Ecosystem Drought Response Timescales from Thermal Emission versus Shortwave Remote Sensing

Abstract

Remote sensing is used for monitoring the impacts of meteorological drought on ecosystems, but few large-scale comparisons of the response timescale to drought of different vegetation remote sensing products are available. We correlated vegetation health products derived from polar-orbiting radiometer observations with a meteorological drought indicator available at different aggregation timescales, the Standardized Precipitation Evapotranspiration Index (SPEI), to evaluate responses averaged globally and over latitude and biome. The remote sensing products are Vegetation Condition Index (VCI), which uses normalized difference vegetation index (NDVI) to identify plant stress, Temperature Condition Index (TCI), based on thermal emission as a measure of surface temperature, and Vegetation Health Index (VHI), the average of VCI and TCI. Globally, TCI correlated best with 2-month timescale SPEI, VCI correlated best with longer timescale droughts (peak mean correlation at 13 months), and VHI correlated best at an intermediate timescale of 4 months. Our results suggest that thermal emission (TCI) may better detect incipient drought than vegetation color (VCI). VHI had the highest correlations with SPEI at aggregation times greater than 3 months and hence may be the most suitable product for monitoring the effects of long droughts.

Exploring the Evolution of Drought Characteristics in Balochistan, Pakistan

“…However, in the context of global warming, assuming temperature to be stationary might lead to misleading conclusions. Therefore, SPEI is better suited for drought assessment, especially under a changing climate where the effect of rising temperatures is significant in drought development [28,29]. SPEI is based on the calculation of a monthly climatic water balance, which is determined by subtracting PET from precipitation [13,30].…”

Challenges in Complementing Data from Ground-Based Sensors with Satellite-Derived Products to Measure Ecological Changes in Relation to Climate—Lessons from Temperate Wetland-Upland Landscapes

“…Even differences in microclimate can cause substantial spatial variability in the timing of leaf onset within distances less than 100 m [ 135 ]. Results from past studies have provided ample evidence that different cover types, indeed species, respond differently to changes in water availability in the landscape (e.g., [ 136 , 137 , 138 , 139 , 140 , 141 ]), and heterogeneity in vegetation may retard detection of drying conditions, as different species can access soil moisture from different depths in the rooting zone after surface water has dried in wetlands [ 142 , 143 , 144 ]. We could expand our future analyses to investigate the degree to which ET, NDVI, and the duration of snow cover are associated with land-cover types in our study areas.…”

Trends in Drought over the Northeast United States

“…However, SPI is based only on precipitation and does not explicitly account for temperature. SPEI is therefore well suited for drought risk assessment and prediction [37,[39][40][41][42].…”

“…Linear regression to detect trends in drought duration was similarly carried out across droughts. Trends in drought characteristics are shown across timescales, normalized to their average values in each gridcell, and mapped for selected timescales including 1 month (the shortest aggregation period) and 12 months (relevant to longer-term impacts on vegetation and water supplies) [41,56].…”