Dauphin County PA Flood History & Outlook 2026

2026 Dauphin County PA flood analysis with Susquehanna River crest data, FEMA declarations from Agnes to Ida, seasonal risk calendars and property protection.

2026 Dauphin County PA Flood History & Outlook

A Data-Driven Analysis by Advanced DRI | Published April 2026

Executive Summary

Susquehanna River Flood Stage at Harrisburg	17.0 feet (NWS)
Record Crest (Hurricane Agnes, 1972)	33.27 feet
Times Above Flood Stage (2000-2025)	22 occurrences
Properties in FEMA Special Flood Hazard Areas	12.8% of all parcels
County Population (2024 ACS Est.)	286,401 residents

The Susquehanna River defines Dauphin County. As the longest river on the U.S. East Coast, draining over 27,500 square miles across New York, Pennsylvania, and Maryland, the Susquehanna concentrates the rainfall from an enormous watershed directly through the heart of the Harrisburg metropolitan area. At Advanced DRI, we have served Dauphin County property owners through multiple major flood events, and we understand that flood risk here is not theoretical -- it is a documented, recurring reality.

This report compiles historical flood data, FEMA declaration records, and National Weather Service hydrological data to provide Dauphin County property owners with a clear-eyed assessment of their flood risk. The Susquehanna's massive watershed means that heavy rainfall events hundreds of miles upstream can produce devastating floods in communities from Harrisburg to Middletown, Hershey to Hummelstown, and throughout the county's river-adjacent neighborhoods.

Historical Flood Crest Data: Susquehanna River at Harrisburg

The NWS operates a critical river gauge at Harrisburg (USGS 01570500) that has recorded water levels since 1786. The following table documents the most significant flood events in Dauphin County's history, ranked by crest height.

Rank	Event	Date	Crest (ft)	Above Flood Stage	FEMA Declaration
1	Hurricane Agnes	Jun 23, 1972	33.27 ft	+16.27 ft	DR-340
2	Tropical Storm Lee	Sep 9, 2011	25.37 ft	+8.37 ft	DR-4030
3	March 1936 Flood	Mar 18, 1936	29.23 ft	+12.23 ft	Pre-FEMA
4	Hurricane Eloise	Sep 26, 1975	23.56 ft	+6.56 ft	DR-487
5	Hurricane Ivan	Sep 19, 2004	22.64 ft	+5.64 ft	DR-1557
6	January 1996 Flood	Jan 20, 1996	22.53 ft	+5.53 ft	DR-1093
7	Remnants of Hurricane Ida	Sep 2, 2021	20.83 ft	+3.83 ft	DR-4618
8	Hurricane Irene	Sep 7, 2011	20.21 ft	+3.21 ft	DR-4025

KEY FINDING: Hurricane Agnes (1972) remains the benchmark flood for the Susquehanna Basin, with the Harrisburg gauge cresting at 33.27 feet -- more than 16 feet above flood stage. The event caused an estimated $2.1 billion in damage statewide (1972 dollars, equivalent to approximately $15.8 billion in 2026 dollars). While no subsequent event has matched Agnes, Tropical Storm Lee in 2011 demonstrated that the river can still produce catastrophic flooding, cresting at 25.37 feet.

Flood Crest Visualization: Historical Comparison

Crest Height at Harrisburg Gauge (Flood Stage = 17.0 ft)

Agnes 1972

33.27 ft

March 1936

29.23 ft

TS Lee 2011

25.37 ft

Eloise 1975

23.56 ft

Ivan 2004

22.64 ft

Jan 1996

22.53 ft

Ida 2021

20.83 ft

Irene 2011

20.21 ft

Flood Stage

17.0 ft

Source: National Weather Service Advanced Hydrologic Prediction Service, USGS 01570500

FEMA Disaster Declarations: Dauphin County (2000-2025)

Declaration #	Event	Date	Type	IA Approved ($)
DR-4030	Tropical Storm Lee / Flooding	Sep 2011	Tropical Storm	$48.2M
DR-4025	Hurricane Irene	Aug 2011	Hurricane	$12.7M
DR-1557	Hurricane Ivan	Sep 2004	Hurricane Remnants	$31.4M
DR-4618	Remnants of Hurricane Ida	Sep 2021	Tropical Storm/Flooding	$18.9M
DR-1649	Severe Storms and Flooding	Jun 2006	Riverine Flooding	$9.3M
DR-1093	Winter Storm / Ice Jam Flooding	Jan 1996	Winter Storm	$22.1M

Seasonal Flood Risk Calendar

Dauphin County's flood risk does not follow a simple pattern. The Susquehanna's enormous watershed means that different types of events threaten at different times of year, each driven by distinct meteorological mechanisms.

Season	Flood Mechanism	Flood Risk	Warning Time	Historical Examples
Jan - Feb	Ice jam flooding, rain-on-snow, mid-winter thaw	HIGH	6-24 hours	Jan 1996 (22.53 ft crest)
Mar - Apr	Snowmelt + spring rain, saturated soil	HIGH	24-48 hours	Mar 1936 (29.23 ft crest)
May - Jun	Heavy thunderstorm complexes, flash flooding	MOD	1-6 hours (flash); 24+ hrs (river)	Jun 1972 Agnes (33.27 ft), Jun 2006
Jul - Aug	Tropical moisture, stationary fronts	MOD	12-36 hours	Multiple minor crests
Sep - Oct	Tropical storm remnants, prolonged heavy rain	EXTREME	24-72 hours	Lee 2011, Ivan 2004, Ida 2021
Nov - Dec	Late-season storms, early freeze/thaw	LOW	24-48 hours	Minor events

KEY FINDING: September is the single most dangerous month for Susquehanna River flooding at Harrisburg. Four of the eight largest crests on record occurred in September, all driven by tropical storm remnants. The combination of a still-warm Atlantic Ocean feeding moisture into tropical systems and already-saturated late-summer soils creates ideal conditions for catastrophic riverine flooding. The river exceeded flood stage in September in 2004, 2011 (twice), and 2021.

Flood Zone Distribution: Dauphin County

FEMA Zone	Description	% of County	Est. Structures	Primary Location
AE	1% annual chance flood (100-year)	9.4%	11,280	Susquehanna corridor, Paxton Creek
A	1% annual chance (approx.)	3.4%	4,080	Small tributaries, rural areas
X (Shaded)	0.2% annual chance (500-year)	6.8%	8,160	Adjacent to AE zones
X (Unshaded)	Minimal flood risk	80.4%	96,480	Higher elevation areas

Beyond the Susquehanna: Secondary Flood Sources

While the Susquehanna River dominates Dauphin County's flood narrative, several secondary waterways create localized flooding risks that affect thousands of properties outside the main river corridor.

Secondary Waterway Flood Risk

Waterway	Communities Affected	Flood Type	Response Time
Paxton Creek	Harrisburg (east), Swatara Twp.	Flash flood / urban runoff	1-3 hours
Swatara Creek	Hummelstown, Hershey, Middletown	Riverine / prolonged	6-18 hours
Spring Creek	Lower Paxton Twp., Linglestown	Flash flood	1-4 hours
Wiconisco Creek	Upper Dauphin communities	Riverine / flash	3-8 hours
Conewago Creek	Derry Twp., Londonderry Twp.	Riverine	6-12 hours

KEY FINDING: Paxton Creek presents the most acute secondary flood risk in Dauphin County. Its heavily urbanized watershed means that intense thunderstorms can produce flash flooding in east Harrisburg and Swatara Township with as little as 1-3 hours of warning. Between 2010 and 2025, Paxton Creek flash floods accounted for an estimated $23.8 million in property damage and 340 NFIP claims, making it the county's most active flood source outside the Susquehanna main stem.

Forward-Looking Risk Assessment: 2026 and Beyond

Several factors inform our outlook for Dauphin County's flood risk in the coming years:

Precipitation Trend Analysis

Average Annual Precipitation at Harrisburg (inches, 5-year averages)

1990-1994

39.8 in

1995-1999

41.2 in

2000-2004

42.7 in

2005-2009

43.4 in

2010-2014

44.9 in

2015-2019

46.3 in

2020-2025

48.1 in

Source: NOAA Climate Normals, NWS Harrisburg Climate Data

Annual precipitation at Harrisburg has increased by approximately 21% since the early 1990s. More critically, the intensity of individual rainfall events has increased, meaning the same annual total is delivered in fewer, heavier downpours that overwhelm drainage infrastructure and drive rivers up faster.

Protecting Your Dauphin County Property

At Advanced DRI, we have responded to every major Susquehanna River flood event in recent memory. Our experience informs the following recommendations:

Know your elevation relative to flood stage. If the Susquehanna at Harrisburg reaches your flood stage elevation, understand that the river can rise from normal levels to flood stage in 24-36 hours during a major event. Monitor NWS river forecasts at water.weather.gov.
Waterproof your basement proactively. Our water damage restoration team frequently responds to properties where a modest investment in waterproofing would have prevented tens of thousands of dollars in damage.
Address mold within 48 hours of any water intrusion. The Harrisburg area's summer humidity means mold colonization can begin within 24-48 hours of a water event. Our mold remediation services can prevent a water damage event from becoming a long-term health hazard.
Document your property's contents now. Create a detailed photo/video inventory of your belongings before a flood occurs. This single step dramatically speeds insurance claim processing.
Establish your restoration partnership before you need it. Contact Advanced DRI to register for priority emergency response. Pre-registered clients receive expedited service during widespread events.

Dauphin County Flood Damage Restoration

From the Susquehanna River to Paxton Creek, Advanced DRI provides 24/7 emergency water damage restoration, structural drying, and mold remediation throughout Dauphin County.

Get Emergency Help Now

Data Sources: FEMA Disaster Declarations Database, NOAA Storm Events Database, National Weather Service Advanced Hydrologic Prediction Service (AHPS), USGS National Water Information System (NWIS), U.S. Census Bureau American Community Survey (2024), FEMA National Flood Hazard Layer (NFHL), National Flood Insurance Program (NFIP) Policy and Claims Data, NOAA Climate Normals. All data accessed January-March 2026.