Characteristics of dry-wet changes in Xinjiang based on SPEI index

Abstract

The standardized precipitation evapotranspiration index (SPEI), calculated from 55 stations 37 over the period 1961-2015, was used to analyze the spatial and temporal variability of the dry 38 and wet climate in Xinjiang on a three and six-month time scale, so as to help to actively deal 39 with the negative effects of climate change and reduce disaster losses. The obtained results 40 show that precipitation and temperature in Xinjiang have an increasing trend, with rates of 41 8.90 mm and 0.39 ºC per decade, respectively. SPEI-3 and SPEI_6 show the same linear 42 change trend, with a change rate of 0.005 and 0.007 per decade, respectively. Severe droughts 43 occurred in 1997 and 2008, and particularly in 2008 SPEI_6, the number of meteorological 44 stations with moderate drought and extreme drought accounted for 60% of all stations. 45 Analysis of Empirical Orthogonal Function (EOF) indicates that SPEI-3 and SPEI_6 have 46 similar spatial distribution in the three EOF modes. EOF1 reflects that the overall dry and wet 0 10 20 30 40 50 1961 1971 1981 1991 2001 2011 Numbers stations Year (a) SPEI_3 Extreme drought Moderate drought Mild drought Normal Mild moist Moderate moist Extreme moist 0 10 20 30 40 50 1961 1971 1981 1991 2001 2011 Numbers stations Year (b) SPEI_6 Extreme drought Moderate drought Mild drought Normal Mild moist Moderate moist Extreme moist 47 changes in the study area were weakening, and there was a drying trend; EOF2 was a reverse 48 change in the northern and Southern Xinjiang; EOF3 shows that the East Tianshan had a 49 drying trend, while the western part of Southern Xinjiang tends to relieve the drought. The 50 spectra of wavelet coherence and cross wavelet transform showed that the SPEI values in 51 Xinjiang have resonance periods of different time scales with the Atlantic multi-year 52 intergenerational oscillation (AMO), El Nino Southern Oscillation (ENSO), North Atlantic 53 Oscillation (NAO), and Pacific interdecadal oscillation (PDO), but in different time-domain 54 correlation has certain differences. Among them, AMO is the main atmospheric circulation 55 factor that affects SPEI in the region.