Abstract:
A rapidly developing “flash” drought struck Northeastern Montana and Western North and South Dakota beginning mid-July 2017, spurred by unusually high temperatures. By August, the drought contributed to 270,000+ acres consumed by wildfire and widespread reductions in range condition and crop production resulting in significant economic loss. Despite mid-September precipitation relief, on-the-ground observers reported ongoing agricultural impacts. Agricultural impacts likely follow vegetation productivity on a range of timescales, with lag and threshold effects relating to atmospheric demand, heat stress, and available soil water. Information on evaporative demand, precipitation deficit, vegetation greenness, and qualitative impact assessments are readily available, and now timely and accurate soil moisture information are available from the Soil Moisture Active Passive (SMAP) Mission, including model enhanced Level 4 Surface and Root Zone soil moisture (L4SM) and Carbon (L4C) products, offering unprecedented opportunity to monitor soil moisture and vegetation productivity (GPP) for agricultural drought. Our objective is to understand the incremental information provided by the SMAP L4 products for monitoring development and recovery of vegetation and agricultural productivity during the 2017 drought. We compare multiple available drought-indicator datasets with crop data to investigate the development of the 2017 Great Plains drought at relevant timescales. L4C GPP indicates that broadleaf croplands (primarily alfalfa, maize, chick peas, and canola) and forests (primarily riparian vegetation) had a threshold response lagging the onset of extreme atmospheric moisture demand by ~2 weeks. Cereal crop (wheat, barley) GPP declined more gradually with impacts persisting into the fall despite the recovery of atmospheric demand to normal levels following precipitation, surface soil moisture recovery, and moderating temperatures in mid-September. L4C GPP spatial patterns closely follow the Palmer Drought Severity Index (PDSI). These findings suggest that SMAP soil moisture is complementary to existing drought products and provides objective corroboration to PDSI, bridging the gap between atmospheric moisture demand, precipitation, and vegetation impacts.