Satellite-based assessment of crop-water uses over the Missouri River Basin for 1986-2018

Abstract:

An evaluation of water use and water availability at a basin and a field-scale is important to ensure the optimized constructive uses of available water resources. In this study, Landsat -derived and the Operational Simplified Surface Energy Balance (SSEBop) model-based actual evapotranspiration (ETa) was used to understand the historical crop water-use dynamics and existing statistical trend over the Missouri River Basin (MRB) for the 1986- 2018 period. Yearly ETa estimations were validated using the water balance evapotranspiration (WBET) approach at the HUC8 sub-basin scale. The validation statistics (r² = 0.91, PBIAS= 4%, and RMSE = 11.8%) indicated a well-captured spatial and temporal variation of ETa and a strong agreement between the WBET and the SSEBop ETa. An increasing trend in yearly ETa from northeast to southwest of MRB was observed. This increasing trend is driven by land use and precipitation amounts across the basin. A 10-year mean ETa over HUC8 subbasins revealed a higher number of subbasins with medium mean ETa (500 mm/year- 750 mm/year) during 2006-2018 than 1986-1995 and 1996-2005 periods. This shift might be explained by the conversion of grassland to agricultural land. The Mann Kendall basin-wide trend analysis showed a non-significant increasing trend in ETa and precipitation, whereas 3-year average precipitation amounts showed a significant increasing trend. Preliminary results for the pixel scale trend analysis suggested around 13.5% and 20.3% of the cropland area is under significant mono-directional trend at 0.05 and 0.1 significance level, respectively. Around 12.5% pixels showed a positive trend and rest 7.8% cropland pixels showed a decreasing trend for the yearly ETa. This spatiotemporal crop water use characteristic analysis at regional and field scales can provide important insights of demand and supply from the areas and can be of utmost importance for water management.