Research On Regional Evaporation Estimation Of Remote Sensing And Its Application For Drought Assessing Based On Refined SSEB Model

The water resource has become a hot issue in the21st century. Evapotranspiration is one important parameter in water cycle, Effective prediction of the evapotranspiration provides scientific basis for rational use and distribution of water resources, and assessing water consumption and monitoring drought situation. The Loess Plateau, located in inland Eurasian continent, is in abundant sunshine, less rainfall. It is the main source and performance of the study area that shortage of water and drought. Estimation of regional Etmeasuremens is still a diffieult issue in water resources assessment. Due to great heterogeneity in land surface, it is difficult to make regional estimation from traditional method using measurements of evaporation Pan represented to regional ET.Remote sensing have obvious advantages on quick monitoring of large scale land surface and has been widely used for regional water cycle study, which has great value for water resources planning and managernent in regional scale.The SSEB model algorithm has been realized through programming interactive data language(IDL)of ENVI platform by using MODIS images and digital elevation, combined with the data of meteorological observation site, and the April-October2000-2011evapotranspiration data sets have been established, while the drought of summer in2009has been monitored.Meanwhile, In order to check the the rationality and reliability of the computational results in this model, which are compared with other model and others research results.The results show that:(1) The ETf(elvi) can reflect the regional drought status and vegetation growth status. The peak value of ETf(elvi) appear in the July-August. The distribution reveal a positive correlation with vegetation coverage, ETf(elvi) on high-coverage is higher than the low-coverage vegetation.(2) In the study area, the sensitivity of ETo to mean air temperature is relatively low. However, due to its great variation, the mean air temperature is the dominant factor inducing the ETo change, hasing positive contribution to the ETo.Solar radiation and wind speed also has greater contribution rate to the ETo change, With negative contribution in most regions.Actual vaporpressure, due to its smaller variation, has minor effects on the ETo, which has positive contribution in northern part and but negative contribution in southern part.(3)Actual evapotranspiration in the Loess Plateau is higer in the southeast than northwest, the peak zone is in the plateau division in east Qinghai and the key soil and water conservation division in the Loess Plateau, while low zone is in the northwest windy sandy division in Inner Mongolia-Ningxia. The distribution of total showed a single peak in each year in the study area, in July and August the evapotranspiration is maximum, in June and September the evapotranspiration is high, in April、May and October the evapotranspiration is minimum. Interannual variability is associated with rainfall highly, the correlation coefficient R2is0.88.The annual ET and NDVI is positive correlation, the correlation coefficient R2is0.75, while the annual ET and LST is negative correlation, the correlation coefficient R2is-0.97,(4) The drought monitoring results derived from SSEB and CI shows the similar space distribution pattern, Comparing with the soil moisture data of field observations, it was found that the RSWI is less affected by the regional climateconditions and crop growth, and therefore it was a more reliable index for assessing the drought situation.