Hydrologic budget and dynamics of a large oligotrophic lake related to hydro-meteorological inputs

• A turbulent diffusion transfer sub-module was developed and coupled to DLM-WQ.
• Isohyetal lines were developed to estimate precipitation distributions.
• The LSPC watershed model was used to generate the stream flows and pollutants.
• The modified DLM-WQ estimates hydrologic budget accurately.
• Estimated and measured lake water levels were in excellent agreement.

SummaryA turbulent diffusion transfer model was developed and coupled to a developed Dynamic Lake Model with Water Quality (DLM-WQ) with the goal of correctly estimating the hydrologic budget of Lake Tahoe (California–Nevada). Isohyetal lines were created using PRISM gridded monthly precipitation data during 1990–2011 to estimate the precipitation distribution directly on the lake. The US Environmental Protection Agency supported watershed model, Loading Simulation Program in C++ (LSPC), was used to generate the stream flows and pollutants loading of 64 streams. The exchange coefficients for latent heat, sensible heat and wind drag (CEN, CHN, and CDN, respectively) and precipitation inputs were calibrated using coefficient of determination (R2) as the objective function and comparing visually the estimated values to those of measured record of 1994 to 2008. CEN, CHN, and CDN were found to be optimum at 1.82 × 10−6, 3.00 × 10−6 and 1.3 × 10−3, respectively for Lake Tahoe. CEN variation results in a greater change in lake water level compared to CHN and CDN. The annual precipitation contour lines indicate a reduction of approximately 35% of Tahoe City precipitation. DLM-WQ estimated 36% reduction of Tahoe City precipitation. Although latent heat loss (17%) is small compared to combined shortwave radiation and longwave radiation (77%) the effect on water balance due to inaccurate estimates of evaporative loss is very large because the ratio of watershed to lake surface area is low at 1.64. Evaporation (32%) is the largest contributor in the hydrologic budget and its accurate estimation is therefore critical and important for sustainable water management. The DLM-WQ estimated water surface temperatures and lake water level were in excellent agreement with those of measured records for the period 1994–2008 with R2 equal to 0.97 and 0.99, respectively.