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Cropland area in north-western China has quadrupled over the past 50 years. The effects of this rapid expansion on regional carbon and water budgets have not been examined quantitatively. In this study, an enhanced Biome-BGC model including crop growth processes was used to quantify the effects on regional net primary productivity (NPP) and evapotranspiration (ET) in a representative catchment. The model results were in good agreement with biometric measurements. The catchment-scale total NPP (TNPP) and total ET (TET) increased by 81.8% and 89.4%, respectively. The increase in cropland area (LUCC) explained 40.3% and 60.5% of the increased TNPP and TET, while management practices (Mana) accounted for 46.1% and 16.8% of the increased TNPP and TET, respectively. Climate change (CLM) had the least influence on the increase in TNPP and TET (accounting for 1.8% and 4.7%). As assuming no interactions between CLM and LUCC, we detected effects of interactions between CLM and Mana (accounting for 10% and 16.8%) and between Mana and LUCC (accounting for 1.8% and 4.7%) on the increased TNPP and TET. These results implied that the rapid expansion of cropland and intensive agricultural management practices had important effects on regional carbon and water budgets. (C) 2013 Elsevier Ltd. All rights reserved.