Soil Moisture Plays Crucial Role in Delineating and Forecasting
Agricultural and Meteorological Drought.
Abstract
Drought is a recurring and extreme hydroclimatic hazard with serious
impacts on agriculture and overall society. Delineation and forecasting
of agricultural and meteorological drought are essential for water
resource management and sustainable crop production. Agricultural
drought assessment is defined as the deficit of root-zone soil moisture
(RZSM) during active crop growing season, whereas meteorological drought
is defined as subnormal precipitation over months to years. Several
indices have been used to characterize droughts, however, there is a
lack of study focusing on comprehensive comparison among different
agricultural and meteorological drought indices for their ability to
delineate and forecast drought across major climate regimes and land
cover types. This study evaluates the role of RZSM from Soil Moisture
Active Passive (SMAP) mission along with two other soil moisture (SM)
based indices (e.g., Palmer Z and SWDI) for agricultural and
meteorological drought monitoring in comparison with two popular
meteorological drought indices (e.g., SPEI and SPI) and a hybrid
(Comprehensive Drought Index, CDI) drought index. Results demonstrate
that SM-based indices (e.g., Palmer Z, SMAP, SWDI) delineated
agricultural drought events better than meteorological (e.g., SPI, SPEI)
and hybrid (CDI) drought indices, whereas the latter three performed
better in delineating meteorological drought across the contiguous USA
during 2015–2019. SM-based indices showed skills for forecasting
agricultural drought (represented by end-of-growing season gross primary
productivity) in the early growing seasons. The results further confirm
the key role of SM on ecosystem dryness and corroborate the SM-memory in
land-atmosphere coupling.