Differences in the ERA5-Land reanalysis and real observation datasets for calculation of drought indices from two distinct points

Even though, droughts usually correspond to smaller latitudes, during the last decade Latvia has faced several long-term drought events. This have caused awareness of more frequent drought episodes in future due to climate change. Accurate and complete meteorological data are required to calculate realistic drought indices and to estimate drought probability in the future.

In places were direct meteorological observation data are absent or dataset is incomplete and not sufficient, data from numerical weather forecasting reanalysis such as ERA5 can be used instead or along with direct observations. Reanalysis provide comprehensive snapshots of conditions at regular intervals over long time periods — often years or decades. The European Center for Medium-Range Weather Forecasts (ECMWF) has released its latest reanalysis product, the ERA5-Land dataset (C3S, 2019).

The goal of this study is to evaluate the ERA5-Land reanalysis product as a substitute for observations in meteorological stations for calculation of drought related indices for time period from 1981 to 2018.  Two meteorological stations more than 200 km apart in Latvia - Riga and Rezekne - were considered. 

Meteoric and agricultural drought indices were calculated with freely available software DrinC (Tigkas et.al., 2013) as well as R – packages spei and pdsi - using monthly mean reanalysis as well as observed meteorological data as input. It is found that meteorological parameters as well as drought indices have high consistency between two data sources. 

References:

Copernicus Climate Change Service (C3S) (2019): C3S ERA5-Land reanalysis. Copernicus Climate Change Service, 12.12.2019.

Tigkas, Dimitris & Vangelis, Harris & Tsakiris, George. (2013). The Drought Indices Calculator (DrinC).

The study is supported by fundamental and applied science research programme, project No.: lzp-2019/1-0165 “Spatial and temporal prediction of groundwater drought with mixed models for multilayer sedimentary basin under climate change”.