Lakes in land surface models: Simulation and validation using satellite measurements.

摘要

This dissertation is part of the long-term research towards building a complete surface water representation in the land surface model, in order to quantify the spatial and temporal variations of surface water bodies, especially lakes, and to further understand the role of lakes in the climate system. Changes in lake water storage reflect variations in climate such as changes in precipitation, land surface evaporation, net river discharge, and groundwater storage. However, owing to the lack of a comprehensive surface water observing system, continental-to-global-scale changes in surface water heights and inundation extent remain poorly understood.;In the previous study, a Catchment-based Hydrologic And Routing Modeling System (CHARMS) was developed to be run on a catchment-based modeling template, which was modified from the grid-based National Center for Atmospheric Research (NCAR) Community Land Model (CLM). In the CHARMS model, the catchment-based CLM was coupled to a catchment-based river routing model, which simulated the movement of water through river channels and floodplains. However, the lake component was not included in the CHARMS routing system. Moreover, in the CLM model, lakes are considered to have a globally consistent depth of 50m and a constant volume. In this dissertation, a lake model (CHARMS-lake) is implemented in the routing path of CHARMS, with the objective of better representing the surface water system in the land surface model.;In Chapter 2 of this dissertation, the CHARMS model is modified. In the previous version of CHARMS model, an explicit representation of lake bodies was missing, with the lakes either ignored from the surface water system or kept constant in storage. In this chapter the routing path for CHARMS is manipulated by adding lakes into the river network. Modeled lake levels for Lake Superior and Lake Victoria are compared with the altimetry data, and the outflow discharge from lake basins is also compared with the model case which assumes no lake in the basin.;The performance of NASA's Gravity Recovery and Climate Experiment (GRACE) detecting changes in land water mass is evaluated in Chapter 3, to test its ability of capturing the hydrologic signal from lakes. After removing the hydrologic leakage from the surrounding area, the gridded GRACE TELLUS RL 05 product is scaled over the 16 largest lakes in the world, and compared with the altimetry data for the period of 2003 to 2010. Statistical analysis is performed to find factors that significantly influence the quality of GRACE observations over lakes.;Chapter 4 of the dissertation studies the physical properties of lakes, such as thermal expansion, as well as lake bathymetry, in order to better understand their impact on lake level variations. The high resolution bathymetry data for the Great Lakes is integrated and the hypsometric curves for the five lakes are plotted. Thermal expansion of the lakes is estimated using the MODIS surface water temperature data for 6 lakes in two different climate zones. The ratio of thermal expansion to the total amount of lake level change is calculated, indicating that in the tropical regions the impact of thermal expansion can be ignored.;This CHARMS-lake model will provide a better understanding of the global hydrologic cycle, and is expected to be coupled to a global scale atmospheric model to study the feedbacks between climate and the terrestrial surface water system.