Abstract: Evapotranspiration(ET) from the land surface is a crucial component of water and energy balance. Understanding of spatiotemporal variation of regional evapotranspiration is of highly valuable to management of water resources and effective promotion of ecological services in Shaanxi Province. Under the support of ArcGIS spatial analysis module, this paper mainly aims at MODIS evapotranspiration data set(MOD16)combined with meteorological datasets to conduct a systematic research on the spatial and temporal characteristics in Shaanxi Province during 2000-2013 and to explore changes of evapotranspiration characteristics in the different functional areas according to the ecological environment features in Shaanxi Province. By calculating the correlation coefficient between MOD16 potential evapotranspiration(PET) and pan evaporation at the beginning of the study, the result indicated that MOD16 products are more applicable for the analysis of spatio-temporal variations of evapotranspiration in Shaanxi Province. Then the statistical analysis of the spatial and temporal distribution of MOD16 products showed as follows:(1)Interannual fluctuations of ET and PET were not significant during 2000-2013. The 13-year mean ET was 490 mm. The 13-year mean PET was 1550 mm. The big gap of ET and PET showed that the land surface was drought in Shaanxi Province. The seasonal variation of ET or PET showed a unimodal pattern. The biggest difference between ET or PET in May was about 145 mm, indicated that the land surface was the thirstiest.(2)The spatial distribution of the ET and PET had obvious regional characteristics. The spatial distribution of ET from south to north decreasing, while PET was increased from south to north. The opposite distribution indicated that the surface moisture was adequately in the south but not enough in the north. By computing trends of the ET and PET, it found that the drought was easing in the midwest Shaanxi but worsening in the mideast during 2000-2013.(3)The intensity orders of ET and PET in each functional area were in opposite directions. Therefore, the order of drought intensity was I(the Controlling Desert Area) > Ⅱ(the Retuning Farmland to Forest in North Area) > Ⅲ(the Retuning Farmland to Forest in Weibei Area) > VⅡ(the Farmland in Guanzhong Area) > V(the Natural Forest in North Area) > IV(the Retuning Farmland to Forest in South Area) > VI(the Natural Forest in South Area). The seasonal variations of ET in each functional area were different, and it can be divided into three types including unimodal type, wave type and bimodal type. The unimodal type had two functional area including IV and VI. The wave type had four functional area including I, Ⅱ, Ⅲ and V. The bimodal type had VⅡ.(4)In addition, with the correlation analysis to meteorological factors and vegetation characteristics, the spatio-temporal variation of evapotranspiration was closely related with climate characteristics especially water-heat conditions and vegetation distribution and growth state.

Key words: MOD16, Shaanxi Province, evapotranspiration, drought