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| Regression correction of Hargreaves equation within a year in China′s agricultural regions |
| XIA Xingsheng1,2, ZHAO Xizhen1, TANG Tong3,4*, PAN Yaozhong1,2 |
| 1. Institute of Remote Sensing Science and Engineering, Faculty of Geographical Science, Beijing Normal University, Beijing 100875, China;2. Academy of Plateau Science and Sustainability, Qinghai Normal University, Xining, Qinghai 810016, China;3. National Disaster Reduction Center of China, Beijing 100124, China; 4. United Nations platform for Space-based Information for Disaster Management and Emergency Response(UN-SPIDER)Beijing Office, Beijing 100124, China |
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Abstract For the question that there is a lack of research on the linear regression correction of the Hargreaves Equation(HS)for entire mainland China, and the existing correction coefficient of regions or stations is not uniform in spatial and temporal scale and difficult to be popularized and applied. Meteorological data, which was included in the Dataset of Monthly Values of Radiation Data from Chinese Surface Stations and the Dataset of Monthly Values of Climate Data from Chinese Surface Stations, were obtained from 1957 to 2016 at 124 sites. Firstly, based on Penman-Monteith(PM)equation and the HS, the average reference crop evapotranspiration—ET0-PM and ET0-HS in each month were calculated. Secondly, using ET0-PM as the truth value, and based on the average ET0-PM and ET0-HS of each region from 1957 to 2010, the correction coefficients of a and b of the HS from 38 agricultural sub-regions in China were obtained by regression analysis. Finally, taking 2011—2016 as the application verification interval, and the monthly change of 6 a mean relative error(RE)before and after correction of ET0-HS by the coefficients obtained from the corrected data was used to verify the applicability of HS correction method recommended by the Food and Agriculture Organization of the United Nations(FAO)in China′s agriculture regions. Based on the comparative analysis of the error results, the monthly optimal values of correction coefficients a and b of HS in each agricultural region were proposed. The results show that:(1)The correction coefficients a and b of HS calcula-ted by regression have no obvious change regularity in all agricultural regions, but the value of coefficient b is relatively stable around 0.8, and the coefficient a varies greatly from -0.22 to 1.10;(2)Before and after correction of ET0-HS have different degree errors, but ET0-HS error after correction will be significantly reduced, with the average RE was reduced by 20% and the maximum RE was reduced by about 100%. Therefore, after verification, the method of HS correction suggested by FAO is simple and easy to ope-rate, and has a certain popularization value for rapidly obtaining accurate ET0 by using simplified methods in various agricultural regions in China.
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Received: 03 June 2019
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