Flo loods ods, , Cl Clim imate te and nd “Cuisinart” Hydrology: A Recipe ipe for or Di Disa sast ster? ? Dr. Katie Hirschboeck Laboratory of Tree-Ring Research & Chair, Global Change Graduate Interdisciplinary Program
QU QUESTI ESTIONS ONS, , QU QUES ESTIONS! TIONS! 1. WHAT IS A FLOOD? . . . and what is a 100-Year Flood? 2. WHY DO WE NEED TO WORRY ABOUT THEM? . . . our Arizona rivers are dry most of the time! 3. WHAT CAUSES FLOODS ? . . . and what difference does this make? 4. WHAT CAN WE LEARN FROM THE PAST? . . . Are there such things as “ Paleofloods ”? 5. WHAT WILL THE FUTURE HOLD? . . . will climate change make floods more extreme? or will they get smaller?
. . . and d what t the heck k is is “CUISINART” HYDROLOGY ???? ???? ?
WH WHAT T IS S A FL FLOOD OOD? Definition: “Any relatively high streamflow that overtops the natural or artificial banks of a river” What about steep-sided Flooding on the Santa Cruz River arroyo channels? These banks aren’t overtopped!
WH WHAT T IS S A FL FLOOD OOD? Another: “An overflowing of water onto land that is normally dry” SOURCE: David Rankin video, posted at Flood Control District of Maricopa County http://www.fcd.maricopa.gov/Education/education.aspx
WH WHAT T IS S A FL FLOOD OOD? Yet another: “The state of a river that is at an abnormally high level” The typically dry Santa Cruz River at very low flow vs. Santa Cruz River at Tucson, Arizona The record flood of October 1983!
A rapid rise in flood level during the January 2010 flooding in Arizona Automatic gaging station Taking a discharge measurement during a flood
streamflow gage Example of an even more rapid rise in flood stage during the January 2010 flooding in Arizona Photos show low flow in Verde River near Clarkdale during July 2009
Why do we need to worry about floods in Arizona when our rivers are dry most of the time? . . . WATCH H SO SOME E OF THESE VIDOES ES OF DESERT T FLOODING DING . . . . http://www.fcd.maricopa.gov/Education/education.aspx SOURCE: David Rankin video, posted at Flood Control District of Maricopa County http://www.fcd.maricopa.gov/Education/education.aspx
More Definitions: “The ANNUAL FLOOD for a given stream is th the e highest est flow w rec ecorded ded at t a p a point t on a s a str trea eam m during ng an any y particular calendar year or water year.” Annual Flood Largest peak in each year Time Series (cubic feet per second) DISCHARGE WATER YEAR
SO WH SO WHAT T IS S A 100 00-YEAR EAR FL FLOOD OOD? ? Def: “The 100-YEAR FLOOD is a flood event that statistically has a 1 out of 100 (or one percent) chance of being equaled or exceeded on a specific watercourse in any given year.” Flood Insurance Rate Maps are based on the 100-Year Floodplain SOURCE: Pima County Regional ( the area that will be inundated Flood Control District http://rfcd.pima.gov by a 100-Year Flood)
DO O WE WE NEED 100 0 YEARS S OF OF FLOO OOD D RECORDS ORDS TO O ESTIMA IMATE TE IT? Nope, the 100-Year Flood is estimated statistically from the available record: ! SOURCE: modified from Jarrett, 1991 after Patton & Baker, 1977
. . . but ut som omet etimes imes Pecos s River r nr the here e are e Coms msto tock, , TX prob oblems lems due ue to o “outliers” Is this a recipe for disaster? SOURCE: modified from Jarrett, 1991, after Patton & Baker, 1977
Flow Time Series A fairly long record with lots of variability . . . . The gage was shut down in 1980
Flow Time Series Flow Time Series The flood of A fairly long record with lots of October 1983! variability . . . . (WY 1984) The gage was shut down in 1980
WH WHAT T CAUSES USES FL FLOOD OODS S ? . . . and what difference does this make? Seasonality of Peak Flooding
FLOOD-CAUSING MECHANISMS Meteorological & climatological flood-producing mechanisms operate at varying temporal and spatial scales
WINTER & SPRING FRONTAL ACTIVITY Schematic showing 3 modes of westerly flow. FLOODING & EL NINO are more likely to be Winter flooding associated with the on the Rillito in Tucson Meridional Jet or Split Jet pattern Roosevelt Dam Jan 1993 Canada del Oro flooding of La Cholla Road Jan 2008
SUMMER CONVECTIVE “Monsoon” THUNDERSTORMS Sabino Canyon flooding July 1999 Rillito July 2006 Typical urban flash flooding in Arizona
ENHANCED PRECIPITATION FROM EASTERN NORTH PACIFIC TROPICAL STORMS IMPORTANT FLOOD- GENERATING TROPICAL STORMS Tropical Storm Norma & Tropical Storm Heather the Labor Day flood Oct 1977 of Sep 1970 Tropical Storm Octave Oct 1983
SO HOW DO WE ADDRESS FLOOD HAZARDS?
http://acwi.gov/hydrology/Frequency/B17bFAQ.html#mixed “Flood magnitudes are determined by many factors , in unpredictable combinations. It is conceptually useful to think of the various factors as "populations" and to think of each year's flood as being the result of random selection of a "population”, followed by random drawing of a particular flood magnitude from the selected population.”
The Standard iid Assumption for FFA The standard approach to Flood Frequency Analysis (FFA) assumes stationarity in the time series & “iid” “ iid ” assumption : independently, identically distributed
Different storm Summer monsoon types produce convective event different flood hydrographs: Discharge Synoptic- scale winter The type of storm event influences the shape of the streamflow Tropical storm or hydrograph other extreme event and the magnitude & persistence of the flood peak Time
Therefore: NEW & USEFUL INFORMATION CLIMATIC CAUSE + FLOODS = FOR EVALUTING FLOOD RISK! It all started with a newspaper ad . . . .
Current practice analyzes floods using “CUISINART” HYDROLOGY! “FLOOD PROCESSOR” With expanded feed tube – for entering all kinds of flood data including steel chopping, slicing & grating blades – for removing unique physical characteristics, climatic information, and outliers plus plastic mixing blade – to mix the populations together
Alternative Conceptual Framework: Time- varying means Time- Mixed frequency varying distributions may variances arise from: • storm types • synoptic patterns Both • ENSO, etc. teleconnections • multi-decadal circulation regimes SOURCE: Hirschboeck, 1988
Can we find out more about what drives this history of flooding? Remember the Santa Cruz record? What t does it look k like when n classif sified ied hydroc ocli limatically? tically? What t kinds ds of storm rms s produc duced ed the biggest st floods? ods?
FLOOD HYDROCLIMATOLOGY = classifying each flood in the record according to cause
Many more winter floods! Historical Flood
FLOOD HYDROCLIMATOLOGY is the analysis of flood events within the context of their history of variation - in magnitude, frequency, seasonality - over a relatively long period of time - analyzed within the spatial framework of changing combinations of meteorological causative mechanisms SOURCE: Hirschboeck, 1988
This framework of analysis allows a flood time series to be combined with climatic information . . . To arrive at a mechanistic understanding of long-term flooding variability and the likelihood of different types of floods occurring.
WHAT CAN WE LEARN FROM LARGE FLOODS OF THE PAST? Here’s evidence that a large flood moved this huge boulder to this height on the floodplain: Scar on tree from flood damage can be dated with Datable flood tree-ring analysis; deposits layers show also reveals the how many larger height of the floods occurred here floodwaters
PALEOFLOOD RESEARCH! Non Non-excee ceede dence nce level el Paleof eoflood lood stage Thres eshold hold level el
FLOOD OD HYDR DROCLIMA CLIMATOL OLOGY GY eval aluate te likel ely y hydroc oclima imatic tic ca causes es of pre-hi historic toric floods ds 1993 1993 Largest est paleof ofloo lood Hist storica orical Flood ( A.D .D. . 1010 +- 95 radiocarbon arbon date)
Compila pilations tions of paleof eoflood lood recor ords ds combined bined with gaged ed recor cords ds su suggest est there could d be a natur ural, al, upper er physical sical limit it to the magnitu itude de of floods ds in a given region ion --- --- will this chang nge e if the climate e chang nges? es? Envelope lope curve e for r Arizona ona peak ak flows
CLASS ACTIVTY !
CONTROLS OF FLOOD HYDROGRAPH CHARACTERISTICS TO HELP YOU IN YOUR ASSESSMENTS
WH WHAT T WI WILL THE FU FUTURE URE HOLD LD? . . . wil ill l cli lima matic tic cha hang nge e ma make e floods ods mo more ext xtreme? me? or r will they get sma maller? er?
(1) A Northward Shift in Winter Storm Track? Roosevelt Dam Winter flooding Jan 1993 on Rillito in Tucson (2) A Change in Frequency or Intensity of Tropical Storms? Some Important Flood- Generating Tropical Storms Tropical storm Octave Oct 1983 (3) A More Intense Sabino Creek July 2006 Summer Monsoon?
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