Publications Published in Journal of Hydrology

1. A methodology to asess relations between climatic variability and variations in hydrologic time series in the southwestern United States. Hanson, R T; Newhouse, M W; Dettinger, M D.
   Journal of Hydrology: 2004
   Notes
   A new method for frequency analysis of hydrologic time series was developed to facilitate the estimation and reconstruction of individual or groups of frequencies from hydrologic time-series and facilitate the comparison of these isolated time-series components across data types, between different hydrologic settings within a watershed, between watersheds, and across frequencies. While climate-related variations in inflow to and outflow from aquifers have often been neglected, the development and management of ground-water and surface-water resources has required the inclusion of the assessment of the effects of climatic variability on the supply and demand and sustainability of use. The regional assessmentof climatic variability of surface-water and ground-water flow throughout the southwestern United States required this new systematic method of hydrologic time-series analysis. To demonstrate the application of this new method, six hydrologic time-series from the Mojave River Basin, California were analyzed. The results indicate that climatic variability exists in all the data types and are partially coincident with known climate cycles such as the Pacific Decadal Oscillation and the El Nino–Southern Oscillation. The time-series also indicate lagged correlations between tree-ring indices, streamflow, stream base flow, and ground-water levels. These correlations and reconstructed time-series can be used to better understand the relation of hydrologic response to climatic forcings and to facilitate the simulation of streamflow and ground-water recharge for a more realistic approach to water-resource management.
   
   
   
2. Assessment of Folsom Lake response to historical and potential future climate scenarios: 1. Forecasting. Carpenter, Theresa M.; Georgakakos, Konstantine P..
   Journal of Hydrology: 2001
   Notes
   In collaboration with operational forecast and management Agencies, an integrated forecast-control system is designed and applied to a major reservoir in California to evaluate the potential benefits of climate information for flood control, hydroelectric energy production, and low flow augmentation. In addition to retrospective studies involving the historical period 1964-1993, system simulations were performed for the future period 2001-2030, under a control and a 1% greenhouse-gas-increase scenario. This paper presents the forecast component formulation and validates ensemble 30-day reservoir-inflow forecasts under a variety of situations. The control component formulation and corresponding reservoir management results are presented in Yao and Georgakakos, this issue. The forecast component is based on ensemble flow forecasting. Quantiles of the distribution of climate-model precipitation simulations are used to select catchment-scale historical daily precipitation time series for the generation of an ensemble of daily reservoir-inflow by hydrologic models. Ensemble generation takes into consideration both atmospheric-forcing and hydrologic-model uncertainties. Principal conclusions of this paper are that the integrated system provides reliable ensemble inflow volume forecasts for the majority of the deciles of forecast frequency, and that the use of climate model simulations is beneficial mainly during high flow periods. It is also found that to maintain reliability for future climate periods, generation of ensemble inflow forecasts should use input time series that reflect potential sharp changes in precipitation amount.
   
   
   
3. Assessment of Folsom Lake response to historical and potential future climate scenarios 2. Reservoir management. Yao, H.; Georgakakos, A..
   Journal of Hydrology: 2001
   Notes
   An integrated forecast-decision system for Folsom Lak, (California) is developed and used to assess the sensitivity of reservoir performance to various forecast-management schemes under historical and future climate scenarios. The assessments are based on various combinations of inflow forecasting models, decision rules, and climate scenarios. The inflow forecasting options include operational forecasts, historical analog ensemble forecasts, hydrologic ensemble forecasts, GCM-conditioned hydrologic ensemble forecasts, and perfect forecasts. Reservoir management is based on either heuristic rule curves or a decision system which includes three coupled models pertinent to turbine load dispatching, short-range energy generation scheduling, and long/mid-range reservoir management. The climate scenarios are based on historical inflow realizations, potential inflow realizations generated by General Circulation Models assuming no CO2 increase, and potential inflow realizations assuming 1% CO, annual increase. The study demonstrates that (1) reliable inflow forecasts and adaptive decision systems can substantially benefit reservoir performance and (2) dynamic operational procedures can be effective climate change coping strategies.
   
   
   
4. Estimation of groundwater pumping as closure to the water balance of a semi-arid, irrigated agricultural basin. Ruud, Nels; Harter, Thomas; Naugle, Alec.
   Journal of Hydrology: 2004
   Notes
   Groundwater pumping is frequently the least measured water balance component in semi-arid basins with significant agricultural production. In this article, we develop a GIS-based water balance model for estimating basin-scale monthly and annual groundwater pumping and apply it to a 2300 km2 semi-arid, irrigated agricultural area in the southern San Joaquin Valley, California. Both, annual groundwater storage changes and pumping are estimated as closure terms. The local hydrology is dominated by distributed surface water supplies, limited precipitation, and large crop water uses; whereas basin-scale runoff generation and groundwater-to-surface water discharges are negligible. Groundwater represents a terminal long-term storage reservoir with distributed inputs and outputs. To capture the spatio-temporal variability in water management and water use, the study area is delineated into 26 water service areas and 9611 individual fields or land units. The model computes conveyance seepage losses external to districts; seepage losses within districts; and net applied surface water of each district. For each land unit, the model calculates the applied water demand; its allotment of delivered surface water; the groundwater pumping required to meet the balance of its applied water demand; and aquifer recharge resulting from deep percolation of applied water and precipitation. These spatially distributed components are aggregated to the basin scale. Estimated annual groundwater storage changes compared well to those computed by the water-table fluctuation method over the 30-year study period, providing an independent verification of the consumptive use estimation. Pumping accounted for as much as 80% of the total applied water in ‘Critical’ water years and as little as 30% in ‘Wet’ years. Pumping estimates are most sensitive to estimation uncertainty of soil available water. They show little sensitivity to estimation errors in effective root depth, irrigation efficiencies, and intra-district seepage losses, although the cumulative sensitivity is significant.
   
   
   
5. Impact of decadal and century-scale oscillations on hydroclimate trend analyses. Chen, Z. H.; Grasby, S. E..
   Journal of Hydrology: 2009
   DOI: 10.1016/j.jhydrol.2008.11.031
   Notes
   Studies of hydro-meteorological time series have identified decadal and inter-decadal oscillations with quasi-cyclic components as part of long-term natural variations in the data. Concerns over impacts of global warming and climate change have led to many studies of sustainable development and adaptation strategies, involving historic trend estimations in order to forecast future trends. This paper demonstrates the impacts of natural oscillations of quasi-cyclic components on the Mann-Kendal and Thiel-Sen tests, the most common methods used for analyzing data trends. Tests on synthetic and real instrumental hydroclimate records suggest that the Mann-Kendall and Thiel-Sen tests are sensitive to oscillations of quasi-cyclic components. Data record length relative to the periodicity of cycles, magnitude, and phase of the longest quasi-cyclic component are the three most important factors affecting these tests. If the length of the record is greater than three cycle lengths, the impact on the M-K and T-S tests should be minimal. Given the predominance of 45-60 year climate cycles observed in instrumental records, trend analyses of time series records <60 years should be done with caution. These results provide insight for appropriate temporal trend analyses of hydroclimate and associate time series. Crown Copyright (C) 2008 Published by Elsevier B.V. All rights reserved.
   
   
   
6. Process-based snowmelt modeling: does it require more input data than temperature-index modeling?. Walter, M. Todd; Brooks, Erin S.; McCool, Donald K.; King, Larry G.; Molnau, Myron; Boll, Jan.
   Journal of Hydrology: 2005
   Notes
   Modeling snow hydrology for cold regions remains a problematic aspect of many hydro-environmental models. Temperature-index methods are commonly used and are routinely justified under the auspices that process-based models require too many input data. To test this claim, we used a physical, process-based model to simulate snowmelt at four locations across the conterminous US using energy components estimated from measured daily maximum and minimum temperature, i.e. using only the same data required for temperature-index models. The results showed good agreement between observed and predicted snow water equivalents, average R² > 0.9. We duplicated the simulations using a simple temperature-index model best fitted to the data and results were poorer, R² < 0.8. At one site we applied the process-based model without substantial parameter estimation, and there were no significant (
   
   
   
7. Temperature index melt modelling in mountain areas. Hock, Regine.
   Journal of Hydrology: 2003
   Notes
   Temperature index or degree-day models rest upon a claimed relationship between snow or ice melt and air temperature usually expressed in the form of positive temperatures. Since air temperature generally is the most readily available data, such models have been the most widely used method of ice and snow melt computations for many purposes, such as hydrological modelling, ice dynamic modelling or climate sensitivity studies. Despite their simplicity, temperature-index models have proven to be powerful tools for melt modelling, often on a catchment scale outperforming energy balance models. However, two shortcomings are evident: (1) although working well over long time periods their accuracy decreases with increasing temporal resolution; (2) spatial variability cannot be modelled accurately as melt rates may vary substantially due to topographic effects such as shading, slope and aspect angles. These effects are particularly crucial in mountain areas. This paper provides an overview of temperature-index methods, including glacier environments, and discusses recent advances on distributed approaches attempting to account for topographic effects in complex terrain, while retaining scarcity of data input. In the light of an increasing demand for melt estimates with high spatial and temporal resolution, such approaches need further refinement and development.