Based on the observation data during the period of the experiment with ‘theoretical study and observations of water and energy exchange and planetary boundary layer on inhomogeneous underlying surface in oasis system’, the influences of surface temperature difference between desert and oasis, buoyancy frequency (Brunt-Visl frequency) and background wind velocity on oasis effect were discussed by a series of idealized numerical tests of BLASIUS (boundary layer above stationary, inhomogeneous uneven surface) model with high resolution and complex terrain. The results show that the cold island effect and humid island effect enhanced with the increase of surface temperature difference between oasis and desert, and the enhancing action mainly occurred below 500 m over the ground. The horizontal range of ‘cold island’ over oasis enlarged and the vertical height of ‘humid island’ decreased with increase of surface temperature difference. The influence on ‘humid island effect’ was about an hour later than that on ‘cold island effect’. The updraft airflow over the oasis increased and the vertical velocity increased over the transition area above 1.5 km height with increase of buoyancy frequency. The symmetry of vertical circulation between oasis and desert decreased with increase of initial background wind speed, and the height of circulation center decreased and the strength weakened.

It is accepted that climate change has a great impact on water cycle and regional water balance，and thus it would change the formation and evolution of drought conditions in some degree．In this context，the standardized precipitation evapotranspiration index(SPEI)，which has also taken another important factor evapotranspiration in the process of regional water balance into consideration，would be more suitable for drought monitoring than the standardized precipitation index (SPI)．The different time scales SPEI can re-flect the duration informations of drought，so the single SPEI of a certain time scale can only indicate a fraction of drought information．In order to form an overall judgement in drought monitoring，a new index called joint drought index (JDI)was established by the combination with different SPEIs．The accuracy and effectiveness of JDI in drought monitoring were then verified by the forecast evaluation　system and comparison with the actual drought． In conclusion，JDI can be used as a new ideal index for future drought monitoring．