Pan, T; Zhang, C; Kuang, WH; Luo, GP; Du, GM; Yin, ZR (2020). Large-scale rain-fed to paddy farmland conversion modified land-surface thermal properties in Cold China. SCIENCE OF THE TOTAL ENVIRONMENT, 722, 137917.

The recent acute evolution of cropland structure in Cold China could lead to rapid rice paddy expansion, potentially altering land-surface thermal processes and influencing climate. To address the issue, this study investigated the changes in cropland type, land-surface temperature (LST) and heat fluxes in the agricultural region of Cold China during 2000-2015 based on time-series of land-use data and MODIS LST product, using the split-window algorithms (SWA) model and the pixel component arranging and component algorithm (PCACA). The investigation revealed large-scale land transformation from rain-fed farmland to paddy field in Cold China during 2000-2015. Compared to the rain-fed farmland, lower LST was observed in paddy field throughout crop growing seasons, with the highest LST threshold found in June (7.17 +/- 1.05 degrees C) and the lowest value found in August (1.04 +/- 0.35 degrees C). The cooling effect of paddy-field ranged from 0.59 +/- 0.06 degrees C, 0.77 +/- 0.07 degrees C, and 1.08 +/- 0.08 degrees C for the low-, medium-, and high-density paddies, respectively. Compared to other months, stronger cooling effect was found in May and June. Further analysis showed the conversion of a rain-fed farmland to paddy field reduced the sensible heat flux and soil heat flux by 52.94 W/m(2) and 15.26 W/m(2), respectively, while increased the latent heat flux and net radiation by 115.66W/m(2) and 47.34W/m(2), respectively. The findings fromthis study indicated the changes in cropland structure and management regime (e.g., irrigation) could profoundly modify land-surface thermal processes and local/regional climate, interfering the signals from global warming. Therefore, instrumental climate data that collected from areas experienced large-scale conversion between rain-fed and paddy farmland should be carefully screened and corrected to prevent land-use induced biases. (C) 2020 Elsevier B.V. All rights reserved.