“Development of Community Water Deficit Index (CWDI) for small to mid-size communities of Southeastern United States” “Development of Community Water Deficit Index (CWDI) for small to mid-size communities of Southeastern United States” By: Vaishali Sharda Puneet Srivastava Dept. of Biosystems Engg, Auburn University Keith Ingram Dept. of Ag and Biol Engg, University of Florida Latif Kalin School of Forestry and Wildlife Sciences, Auburn University Xing Fang Dept of Civil Engg Auburn University Auburn University

Introduction Urban water use o Potential evapotranspiration and rainfall best explains changes in residential water use attributable to climate ( Hughes et al., 1994 ) o Drought conditions subject the municipal water systems to  Increased demands and decreased supplies  Pose serious risk to the performance of the system ( Radwan et al., 1994 ) o Such fluctuation in climatic conditions may cause short term failures in the system

CWDI for Small to Mid-size Communities o Currently available drought information (US Drought Monitor, Lawn and Garden Moisture Index, etc. are not specific to municipal water systems)  High spatial variability of the rainfall in the Southeast  Supply and demand not considered  Do not forecast

Vision Develop a web-based CWDI for water managers of small to mid-size communities in the region o Water supply o Seasonal water demand o High spatial resolution  The communities are of relatively small size o Drought forecast o Provides an easy to use web-interface – help in decision making

Features o User just needs internet access o Delineate supply and demand watersheds o Provide population, historic water usage data etc. o No advanced knowledge required Delineated Supply Watershed

Assumptions o Each community, irrespective of the source of its water supply, has a reservoir(s) where the water is stored before distribution. o The supply going into the reservoir may be directly from a stream, a watershed, a ground water well or purchased from another source. o There is a supply watershed and a demand watershed. The supply watersheds can be different from, same as, or overlapping the demand watershed. o Land cover changes in the supply watersheds are minimal so climate becomes the driving factor affecting the water supply from the watershed.

Basic Principle Supply and Demand Water Balance o Inputs  Runoff from the supply watershed (Curve number method)  Baseflow  Precipitation  Additional water supply sources (purchased water, groundwater etc.) o Outputs  Total water withdrawal (demand)  Evaporation  Mandatory discharge

CWDI Model  Curve Number Selection: Based on the season (dry or growing) and the Antecedent Moisture Condition (AMC)  Evapotranspiration: Most important component  Dynamic demand - irrigation of lawns and golf courses etc.  Dependent on climate  Dynamic demand is given by:  Static Demand: Depends on population  CWDI: Estimated as  If CWDI ≤ 0, => Drought  If CWDI > 0, => No Drought

CWDI Model in STELLA

Drought Forecasting ENSO Outlook and Climate Variables Web Based CWDI Tool Time CWDI

Case Study 1 – City of Auburn Demand Watershed Supply Watershed Lake Ogletree o Current average usage for the water system - 6 MGD o Current water supply capacity MGD o Can purchase up to 3.6 MGD from Opelika Utilities. (used only at certain times during the year)

Why Climate Variability is Important to City of Auburn? Source: Full Pool Phase 1 Phase 2 Phase 3

Case Study 2 – City of Griffin o 2 withdrawal points on Flint river  Griffin (13.2 MGD)  Molena (50 MGD) o 7 customers  people  City of Griffin  Wholesale customers o 24.5 Mgd capacity

Validation - CoA

Validation - CoG Full Pool Phase 1 Phase 2 Phase 3

Scenario Analysis - CoA Irrigation/Dynamic demand

Modeled results - CoA

Drought Forecast-CoA Full Pool Phase 1 Phase 2 Phase 3 Observed

Drought Forecast-CoA

Summary and Future Research o Need of drought information for small to mid-size communities in ENSO related climate variability prone Southeastern US o CWDI methodology developed and tested (validated) for City of Auburn, Alabama and City of Griffin, Georgia o Model tested for forecasting drought at 3-6 months scale based on ENSO outlook. o Quantify the value of this drought information  Impact of drought on supply and demand  Knowledge of drought forecast allows mitigation of negative impacts o Web-based tool for CWDI

Thank You!