Climate processes of lake evaporation and snowmelt runoff: Part I. Evaporation rates from temperature-stratified saline lakes--Mono Lake as a case study. Part II. Snowmelt runoff and climate change--Emerald Lake Basin as a case study.

摘要

In part I, a methodology for determining the evaporation rates from temperature-stratified saline lakes has been developed. The initial motivation was to develop a technique which would be more accurate than the widely used evaporation pan method, and which would use meteorological data inputs that are normally available at weather stations, or are otherwise easy and inexpensive to gather. Four functional modules are combined in the model: a modified mass transfer function, a simulated solar radiation function, a simulated surface energy balance function, and simulated water thermocline function. The outputs of the model are the lake evaporation rate and the lake water temperature. In this study, the model is validated and applied to Mono Lake to simulate saline water evaporation rates. The results compared favorably with results of other saline water evaporation studies, both in economy and accuracy.;In part II, an energy-, momentum-, and mass-balanced snowmelt runoff model was developed to study an alpine watershed with an elevation of 3000 m in the Sequoia National Forest, California. The methodology successfully simulates the snow water equivalent and the daily snowmelt runoff. The benefits of this model are reduction in both data requirement and computer time. Only meteorologic data are required in this model. In order to develop a computationally efficient code, this snowmelt runoff model is discretized into two layers only. This model is at least 20 times faster than Anderson's (1976) model. Furthermore, an attempt to determine snowmelt runoff from a watershed by using the developed energy-based model is conducted. The preliminary results are excellent.;Snowmelt runoff processes in an alpine watershed in the Sequoia National Forest under long-term global warming are analyzed using the above energy based snowmelt runoff model. Under global warming, although there might be more precipitation, the hydrograph of snowmelt runoff would shift between 19 and 93 days earlier and snow season would end between 25 and 68 days earlier at an elevation of 2800 m. The most striking change would be the dramatic decrease in the snow/precipitation ratio at elevations below 2300 m, where the ecological balance would suffer a major impact.