Investigation Of LUCC And ET In Zuli Basin Of The Loess Plateau Using Remotely Sensed Data

Zuli basin, located in the west of the Loess Plateau, is one of poorest regions in China. Land degradation, especially severe soil erosion, adversely influences the ecosystem in the basin. In this thesis, remote sensing is used to derive not only the information about land Use and Land Cover Change (LUCC), but also the surface variables for evaluating regional evapotranspiration (ET). The main researches include two parts:1. Based on Landsat series images in 1978, 1993, 1998, 2001 and 2003, Principal Components Analysis (PCA) is used to transform the original image to the new band combination. Due to the distinctive distribution of different land uses in T_s-NDVI space, T_s and NDVL'are partitioned into the first three PCA components to classify land uses and land covers and LULC maps are created for each of the five studied years. The LULC maps show that farmland acreage increased first and then decreased during the study period (1978-2003), while grassland acreage decreased first and then increased during the same period. After analyzing the relationships between LUCC and natural and human factors, it is concluded tat the main reason of LUCC is policy orientation towards the balance between economy and ecology. That is, the documented farmland acreage increase from 1978 to 1998 was caused by "privatization" policy and the decrease from 1998 to 2003 was related to "ecological restoration" policy.2. SEBAL (Surface Energy Balance Algorithm for Land), a TM-based ET model, is selected to derive the surface biophysical parameters such as NDVI, emissivity, T_s and others The net radiation, soil heat flux and sensible heat flux are then estimated based on the surface biophysical parameters and daily ET is calculated using energy balance equation. With aid of observed climate data, FAO Penman-Monteith equaption is used to calculate the reference ET and crop coefficient. Then, based on the calculated crop coefficient and monthly reference ET, monthly ET is finally estimated. The spatial and temporal comparisons between LULC and ET show that LULC modulates the distribution of energy and water atbasin scale.