Tools For Drought Management Water Management in the face of droughts require Skilful Hydrologic Forecasting/Simulation Tool »Statistical or Hydrologic Models (PRMS, SWAT, etc.) for ~seasonal time scales »Stochastic Flow Simulation tools for longer term (multi-year, decades) planning and management Decision Support tool of the agriculture/water resources system »RiverWare

Seasonal Streamflow Forecast/ Simulation Hydrologic Models –PRMS, SWAT Statistical Models –Nonlinear Regression approach for ensemble forecasts [incorporating large-scale land-ocean- atmospheric information, Grantz et al., 2005; Regonda et al., 2006] –Skilful, provides uncertainty estimates via ensembles

Truckee / Carson Basin - Application Study Area –Hydroclimatology, Management Spring Streamflow Forecast Models [incorporating large-scale land-ocean- atmospheric information, Grantz et al., 2005] Decision Support Model Drive the streamflow forecast through the decision model. Investigate skills in the decision variables

Study Area TRUCKEE CANAL Farad Ft Churchill NEVADA CALIFORNIA Carson Truckee

Average Monthly Flows Primarily snowmelt driven basins (April, May, June) Correlate Fall/ Winter Climate Signals with AMJ Streamflow

Management Issues Irrigation/Agriculture decisions on the Newland Irrigation district are made in Feb much before the peak flow occurs So, skilful long-lead seasonal streamflow forecasts on Truckee and Carson Rivers are required Forecasts determine – How storage targets will be met on the Lahonton reservoir for irrigation – How much water to divert from Truckee to Carson via the Truckee Canal – How much water will be available for Irrigation Truckee Canal

Decision Variables Lahontan Storage Available for Irrigation Truckee River Water Available for Fish Diversion through the Truckee Canal

RiverWare – River and Reservoir Decision Support System Inflow Forecast OR Historical Hydrology OR Stochastic inflows Models interaction of Hydrologic response of River /Reservoir system (includes Hydropower) With Multi-objective operating policies Operational Decisions Predictions Statistical Output Economic Analysis Environ analysis Tradeoff Analysis

Truckee-Carson RiverWare Model

Winter Climate Link 500 mb Geopotential Height Carson Spring Flow High flow years go with S.Westerly winds in the Basin during winter  increased moisture/snow  increased streamflow in spring. Vice-Versa for Low flow years Grantz et al., 2005 – Water Resources Research High flow Years Low flow Years

Identified large scale land-ocean-atmosphere predictors for Truckee/Carson spring (April-June total) streamflow Used a Nonlinear regression framework (local polynomials) to generate ensemble of spring streamflow forecasts Forecasts issued on the 1 st of each month starting from Nov 1 st through April 1 st Skills evaluated using correlation coefficient and RPSS (RPSS = 1 implies categorical forecast, 0, no better than climatology)

Forecasting Results Skills increase with decrease in lead-time Significant skill even on Jan 1 st and Feb 1 st (when snow info is partial)

Forecast Ensembles are Used to drive the Decision Support System for the Truckee/Carson Baisn (Forecast skills of the decision variables evaluated)

Decision Model Results Canal DiversionWater for Fish Irrigation Water Dec 1 st Forecast Feb 1 st Forecast Apr 1 st Forecast Significant skill Especially from Feb1st onwards

Dry Year: 1994 April 1 st February 1 st December 1 st Truckee Forecast Carson Forecast Storage for Irrigation Canal Diversion Water for Fish

Wet Year: 1993 April 1 st February 1 st December 1 st Truckee Forecast Carson Forecast Storage for Irrigation Canal Diversion Water for Fish

Normal Year: 2003 April 1 st February 1 st December 1 st Truckee Forecast Carson Forecast Storage for Irrigation Canal Diversion Water for Fish

Exceedance Probabilities

Summary Developed a streamflow forecast framework incorporating large- scale ocean-atmospheric-land variables Skilful long-lead streamflow forecasts obtained on the Truckee/Carson river basin ~4-5 months ahead of the spring peak flow Developed a Decision Support System that incorporates all the management aspects of the water resources system Skilful streamflow forecasts translated into skills in the decision variables – especially the amount of flow available for irrigation The Integrated streamflow-Decision Support System provides a robust framework for effective management of droughts both in the short and longer time scales Streamflow scenarios can be generated conditioned on climate change, land use change, water use change etc. and management/decision strategies evaluated

Acknowledgements Ms. Katrina Grantz for USBR Truckee Office for financial support of this study CADSWES for computation and logistics support