Abstract
Numerous studies have documented the effects of irrigation on local, regional, and global climate. However, most studies focused on the cooling effect of irrigated dryland in semiarid or arid regions. In our study, we focused on irrigated paddy fields in humid regions at mid to high latitudes and estimated the effects of paddy field expansion from rain-fed farmland on local temperatures based on remote sensing and observational data. Our results revealed much significant near-surface cooling in spring (May and June) rather than summer (July and August) and autumn (September), which was −2.03 K, −0.73 K and −1.08 K respectively. Non-radiative mechanisms dominated the local temperature response to paddy field expansion from rain-fed farmland in the Sanjiang Plain. The contributions from the changes to the combined effects of the non-radiative process were 123.6%, 95.5%, and 66.9% for spring (May and June), summer (July and August), and autumn (September), respectively. Due to the seasonal changes of the biogeophysical properties for rain-fed farmland and paddy fields during the growing season, the local surface temperature responses, as well as their contributions, showed great seasonal variability. Our results showed that the cooling effect was particularly obvious during the dry spring instead of the warm, wet summer, and indicated that more attention should be paid to the seasonal differences of these effects, especially in a region with a relatively humid climate and distinct seasonal variations.
Highlights
It has been widely documented that land use changes (LUC) play an important role in regulating local, regional, and global climate systems [1,2,3]
Based on our previous studies, we developed the land use maps in 2005 and 2015 with humancomputer interaction interpretation based on the Landsat 5 Thematic Mapper (TM) images in 2005 and Landsat 8 Operational Land Imager (OLI) images in 2015 [43,49]
Based on the sp7 aotfia18l comparison analysis between the two land use maps, we intuitively found that great land use changes ttooookk ppllaaccee iinn the Sanjiang Plain, among which the expansion of paddy fifieldss was the most importantt aand signiffiicant llaanndduusseecchhaannggeedduurirninggthtehetetneyneyaersa.rSs.taStitsattiicsatlicaanlaalynsailsyosifsthoef trhaentsrfaenr smfeartrmixaotfrilxanodf luasnedsuhsoewsnhoinwtnheinstuhpepsluemppelnetmmenatemriaaltser(iTaalsbl(eTaSb1l)esSh1o)wshedowtheadt tmhaotremtohraenth1a5n%1o5f%thoef tlahnedlaonfdthoef tShaenSjianjgiaPnlgaiPnlaeixnpeexrpieenriceendcepdadpdayddfyielfideledxepxapnasniosniodnudruinrging20200505toto2021051,5,wwitihth7700%% ooff the iinnccrreeaassee ccoommiinngg ffrroomm ccoonnvveerrssiioonnffrroommrraaiinn--ffeeddffaarrmmllaanndd,wwhhiicchhiissccoonnssiisstteennttwwiitthhYYaann’s’ssstutuddyy[4[433].]
Summary
It has been widely documented that land use changes (LUC) play an important role in regulating local, regional, and global climate systems [1,2,3]. LUC influence climate mainly through biogeochemical and biogeophysical processes [8]. The biogeochemical processes associated with changes in the carbon budget are usually performed at the global scale and require multi-decadal time series [9,10], while biogeophysical processes can influence the atmosphere through land surface energy balance at different time and spatial scales more directly [11,12,13]. The biogeophysical influences are mainly conducted through radiative properties, such as albedo, and non-radiative properties, such as evapotranspiration and roughness length [14]. With the aggravation of regional land development, biogeophysical processes have attracted increasing attention
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