Abstract
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.
Highlights
Quantitative precipitation estimation in mountainous terrain is key for understanding the hydrologic regime in many watersheds worldwide
Other key assumptions of the Orographic Precipitation Model (OPM) are: (1) the clouds consist of condensed water that fully shares the air motion; (2) the clouds form by saturated rising air and evaporate in descending air through unsaturated environments; (3) the clouds always consist of saturated air and unsaturated air never contains clouds; (4) the clouds contain a predefined distribution of rain drop size; (5) the precipitation particles once formed are assumed to be distributed in size; (6) the precipitation drops share the horizontal motion of the air; and (7) the vertical mass transport of precipitation is based on the fall speed of the median-diameter of the precipitation particle by type
1-kmspacing spacingresolution resolution a domain that covers the watershed of Kinneret in order to study the precipitation spatial distribution
Summary
Quantitative precipitation estimation in mountainous terrain is key for understanding the hydrologic regime in many watersheds worldwide. The complex topography in mountainous regions causes the perturbation and deformation of atmospheric fluxes that influence precipitation patterns by mechanically altering the wind patterns and microphysical processes, which impact condensation of the precipitable water [6]. (3) The development of a full-physics model with 1-km resolution over a large area and the necessary sensitivity analyses are () very significant computational tasks that require, in many cases, specialized computer hardware and software These requirements may not be met by hydrologic groups performing local surface precipitation analysis.
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