N. Ohara

Physically Based Estimation of Maximum Precipitation over American River Watershed, California

A methodology for maximum precipitation (MP) estimation that uses a physically based numerical atmospheric model is proposed in this paper. As a case study, the model-based 72-h MP was estimated for the American River watershed (ARW) in California for the December 1996–January 1997 flood event. First, a regional atmospheric model, MM5, was calibrated and validated for the December 1996–January 1997 historical major storm event for the ARW, on the basis of the U.S. National Center for Atmospheric Research (NCAR) reanalysis data to demonstrate the model capability during the historical period. Then, the model-simulated historical storm event was maximized by modifying its boundary conditions. The model-simulated precipitation field in the ARW was successfully validated at nine individual rain gauge stations in the watershed. The computed basin-averaged precipitation was somewhat higher than observations obtained by the spatial interpolation of the rain gauge observations. This result suggests a limitation o...

WEHY-HCM for Modeling Interactive Atmospheric-Hydrologic Processes at Watershed Scale. I: Model Description

AbstractAmong the key problems in atmospheric and hydrologic sciences are the modeling of the interaction between the atmosphere and land surface hydrology while also quantifying the surface/subsurface hydrologic flow processes both in vertical and lateral directions, and modeling the heterogeneity in surface and subsurface hydrologic processes. Meanwhile, in standard water resources engineering practice, the planning and management of the water resources is performed over the geographical region of a watershed. To address these issues, a model of coupled atmospheric-hydrologic processes at the watershed scale, the Watershed Environmental Hydrology Hydro-Climate Model (WEHY-HCM), has been developed. The atmospheric model PSU/NCAR MM5 (Fifth Generation Mesoscale Model) was coupled to the watershed hydrology model WEHY through the atmospheric boundary layer to form the WEHY-HCM. The WEHY-HCM is especially useful for producing nonexistent atmospheric data as input to the modeling of surface and subsurface hy...

Regional Modeling of Climate Change Impact on Peninsular Malaysia Water Resources

The future projections of climate change by means of global climate models of the Earth provide fundamental coarse-grid-resolution hydroclimate data for studies of the effect of climate change on water resources. This paper reports on a study that was performed during 2001–2006, in which the climate change simulations of the coupled global climate model of the Canadian Center for Climate Modeling and Analysis were downscaled by a regional hydroclimate model of Peninsular Malaysia (RegHCM-PM) to the scale of the subregions and watersheds of Peninsular Malaysia (PM), to assess the effect of future climate change on its water resources. On the basis of the simulations of hydroclimatic conditions during the historical period of 1984–1993 and future periods of 2025–2034 and 2041–2050, this report concludes that the overall mean monthly streamflow is approximately the same during both the future period, and the historical period for most of the watersheds of Peninsular Malaysia, except Kelantan and Pahang. In t...

Physically Based Estimation of Maximum Precipitation over Three Watersheds in Northern California: Atmospheric Boundary Condition Shifting

AbstractMaximum precipitation during a historical period is estimated by means of a physically based regional atmospheric model over three watersheds in Northern California: the American River watershed (ARW), the Yuba River watershed (YRW), and the Upper Feather River watershed (UFRW). In Northern California, severe storm events are mostly caused by a high-moisture atmospheric flow from the Pacific Ocean, referred to as atmospheric river (AR). Therefore, a method to maximize the contribution of an AR on precipitation over each of the targeted watersheds is proposed. The method shifts the atmospheric boundary conditions of the regional atmospheric model in space with latitude and longitude so that the AR strikes each of the targeted watersheds in an optimal direction and location to maximize the precipitation over these watersheds. For this purpose, the fifth generation Penn State/National Center for Atmospheric Research (NCAR) Mesoscale Model (MM5) is used as the regional atmospheric model, and the NCAR/...

Coupled Regional Hydroclimate Model and Its Application to the Tigris-Euphrates Basin

To establish a basinwide water management plan for the Tigris-Euphrates (TE) watershed, it is necessary to perform rigorous water balance studies of the whole watershed—at least for critical historical drought and flood conditions and under various water resources development scenarios. Water-balance studies over the watershed require climatic and hydrologic data sets, corresponding to historical critical flood and drought periods, at fine time and spatial grid resolutions provide the necessary hydroclimatic information. The Regional Hydroclimate Model of the Tigris-Euphrates (RegHCM-TE) and the associated geographic information system (GIS) were developed to downscale large-scale atmospheric data sets over the TE watershed and to reconstruct the aforementioned climatic and land hydrologic data sets at fine spatial and time increments. In RegHCM-TE, the earth system over the TE watershed is modeled as a fully coupled system of atmospheric processes aloft coupled with the atmospheric boundary layer, land-s...

Role of Snow in Runoff Processes in a Subalpine Hillslope: Field Study in the Ward Creek Watershed, Lake Tahoe, California, during 2000 and 2001 Water Years

Field study is an essential component of hydrologic science because all hydrological studies must be conducted by such observation-based knowledge of real watersheds. Hillslope runoff processes have been intensively investigated, but the flow process at the boundary between the snowpack and ground surface has not been well documented. A field site at the northwest sector of the Ward Creek watershed, Lake Tahoe Basin, was built for observations of overland flow, subsurface stormflow, and channel flow, simultaneously with atmospheric measurements to examine the hydrology at a snow-covered hillslope. Also, the groundwater table under the snowpack was monitored by shallow wells at the hillslope. All field-measured atmospheric data were synthesized with an energy-balance snow model, and the snowmelt rate and energy balance were computed. The results of the analyses indicate that most of the snowmelt water infiltrated into the topsoil layers and that saturated subsurface flow was the largest contributor to the ...

A Practical Formulation of Snow Surface Diffusion by Wind for Watershed-Scale Applications

Prediction of snow drift is of importance for structure design and traffic management on snowy and windy prairie landscapes. The snow redistribution by wind is also regarded as one of the largest sources of error in hydrologic snowmelt models. In this study, a snow movement equation was generalized and customized for horizontal two-dimensional watershed-scale applications by incorporating snow transport, wind snow diffusion, and snow gravitational movement. Then, the snow surface diffusion process by wind turbulence was formulated in terms of the autocorrelation functions of the measurable wind velocity field using G.I. Taylors theorem. However, analysis of the example wind data suggested a delta correlation in wind turbulent component that resulted from subtracting their moving average values from the original wind speed data. The dynamic model based on the proposed formulation was able to effectively reproduce the observed equilibrium snow profiles affected by wind drifting. A two-dimensional model simulation using a 10 m digital elevation model in Muddy Gap, Wyoming was also presented for qualitative validation of the model in the watershed-scale applications. Additionally, the theoretical extension for preferential snow accumulation process was presented in Appendix Preferential Snow Accumulation by Gravity. These modeling results together with the observations on the prairie suggested the importance of the snow surface diffusion process in addition to the snow transport.

Modeling of Interannual Snow and Ice Storage in High-Altitude Regions by Dynamic Equilibrium Concept

AbstractThe energy and mass balance model for terrestrial ice and snow is an essential tool for the future projection of interannual snow and ice storage including glaciers. However, the snow models in the hydrologic engineering field have barely considered the long-term behavior of the snow and ice storage because the time scale of glacier dynamics is much longer than those of river flow and seasonal snowmelt. This paper proposes an appropriate treatment for inland glaciers as systems in dynamic equilibrium that stay constant under a static climate condition. It is conjectured that the snow and ice vertical movement from high-elevation areas to valleys (lower elevation areas) by means of wind redistribution, avalanches, and glacial motion may be considered as an equilibrator of the snow and ice storage system because it stimulates snow and ice ablation. In order to demonstrate this concept, a simple dynamic equilibrium model for regional to global scales is proposed and applied to the Pamirs. The interan...

Climate Change Assessment of Water Resources in Sabah and Sarawak, Malaysia, Based on Dynamically-Downscaled GCM Projections Using a Regional Hydroclimate Model

AbstractClimate change’s impact on the Sabah and Sarawak water resources in the Northern sector of the Borneo Island, Malaysia, was assessed based on the dynamically-downscaled general circulation model projections (GCMPs) by means of a regional hydroclimate model (RegHCM). Four future projections under the special report on emissions scenarios (SRES) A1B emission scenario from two general circulation models (GCMs) were selected for this study. The RegHCM, which is a coupled nonhydrostatic atmospheric and upscaled land surface process model, is capable of downscaling the outputs of these GCMPs (GCM projections) to the watershed scale at a 9-km grid resolution at hourly time intervals for hundreds of years—a simulation for 420 years was performed in this study. This dynamic downscaling by the RegHCM can incorporate the detailed soil and land-cover data. It is shown in this article that utilizing a methodology that incorporates a GCM, a RegHCM, and a hydrological routing model allows assessing climate chang...

An Eulerian equation for snow accumulation downstream of an object

This study investigated the form of the governing equation for the particle distribution by focusing on the particle motion processes rather than flow regime and particle characteristics. A linear erosion term for a fetch-eddy effect was introduced to the advection dispersion equation. The equation formulated in this paper described most of the particle deposit patterns behind an object including porous and solid snow fences, and a tree. This theory may enable us to estimate particle motion parameters, such as diffusion, drift, and erosion coefficients, from field observed particle distributions. Snow stratigraphy observed by ground penetrating radar (GPR) was used verify to result of the modeled theoretical snow redistribution. These analyses confirmed the effectiveness of the linear erosion term at explaining the particle deposition patterns due to eddys around a porous snow fence. This article is protected by copyright. All rights reserved.