Croplands decreased stability of streamflow with changing climate: An investigation of catchments in Illinois

Croplands can significantly influence the hydrologic response of catchments to climate change in a region but such influence has not been well investigated and quantified. In this study, we firstly use the conceptual hydrological model to investigate the annual water balance for croplands-altered catchments, and the “natural” state without croplands of the catchment can be traced back by setting a zero area of croplands in the calibrated model. The model results are then applied to a hydrologic sensitivity framework with the Budyko-type relationship between hydrologic ratios (i.e. evapotranspiration ratio and water storage change ratio) and the aridity index (E/P) to yield the hydrologic sensitivity coefficients for the croplands-altered and “natural” catchments. The method is applied to investigate three catchments that are rarely affected by inter-basin groundwater flow in Illinois. The results show that croplands significantly increase the actual evapotranspiration (E) and decrease the runoff (Q), while changes in water storage (C) are rarely affected by croplands at the annual time scale. The actual evapotranspiration at the annual timescale is much more sensitive to potential evapotranspiration when the croplands exist. Croplands in Illinois significantly increase the sensitivity of streamflow on the climate change, to at least twice of the sensitivity in the “natural” state. The effectiveness of inter-annual hydrologic sensitivity framework is also demonstrated by hydrological model. This study provides a new simple insight to quantify the inter-annual stability with varying climate and land use at the catchment scale.