Assessing the Quality of GPS Position Time Series for Investigation of Climate Change: Case Study of Europe

The water availability affects human health, agriculture and industry. A steadily warming climate has resulted in more and more droughts in recent years. There is a huge problem with water access in many regions around the world. Hence, the droughts must be regularly controlled. Nowadays, drought is followed by using climate indices created from various inputs data. So, it is difficult to assess which of them is optimal for specific area. Recently, the geodetic contribution to the determination of drought indices have been provided with the used of the Gravity Recovery and Climate Experiment (GRACE) mission data. Although its limitations (i.e. temporal and spatial resolution) it successfully allows to global and regional monitoring. Another geodetic contributor might be the Global Positioning System (GPS). Within this research we assess the severity of droughts for local areas and estimate a new monthly drought severity index (DSI) from GPS. We base on 514 GPS stations located in Europe. We estimate the reliability of GPS-DSI twofold. First, the GRACE-DSI values were determined. We utilize monthly RL06 mascon solution available from Center for Space Research (CSR) with a length of 163 months provided by GRACE and 40 months provided by its follow-on mission (GRACE-FO). Second, using (1) indices determined for hydrological models: WaterGAP Global Hydrological Model (WGHM) and Global Land Water Storage (GLWS) (provided by the University of Bonn science team), and (2) commonly used drought metrics, i.e. the self-calibrating Palmer Drought Severity Index (scPDSI), the Standardized Precipitation Evapotranspiration Index (SPEI), the Standardized Precipitation Index (SPI). We show that the most intense droughts which occurred in northern and southern European regions may be successfully sensed by GPS. In case of climate indices, we obtained positive correlations with GPS-DSI for 35% stations for scPDSI and at least 22%, 27% stations for various SPEI, SPI accumulation period, respectively. For both indices, the largest correlation is seen for more than 65% stations for short accumulation period (1-3 months). The obtained standard deviation values of GPS-DSI and other indices residues show that SPEI and SPI for medium accumulation period (9-12 months) differ in places by as much as 2-3 drought categories compared to GPS.