Abstract: Under the background of global warming, drought has become one of the worst natural disasters, and seriously affects people's production and life. Recently, inclement weather frequently occurred, especially that the localized drought has further aggravated. In northwest Liaoning Province, China where the main crops are corn and rice, the spring drought occurred frequently and has become the key factor affecting the agricultural production in planting season. Therefore, the research of spring drought conditions has important practical significance for relieving drought and controlling desertification in northwest Liaoning. Based on 39 rainfall stations' daily rainfall data from 1971 to 2013 and historical drought information in northwest Liaoning, using the readjusted Z-Index which is obtained by adjusting the critical value of calculated drought frequency at different levels with the theoretical one that is from National Drought Grade Standards, wavelet analysis and kriging spatial interpolation method, this paper analyzed the temporal and spatial characteristics of spring droughts in northwest Liaoning. The results show as follows: (1)compared with the theoretical drought frequency, the drought frequency represented by the readjusted Z-Index matched better to the actual drought in northwest Liaoning; (2)the spring drought frequency changed in Northwest Liaoning, and the rising trend of great drought and severe drought was obvious; from 1970s to the 21st century, the frequency of spring great drought rose from 8.1% to 12.5%, the frequency of spring severe drought rose from 3.6% to 4.8%; (3)spring drought had a 10-year cycle in northwest Liaoning; spring drought is obviously regional, increasing by degrees from the south to north, and the high incidence area of spring drought at different levels mainly concentrated on Chaoyang Prefecture. This study analyzed the evolution law of spring drought in northwest Liaoning, which can provide a reference for the relevant departments to make countermeasures to drought in this area. The main innovation of this article is the proposition of the readjusted Z index.

Key words: spring drought, Z-Index adjustment, evolution rule, spatial and temporal characteristics, north west Liaoning