in Runoff in Runoff
40 RECENT TRENDS IN PRECIPITATION AND STREAMFLOW
USGS Streamflow Measurements
• Are we actually seeing more water in area rivers?
We can confirm with flow measurements taken by the USGS.
Photo Credit: USGS 41 RECENT TRENDS IN PRECIPITATION AND STREAMFLOW
~45% ~50% Water balance estimates are close to changes actually Increase Increase measured in Kankakee and Water in the River Water in the River Vermilion Rivers
42 RECENT TRENDS IN PRECIPITATION AND STREAMFLOW
Number of flood events • Number of flood events on area rivers higher in recent decades, but trend not as clear • Flood events tied more to amount of precipitation over a shorter duration rather than amount of precipitation over an entire year
43 RECENT TRENDS IN PRECIPITATION AND STREAMFLOW
Kankakee River at Momence Iroquois River at Chebanse
44 RECENT TRENDS IN PRECIPITATION AND STREAMFLOW
Vermilion River at Leonore
45 SUMMARY
The National Weather Service forecasts river levels during heavy rain events using a combination of observed precipitation and forecast precipitation Accurate observed precipitation is crucial for accurate river forecasts… volunteer observers in the CoCoRaHS network play an important role where rain gauges are sparse Precipitation has increased about 15% across the Kankakee and Vermilion River Basins, leading to: An increase in river streamflow [Possibly] an increase in the number of flood events (not as certain)
46 QUESTIONS?
W. Scott Lincoln, GISP Senior Service Hydrologist NWS Chicago/Rockford [email protected]
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