Abstract
Agricultural droughts impose many economic and social losses on various communities. Most of the effective tools developed for agricultural drought assessment are based on vegetation indices (VIs). The aim of this study is to compare the response of two commonly used VIs to meteorological droughts—Moderate Resolution Imaging Spectroradiometer (MODIS) normalized difference vegetation index (NDVI) and Soil Moisture and Ocean Salinity (SMOS) vegetation optical depth (VOD). For this purpose, meteorological droughts are calculated by using a standardized precipitation index over more than 24,000 pixels at 0.25° × 0.25° spatial resolution located in central Europe. Then, to evaluate the capability of VIs in the detection of agricultural droughts, the average values of VIs anomalies during dry and wet periods obtained from meteorological droughts are statistically compared to each other. Additionally, to assess the response time of VIs to meteorological droughts, a time lag of one to six months is applied to the anomaly time series of VIs during their comparison. Results show that over 35% of the considered pixels NDVI, over 22% of VOD, and over 8% of both VIs anomalies have a significant response to drought events, while the significance level of these differences and the response time of VIs vary with different land use and climate conditions.
Highlights
Drought is one of the characteristics of the climate system that occurs at any time of the year without any warning and regardless of geographical boundaries or economic and political differences
The time lag of vegetation cover response to meteorological drought is investigated by applying different lag times to the vegetation indices (VIs) anomalies and analyzing their corresponding significance level of differences in the average value of vegetation optical depth (VOD) and normalized difference vegetation index (NDVI) VIs anomalies during wet and dry periods
A comparison of the response time of vegetation covers to the emergence and termination of meteorological droughts (Figure 2A,C for VOD and Figure 2B,D for NDVI) shows that, on average, there is a monotonic relationship between the response time of VOD and NDVI VIs to the meteorological drought events
Summary
Drought is one of the characteristics of the climate system that occurs at any time of the year without any warning and regardless of geographical boundaries or economic and political differences. Multiple studies have shown the far-reaching consequences of droughts and heatwaves on the social and economic conditions of the people in central. Most of the indicators used in drought monitoring studies are based on meteorological variables such as precipitation, temperature, or soil moisture. Among different meteorological drought indices, standardized precipitation index (SPI) has been used in many studies and has been shown to be effective in assessing meteorological drought conditions by using long-term precipitation patterns that are usually tied to streams, reservoirs, and groundwater levels [4,5]
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