Spatio-temporal variability in rice water supply and crop coefficients based on lysimeter measurements at 21 stations in Heilongjiang Province

Accurate assessment of irrigation water resources to meet the sustainable development needs of agriculture relies on the study of the spatial and temporal patterns of change in crop water requirements or evapotranspiration (ET_c). In this study, we derived the rice crop coefficient (K_c) curves from lysimeter experiments at 21 experimental stations for a total of 349 experimental years from 1952 to 2002 in Heilongjiang Province and then further refined the assessment of the spatiotemporal variation characteristics of ET_c, effective precipitation (P_e), irrigation water requirements (IWR) and irrigation water requirement index (IRI) for each growth stage of rice from 1960 to 2015. The results showed that K_c varied throughout the whole growing season at the different experiment stations, and the average K_c values of each station at the initial, mid-season and end of the late season stages were 1.01 ± 0.15, 1.29 ± 0.15, and 0.69 ± 0.23, respectively. In addition, the trends in ET_c (− 0.78 to − 0.02 mm year⁻¹) and IWR (− 0.07 to 0.17 mm year⁻¹) varied widely among the 4 irrigation zones. The region with higher IWRs was primarily located in the eastern and western plains of the study area. The negative trend in IWR in the west was due to a significant decrease in ET_c, however, the positive trend in IWR in the east was due to a significant decrease in P_e. The high and increasing IWR in the east required additional water conservation measures or supplemental irrigation to cope with possible agricultural water shortages. This study highlights the fine estimation of ET_c using lysimeter experiment data and provides a basis for water deployment and related agricultural strategies in the region under climate change.