Analysis Of Dry/Wet Variation Characteristics And Prediction For Years Of Drought In Hexi Region

Drought occurs the most often in China.The arid/semiarid region mainly distributed in northern China,is the most fragile ecosystem and water resources system.Hexi region,which situated the inland,is the most sensitive region with living environment,and also the most important granary.With global warming,Hexi region would have use which way to respond the changes?Whether or not the renalysis datasets apply to Hexi region? What is the Dry/Wet Variation Characteristics in Hexi region?How about the secular variation of droughts in Hexi region?All of these definitely worth exploring.By comparing the the differences between CRU data and observational data-. NCEP reanalysis data and observational data in reflecting surface dry/wet characteristics, we chose a higher potential applicability data-CRU data, which included monthly average precipitation and monthly average evaporation, analyzed characteristics of surface dry/wet variation combined with the calculated surface humidity index-H, standardized precipitation evapotranspiration index-SPEI in Hexi region from 1901 to 2012. The probably genetic mechanism of Hexi drought was also discussed from atmospheric generalcirculation and interaction between ocean and atmosphere. And then we studied the influence of Hexi drought affected from precipitation and temperature by means of the corresponding period relation between them. Finally, the gray neural network prediction model, BP-n-GM (1,1), was used for predicting years of drought occurrence in Hexi Region. The main conclusions were as follows:(1) CRU data is higher applicability than NCEP reanalysis data in Hexi region.Both two datasets, in the area that is close to base station or in the area where has a similar background with base station, the PET, H, SPEI between two data sets and observational data became less diverse.(2) Take Dunhuang, Zhangye, Wuwei as representative stations in Hexi region.Overall, the two data sets are all perform best of in Dun Huang, CRU data perform better in Zhangye than Wu Wei, NCEP reanalysis data perform worst in Zhangye.The minimum differences of PET, H, SPEI between CRU data and observational data located in Dun Huang, the minimum are 0. lmm、0.009、 0.001. The maximum differences located in Wu Wei, the maximum are 13.2mm、0.11、0.009. The average differences in three representative stations are 8.7mm、0.047、0.004; The minimum differences between NCEP reanalysis data and observational data located in Dunhuang, the minimum are 11.7mm、0.016、0.001. The maximum differences located in Zhangye, the maximum are 22.4mm,0.187,0.011. The average differences in these three representative stations are 15.5mm、0.104、0.005.(3) The PET over the past century in Hexi region showed upward trend with rate of 1.94mm/ 10a. The mutation of PET occurred in 1938 and 1992, Since 1992, PET had continued to increasing.But its trend coefficient and climate tendency rate vary in different regions. This Mainly can be seen in its increasing trend rate from southeast to northwest. The maximum rate located in Dunhuang, Jinta, Mazongshan area, which is 4.0mm-5.0mm/10a, the minimum rate located in Zhangye, Wuwei area, which is 0.5mm-1.0mm/10a.(4) Hexi region’s mild drought events increased from 1920 to 1990,while moderate drought decreased showed by SPEI.Since 1990, Hexi region’s drought events increased rapidly, moderate drought became the major format of drought. Dunhuang, Mazongshan have a more significant trend of drought.(5) SPEI of Hexi had different time-scale resonant period with three large-scale oscillation indices(AO、NAO、PDO). The significant positive correlation was found between SPEI and AO、 NAO, while negative correlation between SPEI and PDO.There were not only common patterns of 50-70 months inter-annualresonant period, but also 120 and 250 month inter-decadal resonant period between SPEI and PDO. It is concluded that PDO was the most coincident resonate indice with SPEI.(6) There were significant negative correlation between inter-decadal SPEI anomaly and temperature anomaly, while significant positive correlation between inter-decadal SPEI anomaly and precipitation anomaly,which latency was 3-5 years.The summer and autumn precipitation played a major role in mitigation of Hexi drought, the quick warming in the spring would aggravated Hexi drought, when PDO in its positive phase in winter, it would cause a certain aggravation of Hexi drought.(7) The gray neural network prediction model, BP-n-GM (1,1), was used for predicting years of drought occurrence in Hexi Region. The results show that the next three drought year in Dunhuang would be 2013、2019、2024; The next three drought year in Zhangye would be 2013、 2019、2024; The next three drought year in Wuwei would be 2013、2020、2026.