| With the development of the global warming and the acceleration of water cycle process,extreme drought events are becoming increasingly frequent in China.As an important industrial and agricultural production area,Central China has the important theoretical and practical significance in monitoring and evaluating evapotranspiration and drought conditions.In order to accurately carry out regional drought monitoring,in this paper,the high-resolution meteorological grid data were used to calculate the monthly potential evapotranspiration and actual evapotranspiration in Central China throughout employing multiple methods from 1982 to 2015.The results of potential evapotranspiration obtained from the synthesis methods(Penman and Penman-Monteith),the radiation-decisive method(Priestley-Taylor)and the temperature-decisive method(Thornthwaite)were analyzed.The actual evapotranspiration results calculated by the Maximum Entropy Production(MEP)theory-based evapotranspiration model was verified by the measurements of the eddy-covariance system stations and compared with other actual evapotranspiration product datasets.Based on the calculation and analysis results of regional evapotranspiration,combined with the precipitation grid monthly data,three types of precipitation evapotranspiration indexes were constructed on the monthly,seasonal,semiannual,and annual temporal scales,including the standardized precipitation evapotranspiration index based on Thornthwaite model(SPEI-Th),standardized precipitation evapotranspiration index based on Penman-Monteith model(SPEI-PM),and standardized precipitation actual evapotranspiration index(SPAEI)based on MEP model.Based on the drought statistics data,vegetation health index and historical drought records over the years,the applicability of different drought indexes with multi-temporal scales in central China were evaluated,and the most suitable index and temporal scale for long-term drought monitoring were determined in this study.On this basis,10 drought descriptive indexes related to drought duration,drought frequency and drought intensity were used to analyze the drought characteristics based on the seasonal SPAEI index,and the periodicity and evolution trend of drought were studied in Central China..The main conclusions of this paper are as follows:(1)The high-precision raster evapotranspiration data set in Central China was constructed.As a whole,the Thornthwaite model,Penman-Monteith model,Priestley-Taylor model,and Penman model increase sequentially.The determination coefficient(R~2)of the actual evapotranspiration results obtained from the Maximum Entropy Production(MEP)evapotranspiration model and with that obtained from the Complementary Relation(CR)model is above 0.92,the mean error(ME)is between-26.61mm and 13.30mm,and the 95%regional root mean square error(RMSE)is less than 19.24mm,moreover,the results obtained from MEP model had a closer agreement with sites measurements compared with that of CR model.(2)The precipitation evapotranspiration indices of various temporal scales in Central China were constructed,and the applicability of each index was evaluated by using recorded drought data over the past years.Analysis showed that the log-logistic distribution with three parameters was the most suitable distribution function for each type of precipitation evapotranspiration index,and different types of precipitation evapotranspiration indicators have different judgments on the occurrence and severity of drought.The correlation coefficient between the seasonal standardized precipitation evapotranspiration index(SPAEI)and the actual drought area is above 0.5,and the recognition rate of major historical drought in Henan,Hubei and Hunan are 9/14,8/13 and 7/10,respectively,which has the best applicability among all indexes in Central China.(3)The average annual drought duration in Central China ranged from 3.40?4.46months,and the maximum drought duration occurred during 1997?2001.The average annual drought frequency ranges from 1.06?1.85 times per year,with high frequency distributed in Jianghan Plain and parts of eastern Henan Province.The average annual drought intensity is relatively high in the central part of Central China,which is deeply affected by drought but mostly is moderate and mild drought.Northern Hubei,Southern Hunan,Southwest Hunan,Western Henan,Shangqiu,Zhoukou,Nanyang have higher intensity of annual severe and extreme drought,and are more affected by severe and extreme drought.(4)The drought in the spring of central Hubei,the summer of most southern Hunan,and the winter of northern Henan province showed a decreasing trend.The drought in the year of Enshi area(southwest Hubei),spring and winter of Hengyang and Chenzhou in southern Hunan province,summer of northwest Hubei and parts of Shaoyang region(western Hunan province),and winter of northwestern part of Hubei province all showed an increasing trend(at the significance level of 0.05).In addition,there exists a main drought cycle of 16 months,a short period of 6-8 months and a long cycle of about 6 years in Central China. |
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