Abstract
Satellite soil moisture is a critical variable for identifying susceptibility to hydroclimatic risks such as drought, dryness, and excess moisture. Satellite soil moisture data from the Soil Moisture Active/Passive (SMAP) mission was used to evaluate the sensitivity to hydroclimatic risk events in Canada. The SMAP soil moisture data sets in general capture relative moisture trends with the best estimates from the passive-only derived soil moisture and little difference between the data at different spatial resolutions. In general, SMAP data sets overestimated the magnitude of moisture at the wet extremes of wetting events. A soil moisture difference from average (SMDA) was calculated from SMAP and historical Soil Moisture and Ocean Salinity (SMOS) data showed a relatively good delineation of hydroclimatic risk events, although caution must be taken due to the large variability in the data within risk categories. Satellite soil moisture data sets are more sensitive to short term water shortages than longer term water deficits. This was not improved by adding “memory” to satellite soil moisture indices to improve the sensitivity of the data to drought, and there is a large variability in satellite soil moisture values with the same drought severity rating.
Highlights
Soil moisture is a key variable for identifying and characterizing hydroclimatic risk conditions, as it quantifies water availability for evapotranspiration, plant water uptake, and can indicate where runoff may occur when soils are saturated
The objective of this paper is to examine Soil Moisture Active/Passive (SMAP) soil moisture as an indicator of hydroclimatic risk conditions, including drought and excess moisture
The Palmer Drought Severity Index (PDSI) and the Water Deficit Index (WDI) are not strongly related to each other, indicating that they are capturing different aspects of hyroclimatic extremes, with the WDI capturing shorter term stress impacts and PDSI capturing longer term water availability. These results suggest soil moisture difference from average (SMDA) from both Soil Moisture and Ocean Salinity (SMOS) and SMAP is more sensitive to shorter term stress than longer term risks, but improvements in both soil moisture accuracy, during drying cycles, might improve this
Summary
Soil moisture is a key variable for identifying and characterizing hydroclimatic risk conditions, as it quantifies water availability for evapotranspiration, plant water uptake, and can indicate where runoff may occur when soils are saturated. The risks associated with the hydroclimate include extremes in climate that lead to a high probability of impact on surface water availability and includes events such as drought, dry spells, excess moisture, and flooding [1]. Quantifying these risks, requires developing indicators of the surface water balance and soil moisture is a reflection of how weather and climate have influenced this balance [2]. The launch of the Soil Moisture and Ocean Salinity (SMOS) mission in 2009 and the Soil Moisture Active/Passive (SMAP) mission in 2015, as well as other soil moisture satellite data sets, have helped to bridge part of Geosciences 2018, 8, 127; doi:10.3390/geosciences8040127 www.mdpi.com/journal/geosciences
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