Dynamical downscaling of atmospheric field of the Lake Issyk-kul watershed using CReSiBUC

Hydrological and meteorological observation in high mountains requires much efforts to establish and maintain due to severe climate condition and access to the site. After collapse of the Soviet Union funding for the hydro-meteorological observation have declined significantly in whole Central Asia. As a result, many stations have data missing period. It is almost impossible to describe the detailed spatial structure of atmospheric field in complex terrain from a limited number of observations. Lacking high quality meteorological data is one of the bottlenecks of hydro-meteorological studies in high mountainous areas. In this study, the non-hydrostatic meteorological model CReSiBUC is introduced to reproduce the spatial distribution of atmospheric variables of the Lake Issyk-kul watershed.

CReSiBUC is a coupled model of the meteorological model CReSS (Cloud Resolving Storm Simulator) and the precise land surface model SiBUC (Simple Biosphere model including Urban Canopy). The dynamic process of CReSS is formulated based on the non-hydrostatic and compressible equation system with terrain-following coordinates. The SiBUC calculates surface fluxes and related hydrological quantities considering detailed processes including irrigation at cropland.

Each simulation is divided into 10-day period to update the vegetation parameter suitable for target period. Initial condition of land surface state variables (especially soil wetness and snow cover) are succeeded from the final step of the previous run as those variables change the surface energy balance significantly. As the Lake Issyk-kul has large surface area (6236km²) and depth (mean depth is 278.4m), the difference of lake and land surface temperature can be very large. Furthermore, evaporation from this lake is one of the most important water source in this land-locked region. Fortunately, OSTIA daily 0.05 degree resolution SST product includes the analysis of the Lake Issyk-kul, initial lake surface temperature was given from this product. The initial and the lateral boundary conditions for atmospheric variables were given from global re-analysis product of JMA (JRA55).

Simulated atmospheric variables are compared with available in-situ measurements including glacier melting zone.