Spatio-temporal distribution characteristics of drought in Shandong Province and it relationship with ENSO

Drought is the most devastating natural disaster in the world. In recent years, prolonged droughts with huge impacts had caused enormous economic losses in China. Shandong Province belongs to a semi-humid climate, with complex and diverse underlying surfaces and sparse surface vegetation that is sensitive to climate change. Due to uneven distribution of precipitation during the year, drought and flood disasters in Shandong Province have been frequent, with significant impact on agricultural production and socio-economic development. Given the above, it was pivotal to study the spatial and temporal changes in drought in Shandong Province for application in drought monitoring and water resources management. Based on monthly precipitation and average temperature data from 15 meteorological stations in Shandong Province from 1964-2010, the frequency of drought at different time-scales in Shandong Province was quantitatively analyzed using standardized precipitation evapotranspiration index (SPEI). Using the Mann-Kendall non-parametric test method and Arcgis platform, the trends in temporal and spatial variation of drought in Shandong Province in the recent 50 years were analyzed. In order to study the impact of El Niño/Southern Oscillation (ENSO) on drought in Shandong Province, the continuous wavelet (CWT), cross wavelet transform (XWT) and wavelet coherence spectrum (WTC) were used to analyze the correlation between SPEI and ENSO index with the periodic characteristics. The results showed that SPEI at multiple time-scales reflected drought condition in Shandong Province. The sensitivity of time-varying SPEI was obviously different. The smaller the time-scale was, the greater the variation range was. In the recent 50 years, Shandong Province had an obvious warming trend, which was most significant in the eastern part of the province. Decrease in precipitation and increase in temperature induced warm and dry climate in Shandong, which aggravated drought conditions in the province. The spatial distributions of SPEI and annual precipitation in Shandong Province were consistent with the trend in spatial change, and the trend in the west had become more humid and in the east more dry. On the time scale of drought occurrence, the frequency of monthly drought was higher than that of annually drought, with spring and autumn having the most severe droughts across the four seasons. The highest frequency of drought occurred in West Shandong and Northwest Shandong Plain, with distinctive difference among different regions. With ENSO warm events, Shandong became prone to drought and ENSO cold events reduced droughts conditions. The annual-inter-annual oscillation cycle characteristics of SPEI was 1.0-2.5 years, showing similarity with the characteristics of Multiple ENSO Index (MEI). In high energy sector, the resonance period was 5.0-6.0 years for SPEI and MEI, but 1-2 months ahead of MEI. In low energy sector, there was a negative phase resonance period for SPEI and MEI of 3.0-3.8 years. The study provided a quantitative basis for understanding the spatial and temporal changes in drought in Shandong Province under global climate change. It also was helpful to decision-makers by improving preparedness and adoption of appropriate policies for agricultural management.