Influence of mulched drip irrigation on landscape scale evapotranspiration from farmland in an arid area

Water-saving irrigation measures in arid areas affect evapotranspiration (ET) processes while conserving water. Mulched drip irrigation is considered the most efficient irrigation method because it distributes water uniformly in the soil, restricts deep percolation, and minimizes unproductive evaporation from soil. The effect of mulched drip irrigation on farmland ET during the growing season at a landscape scale remains unclear, despite being vital for developing optimal water resource management strategies in arid areas. To compare the effects of mulched drip irrigation and mulched border irrigation on ET, based on Landsat satellite imagery (2007-2009 with mulched border irrigation, and 2014-2016 with mulched drip irrigation), an improved Surface Energy Balance Algorithm for Land (SEBAL) model was used to evaluate ET for the two periods of an oasis at Sangong River Basin in the arid region of Northwest China. The results show that daily ET rates from farmland managed under mulched drip irrigation were on average 0.2-1 mm.d(-1) higher than under mulched border irrigation between June and August. Correspondingly, the net radiation flux (R) increased 73.32 W.m(-2) on average, and R was found to be the main determinant of the ET differences. Meanwhile, the average land surface albedo decreased by 20%, and negatively correlated with R (P < 0.05), indicating that the land surface albedo was the main factor affecting R. Furthermore, the Normalized Difference Vegetation Index (NDVI) exhibited a significant correlation with land surface albedo. More importantly, the Temperature-Vegetation Dryness Index (TVDI) under mulched drip irrigation was found to be approximately 21% lower than that under mulched border irrigation, indicating that the soil moisture conditions of the farmland under mulched drip irrigation was significantly improved compared to mulched border irrigation. Namely, less water stress resulted in better developed canopy of the crops, which in turn captured more radiation and thus increased ET. In the end, the observed increases in landscape-scale ET under mulched drip irrigation in arid area resulted from enhanced productivity of the crops due to lessened drought stress.