Quantifying the contributions of agricultural oasis expansion, management practices and climate change to net primary production and evapotranspiration in croplands in arid northwest China

• An agricultural module was integrated into the Biome-BGC model.
• The updated model performed well in simulating LAI and biometric variables.
• The simulated total NPP and ET increased significantly in an Oasis region.
• The increased total NPP and ET were mainly attributed from oasis expansion.

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.