Severe Drought in the Spring of 2020 in Poland—More of the Same?

Abstract

Two consecutive dry years, 2018 and 2019, a warm winter in 2019/20, and a very dry spring in 2020 led to the development of severe drought in Poland. In this paper, changes in the Standardized Precipitation-Evapotranspiration Index (SPEI) for the interval from 1971 to the end of May 2020 are examined. The values of SPEI (based on 12, 24 and 30 month windows, i.e., SPEI 12, SPEI 24 and SPEI 30) were calculated with the help of the Penman–Monteith equation. Changes in soil moisture contents were also examined from January 2000 to May 2020, based on data from the NASA Goddard Earth Sciences Data and Information Services Center, presenting increasing water shortages in a central belt of Poland. The study showed that the 2020 spring drought was among the most severe events in the analyzed period and presented decreasing trends of SPEI at most stations located in central Poland. This study also determined changes in soil moisture contents from January 2000 to May 2020 that indicate a decreasing tendency. Cumulative water shortages from year to year led to the development of severe drought in the spring of 2020, as reflected in very low SPEI values and low soil moisture.

Temperature Changes and Their Impact on Drought Conditions in Winter and Spring in the Vistula Basin

“…Additionally, a statistically confirmed lack of winter accumulation (statistically significant increase in the number of days with average and minimum temperature above zero (Figure 3) in winter, decrease in days with snow cover-Figure 10) as well as a deficit of spring precipitation can make this phenomenon perennial. As stated by Pińskwar et al [10] even if months occur with higher than the multi-year average sum of precipitation, this excess may not be sufficient to compensate Spatial variability of temporal changes in SPEI3 for winter and spring in 1951-2020 is presented in Figure 11. In winter, changes indicating deterioration of wetness condition prevail (south part of the catchment).…”

“…Additionally, a statistically confirmed lack of winter accumulation (statistically significant increase in the number of days with average and minimum temperature above zero (Figure 3) in winter, decrease in days with snow cover-Figure 10) as well as a deficit of spring precipitation can make this phenomenon perennial. As stated by Pińskwar et al [10] even if months occur with higher than the multi-year average sum of precipitation, this excess may not be sufficient to compensate for the accumulated deficit. It often happens that during such months there is one episode (lasting up to 2-4 days) with intensive rainfall translating into a high monthly precipitation sum, which is quite quickly drained from the catchment as surface runoff, improving the soil moisture situation for a very short time.…”

“…The process of thaw itself (its rapidity) will depend on temperature passing over the 0 • C threshold value (analysis of number of melting pulses-see Section 3.3 in this Chapter). The extremely warm winters and springs observed in recent years in Poland in the 2018 and 2020 [10,35] point out the need for verification of the long-term directions of change which seems to be very important from the perspective of potential changes in the accumulation of snow and the timing of thawing.…”

“…The Copernicus Climate Change Service/ECMWF (European Centre for Medium-Range Weather Forecasts) reports that the winter of 2020 was the warmest ever observed over Europe [9]. The spring of 2020 in Poland was extremely dry and cumulative water shortages from year to year contributed to dry soil conditions [10]. Snow cover in Poland is characterised by high intra and inter-annual variability [11] with no clear, statistically significant trends in snow cover depth [12,13].…”

“…At the beginning of the 21st century, Europe was hit by a series of severe, long-lasting summer heatwaves and droughts (i.e., 2003,2010,2013,2015,2018,2019) [2, 3,10]. These events were also observed in Poland.…”