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Saint Helena, CA, United States

Yoshitani J.,Japan National Institute for Land and Infrastructure Management | Kavvas M.L.,University of California at Davis | Chen Z.Q.,Bay Delta Office
Journal of Hydrologic Engineering

This paper presents the improved performance of a regional climate model for the Japan region when a fully coupled boundary layer model and an areally averaged land-surface flow model are employed. It also describes results from the application of the regional climate model to the region for climate-change prediction. An integrated regional-scale hydrological-atmospheric model (IRSHAM) was developed for the Japan region that consisted of a 60-km resolution large-domain model nesting a 20-km resolution small-domain model. The small-domain model was equipped with two-way interaction between the areally averaged land-surface parameterization and the first layer of the atmospheric model. A historical period was then simulated by IRSHAM for local precipitation and other hydrological processes. Simulation results showed a significant improvement in the monsoon-affected regional distribution of monthly precipitation in the Japan region. The simulation results correlated with their counterparts observed at the Tsukuba ground station, showing that IRSHAM performed well in predicting daily meteorological changes. IRSHAM performed another run to simulate local-scale effects of the climate change caused by a doubling of the CO 2 concentration based on Meteorological Research Institute general circulation model (GCM) I data. IRSHAM successfully downscaled GCM-I outputs to project local-scale changes in temperature and precipitation over the Japan region. © 2011 American Society of Civil Engineers. Source

Ishida K.,University of California at Davis | Kavvas M.L.,University of California at Davis | Ceyhan S.,University of California at Davis | Ohara N.,University of Wyoming | Chen Z.Q.,Bay Delta Office
World Environmental and Water Resources Congress 2015: Floods, Droughts, and Ecosystems - Proceedings of the 2015 World Environmental and Water Resources Congress

Long-term historical precipitation over Northern California was reconstructed for 137 water years from October, 1871 through September, 2008 by dynamical downscaling based on NOAA Twentieth Century Reanalysis version 2 (20CRv2). The annual maximum values of 6-, 12-, 24-, 48-, 72-, and 96-hour basin-average precipitation were obtained from the reconstructed results for three watersheds in Northern California; American River watershed, Yuba River watershed, and Upper Feather River watershed. The reconstructed results for 137 water years are long enough to conduct a moving window analysis. Then, the moving average of annual maximum basin-average precipitation for each duration is calculated based on a 50-year moving window to analyze the trend of annual maximum values of basin-average precipitation. The analysis shows a clear upward trend for the 50-year moving average over all the three watersheds. © 2015 ASCE. Source

Ejeta M.Z.,Bay Delta Office
World Environmental and Water Resources Congress 2015: Floods, Droughts, and Ecosystems - Proceedings of the 2015 World Environmental and Water Resources Congress

Meteorological and consequently hydrologic regimes in California have started to be predictable using the recently uncovered novel association of these regimes with Saros cycle and analogous orbital geometries of the earth and moon. Building on this observation and previous studies that followed it, this paper presents: (1) a hindsight analysis of meteorological and hydrologic regimes in California for water years 2011 to 2014; and (2) a prediction of a repeat of the wet regimes in California during water years 1997 and 1998 in water years 2015 and 2016. Using the natural streamflows of California's eight major rivers and the National Aeronautic and Space Administration's (NASA) alignment records of the earth, moon, and sun to establish analogous orbital geometries, the paper presents similarities of hydrologic regimes in California during water years 2011-2014 with those during water years 1975-1977, which had, successively, analogous orbital geometries. Thus, the paper attempts to show that the wet regimes in water years 1975 and 2011 followed by the dry regimes during water years 1976 and 1977 and 2012 to 2014, respectively, were predictable. The upcoming water years of 2015 and 2016 are one Saros cycle from water years 1997 and 1998, respectively, and are projected to have, successively, analogous orbital geometries as those of water years 1997 and 1998. Consequently, California may expect during water years 2015 and 2016 a repeat of the wet meteorological and hydrologic regimes of water years 1997 and 1998. While Saros cycle is generally used as instructive for the predictability of these regimes in California, analogous orbital geometries are found to be more robust indicators for their realizations. Therefore, this paper also attempts to show the relative robustness of one and two Saros cycles for identifying: (1) analogous orbital geometries, and (2) infrequent repetitious orbital tendencies such as the orbital geometry of water 2013 during water year 2014. The paper reinforces the suggestion that this association is likely to be on a global scale and continues the call for its analysis on this scale. © 2015 ASCE. Source

Ishida K.,University of California | Kavvas M.L.,University of California | Jang S.,Korea Water Resources Corporation | Chen Z.Q.,Bay Delta Office | And 2 more authors.
Journal of Hydrologic Engineering

Maximum precipitation (MP) was estimated by means of a regional atmospheric model over three watersheds in northern California [(1) the American River watershed (ARW), (2) the Yuba River watershed (YRW), and (3) the Upper Feather River watershed (UFRW)], based on the reconstruction and analyses of the historical severe storms that were recorded over these target watersheds, and where the National Centers for Environmental Prediction (NCEP)/National Center for Atmospheric Research (NCAR) reanalysis data were available for regional atmospheric modeling of the historical storms. Since severe storm events are mainly caused by atmospheric rivers (ARs) in northern California, the contribution of an AR on precipitation over each of the targeted watersheds is maximized to estimate the 72-h MP. For this purpose, the moisture of ARs is maximized after shifting the regional atmospheric model's atmospheric boundary conditions (BCs) in space with respect to latitude and longitude so that the AR strikes each of the targeted watersheds in the optimized location. To maximize the moisture of the AR, the relative humidity at the boundaries of the modeling domain is set at 100%. The 72-h MPs that were estimated by this method are 738, 690, and 513 mm over the ARW, YRW, and UFRW, respectively. The estimated MP values are respectively 1.74, 1.50, and 1.36 times larger than the historical maximum values at the previously mentioned basins. © 2015 American Society of Civil Engineers. Source

Jacobs J.M.,University of New Hampshire | Hsu E.-C.,Bay Delta Office | Choi M.,Hanyang University
Hydrological Processes

Variability and time-stability analysis for field-scale (800 m) Electronically Scanned Thinned Array Radiometer soil moisture within a satellite scale footprint (~50 km) were quantified using observations from the Southern Great Plains Hydrology Experiment 1997 and 1999 (SGP97 and SGP99). The pixels' time-stability properties were examined with respect to soil, vegetation and topographic parameters in order to determine which physical parameters can be used to identify good candidate observation locations for validating soil moisture from satellite observations and global-scale model output. The results show that the time-stability concept remains valid at the satellite scale. The root mean square error values were 1.47, 1.51, 1.93 and 2.32% for the 1st, 2nd, 50th and 100th most stable fields, respectively. The most stable locations had sand and clay percentages consistent with sandy loam soils and moderate to high normalized difference vegetation index values. Neither land cover nor topography properties could be used to identify potentially stable fields in the study region. © 2010 John Wiley & Sons, Ltd. Source

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