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Georgakakos, KP, Guetter AK, Sperfslage JA.  Submitted.  Estimation of Flash Flood Potential for Large Areas. Destructive water : water-caused natural disasters, their abatement and control. ( H LG, Ed.).:87-93., Wallingford: International Association of Hydrological Sciences Abstract
Modrick, TM, Georgakakos KP, Shamir E, Spencer CR.  2017.  Operational quality control and enhancement of radar data to support regional flash flood warning systems. Journal of Hydrologic Engineering. 22   10.1061/(asce)he.1943-5584.0001345   AbstractWebsite

The paper draws from recent experience with operational regional flash flood warning systems deployed worldwide that utilize radar precipitation data as input to provide regional warnings at high spatial resolution. This paper focuses on radar precipitation data quality control and adjustments in context of making the radar data useful in hydrologic application specific to flash flood warnings. Aspects discussed are radar precipitation preprocessing for hydrologic application, identifying regions of inappropriate radar data for hydrologic use, developing bias adjustment strategies using limited rain gauge networks under the radar umbrella, and impacts of radar precipitation uncertainty on soil water estimates that impact in turn predictions and warnings. The bias adjustment strategies presented are twofold: (1)adjusting for the long-term mean bias in the radar precipitation data (climatological bias adjustment), and (2)accounting for event-specific, temporal deviations from the climatological bias (through dynamic bias adjustment). The development of radar data masks for regions of inappropriate radar data are based on the spatial distribution of the probability of detection of positive precipitation as compared to that produced by rain gauges under the radar umbrella. Climatological bias adjustment of radar data in regions not masked is accomplished through a probability matching procedure that involves transformed data from the rain gauges under the radar umbrella and from their embedding radar grid boxes. This allows for intensity-dependent climatological bias adjustment. An adaptive Kalman filter is used for dynamic bias adjustment of radar data to account for temporal deviations of the bias from the climatological values. The use of adjusted radar data as forcing for the land-surface component of the flash flood warning system produces more realistic soil water state for the flash flood warning systems than the unadjusted radar data does. The discussion uses examples from Romania and Mexico. (C) 2016 American Society of Civil Engineers.

Shamir, E, Rimmer A, Georgakakos KP.  2016.  The use of an orographic precipitation model to assess the precipitation spatial distribution in Lake Kinneret watershed. Water. 8   10.3390/w8120591   AbstractWebsite

A high-resolution 3-D orographic precipitation model (OPM) forced by Climate Forecast System (CFS) reanalysis fields was developed for the Lake Kinneret watershed (Israel-Syria-Lebanon territories). The OPM was tuned to represent the interaction between the advected and stratiform rainfall, and the local orographic enhancement. The OPM evaluation was focused on the densely instrumented lower part of the watershed. To evaluate the ungauged upper-elevation, bias-adjusted precipitation estimates from the Global-Hydro-Estimator were used. The OPM simulates higher rainfall amounts in the upper-elevation watershed compared to currently used rainfall estimates from an elevation dependent regression. The larger differences are during rain events with southwesterly wind flow and high moisture flux. These conditions, according to the OPM, are conducive to enhanced orographic lifting in the Hermon Mountain. A sensitivity analysis indicated that the higher wind speeds for southwesterly-northwesterly trajectories generate significant orographic lifting and increase the precipitation differences between the lower and upper elevations.

Posner, AJ, Georgakakos KP.  2015.  Normalized Landslide Index Method for susceptibility map development in El Salvador. Natural Hazards. 79:1825-1845.   10.1007/s11069-015-1930-4   AbstractWebsite

El Salvador and Central America in general are highly prone to landsliding. In November 1998, Hurricane Mitch killed 240 people, displaced about 85,000 people, caused more than $600 million in economic losses, and damaged about 60 % of the nation's roads (Rose et al. in Natural hazards in El Salvador. Geologic Society of America of special paper 375, Boulder, 2004). An understanding of susceptibility of locations to landsliding is critical for development and mitigation planning. This work presents the development of the Normalized Landslide Index Method which is a derivative of the bivariate statistical methods commonly used in landslide susceptibility assessment. The resultant map was amended through a tangential analysis, also commonly used in landslide susceptibility mapping, the Analytical Hierarchy Process (AHP), which reduces multi-criteria analysis to pair-wise comparisons. The assimilation of results from the AHP analysis into the statistically derived susceptibility map skewed the original results by emphasizing the extremes already found. It was determined that addition of AHP results did not increase the value of the derived susceptibility map. Finally, a physically based a priori approach to landslide susceptibility mapping, developed by El Salvador National Service of Territorial Studies, was compared to the statistically derived map developed herein. It was found that the a priori approach was not sufficiently discriminant to be useful for planners and regulators, as very large areas were designated high susceptibility that included areas with low slope angles. The development of the normalized landslide index is a significant improvement to the class of bivariate statistical strategies to assess regional landslide susceptibility.

Dettinger, M, Udall B, Georgakakos A.  2015.  Western water and climate change. Ecological Applications. 25:2069-2093. AbstractWebsite

The western United States is a region long defined by water challenges. Climate change adds to those historical challenges, but does not, for the most part, introduce entirely new challenges; rather climate change is likely to stress water supplies and resources already in many cases stretched to, or beyond, natural limits. Projections are for continued and, likely, increased warming trends across the region, with a near certainty of continuing changes in seasonality of snowmelt and streamflows, and a strong potential for attendant increases in evaporative demands. Projections of future precipitation are less conclusive, although likely the northernmost West will see precipitation increases while the southernmost West sees declines. However, most of the region lies in a broad area where some climate models project precipitation increases while others project declines, so that only increases in precipitation uncertainties can be projected with any confidence. Changes in annual and seasonal hydrographs are likely to challenge water managers, users, and attempts to protect or restore environmental flows, even where annual volumes change little. Other impacts from climate change (e.g., floods and water-quality changes) are poorly understood and will likely be location dependent. In this context, four iconic river basins offer glimpses into specific challenges that climate change may bring to the West. The Colorado River is a system in which overuse and growing demands are projected to be even more challenging than climate-change-induced flow reductions. The Rio Grande offers the best example of how climate-change-induced flow declines might sink a major system into permanent drought. The Klamath is currently projected to face the more benign precipitation future, but fisheries and irrigation management may face dire straits due to warming air temperatures, rising irrigation demands, and warming waters in a basin already hobbled by tensions between endangered fisheries and agricultural demands. Finally, California's Bay-Delta system is a remarkably localized and severe weakness at the heart of the region's trillion-dollar economy. It is threatened by the full range of potential climate-change impacts expected across the West, along with major vulnerabilities to increased flooding and rising sea levels.

Shamir, E, Megdal SB, Carrillo C, Castro CL, Chang HI, Chief K, Corkhill FE, Eden S, Georgakakos KP, Nelson KM, Prietto J.  2015.  Climate change and water resources management in the Upper Santa Cruz River, Arizona. Journal of Hydrology. 521:18-33.   10.1016/j.jhydrol.2014.11.062   AbstractWebsite

Episodic streamflow events in the Upper Santa Cruz River recharge a shallow alluvial aquifer that is an essential water resource for the surrounding communities. The complex natural variability of the rainfall-driven streamflow events introduces a water resources management challenge for the region. In this study, we assessed the impact of projected climate change on regional water resources management. We analyzed climate change projections of precipitation for the Upper Santa Cruz River from eight dynamically downscaled Global Circulation Models (GCMs). Our analysis indicates an increase (decrease) in the frequency of occurrence of dry (wet) summers. The winter rainfall projections indicate an increased frequency of both dry and wet winter seasons, which implies lower chance for medium-precipitation winters. The climate analysis results were also compared with resampled coarse GCMs and bias adjusted and statistically downscaled CMIP3 and CMIP5 projections readily available for the contiguous U.S. The impact of the projected climatic change was assessed through a water resources management case study. The hydrologic framework utilized includes a rainfall generator of likely scenarios and a series of hydrologic models that estimate the groundwater recharge and the change in groundwater storage. We conclude that climatic change projections increase the uncertainty and further exacerbate the already complicated water resources management task. The ability to attain an annual water supply goal, the accrued annual water deficit and the potential for replenishment of the aquifer depend considerably on the selected management regime. (C) 2014 The Authors. Published by Elsevier B.V.

Peleg, N, Shamir E, Georgakakos KP, Morin E.  2015.  A framework for assessing hydrological regime sensitivity to climate change in a convective rainfall environment: a case study of two medium-sized eastern Mediterranean catchments, Israel. Hydrology and Earth System Sciences. 19:567-581.   10.5194/hess-19-567-2015   AbstractWebsite

A modeling framework is formulated and applied to assess the sensitivity of the hydrological regime of two catchments in a convective rainfall environment with respect to projected climate change. The study uses likely rainfall scenarios with high spatiotemporal resolution that are dependent on projected changes in the driving regional meteorological synoptic systems. The framework was applied to a case study in two medium-sized Mediterranean catchments in Israel, affected by convective rainfall, by combining the HiReS-WG rainfall generator and the SAC-SMA hydrological model. The projected climate change impact on the hydrological regime was examined for the RCP4.5 and RCP8.5 emission scenarios, comparing the historical (beginning of the 21st century) and future (mid-21st-century) periods from three general circulation model simulations available from CMIP5. Focusing on changes in the occurrence frequency of regional synoptic systems and their impact on rainfall and streamflow patterns, we find that the mean annual rainfall over the catchments is projected to be reduced by 15% (outer range 2-23 %) and 18% (7-25 %) for the RCP4.5 sand RCP8.5 emission scenarios, respectively. The mean annual streamflow volumes are projected to be reduced by 45%(1060 %) and 47% (16-66 %). The average events' streamflow volumes for a given event rainfall depth are projected to be lower by a factor of 1.4-2.1. Moreover, the streamflow season in these ephemeral streams is projected to be shorter by 22% and 26-28% for the RCP4.5 and RCP8.5, respectively. The amplification in reduction of streamflow volumes relative to rainfall amounts is related to the projected reduction in soil moisture, as a result of fewer rainfall events and longer dry spells between rainfall events during the wet season. The dominant factors for the projected reduction in rainfall amount were the reduction in occurrence of wet synoptic systems and the shortening of the wet synoptic systems durations. Changes in the occurrence frequency of the two dominant types of the regional wet synoptic systems (active Red Sea trough and Mediterranean low) were found to have a minor impact on the total rainfall.

Georgakakos, AP, Yao HM, Georgakakos KP.  2014.  Ensemble streamflow prediction adjustment for upstream water use and regulation. Journal of Hydrology. 519:2952-2966.   10.1016/j.jhydrol.2014.06.044   AbstractWebsite

Hydrologic model forecasts are commonly biased in watersheds where water use and regulation activities cause flow alterations. Furthermore, direct accounting of such biases in forecast preparation is impractical as the information required is extensive and usually unavailable. This article introduces a new method to characterize the aggregate flow alteration biases and associated uncertainty in watersheds with important but largely undocumented water use and regulation activities. It also uses these assessments to adjust the ensemble streamflow predictions at downstream locations. The method includes procedures to (a) detect the presence of significant upstream regulation and water use influences; (b) correct the ensemble streamflow predictions and associated uncertainty for any biases in periods when such influences are detectable; and (c) assess the adjusted forecast reliability improvements. Applications in three watersheds of the American River in California demonstrate that the new method leads to significant forecast skill improvements and is also readily applicable to other regions. (C) 2014 Elsevier B.V. All rights reserved.

Georgakakos, KP, Graham NE, Modrick TM, Murphy MJ, Shamir E, Spencer CR, Sperfslage JA.  2014.  Evaluation of real-time hydrometeorological ensemble prediction on hydrologic scales in Northern California. Journal of Hydrology. 519:2978-3000.   10.1016/j.jhydrol.2014.05.032   AbstractWebsite

The paper presents an evaluation of real time ensemble forecasts produced during 2010-2012 by the demonstration project INFORM (Integrated Forecast and Reservoir Management) in Northern California. In addition, the innovative elements of the forecast component of the INFORM project are highlighted. The forecast component is designed to dynamically downscale operational multi-lead ensemble forecasts from the Global Ensemble Forecast System (GEFS) and the Climate Forecast system (CFS) of the National Centers of Environmental Prediction (NCEP), and to use adaptations of the operational hydrologic models of the US National Weather Service California Nevada River Forecast Center to provide ensemble reservoir inflow forecasts in real time. A full-physics 10-km resolution (10 km on the side) mesoscale model was implemented for the ensemble prediction of surface precipitation and temperature over the domain of Northern California with lead times out to 16 days with 6-hourly temporal resolution. An intermediate complexity regional model with a 10 km resolution was implemented to downscale the NCEP CFS ensemble forecasts for lead times out to 41.5 days. Methodologies for precipitation and temperature model forecast adjustment to comply with the corresponding observations were formulated and tested as regards their effectiveness for improving the ensemble predictions of these two variables and also for improving reservoir inflow forecasts. The evaluation is done using the real time databases of INFORM and concerns the snow accumulation and melt seasons. Performance is measured by metrics that range from those that use forecast means to those that use the entire forecast ensemble. The results show very good skill in forecasting precipitation and temperature over the subcatchments of the INFORM domain out to a week in advance for all basins, models and seasons. For temperature, in some cases, non-negligible skill has been obtained out to four weeks for the melt season. Reservoir inflow forecasts exhibit also good skill for the shorter lead-times out to a week or so, and provide a good quantitative basis in support of reservoir management decisions pertaining to objectives with a short term horizon (e.g., flood control and energy production). For the northernmost basin of Trinity reservoir inflow forecasts exhibit good skill for lead times longer than 3 weeks in the snow melt season. Bias correction of the ensemble precipitation and temperature forecasts with fixed bias factors over the range of lead times improves forecast performance for almost all leads for precipitation and temperature and for the shorter lead times for reservoir inflow. The results constitute a first look at the performance of operational coupled hydrometeorological ensemble forecasts in support of reservoir management. (C) 2014 Elsevier B.V. All rights reserved.

Shamir, E, Georgakakos KP.  2014.  MODIS Land Surface Temperature as an index of surface air temperature for operational snowpack estimation. Remote Sensing of Environment. 152:83-98.   10.1016/j.rse.2014.06.001   AbstractWebsite

Regional operational modeling systems that support forecasters for the real-time warning of flash flood events often suffer from lack of adequate real-time surface air temperature data to force their accumulation and ablation snow model. The Land Surface Temperature (LST) product from MODIS, which provides four instantaneous readings per day, was tested for its feasibility to be used in real-time to derive spatially distributed surface air temperature (T-a) forcing for the operational snow model. The study was conducted in the Southeast region of Turkey using an atypically dense network of hourly T-a, daily snow depth, snow water equivalent (SWE), and rainfall datasets for the period: October 2002-September 2010. A comparison between the T-a and the corresponding LST grid-cell data indicated close associations that are different in nature for periods with and without snow on the ground. The LST-derived T-a was compared with that obtained from on-site gauge-based interpolation procedures and climatological time series. The LST-derived T-a was found inferior only to the T-a derived from the interpolation of the dense gauge network (31-gauges). Snow-pack simulations using estimated T-a time series were compared to simulations that were forced by the observed T-a at each site of 18 sites. The 1ST-derived T-a performed well in simulating snow mass and maximum SWE magnitude, while it did not represent well the timing of the annual peak of SWE and the duration of spring melt. Our study concluded that the MODIS/LST product can be a valuable additional source of real time forcing data for regional operational snow models, especially in remote mountainous areas with sparse telemetric data. (C) 2014 Elsevier Inc. All rights reserved.

Murphy, MJ, Georgakakos KP, Shamir E.  2014.  Climatological analysis of December rainfall in the Panama Canal Watershed. International Journal of Climatology. 34:403-415.   10.1002/joc.3694   Abstract

Monthly accumulated precipitation over the tropical Panama Canal Watershed has the largest interannual variability in December, with the wettest month on record being December 2010. December accumulated precipitation over the watershed is found to vary with sea surface temperature (SST) anomalies in both the tropical North Atlantic and equatorial Pacific oceans, but a considerably stronger relationship is found with the difference between these SST anomalies. The configuration of SST anomalies in these two ocean basins during December has a strong effect on the flux of low-level moisture over the Caribbean Sea, southern Central America, and the eastern Pacific Ocean through the modification of the Caribbean Low-Level Jet (CLLJ) and the Chorro del Occidente Colombiano (CHOCO) jet. Wet Decembers in the watershed are associated with cool (warm) SST anomalies in the tropical Pacific (North Atlantic), a weakening (strengthening) of the CLLJ (CHOCO jet), and increased moisture convergence over and around Panama, with the opposite conditions associated with dry Decembers. The SST anomalies in these two ocean basins affect the distribution of daily precipitation during December differently, with SST anomalies in the Pacific (Atlantic) predominately associated with changes in the frequency of heavier (lighter) precipitation. The analysis shows that December 2010 followed the pattern of associations of wet Decembers but with the highest intensity of precipitation and CHOCO jet strength

Shamir, E, Georgakakos KP, Spencer C, Modrick TM, Murphy MJ, Jubach R.  2013.  Evaluation of real-time flash flood forecasts for Haiti during the passage of Hurricane Tomas, November 4-6, 2010. Natural Hazards. 67:459-482.   10.1007/s11069-013-0573-6   AbstractWebsite

The January 2010 earthquake that devastated Haiti left its population ever more vulnerable to rainfall-induced flash floods. A flash flood guidance system has been implemented to provide real-time information on the potential of small (similar to 70 km(2)) basins for flash flooding throughout Haiti. This system has components for satellite rainfall ingest and adjustment on the basis of rain gauge information, dynamic soil water deficit estimation, ingest of operational mesoscale model quantitative precipitation forecasts, and estimation of the times of channel flow at bankfull. The result of the system integration is the estimation of the flash flood guidance (FFG) for a given basin and for a given duration. FFG is the amount of rain of a given duration over a small basin that causes minor flooding in the outlet of the basin. Amounts predicted or nowcasted that are higher than the FFG indicate basins with potential for flash flooding. In preparation for Hurricane Tomas' landfall in early November 2010, the FFG system was used to generate 36-h forecasts of flash flood occurrence based on rainfall forecasts of the nested high-resolution North American Model of the National Centers for Environmental Prediction. Assessment of the forecast flood maps and forecast precipitation indicates the utility and value of the forecasts in understanding the spatial distribution of the expected flooding for mitigation and disaster management. It also highlights the need for explicit uncertainty characterization of forecast risk products due to large uncertainties in quantitative precipitation forecasts on hydrologic basin scales.

Shamir, E, Ben-Moshe L, Ronen A, Grodek T, Enzel Y, Georgakakos KP, Morin E.  2013.  Geomorphology-based index for detecting minimal flood stages in arid alluvial streams. Hydrology and Earth System Sciences. 17:1021-1034.   10.5194/hess-17-1021-2013   AbstractWebsite

Identification of a geomorphic index to represent lower thresholds for minor flows in ephemeral, alluvial streams in arid environments is an essential step as a precursor for reliable flash flood hazard estimations and establishing flood warning systems. An index, termed Alluvial wadi Flood Incipient Geomorphologic Index (AFIG), is presented. Analysis of data from an extensive field survey in the arid ephemeral streams in southern and eastern Israel was conducted to investigate the AFIG and the control over its value across the region. During the survey we identified distinguishable flow marks in the lower parts of streams' banks, such as niches, vegetation line, and change in bank material, which are indicative of low flows. The cross-sectional characteristics of the AFIG were studied in relationship with contributing drainage basin characteristics such as lithology, topography, and precipitation. Drainage area and hardness of the exposed lithology (presented as a basin-wide index) are the preferred descriptors to be used in estimating a specific AFIG in unsurveyed sites. Analyses of discharge records from seven hydrometric stations indicate that the recurrence interval of the determined AFIG is equal to or more frequent than 0.5 yr.

Shamir, E, Georgakakos KP, Murphy MJ.  2013.  Frequency analysis of the 7-8 December 2010 extreme precipitation in the Panama Canal Watershed. Journal of Hydrology. 480:136-148.   10.1016/j.jhydrol.2012.12.010   AbstractWebsite

The 7-8 December 2010 rainfall event in Panama produced record rainfall and streamflow that are about twice as much as for the previously observed large event in record, In this study we ask whether before the occurrence of this rainfall event, a return period estimate using the historical record and the commonly used statistical asymptotic distributions of extreme values could have indicated that such an event is probable. We examined the daily and 24-h mean areal rainfall over the entire Panama Canal Watershed with the Generalized Extreme Value, Gumbel, and Generalized Pareto distributions using the maximum likelihood approach for the parameter and uncertainty bounds estimation. We found that the solutions that maximized the log likelihood for these three distributions yield return period estimates that are larger than 2000 years. These return periods imply that the 2010 rainfall event was practically unforeseen. It is only the careful implementation of these distributions with full uncertainty analysis to define confidence intervals that yields estimates of return periods with substantial probabilities for such an event to occur. The GEV was found to be the most adequate distribution for this analysis, and the commonly-used Gumbel distribution, although indicated a good fit to the annual maxima series, attributed an extremely low probability for the occurrence of this event. (C) 2012 Elsevier B.V. All rights reserved.

Cheng, FY, Georgakakos KP.  2011.  Wind speed interpolation in the vicinity of the Panama Canal. Meteorological Applications. 18:459-466.   10.1002/met.237   AbstractWebsite

A simplified boundary layer (SBL) model formulation is tested against the mesoscale meteorological model MM5 with respect to the 2 km interpolation of hourly surface wind station data for stations in the close vicinity of the Panama Canal. The required short computation time for the real time interpolation of the wind during air pollution incidents involving crossing cargo ships makes the use of simplified wind models an alternative to the full implementation of mesoscale models. The SBL model does take into consideration the land cover of the ground surface, which exhibits substantial variability in the study region. The SBL model produces features of wind speed that are similar to those of the MM5 simulation along the better-observed Canal centreline. The presence of orographic features makes the applicability of the simplified formulation reasonable only near the Canal where the terrain has small undulations. The simulated wind fields show that the dry season (January to April) is more spatially and temporally coherent than the wet season and that it also has higher wind speeds than the wet season. The evening hours have higher wind speeds than the morning hours in both seasons. The simulated wind exhibits higher average wind speeds and higher frequencies of exceeding 5 m s-1 within the Gatun Lake on the Caribbean side of the Isthmus and the entrance/exit of the Canal on the Caribbean and Pacific coasts. These results are useful for the development of effective disaster mitigation strategies for air pollution events in the region. Copyright (C) 2011 Royal Meteorological Society

Cheng, FY, Georgakakos KP.  2011.  Statistical analysis of observed and simulated hourly surface wind in the vicinity of the Panama Canal. International Journal of Climatology. 31:770-782.   10.1002/joc.2123   AbstractWebsite

Surface wind patterns at the Panama Canal vicinity are identified on the basis of 6 years of observed hourly surface wind data and with the use of high-resolution numerical model simulations. Statistical analysis of the observed wind at various stations in the Panama Canal is presented, together with the analysis of simulated surface wind fields that are obtained from the MM5 mesoscale meteorological model using surface wind assimilation and forced by North American regional reanalysis data. The performance analysis indicates that the 2-km-resolution MM5 model surface wind simulations have skill when compared with the observations at the measurement sites. The analysis of the wind fields for the period 2002-2007 shows that the dry season (January to April) is more spatially and temporally coherent than the wet season in the region. The simulated wind shows that the average wind speed reaches up to 7-8 m s(-1) and the frequency of exceeding 5 m s(-1) reaches up to 0.7-0.8 in Lake Gatun, the entrance/exit of the Canal in the Caribbean and Pacific coasts, and at high elevations. The dry season exhibits higher climatological wind speeds and exceedence frequencies than the wet season but the wet season shows greater spatial variability. For both seasons, the morning hours have lower average winds than the evening hours. The analysis underlines the significant influence of convection, sea breeze and local conditions (elevation gradients and land surface cover) in the observed and simulated surface wind patterns. The information presented herein, particularly as regards the Canal centerline results, may be useful for identifying the effects of air pollution from sources aboard transiting cargo ships on large communities in the Canal vicinity (e. g. Panama City). Information presented is also relevant to regional wind energy studies and fog formation analyses. Copyright (C) 2010 Royal Meteorological Society

Georgakakos, KP, Graham NE, Carpenter M, Yao H.  2011.  Integrating climate-hydrology forecasts and multi-objective reservoir management for northern California. Eos, Transactions American Geophysical Union. 86:122-127.   10.1029/2005EO120002   Abstract

The Integrated Forecast and Reservoir Management (INFORM) Project was conceived to demonstrate increased water-use efficiency in Northern California water resources operations through (1) the innovative application of climate, hydrologic, and decision science, and (2) reciprocal technology transfer activities between the INFORM scientists and the staff of federal and state agencies with an operational forecast and management mandate in Northern California.Toward achieving this goal, INFORM objectives include implementing a prototype integrated forecast-management system for primary Northern California reservoirs, for individual reservoirs as well as system-wise. Project objectives also include demonstrating the utility of climate and hydrologic forecasts through near-real-time tests of the integrated system with actual data and management input.

Villarini, G, Krajewski WF, Ntelekos AA, Georgakakos KP, Smith JA.  2010.  Towards probabilistic forecasting of flash floods The combined effects of uncertainty in radar-rainfall and flash flood guidance. Journal of Hydrology. 394:275-284.   10.1016/j.jhydrol.2010.02.014   AbstractWebsite

The flash flood guidance system (FFGS) is an operational system which assists forecasters to issue flash flood warnings and watches over the conterminous United States Currently It is a deterministic system given a specified precipitation accumulation over a basin and Dyer a time period issuing of flash flood watches and warnings is considered depending on the exceedance of a certain threshold value (flash flood guidance - FFG) For given channel characteristics and initial soil moisture conditions FFG values are computed with the use of a hydrologic model The purpose of this study is to consider the effects of radar-rainfall and flash flood guidance uncertainties on the FFGS The errors in the FFG are accounted for by quantifying the uncertainties due to the estimation of the hydraulic and terrain characteristics and the hydrologic model parameters and initial state To account for the uncertainties in radar-rainfall the authors use an empirically-based radar-rainfall error model This model requires calibration for each application region and it accounts for range effects synoptic conditions space-time resolutions and the spatial and temporal dependences of the errors Thus the combined effects of uncertainty in both radar-rainfall and FFG can be assessed The results are exemplified through two cases in a small basin in the Illinois River Basin The potential of transforming FFGS Into a probabilistic system is also discussed (C) 2010 Elsevier B V All rights reserved

Shamir, E, Lee BJ, Bae DH, Georgakakos KP.  2010.  Flood Forecasting in Regulated Basins Using the Ensemble Extended Kalman Filter with the Storage Function Method. Journal of Hydrologic Engineering. 15:1030-1044.   10.1061/(asce)he.1943-5584.0000282   AbstractWebsite

An ensemble extended Kalman filter (EEKF) formulation is applied to a regulated basin. The existing event-based storage function method for the prediction of flow is enhanced to incorporate continuous soil water accounting and to be suitable for application in large watersheds with several tributaries. The formulation is complemented by EEKF, which utilizes flow and reservoir level observations to update catchment soil water and channel states, and reservoir storage estimates predicted by the model. The formulated forecast is suitable for operational application. Ensemble precipitation predictions are generated to serve as input to the forecast system, and the results are intercompared using two different statistical approaches. These predictions together with parametric uncertainty models constitute the basis of the ensemble flow predictions by the model. A case study is presented that demonstrates the implementation and evaluation of the method with respect to the prediction of large flow events in a 4,500-km(2) regulated basin, a tributary to Nakdong River in Korea, using hourly data for the period January 2006-August 2008. A significant finding is that although the calibrated-model simulations reproduce well the observations, without the updating procedure, it forecasted poorly the high-flow events. The EEKF-based forecast system improves the forecast of the high-flow events with respect to time and magnitude and yields higher scores for the probability of detection and false alarm rate associated with the exceedance of high-flow thresholds.

Graham, NE, Georgakakos KP.  2010.  Toward Understanding the Value of Climate Information for Multiobjective Reservoir Management under Present and Future Climate and Demand Scenarios. Journal of Applied Meteorology and Climatology. 49:557-573.   10.1175/2009jamc2135.1   AbstractWebsite

Numerical simulation techniques and idealized reservoir management models are used to assess the utility of climate information for the effective management of a single multiobjective reservoir. Reservoir management considers meeting release and reservoir volume targets and minimizing wasteful spillage. The influence of reservoir size and inflow variability parameters on the management benefits is examined. The effects of climate and demand (release target) change on the management policies and performance are also quantified for various change scenarios. Inflow forecasts emulate ensembles of dynamical forecasts for a hypothetical climate system with somewhat predictable low-frequency variability. The analysis considers the impacts of forecast skill. The mathematical problem is cast in a dimensionless time and volume framework to allow generalization. The present work complements existing research results for specific applications and expands earlier analytical results for simpler management situations in an effort to draw general conclusions for the present-day reservoir management problem under uncertainty. The findings support the following conclusions: (i) reliable inflow forecasts are beneficial for reservoir management under most situations if adaptive management is employed; (ii) tolerance to forecasts of lower reliability tends to be higher for larger reservoirs; (iii) reliable inflow forecasts are most useful for a midrange of reservoir capacities; (iv) demand changes are more detrimental to reservoir management performance than inflow change effects of similar magnitude; (v) adaptive management is effective for mitigating climatic change effects and may even help to mitigate demand change effects.

O'Hara, JK, Georgakakos KR.  2008.  Quantifying the urban water supply impacts of climate change. Water Resources Management. 22:1477-1497.   10.1007/s11269-008-9238-8   AbstractWebsite

The difference in timing between water supply and Urban water demand necessitates water storage. Existing reservoirs were designed based upon hydrologic data from a given historical period, and, given recent evidence for climatic change, may be insufficient to meet demand under future climate change scenarios. The focus Of this study is to present a generally applicable methodology to assess the ability of existing storage to meet urban water demand under present and projected future climatic scenarios, and to determine the effectiveness of storage capacity expansions. Uncertainties in climatic forcing and projected demand scenarios are considered explicitly by the models. The reservoir system in San Diego, California is used as a case study. We find that the climate change scenarios will be more costly to the city than scenarios using historical hydrologic parameters. The magnitude of the expected costs and the optimal investment policy are sensitive to projected population growth and the accuracy to which Our model can predict spills.

Georgakakos, KP, Graham NE.  2008.  Potential benefits of seasonal inflow prediction uncertainty for reservoir release decisions. Journal of Applied Meteorology and Climatology. 47:1297-1321.   10.1775/2007jamc1671.1   AbstractWebsite

This paper examines the conditions for which beneficial use of forecast uncertainty may be made for improved reservoir release decisions. It highlights the parametric dependencies of the effects of uncertainty in seasonal inflow volumes on the optimal release and objective function of a single reservoir operated to meet a single volume target at the end of the season under volume and release constraints. The duration of the "season" may be one or several months long. The analysis invokes the application of Kuhn-Tucker theory, and it shows that the presence of uncertainty introduces complex dependence of the optimal release and objective function on the reservoir parameters and uncertain inflow forcing. The seasonal inflow volume uncertainty is represented by a bounded symmetric beta distribution with a given mean, which is considered to be unbiased, and a half-range Q(R). The authors find that the use of predicted inflow uncertainty is particularly beneficial during operation with a volume target that is either near reservoir capacity or near zero reservoir volume, with the optimal release being directly dependent on QR in these situations. This positive finding is moderated by the additional finding that errors in the estimation of predicted QR can result in significant operation losses (larger deviations from the target volume) that are due to suboptimal release decisions. Furthermore, the presence of binding release constraints leads to loss of optimal release and objective function benefits due to the seasonal inflow uncertainty predictions, suggesting less rigid release policies for improved operations under uncertain forecasts. It is also shown that the reservoir capacity values for which optimal reservoir operations are most sensitive to seasonal inflow uncertainty predictions are found to be at most 5 times the uncertainty range of the predicted seasonal inflow volume and to be at least as large as the uncertainty range of predicted inflow volumes. Suggestions for continued research in this area are offered.

Taylor, SV, Cayan DR, Graham NE, Georgakakos KP.  2008.  Northerly surface winds over the eastern North Pacific Ocean in spring and summer. Journal of Geophysical Research-Atmospheres. 113   10.1029/2006jd008053   AbstractWebsite

Persistent spring and summer northerly surface winds are the defining climatological feature of the western coast of North America, especially south of the Oregon coast. Northerly surface winds are important for upwelling and a vast array of other biological, oceanic, and atmospheric processes. Intermittence in northerly coastal surface wind is characterized and wind events are quantitatively defined using coastal buoy data south of Cape Mendocino on the northern California coast. The defined wind events are then used as a basis for composites in order to explain the spatial evolution of various atmospheric and oceanic processes. Wind events involve large-scale changes in the three-dimensional atmospheric circulation including the eastern North Pacific subtropical anticyclone and southeast trade winds. Composites of QSCAT satellite scatterometer wind estimates from 1999 to 2005 based on a single coastal buoy indicate that wind events typically last 72-96 h and result in anomalies in surface wind and Ekman pumping that extend over 1000 km from the west coast of North America. It may be useful to consider ocean circulation and dependent ecosystem dynamics and the distribution of temperature, moisture, and aerosols in the atmospheric boundary layer in the context of wind events defined herein.

Shamir, E, Meko DM, Graham NE, Georgakakos KP.  2007.  Hydrologic model framework for water resources planning in the Santa Cruz River, southern Arizona. Journal of the American Water Resources Association. 43:1155-1170.   10.1111/j.1752-1688.2007.00095.x   AbstractWebsite

The authors develop a model framework that includes a set of hydrologic modules as a water resources management and planning tool for the upper Santa Cruz River near the Mexican border, Southern Arizona. The modules consist of: ( 1) stochastic generation of hourly precipitation scenarios that maintain the characteristics and variability of a 45- year hourly precipitation record from a nearby rain gauge; ( 2) conceptual transformation of generated precipitation into daily streamflow using varied infiltration rates and estimates of the basin antecedent moisture conditions; and ( 3) surface- water to ground- water interaction for four downstream microbasins that accounts for alluvial ground- water recharge, and ET and pumping losses. To maintain the large inter- annual variability of streamflow as prevails in Southern Arizona, the model framework is constructed to produce three types of seasonal winter and summer categories of streamflow ( i. e., wet, medium, or dry). Longterm ( i. e., 100 years) realizations ( ensembles) are generated by the above described model framework that reflects two different regimes of inter annual variability. The first regime is that of the historic streamflow gauge record. The second regime is that of the tree ring reconstructed precipitation, which was derived for the study location. Generated flow ensembles for these two regimes are used to evaluate the risk that the regional four ground- water microbasins decline below a preset storage threshold under different operational water utilization scenarios.

Shamir, E, Wang J, Georgakakos KP.  2007.  Probabilistic streamflow generation model for data sparse arid watersheds. Journal of the American Water Resources Association. 43:1142-1154.   10.1111/j.1752-1688.2007.00094.x   AbstractWebsite

The authors present a model that generates streamflow for ephemeral arid streams. The model consists of a stochastic hourly precipitation point process model and a conceptual model that transforms precipitation into flow. It was applied to the Santa Cruz River at the border crossing from Mexico into Southern Arizona. The model was constructed for four different seasons and three categories of inter- annual variability for the wet seasons of summer and winter. The drainage area is ungauged and precipitation information was inferred from a precipitation gauge downstream. The precipitation gauge record was evaluated against simulated precipitation from a mesoscale numerical weather prediction model, and was found to be the representative of the regional precipitation variability. The flow generation was found to reproduce the variability in the observed record at the daily, seasonal and annual time scales, and it is suitable for use in planning studies for the study site.