Simulations of the Summer Hydrometeorological Processes of Lake Kinneret

Abstract

Lake Kinneret is a 168-km2 lake located in northern Israel. It provides about 50% of the drinking water consumed in this arid country. To manage correctly this vital water resource, it is essential to understand the various hydrometeorological processes that affect its water budget and, in particular, its evaporation. The complexity of the terrain in this region (varying from ≈2800 m to ≈−410 m within a short distance), combined with different types of soil and ground covers surrounding the lake, results in complicated microscale and mesoscale atmospheric motions, including sea, lake, and land breezes, as well as anabatic and katabatic winds. The Regional Atmospheric Modeling System (RAMS), a state-of-the-art nonhydrostatic model with two-way interactive multigrid nesting and four-dimensional data assimilation capabilities, was used, together with observations collected near the western and eastern shores of the lake, to study these processes. It was configured with two nested grids centered in the middle of the lake: 1) a coarse grid with 4 km × 4 km grid elements representing a 264 km × 240 km domain including Mount Hermon, the Dead Sea, the Golan Heights, and the Mediterranean coast; and 2) a fine grid with 1 km × 1 km grid elements covering a 42 km × 50 km domain. Two three-day periods in the summers of 1992 and 1993, during which hydrometeorological observations were available, were simulated. To account for synoptic conditions, the National Centers for Environmental Prediction–National Center for Atmospheric Research mandatory-level reanalyses produced every 6 h for these periods were assimilated by the model. The strength and timing of the various atmospheric motions that develop in that region and their interactions significantly affect the hydrometeorological processes of the lake, which are subject to important diurnal and spatial variations of wind intensity and direction, temperature, humidity, and fluxes. Since these processes have a strong feedback on the lake hydrodynamics and thermal structure, it is concluded that the development of a coupled lake–atmosphere model is needed to provide good estimates of lake evaporation when lake water surface temperatures are not available. Here, it is demonstrated that RAMS performs properly, given the particular complexity of the Lake Kinneret system and the uncertainty inherent in observations above turbulent water.