DROUGHT MONITORING FOR THE MIDDLE REACHES OF YARLUNG ZANGBO RIVER AND ITS TWO TRIBUTARIES FROM SATELLITE IMAGES

摘要

The middle reaches of Yarlung Zangbo Riverrn(YR) and its two tributaries (Lhasa River andrnNianchu River) is a main agricultural region inrncentral Tibet Autonomous Region. Droughtrnmonitoring has significant meaning for localrncrop growth monitoring, crop yield assessmentrnand disaster monitoring. It also has greatrntheoretical importance for understanding localrnenergy and water balance status. In this paper,rnMODIS data on 14 April 2003, 16 October 2003rnunder nearly clear weather conditions arernselected as the spring and autumn cases. Thernland surface parameters, such as land surfacerntemperature (LST), albedo, NormalizedrnDifference Vegetation Index (NDVI), emissivityrnetc., have been derived from different algorithmsrnfor MODIS data. In combination withrnmeteorological data, the drought severity indexrn(DSI) is determined by applying Surface EnergyrnBalance System (SEBS). The estimations showrnthat spring drought is much more severe thanrnautumn drought. The river runoff is the dominantrnfactor for spring drought. The spatial variationsrnof drought conditions in the middle reaches ofrnYR and its two tributaries can also be clearlyrnidentified.